EP3186403A1

EP3186403A1 - Reuse of by-products from metallurgical processes, processing of waste materials and products thereof

Info

Publication number: EP3186403A1
Application number: EP15763073.2A
Authority: EP
Inventors: Rhys Darlow LLOYD; Paul NOTT
Original assignee: Darlow Lloyd & Sons Ltd
Current assignee: Darlow Lloyd & Sons Ltd
Priority date: 2014-09-05
Filing date: 2015-09-04
Publication date: 2017-07-05
Also published as: WO2016034884A1; GB2529874A; GB2530663A; GB201515677D0; GB201415733D0

Abstract

The present invention provides four methods of re-using metallurgical process by-products. The first is a method of processing contaminated mill scale, comprising: combining it with water;subjecting it to three or more stages of attrition;and adding one or more chemical agents. The second is a method of processing contaminated mill sludge, comprising: diluting it with water; subjecting it to attrition using a jet pump; treating it by electro-coagulation; and separating ferrous material from the contaminants. The third is a method of treating by-products of a steel production process, comprising: separating the materials on the basis of density, and magnetically beneficiating part of the materials that have been separated. The fourth is a method of treating contaminated slag, comprising: separating it by particle size; subjecting at least part of it to attrition in a flow of water; and magnetically separating at least part of it. A fifth method is provided for making a load bearing material, comprising: mixing a waste material, water, an absorbing agent and a cementitious material (comprising 2-75% calcium oxide, 0.5 - 35% alumina,0.1 - 40% silica,and 0-50%other);and adding water to the mixture to adjust the viscosity.

Description

Reuse of by-products from metallurgical processes, processing of waste materials and products thereof

Field of the Invention

The present invention has five aspects.

The first four aspects concern the re-use of

metallurgical process by-products. More particularly, but not exclusively, the invention concerns the reuse of by- products generated from steel production.

In a fifth aspect the present invention concerns the processing of waste material and products thereof. More particularly, the invention is concerned with a method of making a load bearing material from a waste material and to load bearing materials produced from such methods.

Background to the first aspect of the Invention The production of hot rolled steel in steel rolling mills may produce large quantities of mill scale as a byproduct. Mill scale comprises various iron oxides that are formed on the surface of the steel; after production the mill scale becomes flaky and breaks off or is removed. Mill scale typically comprises high levels of ferrous metals, for example it may be 65% to 75% iron by mass. However it is typically contaminated with oils used to lubricate machinery used in the rolling mills, generally oil contamination levels are between 0.5% and 2.5%. Smaller particles of mill scale are similarly produced as mill sludge and are often further contaminated with between 2% to 8% oil. Sintering can recycle mill scale for use in a blast furnace; however the hydrocarbons which make up the oil impurities can contaminate the air when they burn and the oil can otherwise cause fouling of filters and other machinery.

By-products, such as those mentioned above, have often been regarded as unrecoverable waste and sent to landfill. However several factors including: increases in the cost of raw materials, increases in the costs associated with sending waste to landfill, environmental concerns, and changing attitudes regarding waste, have led to the need for processes for recovering useable raw materials from waste.

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of treating by-products of metallurgical processes.

Summary of the first aspect of the Invention

The present invention provides a method of processing mill scale, the method comprising the steps of: providing contaminated mill scale from the processing of steel;

combining the contaminated mill scale with a first quantity of water; subjecting the contaminated mill scale to three or more stages of attrition to reduce the level of

contaminants; and adding one or more chemical agents to the contaminated mill scale.

We have found that by using three or more stages of attrition it becomes possible to provide a process in which contamination of the mill scale can be substantially reduced at modest levels of energy consumption. The mill scale which is provided to the process may be produced as a by-product of one or more processes relating to steelmaking, and predominantly, but not exclusively, from hot rolling of steel (in steel rolling mills) . The mill scale may be a mixture of mill scales from a plurality of processes or sources.

The mill scale may largely comprise iron and/or iron oxide particles. The particle size may vary depending on the process from which the mill scale originates, for example if hot steel is made into cast ingots the mill scale may typically consist of smaller particles. The particles may have an average particle size greater than 0.5mm. The particles may have an average particle size greater than lmm. The mill scale may be in flakes or be substantially granular. The mill scale may comprise 50% to 90% ferrous metal. The mill scale may comprise 55% to 75% ferrous metal. The mill scale may comprise 65% to 75% ferrous metal.

Throughout this specification where proportions of materials are given, whether as percentages or parts ratios, those proportions are by mass (unless otherwise stated) .

The mill scale so provided may be contaminated with contaminants including, but not limited to, oil, grease silica, and/or salts. The mill scale contaminated with oil may comprise an oil contamination level of 0.1% to 10%. The mill scale may comprise an oil contamination level of 0.5% to 10%. The mill scale may comprise an oil contamination level of 0.2% to 5%. The mill scale may comprise an oil contamination level of 0.5% to 2.5%. The contaminated mill scale may be tested for the level and/or type of

contaminants present. The contaminated mill scale may be tested preceding, during, or after any step in the method. It will be understood that mill scale provided to the process will be considered to be contaminated mill scale, regardless of the actual levels and types of contaminants present .

The mill scale provided to the process may include water. The moisture content may be 20% to 30%. Typically mill scale provided directly from rolling mills will have a higher moisture content than that which has been provided from a stock pile of mill scale. However the moisture content of stockpiled mill scale may depend on environmental conditions .

Contaminated mill scale, provided directly from a metallurgical process plant or otherwise, may contain unwanted debris and tramp material. The debris and tramp material typically comprises waste such as stones, shredded tyre rubber, pieces of scrap metal, lumps of steel and the like. This debris and tramp material can damage machinery, introduce further contaminants into the mill scale and/or reduce the effectiveness of the mill scale processing. As a result the debris and tramp material may preferably be removed from the mill scale so provided. Preferably the debris and tramp material is removed from the mill scale prior to any other processing steps. The debris and tramp material may be removed by a screening plant. The

contaminated mill scale may be screened to remove particles which exceed a maximum lump size, for example 16mm lumps. The screening plant may pass the contaminated mill scale through at least one mesh screen having a predetermined mesh size. The at least one mesh screen may have openings in the range 6mm to 25mm, preferably 10mm to 20mm, for example the at least one mesh screen may have 16mm openings. The screens may vibrate to help material pass through the screens. The configuration of the screening plant may be altered

depending on the mill scale so provided. The method may therefore include a step of configuring the screening plant in dependence on the characteristics of the mill scale so provided. For example finer mill scale may require longer screening decks. Valuable material so removed in the screening process, for example lumps of metal such as steel, may be collected and sent for reuse in a metallurgical process .

The contaminated mill scale may be graded. The

particles may be graded in a grading device. The grading process may sort and separate the mill scale particles by size. The grading device may employ a plurality of mesh screens having different mesh sizes; mill scale particles which are smaller than the openings in a particular mesh may pass through the mesh, and mill scale particles which are larger than the openings in a particular mesh may not pass through the mesh. Particularly fine mill scale particles, for example mill scale particles smaller than 1mm may be removed, for example using a 1mm screen, and sent for separate treatment. The contaminated mill scale may be graded as part of the same step which removes debris and tramp material, as described above.

The contaminated mill scale may be combined with liquid to form a slurry. The liquid may be water. The mill scale may be combined with a first quantity of water to form a first slurry. The contaminated slurry may be combined with liquid to form a slurry in a mixing unit.

Attrition of particles occurs when particles are vigorously mixed and forced against each other. The collision of the particles results in a scrubbing action which acts to remove contaminants from the surfaces of the particles. The attrition acts to promote separation between contaminants such as oils and the surface of the mill scale particles. Sufficient attrition of the contaminated mill scale particles may remove some, if not substantially all, of the oil contained on the surface of the mill scale. The oil so removed may be left emulsified, suspended, dissolved, or otherwise dispersed in the liquid.

The contaminated mill scale and water mix may be fed into the attrition units. Each attrition unit may comprise a receiving portion for receiving contaminated mill scale and mixing it with liquid of the attrition unit. The attrition units may churn, mix and/or tumble the slurry to effect attrition between the mill scale particles. The attrition units may comprise paddles, blades, rotational shafts, Archimedes screws, water jets, and/or other churning equipment. The attrition units may each have a power rating of between lOkW and lOOkW.

Liquid, for example water, may be input into the attrition unit. Liquid, for example water contaminated with oil emulsion, may be output from the attrition unit. Clean liquid may substantially continuously be provided to the attrition unit and contaminated liquid may substantially continuously be removed from the attrition unit. The attrition units may have a fluid capacity of between 500 litres and 5000 litres. The attrition units may have a fluid capacity of between 500 litres and 2000 litres.

The attrition units may subject the mill scale to attrition for a predefined period of time. The attrition units may subject the mill scale to attrition for long enough to dissipate, substantially evenly, the oil, so released from the mill scale, throughout the medium. The attrition units may subject the mill scale to attrition for long enough to disperse, substantially evenly, any chemical agents added to the contaminated mill scale. The particles may be subject to attrition for a total period of 1 to 10 minutes. The particles may be subject to attrition for a total period of 3 to 8 minutes. The particles may be subject to attrition for a total period of 4 to 5 minutes. The time scale for subjecting the particles to attrition may depend on the oil contamination levels in the mill scale so provided .

One or more chemical agents may be added to the contaminated mill scale. The one or more chemical agents may be added to the mill scale prior to, during or after the contaminated mill scale is subjected to attrition. The one or more chemical agents may comprise a surfactant. The surfactant may emulsify or disperse some or all of the contaminants .

Following attrition in an attrition unit the mill scale slurry may be fed out of the attrition unit. Following attrition in an attrition unit the mill scale may be transported out of the attrition unit and out of the liquid, it will be appreciated that the mill scale may retain some liquid on its surface and so may not be dry.

The mill scale may be rinsed. The rinsing may

substantially replace any liquid mixed with the contaminated mill scale. The rinsing may allow the contaminants so removed from the mill scale, which are dispersed in the liquid, to be removed. The liquid may be sent to a treatment plant for treating. The mill scale may be rinsed with substantially clean water. The rinsing may occur in the attrition units. The rinsing may occur in a rinsing unit. Following a rinsing step the contaminated mill scale may comprise reduced levels of contaminants.

The stages of attrition may be defined as distinct periods or steps in the attrition process, distinguished primarily by using different equipment to effect attrition, but the stages may also be distinguished by the settings used on the attrition equipment, the features installed in the attrition units, the intensity of the attrition and the like.

For a process wherein the stages of attrition are primarily distinguished by the attrition equipment, the mill scale and other material may be input to certain equipment, move substantially continuously through that equipment, wherein it will undergo a stage of attrition, and be output. Alternatively, the mill scale may be subjected to stages of attrition in substantially distinct batches. The mill scale may be transported through the process by the direct action of machinery on the mill scale and/or by the flow of the medium with which the mill scale is mixed. For example the mill scale may be transported through the process by a conveyer, the churning equipment, a current created by the churning equipment and/or a current created by a pump.

In a process comprising three or more stages of attrition, a first stage of attrition may comprise feeding contaminated mill scale and water mix (a first slurry) into a first attrition unit. Alternatively, the contaminated mill scale may be provided directly into the attrition unit, for example from a screening plant, so that the contaminated mill scale is mixed with water to form the first slurry in the attrition unit. The first attrition unit may have a fluid capacity of between 500 litres and 1000 litres. The first attrition unit may subject the mill scale particles to high intensity attrition for a first period of time. The first attrition unit may comprise paddles and rotational shafts to cause the mill scale particles to collide, thereby causing attrition. The first attrition unit may have a power rating of between 80kW and 100KW. The first attrition unit may subject the mill scale to attrition for a predefined period of time. The first attrition unit may subject the mill scale to attrition for a first period of time which is long enough to dissipate, substantially evenly, the oil, so released from the mill scale, throughout the slurry. The first attrition unit may subject the mill scale to attrition for a first period of time which is long enough to disperse, substantially evenly, any chemical agents added to the contaminated mill scale. The first attrition unit may subject the mill scale to attrition for 1 to 2 minutes.

One or more first chemical agents may be added to the contaminated mill scale during a first stage of attrition in a first attrition unit. The first chemical agent may be a surfactant .

Following a first stage of attrition the mill scale may be transported out of the liquid of the first attrition unit. Following a first stage of attrition the mill scale may be rinsed. The mill scale may be rinsed by spraying liquid over the mill scale. The mill scale may be rinsed as it is transported out of the first attrition unit. Following a first stage of attrition the mill scale may be mixed with a second quantity of water to form a second slurry. The mill scale may be fed into a second attrition unit. The mill scale may be mixed with a second quantity of water in the second attrition unit to form a second slurry. The second attrition unit may have a larger fluid capacity than the first attrition unit. The second attrition unit may have a fluid capacity of between 1000 litres and 1400 litres. The mill scale may be subjected to a second stage of attrition. The second attrition unit may be the same as the first attrition unit. The second attrition unit may be the same machine as the first attrition unit set to operate in a different way. The second attrition unit may be a different unit to the first attrition unit. The second attrition unit may comprise paddles, rotational shafts and Archimedes screws to cause the mill scale particles to collide and subject them to attrition. The second attrition unit may subject the mill scale to attrition for a second period of time. The second period of time may be long enough to dissipate, substantially evenly, the oil, so released from the mill scale, throughout the slurry. The second period of time may be long enough to disperse, substantially evenly, any chemical agents added to the contaminated mill scale. The second period of time may be 1 to 2 minutes.

The second stage of attrition may be of a lower

intensity than the first stage of attrition. The rotational shafts of the second attrition unit may rotate at slower speeds than those of the first attrition unit. The second attrition unit may not impart as much energy to the mill scale as the first attrition unit. The second attrition unit may have a power rating which is lower than the first attrition unit. The second attrition unit may have a power rating of between 50kW and 80KW. One or more second chemical agents may be added to the mill scale during the second stage of attrition. The one or more chemical agents added to the mill scale during the second stage of attrition may comprise a surfactant.

The slurry may be aired. The slurry may be aired following a stage of attrition. The slurry may be aired by transportation on a conveyor, for example between attrition units .

The mill scale may be fed into a third attrition unit. The mill scale may be mixed with a third quantity of water in the third attrition unit to form a third slurry. The third attrition unit may have a larger fluid capacity than the second attrition unit. The third attrition unit may have a fluid capacity of between 1400 litres and 1800 litres. The mill scale may be subjected to a third stage of attrition. The third stage of attrition may enable the release and removal of oil based emulsions in the mill scale. The third attrition unit may be the same as the first and/or second attrition unit. The third attrition unit may be the same machine as the first and/or second attrition unit set to operate in a different way. The third attrition unit may be a different unit to the first and/or second attrition unit. The third attrition unit may comprise one or more Archimedes screws. The third attrition unit may subject the mill scale to attrition for a third period of time. The third period of time may be long enough to enable the release and removal of oil based emulsions in the mill scale.

The third attrition unit may principally aid de- watering of the mill scale. The third attrition unit may operate at a slower speed than preceding attrition units.

Rotational shafts of the third attrition unit may rotate at slower speeds than those of the first and second attrition units. The third stage of attrition may be of a lower intensity than the first and second stages of attrition. The third attrition unit may not impart as much energy to the mill scale as the first or second attrition unit. The third attrition unit may have a power rating which is lower than the second attrition unit. The third attrition unit may have a power rating between lOkW and 50kW.

One or more third chemical agents may be added to the mill scale during a third stage of attrition in a third attrition unit. The third chemical agent may comprise a surfactant .

The applicant has found that a method of treating contaminated mill scale in successively less intense stages of attrition has the advantage of utilising less energy over the course of the process, yet producing similar overall reductions in the levels of contaminants, when compared to treating contaminated mill scale in substantially equally intense stages of attrition.

The person skilled in the art will understand that intensity of attrition is dependent on a number of factors and is therefore hard to quantify, but it is best thought of in terms of the energy imparted on the slurried particles of mill scale. Factors affecting intensity of attrition include: the power output / power rating of the attrition units, the rotational speed of the shafts, the angle and configuration of the blades on the shafts, the proximity of the shafts (if more than one shaft is present), the depth of the slurry in the attrition unit, and the fluid capacity of the attrition unit in relation to the above. The applicant has additionally found that three stages of attrition consistently produce treated mill scale of a satisfactorily low contaminant level. Three stages of attrition of successively lower intensity being found to represent a desirable balance between energy use and contaminant level in the treated mill scale.

The level of contaminants in the mill scale may be tested. If the level of contaminants is not below a minimum threshold level the mill scale may be sent for further treatment, for example the mill scale may undergo further stages of attrition and/or chemical addition.

Following the stages of attrition, residual liquid mixed with the mill scale may be removed. The treated, or cleaned, mill scale may then be dried. The mill scale may be actively dried by passing it through driers. The mill scale may be dried by stock piling the mill scale and allowing excess moisture to drain from it.

The treated mill scale may be reused in a steel making process. The mill scale may be sintered.

The operation of the treatment units (i.e. the

screening units, mixing units, attrition units and the like) may be controlled by a treatment control centre. The flow of material through the treatment units may be automatically controlled. The level of fluid in the treatment units may be automatically controlled. The treatment units may comprise fluid level sensors, for example ultrasonic level sensors. The level of fluid in the units may determine the operation of fluid input and output pumps which pump fluid to and from the units. For example: if the fluid level is higher than a certain threshold level then the output pump alone may operate to remove water from the unit, if the fluid level is lower than a threshold level the input pump alone may operate to add fluid to the tank, and/or if the fluid is within a specific range both pumps may operate to ensure a continuous flow of fluid through the unit. The treatment control centre may automatically operate valves and/or pumps to control the flow of surfactants.

The treatment control centre may control the speed of the motors, mixers, and/or rotational shafts. The operation of valves for the removal of process material from a treatment unit may be controlled by the treatment control centre and/or by a timer.

The turbidity of the fluids may be measured. The turbidity of the slurry may be measured.

The treatment control centre may be configured so that it can be remotely accessed and/or controlled, for example via a web portal. The treatment control centre may alert one or more designated operators in the event of a fault or if certain predefined criteria are met. The treatment control centre may alert one or more designated operators via an automatic SMS and/or email alert.

Any water used in the process may be sent to a water treatment plant. The water treatment plant may treat the water and return it to the process for reuse in one or more stages of the treatment process.

The present invention further provides an apparatus for carrying out a method as defined above.

The apparatus may comprise one or more attrition units, a screening plant, and/or one or more mixing units.

It will of course be appreciated that features

described in relation to the method of the present invention may be incorporated into the apparatus of the present invention .

Background to the second aspect of the Invention

The production of hot rolled steel in steel rolling mills may produce large quantities of mill scale as a byproduct. Mill scale comprises various iron oxides that are formed on the surface of the steel; after production the mill scale becomes flaky and breaks off or is removed. Mill scale typically comprises high levels of ferrous metals, for example it may be 65% to 75% iron by mass. However it is typically contaminated with oils used to lubricate machinery used in the rolling mills, generally oil contamination levels are between 0.5% and 2.5%. Smaller particles of mill scale are similarly produced as mill sludge and are often further contaminated with between 2% to 8% oil. Sintering can recycle mill scale for use in a blast furnace; however the hydrocarbons which make up the oil impurities can contaminate the air when they burn and the oil can otherwise cause fouling of filters and other machinery.

Summary of the second aspect of the Invention

The present invention provides a method of processing mill sludge, the method comprising steps of: providing contaminated mill sludge; diluting the contaminated mill sludge with process water; removing contaminants from the mill sludge through electro-coagulation; removing

contaminants from the mill sludge using a lamella clarifier; separating the process water from the mill sludge.

The mill sludge which is provided to the process may be produced as a by-product of one or more processes relating to steelmaking, and predominantly, but not exclusively, from hot rolling of steel (in steel rolling mills) . The mill sludge may be a mixture of mill sludge from a plurality of processes or sources.

The mill sludge may largely comprise iron and/or iron oxide particles. The particle size may vary depending on the process from which the mill sludge originates. The particle size may be 1 micron to 3000 microns (1 micron = l*10^~6m) . The particle size may be 5 microns to 950 microns. The mill sludge may comprise small flakes or be substantially granular. The mill sludge may comprise 50% to 90% ferrous metal. The mill sludge may comprise 55% to 75% ferrous metal .

Throughout this specification where proportions of materials are given, whether as percentages or parts ratios, those proportions are by mass (unless otherwise stated) . The mill sludge so provided may be contaminated with contaminants including, but not limited to, oil, fatty oil emulsion, grease, carbon, silica, and/or salts. The mill sludge contaminated with oil may comprise an oil

contamination level of 0.1% to 25% and it may be 1% to 25%. The mill sludge may comprise an oil contamination level of 1% to 15%. The mill sludge may comprise an oil contamination level of 2% to 8%. The contaminated mill sludge may be tested for the level and/or type of contaminants present. It will be understood that mill sludge provided to the process will be considered to be contaminated mill sludge,

regardless of the actual levels and types of contaminants present .

Contaminated mill sludge, provided directly from a steel plant or otherwise, may contain unwanted debris and tramp material. The debris and tramp material typically comprises waste such as stones, shredded tyre rubber, pieces of scrap metal, lumps of steel and the like. This debris and tramp material can damage machinery, introduce further contaminants into the mill sludge and/or reduce the

effectiveness of the mill sludge processing. As a result the debris and tramp material may preferably be removed from the mill sludge so provided. Preferably the debris and tramp material is removed from the mill sludge prior to any other processing steps. The debris and tramp material may be removed by screening the mill sludge. The debris and tramp material may be removed by screening the mill sludge through a first screening unit. The first screening unit may comprise at least one mesh screen. The at least one mesh screen may vibrate to help material pass through it. The at least one mesh screen may have openings in the range 60mm to 80mm.

The material may be transported by an auger screw. The auger screw may be used to transport material from one step of the treatment process to a subsequent step of the treatment process. The auger screw may transport the material, from which debris and tramp material has been removed, to a subsequent step of the treatment process.

The mill sludge may be screened to remove oversized lumps of mill sludge. Oversized lumps of mill sludge may be too heavy or too large to be treated. The mill sludge may be screened in a second screening unit. The second screening unit may comprise one or more mesh screens having

predetermined mesh sizes. The screens may vibrate to help material pass through them. The second screening unit may comprise consecutive screens having increasingly small openings. Having multiple screens may reduce the tendency of the screens to clog up with material. The second screening unit may alternatively or additionally comprise a rotating trommel. In the second screening unit water sprayers may be provided to spray water over the screens. Water sprayers may help material pass through the screens and prevent the screens from clogging up. Oversized particle which do not pass through the screens may be collected and disposed of or sent for alternative treatment.

The mill sludge may be received by a jet pump. The jet pump may be configured to dilute the mill sludge with a liquid, for example water, preferably in a predefined ratio, thereby forming mill sludge slurry. For example, the mill sludge may be mixed with water in a ratio of 1 part mill sludge to 10 parts water. The mill sludge slurry may be accelerated through the jet pump. The jet pump may subject the mill sludge to a high intensity wash. The jet pump may vigorously mix the mill sludge slurry thereby causing attrition between the mill sludge particles. The jet pump may break up mill sludge clumps, lumps or particles into smaller particles.

Attrition of particles may occur when particles are forced against each other or forced against the surfaces of the mixing equipment. The collision of the particles may result in a scrubbing action which acts to remove

contaminants from the surfaces of the particles. The

attrition may promote separation between contaminants such as oils and the surface of the mill sludge particles.

Sufficient attrition of the contaminated mill sludge may remove some, if not substantially all, of the oil contained on the surface of the mill sludge particles. The oil so removed may be left emulsified, suspended, dissolved, or otherwise dispersed in the liquid.

There may be provided a receiving tank for receiving mill sludge slurry so output from the jet pump. The

receiving tank may substantially slow and/or reduce the pressure of the mill sludge slurry output from the jet pump. Reducing the flow rate of the mill sludge may prevent damage to, and improve the effectiveness of, downstream treatment units. The receiving tank may comprise a mixing element for mixing the material which may prevent the mill sludge particles from settling in the tank.

The mill sludge slurry may be subjected to electrocoagulation. The slurry may be subject to electro- coagulation in an electro-coagulation unit comprising one or more pairs of electrodes. For example, the electro- coagulation unit may comprise four pairs of electrodes, each pair comprising an anode and a cathode. Consecutive pairs of electrodes may be arranged substantially in-line. The electro-coagulation may cause contaminants, such as heavy metals, emulsified oils and suspended solids to coagulate, precipitate and/or form floe.

An advantage of using electro-coagulation to treat the mill sludge is that it is able to separate emulsified oil and grease and other small contaminants from the mill sludge without the need for chemicals, which can be expensive and raise environmental concerns, or mechanical filters, which need to be replaced and can be damaged by emulsified oil and grease. The rate of electro-coagulation may easily be controlled by altering the current supplied to the

electrodes. For example, an increased rate of electrocoagulation can be achieved by increasing the potential difference between the electrodes.

Following and/or during electro-coagulation,

contaminants such as oils, carbon and other smaller

particles ("lights") may float to the top of the mill sludge slurry, forming floating floe. Bubbles created at an electrode may also increase the flocculation of such contaminants. The floating floe may be skimmed from the top of the mill sludge slurry.

Following and/or during electro-coagulation, heavy metals and larger particles ("heavies") may sink to the bottom of the mill sludge slurry, forming metallic sludge. Metallic sludge, containing iron and iron oxide coagulates, may be removed from the mill sludge slurry by draining or pumping the sludge from the bottom of the mill sludge slurry . The heavies and lights may be separated, as above, in the electro-coagulation unit itself. Preferably the heavies and lights may be separated in a separate unit. For example the heavies and lights may be separated in a flotation tank, which may comprise vertical baffles past which the mill sludge slurry passes. Alternatively, and preferably

additionally, the heavies and lights may be separated in a lamella clarifier, which may comprise a set of inclined plates between which the mill sludge slurry flows. Heavies and lights may also be separated/removed using a filter and/or other means .

Typically the lights are disposed of as waste or sent for further processing (separately to the mill sludge) . The remaining liquid may be disposed of, sent for further processing and/or reused in the mill sludge treatment process. The heavies, i.e. the metallic sludge, so removed from the mill sludge slurry may substantially comprise iron and/or iron oxide particles and may therefore constitute treated mill sludge.

Ballast material may be added to the mill sludge.

Ballast material may be added to the mill sludge if oil levels exceed a maximum threshold level. Ballast material may comprise a material having 50 micron to 700 micron sized particles. Ballast material may comprise fine limestone sand. Ballast material may abrade the surface of mill sludge particles thereby increasing separation of oils from the mill sludge. Ballast material may also adsorb oils in the mill sludge slurry, thereby allowing them to be removed with the larger, more easily removed, ballast material particles. Ballast material may be added to the mill sludge during screening of the mill sludge. For example, the ballast material may be added into the trommel.

A chemical agent may be added to the mill sludge to increase the removal of contaminants, for example a

surfactant may be added to increase the emulsification of oils in the mill sludge.

The treated mill sludge may be dried. The mill sludge may be dried by passing it through a de-watering unit such as a heater, and/or be left to drain in drying beds.

Dried mill sludge may be beneficiated to remove ballast material from the mill sludge. The step of removing ballast material from the mill sludge increases the proportion of ferrous metals in the mill sludge. The mill sludge may be magnetically beneficiated, for example in a magnetic beneficiation unit comprising a rotating magnetised drum. The magnetic particles may pass the rotating magnetised drum, sufficiently magnetic particles may be attracted and held to the sides of the rotating drum until they are carried out of the magnetic field and transferred to a collector, the nonmagnetic or less magnetic particles may be collected as waste.

The operation of some or all of the treatment units (i.e. the screening units, mixing units, attrition units and the like) may be controlled by a treatment control centre. The flow of material through the treatment units may be automatically controlled. The level of fluid in the

treatment units may be automatically controlled. The treatment units may comprise fluid level sensors, for example ultrasonic level sensors. The level of fluid in the units may determine the operation of fluid input and output pumps which pump fluid to and from the units. For example: if the fluid level is higher than a certain threshold level then the output pump alone may operate to remove water from the unit, if the fluid level is lower than a threshold level the input pump alone may operate to add fluid to the tank, and/or if the fluid is within a specific range both pumps may operate to ensure a continuous flow of fluid through the unit. The treatment control centre may automatically operate valves and/or pumps to control the flow of surfactants.

The treatment control centre may control the speed of the motors, mixer, and/or rotational shafts. The treatment control centre may control the voltage across the electrodes of the electro-coagulation unit. The operation of valves for the removal of sludge, for example from the bottom of a flotation unit, may be controlled by the treatment control centre and/or by a timer.

The turbidity of the treated fluid may be measured. The turbidity of the slurry may be measured. The turbidity of the liquid (process water) output from the lamella clarifier may be measured. The turbidity of the liquid (process water) output from the lamella clarifier may be used to control the operation of one or more treatment units. For example, a feedback loop may exist wherein the turbidity measurement influences the voltage between the electrodes of the electro-coagulation unit, for example if the level of turbidity exceeded a threshold level the voltage may be increased .

Contaminants separated from the mill sludge may be sent to an emulsion splitter. More particularly the light particles and any oily water collected may be sent to an emulsion splitter for separation of the oil from the process liquid. The oil may be further processed and/or used as a fuel. Any water used in the process may be sent to a water treatment plant. The water treatment plant may treat the water and return it to the process for reuse in one or more stages of the treatment process.

The apparatus may comprise a jet pump, an electro- coagulation unit, a flotation tank, a lamella clarifier, a particle size separator, an attrition unit, a magnetic beneficiation unit, an air separator, a flotation unit, an eddy current separator and/or a treatment control centre.

It will of course be appreciated that features

Background to the third aspect of the Invention

Hot metallurgical processes, such as the production of pig iron in a blast furnace, typically produce as a byproduct fumes and dust comprising metal or metallic

compounds. In modern metallurgical process plants the air comprising the fumes and dust expelled from molten metal, for example in a blast furnace, is typically drawn away through venting systems. The venting systems filter the air of fumes, dust and other particulates before the air is released into the atmosphere or recirculated.

Although these by-products may contain significant quantities of useful material, such as iron and other metals, the useful materials are typically mixed with high levels of contaminants which restrict their reuse. For example, a mixture of oxides is expelled from the top of a blast furnace. The oxide particulates form dust which collects in the venting systems and filters associated with the blast furnace. The major component of this dust is iron oxide, which it would be desirable to reuse. However, other oxides (such as those of zinc and alkaline metals) are also present which prevent the direct reuse of blast furnace dust.

By-products, such as those mentioned above, have often been regarded as unrecoverable waste and sent to landfill. However several factors including increases in the cost of raw materials, increases in the costs associated with sending waste to landfill, environmental concerns, and changing attitudes regarding waste, have led to the need for processes for recovering useable raw materials from waste materials. Furthermore, in some cases the by-products contain toxic elements (such as zinc, cadmium, chromium and arsenic) that make them hazardous and unacceptable for landfill .

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of treating by-products of metallurgical processes. Summary of the third aspect of the Invention

The present invention provides a method of treating byproducts of a steel production process, the method

comprising the steps of: providing one or more by-products of a steel production process; separating the materials in at least one of the by-products into two or more categories of material, including a first category of material

comprising materials for re-use in a steel production process; and magnetically beneficiating the first material to separate magnetically a treated material having a higher content of iron than the first material.

The one or more by-products may include metal dust and/or metal oxide dust. The one or more by-products may include waste oxide dust, flue dust, fume dust and/or a slurry thereof.

More specifically the by-products may include, but are not limited to: blast furnace dust, steel making dust, including Basic Oxygen Steelmaking (BOS) dust, electric arc furnace dust and/or milling waste. More generally the byproducts may be derived from other suitable iron or iron oxide bearing waste streams.

By way of example the one or more by-products may comprise: ferrous metal, oils, silicon, zinc, magnesium, lime, chlorides, other salts and metals, and oxides thereof. The by-product material so provided may be a mixture of one or more by-products from one or more metallurgical

processes. The one or more by-products may comprise more than 35% iron, preferably more than 45% iron.

At least one of the one or more by-products may be provided mixed with a liquid, for example water, possibly as a result of a wet dust capturing process. By-products mixed with water may be in the form of slurry. For example, waste oxide slurry, flue dust slurry, fume dust slurry, and the like. The slurry may comprise metallurgical process by- products and water, typically 50% to 90% water, more typically 70% to 90% water. Alternatively or additionally, the one or more by-products may be provided as a

substantially dry granular material. Alternatively or additionally, the one or more by-products may be provided as a cake, comprising moist by-product, typically having 20% moisture content.

Throughout this specification where proportions of materials are given whether as percentages or parts ratios, those proportions are by mass.

The by-products may be collected from venting systems and/or filter systems associated with a steel production process .

The steel production process or processes from which the one or more by-products are derived may include a process in which metallic fumes and/or metallic particulates (dust) is produced. For example, the steel production process or processes from which the one or more by-products are derived may include: the production of pig iron in a blast furnace, steel making including Basic Oxygen

Steelmaking (BOS), electric arc furnaces and/or mill processes .

The one or more by-products so provided to the process may be treated to remove unwanted debris and/or tramp material. The debris and tramp material typically comprises waste such as stones, shredded tyre rubber, pieces of scrap metal, lumps of metal and the like. This debris and tramp material can damage machinery and introduce contaminants into the process. Preferably the debris and tramp material is removed from the one or more by-products prior to any other processing steps. The debris and tramp material may be removed by a screening plant. The one or more by-products may be screened to remove particles which exceed a maximum lump size. The one or more by products may be screened by passing them though at least one mesh screen having a predetermined mesh size. The at least one mesh screen may for example have openings in the range 1mm to 6mm,

preferably 3mm to 6mm. A suitable shape of mesh may be chosen, for example a square, diamond or elongate mesh may be used, other forms or shapes of mesh may also be used.

Typically, by-product material which is provided as a substantially dry material is contaminated to such an extent that pre-screening is desired. Typically, by-product provided as a slurry, directly from the metallurgical process in which it is produced, is substantially free from contaminants such that it may not require pre-screening. There may therefore be a step of ascertaining the

composition or contaminant level of the one or more byproducts and deciding whether pre-screening should take place .

Valued material may be identified in the one or more by-products among or in addition to the debris and tramp material. For example, these valued materials may include large particles or lumps of iron, zinc, manganese, aluminium and/or other, typically non-ferrous, metals. These valued materials may be collected for reuse, and, if desired, reused without further processing. There may be a step of mixing one or more by-products from a first metallurgical (for example steel production) process with one or more by-products from a second

metallurgical (for example steel production) process. The first metallurgical process may be the same or different to the second metallurgical process. For example, flue dust from a BOS process may be mixed with waste oxide dust from a blast furnace, for example in a ratio of two parts BOS process flue dust to one part blast furnace waste oxide dust. Alternatively or additionally, flue dust from a first BOS process may be mixed with flue dust from a second BOS process. The one or more by-products may be mixed in a mixing unit. The one or more by-products may be mixed with raw materials or other by-products. For example the one or more by-products may be mixed with particles of iron from ground slag, in order to increase the iron content of the treated product.

The materials in the one or more by-products may be classified into one or more categories of material. The materials in the one or more by-products may be classified as a material for potential reuse in a metallurgical process (a valued / useful material) . The materials in the one or more by-products may be classified as a waste material.

Materials for potential reuse in a metallurgical process may comprise iron and/or iron oxide. Waste materials may comprise zinc, calcium, sodium and/or other non-ferrous metals or non-ferrous metal oxides.

The composition of the one or more by-products may be ascertained. One or more compounds and/or elements in the one or more by-products may be identified. The

identification of the compounds and/or elements may for example include undertaking chemical analysis of the one or more by-products .

The material in the one or more by-products may be separated using a separation unit. The separation unit may be configured such that particles comprising more than a minimum threshold amount of material for potential reuse in a metallurgical process are separated from particles

comprising less than a minimum threshold amount of material for potential reuse in a metallurgical process. The minimum threshold amount may be 45% by weight of material for potential reuse. The minimum threshold amount may be 55% by weight of material for potential reuse. The minimum

threshold amount may be 65% by weight of material for potential reuse.

The separation unit may be a density separation unit and separate materials on the basis of their density. The separation unit may separate the materials according to the weight, density and/or size of the particles (or a

combination of these attributes) . The separation unit may separate particles of higher density, such as ones with substantial iron content, from particles of lower density, such as ones with substantial zinc, calcium and/or sodium content .

The separation unit may be a hydrocyclone. A

hydrocyclone may be used to separate relatively wet byproduct material. The separation system may be a centrifuge. A centrifuge may be used to separate relatively dry byproduct material. The separation system may be a diffused air flotation system. The separation system may be a

dissolved air flotation system. Thus the materials in the one or more by-products may additionally or alternatively be classified as a material having a density above a certain threshold or as a material having a density below a certain threshold .

Following separation, the one or more by-products may comprise a higher proportion of materials for potential reuse in a metallurgical process, such as iron. Of course it will be appreciated that the separation step may not separate all the waste materials from the materials for potential reuse. Following separation, the proportion of material (in the one or more by-products) which is suitable for potential reuse may increase by 3% to 15% (3% to 15% enrichment) . Following separation, the proportion of material (in the one or more by-products) which is suitable for potential reuse may increase by 3% to 8% (3% to 8% enrichment) . For example, the one or more by-products provided to the process may comprise 40% to 45% iron and after separation on the basis of particle density, the one or more by-products may comprise 45% to 50% iron.

The one or more by-products may be magnetically beneficiated . The one or more by-products may be

beneficiated by one or more magnetic beneficiation units. The magnetic beneficiation may subject the one or more byproducts to a magnetic field. The magnetic beneficiation unit may comprise a rotating drum magnetic separator. The magnetic beneficiation units may be similar to those known in the art of magnetically beneficiating iron ore.

For example, the magnetic beneficiation unit may comprise a conveyer which feeds particles past a rotating drum, there may be a stationary magnet inside a portion of the drum which creates a magnetic field to attract magnetic particles to the drum, magnetic particles may be attracted towards and held to the sides of the rotating drum until they are carried out of the magnetic field and transferred to a collector, the nonmagnetic or less magnetic particles pass the drum and may be sent to a higher intensity magnetic separator or collected as waste.

Several drums may be set up in series to improve the magnetic recovery process. The magnetic beneficiation may occur in a wet or dry environment. The magnetic

beneficiation may remove ferrous, ferromagnetic and/or paramagnetic materials from the by-product material. The magnetic beneficiation may be a multi-step process depending on the composition of the by-product material.

In another example, the magnetic beneficiation unit may comprise a magnetised rotating disk. A portion of the magnetic disk may pass through a slurry of the one or more by-products . Magnetic particles may be attracted to and held to the sides of the rotating disk and carried out of the slurry. The rotating disk may pass a scraper which scrapes the magnetic particles off the rotating disk into a

collector where they can be collected.

Following magnetic beneficiation, the proportion of material (in the one or more by-products) which is suitable for potential reuse may typically increase by 3% to 6% (3% to 6% enrichment) . Following magnetic beneficiation, the proportion of material (in the one or more by-products) which is suitable for potential reuse may increase by 3% to 10% (3% to 10% enrichment) . For example, following magnetic beneficiation the one or more by-products may comprise 45% to 50% iron and after magnetic beneficiation, the one or more by-products may comprise 50% to 55% iron. The speed of rotation of the magnetic drum may affect the enrichment of the magnetic beneficiation .

The one or more by-products may be chemically

beneficiated . The chemical beneficiation may comprise adding one or more chemical agents to the one or more by-products. The one or more chemical agents may comprise an acidic chemical. The one or more chemical agents may comprise an acid having a pH less than 3.5. The one or more chemical agents may comprise an acid having a pH in the range 1 to 5, for example pH 3. The one or more chemical agents may be selected to remove or displace contaminants in the valued material in the one or more by-products . The one or more chemical agents may remove or displace unwanted materials, such as zinc, from valued materials (suitable for re-use in a metallurgical process), such as iron. The one or more chemical agents may separate metals which are chemically bound together, thus facilitating the release of valued materials from waste materials. The one or more chemical agents may comprise a surfactant, for removing oil

contaminants .

The one or more by-products may contain water or another liquid following one or more stages of treatment. The one or more by-products may therefore be dried in a drying apparatus such as a drying bed.

The one or more by-products may be mixed with one or more absorber materials in order to absorb moisture in the one or more by-products . The one or more by-products may be mixed with one or more absorber materials before separation. The one or more by-products may be mixed with one or more absorber materials after separation and before magnetic beneficiation . The one or more by-products may be mixed with one or more absorber materials after separation and after magnetic beneficiation . The one or more by-products may be mixed with one or more absorber materials as a part of the drying process. The absorber materials may comprise a low carbon cementitious material. The absorber materials may comprise lime or a highly alkaline material, for example quicklime. The absorber material may exothermically react with the by-products; this enhances drying of the material. The absorber may advantageously adsorb and/or absorb contaminants, such as oil, in the one or more by-products. The one or more by-products may be mixed with one or more absorber materials in a mixing unit such as a cement mixing plant .

The one or more by-products that have been treated (the treated material) may be a dry powder. The treated material my comprise iron and/or iron oxide powder. In the treated material, the proportion of material suitable for potential reuse may be 5% to 25% higher than the proportion of material suitable for potential reuse in the one or more by- products so provided (5% to 25% enrichment) . In the treated material the proportion of material suitable for potential reuse may optionally be 5% to 15%, optionally 8% to 5%, optionally 12% to 15%, higher than the proportion of material suitable for potential reuse in one or more by- products so provided (5% to 15%, 8% to 15%, 12% to 15% enrichment respectively) . For example, the one or more byproducts so provided may comprise 40% iron and the treated material may comprise between 52% and 55% iron (12% to 15% enrichment) . In another example, the one or more by-products so provided may comprise 50% iron and the treated material may comprise 70% iron (20% enrichment) . The treatment process may be configured such that the treated material may comprise 55% or 62% iron.

The treated material may be mixed with raw materials or other by-products . For example the treated material may be mixed with particles of iron from ground slag, in order to increase the iron content of the treated product.

The treated material may be reused as an input material to a metallurgical process, for example a steel production process or an iron production process. The metallurgical process may be the same process as the process which

produced the one or more by-products. The metallurgical process may be a different process to the process which produced the one or more by-products. The metallurgical process may be a steel production process and/or another process in which molten material containing iron is

generated .

The treated material may be combined with a raw

material before reuse in a metallurgical process. The treated material may undergo further treatment before reuse. For example, the treated material may be sintered.

Alternatively the material may be mixed with a binder, such as molasses or a cementitious material. The material and binder may be formed into briquettes, blocks or other units of material, for example by moulding or extrusion. The briquettes may be tumbled to smooth their edges. Relatively small briquette particles formed during tumbling may be reused and/or re-bound in further briquettes. Blocks may be broken up to form aggregate.

Waste material so removed from the one or more by- products in the treatment process may contain other valuable materials, such as aluminium and/or calcite. The waste materials may therefore be reused, recycled or further processed. For example, calcite may be used in the

production of cementitious materials. The suitability of the waste material for recycling and/or the composition of the waste material may therefore be tested. Advantageously, the waste material may be reused to make binder and/or absorber material .

The method may optionally include a step of carrying out a metallurgical process, for example a steel production process, to generate one or more by-products.

The method of treating by-products of metallurgical processes may be carried out substantially on the site of the metallurgical process plant from which the one or more by-products are derived. Alternatively or additionally the method of treating by-products of metallurgical processes may be carried out at a substantially separate location.

The apparatus may comprise a density separator, a magnetic beneficiation unit, a diffused air flotation unit, a hydrocyclone , and/or a centrifuge.

It will of course be appreciated that features

described in relation to the method of the present invention may be incorporated into the apparatus of the present invention.

Background of the fourth aspect of the Invention

During the handling of molten material in industrial metallurgical process plants, there is liable to be some spillage. In steelmaking processes, for example the Basic Oxygen Steelmaking (BOS) process, a small percentage of molten slag gets spilt when transporting and decanting the slag. Slag may be processed for use in Tarmacadam. However, spilt slag typically becomes contaminated with refuse, oils, scrap metal and the like. The contaminants present will typically render spilt slag unsuitable for use in

Tarmacadam.

In general the spilt slag is collected from the floor of a steelworks, along with all the other waste which may be present. The material, known as dirty slag, clean-up slag, steel making sweepings, slag rubble and slag refuse (among other colloquial names), is typically sent to a metal recovery plant, where major ferrous components are

recovered, and landfilled. This is an environmentally and expensive way of dealing with such material.

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of treating contaminated slag.

Summary of the fourth aspect of the Invention

The present invention provides a method of treating contaminated slag from a steelmaking process, the method comprising the steps of:

providing contaminated slag from one or more

steelmaking processes;

separating the contaminated slag by particle size;

subjecting at least part of the contaminated slag separated by particle size to attrition while it is in a flow of water; and carrying out a magnetic separation step on at least part of the contaminated slag that has been subjected to attrition .

The contaminated slag provided to the process may be produced in a steelmaking process in which molten slag is a by-product. For example, the molten slag may be produced in one or more of: the production of pig iron in a blast furnace, Basic Oxygen Steelmaking (BOS), steelmaking in an electric arc furnace, and/or other variants of steelmaking. Preferably the contaminated slag is contaminated BOS slag.

The contaminated slag may be produced as a result of spillage of molten material. Alternatively the slag may be contaminated in another manner. The contaminated slag may be collected from the floor or catchment area of a

metallurgical process plant. Additionally or alternatively, the contaminated slag may be present in landfill and be provided directly from a landfill site.

The contaminated slag may include, but is not limited to: slag (e.g. blast furnace slag, steelmaking sweepings, BOS slag, electric arc furnace slag, slag rubble, slag refuse, dirty slag, clean-up slag) , coal, coke, wood, paper, plastic, cardboard, refectories, ferrous waste (e.g. steel, skull, desulph skull, ferrous scrap of various sizes

(typically having a size smaller than 0.5m), congealed blended steel and slag), non-ferrous metallic waste (e.g. copper, brass, aluminium, tin, stainless steel) and/or flux replacements (e.g. olivine) .

The contaminated slag may be separated by particle size. The contaminated slag may be separated by particle size in a screening unit comprising one or more screens, for example mesh screens, having openings of a predetermined size, the contaminated slag being separated by size in dependence on the size of the openings. It will be

appreciated that all measurements of particle size mentioned in this document are determined by whether a particle would pass through, when sieved or screened, a mesh having square apertures of that size.

The screening unit may separate out large ("oversized") particles of contaminated slag which may damage or clog machinery downstream. Contaminated slag particles larger than a certain size, for example, larger than 150mm, 175mm, or 200mm, may be considered to be oversized.

Oversized particles may be processed separately to the smaller particles. Processing of oversized particles may separate components such as skulls, plate, refractory, refractory shells and/or BOS slag aggregate. Oversized particles may be separated by an excavator and magnet.

The screening unit may separate out fine particles of contaminated slag ("fines") . Contaminated slag particles smaller than a certain size, for example, smaller than 8mm, 6mm, or 4mm, may be considered to be fines.

The screening unit may additionally separate out large particles of contaminated slag. Large particles of

contaminated slag may be bigger than 40mm, 45mm, or 50mm, and be smaller than oversized particles. For example large particles might lie in the range 45mm to 175mm.

The screening unit may additionally separate out small particles of contaminated slag. Small particles of

contaminated slag may be smaller than 40mm, 45mm, or 50mm, and be bigger than fines. For example small particles might lie in the range 6mm to 45mm. It should also be appreciated that separation of particles by screening is unlikely to be wholly accurate and precise; therefore, in a given sample of particles so separated out by screening, there is likely to be a minor fraction of particles whose sizes fall outside of the desired range.

At least part of the contaminated slag may be

magnetically separated, for example by being passed beneath an overband magnet. The magnetic separation may collect particles with a significant ferrous metal content without the need to expend energy processing them further.

At least part of the contaminated slag so separated may be fed into a flotation system and/or a wash screen. Thus the method may include carrying out a flotation step on at least part of the contaminated slag. Preferably the large particles (e.g. 45mm-175mm sized particles) of contaminated slag may be fed into the flotation system and/or the wash screen. The flotation system may comprise a water filled tank which receives the contaminated slag. Light and/or low density materials ("lights"), for example, dust fines, wood, paper and/or plastic, may float to the top of the tank. The light and/or low density materials may be skimmed from the surface of the water or flow over a weir. The light and/or low density materials may subsequently be screened by the wash screen and collected. Heavy and/or high density materials ("heavies"), for example, slag aggregate,

refractory and/or metallic material, may sink to the bottom of the tank. The heavy and/or high density materials may be removed from the bottom of the tank and may subsequently be screened by the wash screen and collected. It will be appreciated that low density or high density can be understood to mean lower density than water or higher density than water. Thus, low density components of the contaminated slag may be separated from high density

components of the contaminated slag.

At least part of the contaminated slag so separated may be fed into an attrition unit. Preferably the small

particles (e.g. 6mm-45mm sized particles) of contaminated slag may be fed into the attrition unit. The attrition unit may comprise a water filled tank which is preferably

configured to vigorously mix the contaminated slag. The attrition unit may comprise mixing equipment, for example, paddles, blades, rotational shafts, Archimedes screws (auger screws), and/or water jets. The attrition unit may comprise a tank having at least one rotatable shaft running along its length. Paddles and/or Archimedes screws may be mounted on the rotatable shaft for mixing the contaminated slag and transporting the contaminated slag along the length of the attrition unit. The tank may be inclined.

The attrition unit may include a receiving portion for receiving the contaminated slag and mixing it with a

quantity of water. The receiving portion, and preferably the attrition unit as a whole, may act as a flotation system in a similar way to the flotation system mentioned above. Light and/or low density materials, for example, dust fines, wood, paper and/or plastic, may float to the surface of the water. The light and/or low density materials may be mechanically removed or flow over a weir under the influence of water currents. Heavy and/or high density materials, for example, slag aggregate, refractory and/or metallic material, may sink to the bottom of the water. The heavy and/or high density materials may then be transported through the attrition unit by the direct influence of the mixing equipment .

The attrition unit may substantially clean the particles of contaminated slag by causing attrition between the surfaces of the particles. Any oil absorbed onto the surface of the slag particles may be at least partly removed and dispersed into the water. Clean water may be provided to the attrition unit and contaminated water may be removed from the attrition unit. Particles of contaminated slag may be broken up into smaller particles of contaminated slag, for example small particles of contaminated slag may be broken into fines. Breaking-up of particles may assist recovery of the individual components of contaminated slag.

It may be the case that the attrition unit acts as a flotation system for separating light and/or low density materials from heavy and/or high density materials. The mixing equipment may transport the heavy and/or high density materials through the attrition unit and out of the water.

The material transported through the attrition unit may be separated by particle size by a mesh screen. The mesh screen may be a belt for transporting the contaminated slag between treatment units, for example between the attrition unit and another unit. Fine particles of contaminated slag (fines) may be produced in the attrition unit as larger particles are broken up, fines may therefore be collected in a fines trap beneath the screen.

Fines may comprise flux replacement material, for example olivine replacement material; the fines may be processed to separate out the flux replacement material. For instance, fines having a particle size of less than 3mm may be collected for use as a flux replacement. Fines having a particle size of more than 3mm may be collected for use in other aspects of the steel making process and associated operations .

At least part of the contaminated slag may be passed into an air separator, such as an air screen separator. Thus the method may include carrying out an air blowing

separation step on at least part of the contaminated slag. Preferably the material transported in the second direction in the attrition unit may be passed into the air separator. The air separation step may comprise carrying out an air blowing separation in an air screen separator. The

separation step may employ a blower unit configured to blow air at the contaminated slag. The air separator may be a high intensity air/screen separator (HIAS) . The air

separator may remove lighter components of contaminated slag from heavier components of contaminated slag by blowing it from the remaining slag. The air separator may remove wood, paper, plastics and/or fines, which are subsequently collected. The contaminated slag may be wet or dry when it enters the air separator. Advantageously, the air separator may remove surface water from the contaminated slag; surface water may hinder some downstream processes.

At least part of the contaminated slag may subsequently be magnetically separated. Preferably, the heavier

components of the contaminated slag not blown away by the air separator may be magnetically beneficiated . The

contaminated slag may be magnetically separated by passing it under an overband magnet. The magnetic separation may remove and collect ferrous materials and particles having a substantial ferrous metal content; for example, a ferrous metal content which exceeds 40%, 50%, 60% or 70%. Ferrous materials of a particular range of ferrous metal content may be collected: for example ferrous materials with a ferrous metal content in the range of 40% to 60% may be collected.

At least part of the contaminated slag may be screened to remove and collect particles smaller than 20mm, 25mm, or 30mm. Preferably the remaining contaminated slag not removed by magnetic separation may be screened.

At least part of the contaminated slag may be passed into an eddy current separator. Thus the method may include carrying out an eddy current separation step on at least part of the contaminated slag. Preferably the remaining contaminated slag not removed by magnetic separation, or subsequent screening, may be separated by the eddy current separator. The eddy current separator may separate non- metallic materials and non-ferrous/low-ferrous metallic materials. The eddy current separator may additionally separate ferrous materials. The material separated by the eddy current separator may be collected.

Any material separated out and/or collected may be further treated, disposed of as waste or otherwise reused. For example, ferrous materials may be sintered or added directly to a blast furnace; BOS slag aggregate may be crushed and further de-metalled; large particles of BOS refuse may be separated on a manual picking line; fine particles may be magnetically beneficiated . Some separated particles may be used for road surfacing; materials high in calcium may be used as a flux replacement material. The present invention further provides an apparatus for carrying out a method as defined above.

The apparatus may comprise a particle size separator, an attrition unit, a magnetic beneficiation unit, an air separator, a flotation unit, and/or an eddy current

separator .

It will of course be appreciated that features

Background of the fifth aspect of the Invention

Many industrial processes result in toxic waste materials. For example in the steel industry various byproducts are created that are not easily disposed of because of toxic substances in the material. Examples of toxic substances produced are heavy metals such as lead and zinc and hydrocarbons, such as oils. By-products that contain such substances are at best expensive to dispose of, because of landfill charges and/or the costs of treatments to make the substances suitable for landfill.

In GB 2401104A, the contents of which is incorporated herein by reference, a cementitious material that is made partly from waste material is described. The principal use of that material that is described is as a partial

replacement for Portland cement. The material is therefore intended to be suitable for a wide variety of applications. That imposes restrictions on the types and amounts of waste material that can be incorporated in the cementitious material. In particular it is not appropriate to employ toxic waste material in the cementitious material

The present invention seeks to mitigate the above- mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved method of making a load bearing material.

Summary of the fifth aspect of the Invention

The present invention provides a method of making a load bearing material, the method comprising the steps of:

providing a waste material;

mixing the waste material, water, an absorbing agent and a cementitious material; and

adding further water to the mixture to adjust the viscosity of the mixture;

wherein the cementitious material has a composition in the following range:

calcium oxide 2% to 75%

alumina 0.5 to 35%

silica 0.1 to 40%

other components 0 to 50%

The cementitious material of the present invention may be one of the cementitious materials described in GB2401104; in accordance with the invention an absorbing agent and cementitious material is mixed with the waste material. In that way it is possible to produce a load bearing material which has toxic waste materials bound into it and which, because the toxic materials are bound in, can be put to use rather than creating a toxic waste disposal problem. The load bearing material may not have such good properties as conventional concrete and its applications may be more limited but we have recognised that is not a major

disadvantage, provided that there are still some useful applications available for the material. In this respect it should be noted that even an application that generates no profit but is cost neutral and would not be attractive in most circumstances is likely to be financially attractive in the present invention because disposal of the toxic

materials by other means would involve substantial cost.

The invention is of particular advantage when the waste material is a toxic waste material; such a material is one that would have an adverse environmental impact on its surroundings if it were simply included as landfill without additional treatment.

The other components of the cementitious material may comprise at least 3% MgO.

The amount of calcium oxide in the cementitious material is preferably in the range of 20 to 75% and more preferably is in the range of 40 to 60%.

The amount of alumina in the cementitious material is preferably in the range of 5 to 20% and more preferably is in the range of 8 to 15%.

The amount of silica in the cementitious material is preferably in the range of 10 to 40% and more preferably is in the range of 10 to 40%.

The other components are preferably in the range of 0 to 30%.

The cementitious material may be a low carbon cement. The waste material may first be mixed with water, then mixed with an absorbing agent and then mixed with a

cementitious material.

The absorbing agent, which may alternatively be

referred to as a stabilizing agent, may be a lime-based agent. The absorbing agent may comprise more than 50% lime. The lime may be a non-hydraulic lime.

The method may be carried out as a batch process. A single batch may comprise more than 1000kg of waste

material; in examples of the invention described below a single batch comprises more than 3,000kg of waste material.

The waste material may be from a steel production process. The particle size of the waste material is

preferably less than 60mm and more preferably less than 40mm.

The waste material may comprise more than 25%, and may comprise more than 35%, of the mixture of waste material, water, absorbing agent and cementitious material. It is desirable that a substantial amount of waste material is incorporated in the process.

A wide variety of waste materials may be provided for mixing with the cementitious material, which acts as a binder. For example, the waste material may comprise more than 2% hydrocarbons and may comprise more than 8%

hydrocarbons. The hydrocarbons may be oils. Waste material of this kind is found in various waste products from steel production processes, including mill scale and mill sludge generated during such production.

The waste material may alternatively or additionally comprise more than 0.5% heavy metals. The waste material may comprise more than 0.5% of one or more metals selected from the group comprising lead, zinc, titanium, vanadium, iron, manganese, chromium, barium, phosphorus, potassium,

aluminium and compounds containing those metals.

The strength of the material may be more than 1 N/mm², or more than 3 N/mm², and may even be more than 5 N/mm².

Whilst it is generally not disadvantageous for the strength of the material to be higher, it is usually preferred that the strength of the material is not more than 50 N/mm², more preferably not more than 25 N/mm² and even more preferably not more than 15 N/mm²; by accepting a lower strength material it becomes possible to bind into the material a wider range of toxic materials and/or a higher proportion of toxic materials.

The mixing step(s) of mixing the waste material, the water and the absorbing agent may be carried out in less than 5 minutes.

The process may be carried out in ambient conditions without heating any of the materials. It is an advantageous feature of the process that it may be carried out without heating .

The waste material and water may first be mixed; the duration of that mixing may be less than one minute. The absorbing agent may then be mixed into the mixture; the duration of that mixing may be less than one minute.

In one example of the invention the cementitious material may then be mixed into the mixture; the duration of that mixing may be less than one minute. Further water may then be added to the mixture to increase its flowability (ie reduce its viscosity) to a desired level.

The method may further include the subsequent step of laying the material in one or more layers. Each layer may have a thickness in the range of 200mm to 600mm; the thickness may be in the range of 300mm to 400mm.

The method may further include the step of laying a top layer of another material, for example tarmacadam or high strength concrete over the one or more layers to form a load bearing structure suitable for vehicular traffic. The load bearing structure may be a road.

In another example of the invention, the waste material is mixed with the water and absorbing agent and a period of more than 12 hours passes before the cementitious material is added. The duration of the mixing of the cementitious material may be less than one minute. Further water may then be added to the mixture to increase its flowability (ie reduce its viscosity) to a desired level.

The method may include the subsequent step of pouring the material into a plurality of moulds. The moulds may be of generally cuboidal shape. The generally cuboidal moulds may incorporate recesses and/or projections to create corresponding formations in the moulded products. The moulds may have a cubic capacity of more than 0.2m³ and may have a cubic capacity of more than 0.5m³. It is desirable to have relatively large moulded products. The cubic capacity of the moulds may be less than 3m³.

The method may further include the subsequent steps of removing the moulds to leave blocks of load bearing material. The blocks may be used in various ways. For example, the blocks may be arranged in rows on top of one another to define a wall.

The present invention further provides a load bearing material made from a method as defined above. The load bearing material may comprise a load bearing sub-base, for example for a road. The load bearing material may comprise a block.

The load bearing material may include (toxic) waste material that is bound into the load bearing material such that it does not leach from the material when exposed to water. The non-leaching may be tested by employing the test described in the Environment Agency publication EA NEN 7375:2004.

In the description above of the five different aspects of the invention, each aspect is described

separately. It should, however, be understood that the different aspects of the invention may be combined together in any combination. For example the first and second aspects of the invention relate to processing waste from steel rolling mills and may therefore be carried out at the same location. Since all the aspects of the invention are applicable to a steel production facility, they may be present in any combination at such a facility; furthermore equipment employed in respect of carrying out one aspect of the invention may also be used, where appropriate, in another aspect of the invention.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a schematic diagram showing the steps taken / flow of material in relation to a method embodying the first aspect of the invention; Figure 2 shows a schematic diagram showing the steps taken / flow of material in relation to a method embodying the second aspect of the invention;

Figure 3 shows a schematic diagram showing the steps taken / flow of material in relation to a method embodying a third aspect of the invention;

Figure 4 shows a schematic diagram showing the steps taken / flow of material in relation to a method embodying a fourth aspect of the invention; and

Figure 5 is a schematic isometric view of a block that may be moulded from a load bearing material embodying the fifth aspect of the invention.

Detailed Description

A method of treating contaminated mill scale will now be described, with reference to Figure 1.

Unprocessed contaminated mill scale 302 is provided; the mill scale having been removed from hot rolled steel in a steel rolling mill. The contaminated mill scale comprises particles and flakes comprising 75% iron oxide and a 2% oil content .

The contaminated mill scale 302 is loaded by a front end loader into the feed end of a screening plant 304. The screening plant comprises two screening decks comprising vibrating mesh screens. The screening plant 304 screens the mill scale 302 for debris and tramp material 306 above a minimum particle size by passing the mill scale through a mesh screen having 16mm openings. The oversized debris and tramp material 306 which does not pass through the screen is removed and disposed of.

The screening plant 304 also grades the mill scale 302 by particle size. Particles sized between 0 and 1 mm 308 will be sent for separate processing.

The mill scale is then fed by a conveyer into a first attrition unit, referred to herein as a High Intensity Attrition Unit (HIAU) 312. The HIAU 312 comprises a

receiving portion which receives the mill scale 302 and mixes it with water to form a first slurry. The HIAU 312 comprises an inclined tank having two rotatable shafts running along its length. Paddles are mounted on the rotatable shafts. The HIAU 312 has a power rating of 90kW. The power output is split between the two shafts. In use the shafts and paddles rotate at a speed which violently churns the first slurry and subjects it to a severe mechanical action in which the particles in the first slurry are subjected to a high level of attrition. The paddles on the two shafts overlap, although do not contact one another, thereby increasing the level of attrition in the region between the shafts. The fluid capacity of the HIAU 312 is approximately 800 litres.

A first surfactant 314 is introduced into the HIAU 312 during operation of the unit. During attrition by the HIAU 312 oil absorbed onto the surface of the mill scale

particles is partly removed and dispersed into the first slurry. The first surfactant 314 then emulsifies the oil in the water. Solids in the first slurry are transported along the length of the HIAU 312 by the action of the paddles. Typically a particle would on average take 1 to 2 minutes to pass through the HIAU 312. Substantially clean water is input into the HIAU 312 and contaminated water is output from the HIAU 312, such that clean water is substantially continuously be provided to the attrition unit and contaminated liquid is

substantially continuously be removed from the attrition unit. The contaminated water is sent for treatment wherein the contaminants are removed and the water is cleaned for reuse in the process.

The mill scale particles which are transported through the HIAU 312 are rinsed by water from spray bars as they exit the unit.

The mill scale 302 is fed into a second attrition unit, referred to herein as a Medium Intensity Attrition Unit (MIAU) 316. The MIAU 316 comprises a receiving portion which receives the mill scale 302 and mixes it with water to form a second slurry. The MIAU 316 comprises a tank having two rotatable shafts running along its length. The rotatable shafts feature Archimedes screws and paddles mounted to them wherein the paddles of the two shafts overlap. In use the shafts rotate at a speed which churns the second slurry and subjects it to a mechanical action in which the particles in the second slurry are subjected to a moderate level of attrition. The MIAU 316 is less powerful than the HIAU 312 and subjects the slurry to a lower intensity of attrition than the HIAU 312. The MIAU 316 has a power rating of 60kW, the power output split between the two shafts. The fluid capacity of the MIAU 316 is approximately 1200 litres.

A second surfactant 318 is introduced into the MIAU 316 during operation of the unit. During attrition by the MIAU 316 the remaining oil absorbed onto the surface of the mill scale particles is partly removed and dispersed into the slurry 315. The second surfactant 318 then emulsifies the oil in the water. The slurry is transported through the MIAU 316 by the paddles and Archimedes screws. Typically a particle would on average take 1 to 2 minutes to pass through the MIAU 316.

As in the HIAU 312, substantially clean water is input into the MIAU 316 and contaminated water is output from the MIAU 316, such that clean water is substantially

continuously be provided to the attrition unit and

contaminated liquid is substantially continuously be removed from the attrition unit.

The mill scale particles which are transported through the MIAU 316 exit the unit and fall onto a conveyer. The mill scale 302 is aired as it is transported to a third attrition unit.

The third attrition unit, referred to herein as a Low Intensity Attrition Unit (LIAU) 322, subjects the mill scale to a third stage of attrition. The LIAU 322 comprises a receiving portion which receives the mill scale 302 and mixes it with water to form a third slurry. The LIAU 322 comprises a tank having two rotatable shafts running along its length. The rotatable shafts comprise Archimedes screws. In use the shafts and Archimedes screws rotate subjecting the third slurry to further attrition which is lower still in intensity than the attrition in the MIAU 316. The LIAU 322 has a power rating of 22kW, the power being split between the two shafts. The fluid capacity of the LIAU 322 is approximately 1600 litres.

As in the HIAU 312 and MIAU 316, substantially clean water is input into the LIAU 322 and contaminated water is output from the LIAU 322, such that clean water is substantially continuously be provided to the attrition unit and contaminated liquid is substantially continuously be removed from the attrition unit.

A third surfactant 324 is introduced into the third slurry during the operation of the LIAU 322. The third chemical agent 324 is introduced into the LIAU 322 at various locations in the unit. During attrition by the LIAU 322 the remaining oil absorbed onto the surface of the mill scale particles is partly removed and dispersed into the third slurry. The third surfactant 324 then emulsifies the oil in the water. The third slurry is transported through the LIAU 324 by the action of the Archimedes screw.

Following treatment in the three attrition units 312, 316, 322 treated mill scale 326 is output onto a conveyer which transports the treated mill scale 326 to drying beds 328 for drying.

Whilst the first aspect of the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

A method of treating contaminated mill sludge will now be described, with reference to Figure 2.

Unprocessed contaminated mill sludge 402 is provided; the mill sludge having been provided from a steel rolling mill. By way of example, the contaminated mill sludge comprises: approximately 75% iron oxide particles and flakes having an average particle size of less than 1 millimetre, and approximately 6% oils. The contaminated mill sludge 402 is loaded directly to the feed hopper of a first screening unit 404. The first screening unit 404 comprises an inclined vibrating mesh screen having 80mm openings. The mesh screen removes large particles of metal, debris and tramp material from the contaminated mill sludge 402 which may otherwise damage the machinery .

The contaminated mill sludge 402 which passes through the mesh screen of the first screening unit 404 drops into an auger screw 406. The auger screw 406 transports the mill sludge 402 to a second screening unit 408 comprising a rotating trommel. The rotating trommel comprises a

cylindrical 3mm mesh screen. Mill sludge 402 is fed into the trommel at one side and oversized particles which cannot pass through the screen exit at the other side.

Ballast material 412 comprising fine limestone sand (50 to 700 micron sized particles) is also fed into the trommel. Ballast material is added in the ratio of 1 part ballast material to 10 parts mill sludge (by mass) . The ballast material 412 is thereby mixed with the mill sludge. Water 410 is sprayed into the trommel to help the mill sludge particles 402 and ballast material particles 412 pass through the screen.

The mill sludge 402 and ballast material 412 which passes through the trommel of the second screening unit 408 is fed into a jet pump 414. The jet pump 414 is configured to receive mill sludge 402 and ballast material 412 and water 410 in the ratio 1 part mill sludge 402 and ballast material 412 to 10 parts water 410. The mill sludge 402, ballast material 412 and water 410 mixture forms mill sludge slurry . The action of the jet pump 414 vigorously mixes the mill sludge slurry. The jet pump 414 causes attrition between the mill sludge particles, between the mill sludge particles and the jet pump 414, and between the mill sludge particles and the other surfaces of the jet pump 414. The collisions and attrition of the mill sludge particles break up clumps of mill sludge and separates oils from the surface of the mill sludge particles. The ballast material 412 abrades the surface of the mill sludge particles increasing separation of oils from the surface of the particles. The ballast material 412 also adsorbs oils in the mill sludge slurry .

The mill sludge slurry exits the jet pump 414 having a pressure of approximately lObar. The mill sludge slurry is then passed into a receiving tank 416. The receiving tank

416 reduces the speed and pressure of the mill sludge slurry output from the jet pump 414. The receiving tank comprises mixing equipment to prevent the mill sludge 402 and ballast material 412 from settling in the receiving tank 416.

The mill sludge slurry is then fed into an electrocoagulation unit 418. The electro-coagulation unit 418 comprises four consecutive pairs of aluminium electrodes, past which the mill sludge slurry passes. Electrocoagulation causes the contaminants in the water, including metal ions, emulsified oils and suspended solids, to coagulate, precipitate and form floe.

Following electro-coagulation the mill sludge slurry is fed to a flotation tank 420. The flotation tank 420

comprises a series of vertical baffles under and over which the mill sludge slurry flows. Lighter coagulated and precipitated material floats to the top of the flotation tank 420 forming floating floe. Skimmers skim the floating material from the top of the floatation tank 420. The lighter material ("lights") 422 typically comprises oils, carbon and other small particles.

Heavier coagulated and precipitated material

("heavies") 424 skinks to the bottom of the flotation tank 420 forming sludge. The bottom of the tank is configured such that the sludge drains to toward an outlet valve. The outlet valve is controlled by a timer and periodically opens to release the sludge. The sludge typically comprises metal and metal oxide particles, principally iron and iron oxide, as well as ballast material 412 and other large and heavy particles .

The mill sludge slurry, which comprises the remaining lights 422 and heavies 424, is fed into a lamella clarifier 426. The lamella clarifier 426 comprises a set of inclined plates between which the mill sludge slurry flows. As in the floatation tank, heavies 424 sink to the bottom of the lamella clarifier 426 forming sludge which is periodically drained out, and Lights 422 float to the top of the lamella clarifier 426 forming floating floe which is skimmed off. The remaining water which passes through the lamella clarifier is sent for further processing and is subsequently reused in the treatment process, for example by being sprayed into the trommel or fed into the jet pump.

The sludge (treated mill sludge), comprising heavies 424 drained from the bottom of the floatation tank and lamella clarifier, is dried by passing it through a hot drier 428. The hot drier 428 comprises an auger screw which transports the treated mill sludge through a heated pipe. The dried treated mill sludge is then beneficiated to remove the ballast material and increase the proportion of ferrous metals in the treated mill sludge. The mill sludge is beneficiated in a magnetic beneficiation unit 430

comprising a rotating magnetised drum. The mill sludge particles are fed onto the rotating drum, a stationary magnet inside a portion of the drum creates a magnetic field to attract magnetic particles 432, principally the iron/iron oxide particles, to the drum. The magnetic particles 432 are magnetically held to the sides of the rotating drum until they are substantially carried out of the magnetic field created by the stationary magnet. The magnetic particles 432 then fall from the drum and are collected. Non-magnetic particles, including the ballast material and particles containing only a small amount of magnetic material, are not attracted to the rotating drum as they pass it and are sent to a waste collector.

Whilst the second aspect of the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

A method of treating by-products of metallurgical processes will now be described, with reference to Figure 3.

According to the first embodiment of the invention there is provided a mixture comprising two parts BOS plant waste oxide and one part flue dust. The BOS plant waste oxide and flue dust mixture is provided mixed with water in the form of BOS plant waste oxide and flue dust slurry 102. The BOS plant waste oxide slurry 102 having an approximate water content of 60%. Table 1 provides, by way of example only, the ratio of the main elements and compounds (not including water) present in a sample of BOS plant waste oxide and flue dust slurry (proportions by mass) .

Table 1

The BOS plant waste oxide and flue dust slurry 102 is fed into a screening plant 104 where it is screened. The screening plant 104 screens the BOS plant waste oxide and flue dust slurry 102 for oversized particles, debris and tramp material 106. Oversized particles, debris and tramp material 106 may block or damage the process machinery and contaminate the treated BOS plant waste oxide and flue dust. The screening plant comprises a vibrating grid comprising a 4mm mesh screen. Particles, debris and tramp material 106 larger than the screen's openings will not pass through the vibrating screen and are removed and disposed of.

The screened BOS plant waste oxide and flue dust slurry 102 is then fed into a mixing plant 108. The mixing plant 108 comprises an industrial cement mixing unit. An absorber material 110, which in this particular example is quicklime, is added to the BOS plant waste oxide and flue dust slurry 102 in the mixing plant 108. The quicklime 110 is added such that the BOS plant waste oxide and flue dust slurry 102 and quicklime 110 mixture comprises 5% quicklime. The mixing plant mixes the BOS plant waste oxide and flue dust slurry 102 and quicklime 110 until the quicklime 110 is

substantially evenly distributed throughout the mixture. The absorber material will further absorb any oil contaminants present in the BOS plant waste oxide and flue dust slurry 102.

The mixture of the BOS plant waste oxide and flue dust slurry 102 and the quicklime 110 is then fed into a

hydrocyclone 112 for separation. The hydrocyclone 112 is configured such that the proportion of iron in the underflow (the larger and/or higher density material which outlets at the bottom of the hyrdrocyclone ) is 5% to 8% higher than the proportion of iron in the BOS plant waste oxide and flue dust slurry provided.

The overflow material (the smaller and/or lower density material which outlets at the top of the hydrocyclone) is fed into a waste treatment plant wherein the waste is disposed of and the water is cleaned for reuse.

The underflow slurry is fed into a magnetic

beneficiation unit 114. The magnetic beneficiation unit comprises a rotating drum past which the underflow particles are fed. A stationary magnet inside a portion of the drum creates a magnetic field to attract magnetic particles, principally iron oxide particles, to the drum. Sufficiently magnetic particles are magnetically held to the sides of the rotating drum until they are substantially carried out of the magnetic field created by the stationary magnet. The magnetic particles then fall from the drum and are

collected. Non-magnetic particles, and particles containing only a small amount of magnetic material, are not attracted to the rotating drum as they pass it and are sent to a waste collector. The magnetic beneficiation unit 114 is configured such that the proportion of iron in the sufficiently magnetic product is 3% to 6% higher than the proportion of iron in the underflow slurry. In another embodiment (not shown) the nonmagnetic or less magnetic particles that pass the drum are sent to a second higher intensity magnetic separator, where the particles are again separated into magnetic particles and non-magnetic and partially magnetic waste.

The magnetic particles which are collected are sent for drying in a heater unit to produce an iron oxide rich powder 116.

The proportion of iron in the treated material is 12% to 15% higher than the proportion of iron in the one or more by-products so provided (12% to 15% enrichment) . Table 2 provides, by way of example only, the ratio of the main elements and compounds present in a sample of treated BOS plant waste oxide and flue dust.

Table 2

Material sent to the waste collector during magnetic beneficiation is tested for recycling. Materials identified as recyclable are collected and sent for

recycling; unwanted materials are disposed of accordingly.

Whilst the third aspect of the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described .

In a first variation, the mixture of the quicklime and the BOS plant waste oxide and flue dust slurry, as described above, undergoes separation in a diffused air flotation system (as opposed to a hydrocyclone ) . The diffused air flotation system passes microbubbles through the slurry inside a tank. The microbubbles adhere to the suspended particles. Particles which are below a threshold density will float to the surface forming a froth which is skimmed from the surface of the tank. Particles which are above a threshold density will be too heavy to rise to the surface and will settle at the bottom of the tank as sludge, or will they be kept in suspension. The diffused air flotation system is configured such that particles having a density equal to or higher than the density of iron oxide will not float to the surface. Similarly to the hydrocyclone , the diffused air flotation system is configured such that the proportion of iron in the slurry is 5% to 8% higher than the proportion of iron in the BOS plant waste oxide and flue dust slurry provided. The separated BOS plant waste oxide and flue dust slurry is then processed as above.

In a second variation, substantially dry BOS plant waste oxide and flue dust granules are provided as starting material. The BOS plant waste oxide and flue dust slurry is fed by a conveyor into a screening plant where it is screened for oversized particles and mixed with an absorber material as described above. In this second variation the hydrocyclone is replaced with a centrifuge for separation. The centrifuge is configured such that particles having a density equal to or higher than the density of iron oxide are substantially separated from particles comprising lower density materials. The particles comprising lower density materials are then fed into a waste treatment plant. The particles comprising higher density materials are fed into a dry magnetic beneficiation unit and are magnetically beneficiated in a similar manner to before.

In a third variation, BOS plant waste oxide slurry and blast furnace waste oxide slurry are provided as starting material. The BOS plant waste oxide slurry and the blast furnace waste oxide slurry are fed into a mixing plant where they are thoroughly mixed, an absorber material is also added to the mixing unit and included in the mix. The BOS plant waste oxide, blast furnace plant waste oxide and absorber material are then fed into a hydrocyclone for classification and treatment as above.

A method of treating contaminated slag will now be described, with reference to Figure 4.

Unprocessed BOS refuse 202 (contaminated slag from a BOS process) is provided.

The unprocessed BOS refuse 202 is screened in a first screening unit 204 comprising a mesh screen having 175mm openings. The screening unit removes oversized particles 206 of a particle size larger than 175mm.

The oversized particles 206 are subsequently sent for separation by an excavator and magnet into components including skulls (175mm+), plate (175mm+), refractory

(175mm+) and non-metallic (175mm+) .

The (0mm-175mm) BOS refuse particles are passed beneath an overband magnet 208. The overband magnet 208 attracts and removes (0mm-175mm) ferrous particles 210 having a

significant ferrous metal content.

The remaining (0mm-175mm) BOS refuse particles are screened in a second screening unit 212. The second

screening unit comprises a plurality of mesh screens configured to separate out: fine BOS refuse particles 214 having a particle size smaller than 6mm; small BOS refuse particles 216 having a particle size from 6mm to 45mm; and large BOS refuse particles 218 having a particle size from 45mm to 175mm.

The fine (0mm-6mm) BOS refuse particles 214 are collected for use as a flux replacement.

The large (45mm-175mm) BOS refuse particles 218 are fed into a flotation system 220 and wash screen. The flotation system 220 comprises a water filled tank which receives the large BOS refuse particles 218. Low density materials 222, including wood, paper and plastic, float to the top of the tank and flow over a weir and are subsequently screened by the wash screen. High density materials 224, including

45mm-175mm BOS refuse particles, sink to the bottom of the tank and are removed from there.

The small (6mm-45mm) BOS refuse particles 216 are fed into an attrition unit, herein referred to as a High

Intensity Attrition Unit (HIAU) 226. The HIAU 226 comprises a water filled tank having two rotatable shafts running along its length. The tank is inclined and the level of water in one end of the tank is higher than the level of water in the other end of the tank. Archimedes screws are mounted to the rotatable shafts. The Archimedes screws are configured to mix the contents of the tank and transport solid material up the incline toward one end of the tank. In use, the rotatable shafts of the attrition unit rotate at a speed which vigorously mixes the contents of the tank.

The small BOS refuse particles 216 are received in a receiving portion of the HIAU 226 where the small BOS refuse particles 216 are mixed with water. High density components 230 of the small BOS refuse 216, including slag aggregate, refractory and metallic waste, will sink and interact with the Archimedes screws. The high density components 230 of the small BOS refuse 216 will be subjected to attrition as they interact with the Archimedes screws and are forced against each other. The attrition may break up some of the small BOS refuse particles 216 and help remove oils and other contaminants on the surfaces of the particles, thereby substantially cleaning the small BOS refuse particles 216. The Archimedes screws will transport the high density components 230 of the small BOS refuse 216, in a first direction along the length of the HIAU 226.

Low density components 228 of the small BOS refuse 216, including dust fines, wood, paper and plastic, float or are substantially suspended in the water in the HIAU 226. The low density components 228 are transported under the influence of water currents in a second direction counter to the movement of the high density components 230. The low density materials 228 flow over a weir and exit the HIAU 226 at the opposite end to the end which the high density components 230 exit.

The BOS refuse transported in the first direction in the HIAU 226 is fed onto a mesh belt 232 having 6mm

openings. BOS refuse fines 234 (for example those created from the breakup of larger particles in the attrition unit) fall through the mesh into a fines trap where they are collected. The fines 234 are then separated into 0mm-3mm flux replacement material, and 3mm-6mm waste material.

The BOS refuse, is transported by the mesh belt 232 to an air separator, known herein as a high intensity

air/screen separator (HIAS) 236. The HIAS 236 comprises a blower unit configured to blow air at the BOS refuse. The HIAS 236 removes and collects light components 238 of the clean 6mm-45mm BOS refuse contaminated slag, such as wood, paper, plastics and fines, by blowing them from the

remaining BOS slag.

The remaining clean 6mm-45mm BOS refuse is subsequently magnetically separated by passing it under an overband magnet 240. Particles of 6mm-45mm BOS refuse substantially comprising ferrous material (E-scrap) 242 are removed by the overband magnet 240.

A third screening unit 244 separates out 6mm-25mm BOS refuse 246, which typically comprises 6mm-25mm BOS slag aggregate.

The remaining 25mm-45mm BOS refuse is fed into an eddy current separator 248. The eddy current separator 248 separates the remaining 25mm-45mm BOS refuse into: 25mm-45mm high-ferrous material 250, 25mm-45mm non-ferrous/low-ferrous metallic material 252, and 25mm-45mm non-metallic material 254.

Whilst the fourth aspect of the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

Two examples of the fifth aspect of the invention will now be described, the examples beginning with the same starting waste material but resulting in different load bearing products. In each case the process will first be described in outline and then a more detailed description will be provided. EXAMPLE 1

A first example of the invention, in which various hot mill sludges from a steel making process are each used in a batch process to make a low strength load bearing material for use as a sub-base for a road or the like, will now be described in general terms. The steps in the example are as follows :

1. An excavator introduces filter-pressed hot mill sludge into the drum of a forced action paddle mixer and at the same time water is added to the mixer drum.

2. A pre-blended absorbing agent is then added via an

auger and further mixing takes place in the drum.

3. A cementitious material is then added via an auger and further mixing takes place in the drum.

4. Water is added to the mixture in the drum to increase the workability of the mixture.

5. The mixture is then emptied from the mixer drum into an articulated dump truck and transported to the site where it will be used.

6. The mixture is tipped from the dump truck into the area where it is to be laid as a sub-base and is laid in several layers which are mechanically pressed to remove air voids .

7. Once the final layer has been laid and pressed any

excess material around edges of the layers is cut off.

8. The layers are then left in the open air to cure and finally a capping layer of a desired kind is laid over the sub-base. The example of the process described in outline above will now be described in more detail, using the same numbered steps as are used above:

1. An excavator introduces 3,400kg of filter-pressed hot mill sludge into the drum of a forced action paddle mixer. At the same time 1800 litres of water is added to the mixer drum. The sludge and water are mixed for about 30 seconds.

A pre-blended absorbing agent is then added via an auger and further mixing takes place in the drum for about 15 seconds. The absorbing agent is a lime-based absorber and is sold under the trade mark CenDri by Cenin Ltd.

1,000kg of a cementitious material in the form of a low carbon cement is then added via an auger from a storage silo and further mixing takes place in the drum for about 30 seconds. The low carbon cement is that sold under the trade mark CenPave by Cenin Ltd. Its main constituents are approximately as follows: CaO 52%; Si0₂ 27%; A1₂0₃ 12%; Fe₂0₃ 0.8%; MgO 5.5%.

Water is added to the mixture in the drum to increase the workability of the mixture. The amount of water is adjusted to arrive at a "slump test" value of between 10mm and 80mm resulting in a mixture that is in a semifluid state. The amount of water added in this step is between 100 and 1,000 litres.

The mixture is then emptied from the mixer drum into an articulated dump truck and transported to the site where it will be used.

The mixture is tipped from the dump truck into the area where it is to be laid as a sub-base. It is then laid in several layers, each approximately 350mm thick.

Each layer is mechanically pressed to remove air voids. The material may be tipped in one location and material moved by an excavator to provide the additional layers or the dump truck may tip the material for each layer separately . 7. Once the final layer of the mixture has been laid and pressed any excess material around edges of the layers is cut off.

8. The layers are then left in the open air to cure for 12 to 24 hours. After that curing the compressive strength of the sub-base has some strength (for example 1 to 2 N/mm2 ) , enabling work to be carried out on top of it; the sub-base continues to strengthen over the following 15 to 30 days reaching a final strength in the range of 5 to 15 N/mm². Finally a capping layer of a desired kind is laid over the sub-base. In this particular example the capping layer is high strength concrete and the final load bearing product is a road. EXAMPLE 2

In the second example of the invention, various hot mill sludges from a steel making process are each used in a batch process to make a low strength load bearing material for use as low-strength load bearing blocks. The steps in the example will now be described in general terms as follows :

2. A pre-blended absorbing agent is then added via an

auger and further mixing takes place in the drum.

3. The mixture is then emptied from the mixer drum and placed in a storage area, either directly, or by being transported there in a dump truck. 4. The mixture is then left for a period of time to allow the materials to react and stabilize to form what is referred to herein as a "Pre Blend".

5. An excavator then introduces the Pre Blend into the drum of the same forced action paddle mixer or another one .

6. A cementitious material is then added via an auger and further mixing takes place in the drum.

7. Water is added to the mixture in the drum to increase the workability of the mixture.

8. The mixture is then emptied from the mixer drum into a concrete wagon mixing truck and transported to a block moulding area.

9. The mixture is then poured in layers into open-topped moulds, and a vibration rod used continuously to release trapped air. The moulds are of a generally cuboid shape.

10. Once each mould is full, a levelling bar is used to smooth off the exposed face of the mixture.

11. After some further time, the moulds are removed for re-use, leaving the blocks fully formed.

12. The blocks are then left in a storage area in the open air to cure.

13. After curing, the blocks are ready for use, for example for arranging in staggered rows on top of one another to define a wall.

The second example of the process described in outline above will now be described in more detail, using the same numbered steps as are used abo An excavator introduces 3,400kg of filter-pressed hot mill sludge into the drum of a forced action paddle mixer. At the same time 500 litres of water is added to the mixer drum. The sludge and water are mixed for about 30 seconds.

The mixture is then emptied from the mixer drum and placed in a storage area, either directly, or by being transported there in a dump truck.

The mixture is then left for about 24 hours to allow the materials to react and stabilize to form what is referred to herein as a "Pre Blend".

An excavator then introduces 6,400 kg of the Pre Blend into the drum of the same forced action paddle mixer or another one.

1,000kg of a cementitious material in the form of a low carbon cement is then added via an auger from a storage silo and further mixing takes place in the drum for about 30 seconds. The low carbon cement is that sold under the trade mark CenPave by Cenin Ltd. Its main constituents are approximately as follows: CaO 52%;

Si0₂ 27%; A1₂0₃ 12%; Fe₂0₃ 0.8%; MgO 5.5%.

Water is added to the mixture in the drum to increase the workability of the mixture. The amount of water is adjusted to arrive at a "slump test" value of between 100mm and 150mm resulting in a mixture that is in a semi-fluid state, and more flowable than in the first example described above. The amount of water added in this step is between 100 and 1,000 litres.

9. The mixture is then poured in layers into open-topped moulds that are pre-treated with oil to prevent bonding of the mixture to the mould walls, and a vibration rod used continuously to release trapped air. The moulds are of a generally cuboidal shape with each of the five walls defining the cuboid provided as separate elements and detachably fixed together with seals between ad acent wall edges. The moulds have a length of

1600mm, a width of 800mm and a depth of 800mm. The mixture is poured into the moulds in three layers and a series of moulds are set up on a recycling belt to allow the mixture to be poured into the moulds in turn.

11. After 24 to 48 hours, the moulds are dismantled and removed for re-use, leaving the blocks fully formed. The moulds can be tipped onto their sides to facilitate this process.

12. The blocks are then left in a storage area in the open air to cure. The blocks are cured for a further 1 to 5 weeks to gain strength. After that curing the compressive strength of the blocks is in the range of 5 to 15 N/mm².

13. After curing, the blocks are ready for use, for example for arranging in staggered rows on top of one another to define a wall. In the examples above, various hot mill sludges of differing compositions were employed. The ranges of the compositions of the sludges were as follows: S1O₂ 1-10%; AI₂O₃ 0.1-3.0%; Mn 0.2-0.5%; CaO 0.5-20%; MgO 0-0.8%; P₂0₅0- 0.15%; Ti0₂ 0-0.3%; Na₂0 0-0.6%; K₂0 0-0.25%; Zn 0.05-0.35%; C 5-25%; S 0.05-0.5%; FeO 15-50%; Fe₂0₃25-45%. The sludges lost 8-25% of their mass when volatiles were burnt off in testing to assess hydrocarbon levels.

Whilst two particular examples of processes according to the fifth aspect of the invention have been described, it should be understood that many variations may be made within the scope of the invention.

One such variation is that it may be desirable in certain applications to add other materials, in particular but not exclusively, aggregate or sand to the materials that are mixed. The aggregate or sand may be added at any appropriate stage. Most commonly the aggregate would be of 10mm to 25mm particle size.

For example, the blocks of Example 2 are described as cuboidal . Whilst the blocks may be precise cuboids, it is also possible to produce blocks of a slightly different shape by selecting walls for the mould that are not simply planar on their interior surfaces. Fig. 5 shows an

isometric view of a block 1 provided with a top face having upstanding parts 2 and a bottom face (not shown) formed with corresponding recesses. The upstanding parts 2 on the top face of the block may engage in corresponding recesses (not shown) formed in the bottom face of a similar, second, block placed on top of the first block to provide interlocking formations holding the blocks in position relative to one another .

Where in the foregoing description, integers or elements are mentioned which have known, obvious or

foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other

embodiments .

Claims

1. A method of processing mill scale, the method

comprising the steps of:

providing contaminated mill scale from the processing of steel;

combining the contaminated mill scale with a first quantity of water;

subjecting the contaminated mill scale to three or more stages of attrition to reduce the level of contaminants; adding one or more chemical agents to the contaminated mill scale.

2. A method according to claim 1, wherein the step of subjecting the contaminated mill scale to three or more stages of attrition comprises subjecting the contaminated mill scale to attrition in an attrition unit, the attrition unit comprising a rotatable shaft comprising an Archimedes screw and/or paddles.

3. A method according to any preceding claim, wherein the step of subjecting the contaminated mill scale to three or more stages of attrition comprises subjecting the mill scale to three or more stages of attrition wherein each stage of attrition is less intense than the previous stage of attrition .

4. A method according to any preceding claim, wherein the contaminated mill scale is subjected to three or more stages of attrition in three or more distinct attrition units.

5. A method according to any preceding claim, wherein the step of adding one or more chemical agents to the

contaminated mill scale comprises adding three or more chemical agents to the mill scale, one chemical agent being added during each stage of attrition.

6. A method according to any preceding claim, wherein the chemical agent is a surfactant.

7. A method according to any preceding claim, wherein the step of providing contaminated mill scale comprises

providing mill scale comprising 50 to 90% ferrous metals.

8. A method according to any preceding claim, wherein the step of providing contaminated mill scale comprises

providing mill scale comprising 55% to 75% ferrous metals.

9. A method according to any preceding claim, wherein the step of providing contaminated mill scale comprises

providing mill scale having an average particle size greater than 1mm.

10. A method according to any preceding claim, wherein the step of providing contaminated mill scale comprises

providing mill scale with an oil contamination level of 0.5% to 10%.

11. A method according to any preceding claim, wherein the method includes a step of using the treated mill scale in a metallurgical process.

12. A method according to any preceding claim, wherein the method includes a step of removing tramp material from the contaminated mill scale.

13. A method according to any preceding claim, wherein the method includes a step of grading the contaminated mill scale, wherein the mill scale is separated by particle size.

14. A method according to any preceding claim, wherein the method includes a step of rinsing the contaminated mill scale .

15. An apparatus arranged to carry out a method according to any preceding claim.

16. A method of processing mill sludge, the method

comprising steps of:

providing contaminated mill sludge, the contaminated mill sludge comprising particles of ferrous material

contaminated with one or more contaminants;

diluting the contaminated mill sludge with process water to form mill sludge slurry;

subjecting the contaminated mill sludge slurry to attrition using a jet pump;

treating the mill sludge slurry by electro-coagulation; substantially separating the ferrous material from the contaminants, thereby producing treated mill sludge.

17. A method according to claim 16, wherein the

contaminants include one or more of: oil, grease, carbon, silica, and/or salts.

18. A method according to claim 16 or 17, wherein the step of providing contaminated mill sludge comprises providing contaminated mill sludge comprising 1% to 25% oil.

19. A method according to any of claims 16 to 18, wherein the contaminated mill sludge is diluted with process water in the jet pump.

20. A method according to any of claims 16 to 19, wherein the ferrous material is substantially separated from the contaminants in a flotation tank and/or a lamella clarifier.

21. A method according to any of claims 16 to 20, wherein the method includes a step of magnetically beneficiating the mill sludge.

22. A method according to any of claims 16 to 21, wherein the method includes a step of adding a ballast material to the contaminated mill sludge.

23. A method according to any of claims 16 to 22, wherein the method includes a step of adding a chemical agent to the contaminated mill sludge.

24. A method according to claim 23, wherein the chemical agent is a surfactant.

25. A method according to any of claims 16 to 24, wherein the method includes a step of removing debris and tramp material from the contaminated mill sludge.

26. A method according to any of claims 16 to 25, wherein the method includes a step of drying the treated mill sludge .

27. A method according to any of claims 16 to 26, wherein the method includes a step of sending contaminants,

separated from the mill sludge, to an emulsion splitter.

28. A method according to any of claims 16 to 27, wherein the method includes a step of removing ballast material from the mill sludge.

29. A method according to any of claims 16 to 28, wherein the process water is cleaned and reused in one or more steps of the method.

30. A method according to any of claims 16 to 29, wherein the method includes a step of providing a treatment control centre to control at least some of the treatment units.

31. An apparatus arranged to carry out a method according to any of claims 16 to 30.

32. A method of treating by-products of a steel production process, the method comprising the steps of:

providing one or more by-products of a steel production process ;

separating, on the basis of density, the materials in at least one of the by-products into two or more materials, including a first material comprising materials for re-use in a steel production process; magnetically beneficiating the first material to separate magnetically a treated material having a higher content of iron than the first material.

33. A method according to claim 32, wherein the step of providing one or more by-products comprises providing one or more of the following: waste oxide dust, flue dust, fume dust and/or a slurry thereof.

34. A method according to claim 32 or 33, wherein the one or more by-products are produced in of one or more of the following processes: the production of pig iron in a blast furnace, Basic Oxygen Steelmaking, the production of iron and/or steel in an electric arc furnace, mill processes.

35. A method according to any of claims 32 to 34, wherein the proportion of iron in the treated material is 5% to 25% higher than the proportion of iron in the one or more byproducts so provided.

36. A method according to any of claims 32 to 35, wherein the treated material is used as an input material for a steel production process.

37. A method according to claim 36, wherein the steel production process is the same process which generated the one or more by-products .

38. A method according to any of claims 32 to 37, wherein the step of separating the materials comprises separating the materials using a diffused air flotation unit.

39. A method according to any of claims 32 to 38, wherein the step of separating the materials comprises separating the materials using a hydrocyclon

40. A method according to any of claims 32 to 39, wherein the step of separating the materials comprises separating the materials using a centrifuge.

41. A method according to any of claims 32 to 40, wherein the step of magnetically beneficiating the one or more byproducts comprises a rotating drum magnetic separator.

42. A method according to any of claims 32 to 41, wherein the one or more by-products are chemically beneficiated by adding one or more chemical agents.

43. A method according to claim 42, wherein the one or more chemical agents comprise an acid having a pH in the range of 1 to 5.

44. A method according to any of claims 32 to 43, wherein the method includes a step of carrying out a steel

production process and producing the one or more by- products .

45. A method according to any of claims 32 to 44, wherein the method includes a step of removing tramp material from the one or more by-products .

46. A method according to any of claims 32 to 45, wherein the method includes a step of mixing the one or more byproducts with one or more absorber materials.

47. A method according to any of claims 32 to 46, wherein the method includes a step of mixing two or more by-products from two or more distinct steel production processes.

48. A method according to any of claims 32 to 47, wherein the method includes a step of testing the suitability of the one or more waste materials for recycling.

49. A method according to any of claims 32 to 48, wherein the method includes a step of mixing the one or more byproducts with a binder.

50. A method according to claim 49, wherein the method includes a step of moulding the one or more by-products and binder mixture into one or more units of material.

51. An apparatus arranged to carry out a method according to any of claims 32 to 50.

52. A method of treating contaminated slag from a

steelmaking process, the method comprising the steps of: providing contaminated slag from one or more

steelmaking processes;

separating the contaminated slag by particle size;

subjecting at least part of the contaminated slag separated by particle size to attrition while it is in a flow of water; and

carrying out a magnetic separation step on at least part of the contaminated slag that has been subjected to attrition .

53. A method according to claim 52, wherein the contaminated slag is dirty slag, clean-up slag, steel making sweepings, slag rubble and/or slag refuse.

54. A method according to claim 52 or 53, wherein the contaminated slag comprises BOS slag produced in a Basic Oxygen Steelmaking process.

55. A method according to any of claims 52 to 54, wherein the method includes carrying out an air blowing separation step on at least part of the contaminated slag.

56. A method according to claim 55, wherein the air blowing separation step comprises carrying out air blowing

separation in an air screen separator.

57. A method according to any of claims 52 to 56, wherein the method includes carrying out a flotation step on at least part of the contaminated slag.

58. A method according to any of claims 52 to 57, wherein the method includes carrying out an eddy current separation step on at least part of the contaminated slag.

59. A method according to any of claims 52 to 58, wherein low density components of the contaminated slag are

separated from high density components of the contaminated slag .

60. A method according to claim 59, wherein the low density materials include at least one of: dust fines, wood, paper and/or plastic.

61. A method according to claim 59 wherein the high density materials include at least one of: slag aggregate,

refractory material and/or metallic material.

62. A method according to any of claims 52 to 61, wherein the step of separating the contaminated slag by particle size comprises separating out contaminated slag by particle size by way of at least one mesh screen.

63. A method according to any of claims 52 to 62, wherein the step of subjecting at least part of the contaminated slag separated by particle size to attrition comprises subjecting the contaminated slag to attrition in an

attrition unit, the attrition unit comprising a rotatable shaft comprising an Archimedes screw and/or paddles.

64. A method according to any of claims 52 to 63, wherein the contaminated slag is separated into materials including a material for flux replacement.

65. A method according to any of claims 52 to 64, wherein the contaminated slag is separated into materials including a material comprising more than 40% ferrous metal.

66. A method according to any of claims 52 to 65, wherein the contaminated slag is separated into materials including a material comprising more than 60% ferrous metal.

67. A method according to any of claims 52 to 66, wherein the contaminated slag is separated into materials including slag aggregate.

68. An apparatus arranged to carry out a method according to any of claims 52 to 67.

69. A method of making a load bearing material, the method comprising the steps of:

providing a waste material;

adding further water to the mixture to adjust the viscosity of the mixture;

wherein the cementitious material has a composition in the following range:

calcium oxide 2 to 75g.

o

alumina 0.5 to 35g.

o

silica 0.1 to 40g.

o

other components 0 to 50o

o

70. A method according to claim 69, wherein the other components of the cementitious material comprises at least 3% MgO.

71. A method according to claim 69 or 70, wherein the waste material is first mixed with water, is then mixed with the absorbing agent and is then mixed with the cementitious material .

72. A method according to any of claims 69 to 71, carried out as a batch process, wherein a single batch comprises more than 1000kg of waste material.

73. A method according to any of claims 69 to 72, wherein the waste material comprises more than 25% of the mixture of waste material, water, absorbing agent and cementitious material .

74. A method according to any of claims 69 to 73, wherein the waste material comprises more than 2% hydrocarbons.

75. A method according to any of claims 69 to 74, wherein the waste material comprises more than 0.5% heavy metals.

76. A method according to any of claims 69 to 75, wherein the waste material comprises more than 0.5% of one or more metals selected from the group comprising lead, zinc, titanium, vanadium, iron, manganese, chromium, barium, phosphorus, potassium, aluminium and compounds containing those metals.

77. A method according to any of claims 69 to 76, wherein the waste material is from a steel production process.

78. A method according to claim 77, wherein the waste material is mill sludge from a steel production process.

79. A method according to any of claims 69 to 78, wherein the compressive strength of the load bearing material is in the range of 3 to 15 N/mm².

80. A method according to any of claims 69 to 79, wherein the mixing step(s) of mixing the waste material, the water, the absorbing agent and the cementitious material are carried out in less than 5 minutes.

81. A method according to any of claims 69 to 80, further including the subsequent step of laying the material in one or more layers.

82. A method according to claim 81, wherein each layer has a thickness in the range of 200mm to 600mm.

83. A method according to claim 81 or 82, further including the step of laying a top layer of another material over the one or more layers to form a load bearing structure suitable for vehicular traffic.

84. A method according to any of claims 69 to 80, wherein the waste material is mixed with the water and absorbing agent and a period or more than 12 hours passes before the cementitious material is added.

85. A method according to claim 84 or any of claims 69 to 80, further including the subsequent step of pouring the material into a plurality of moulds.

86. A method according to claim 85, wherein the moulds are of generally cuboidal shape.

87. A method according to claim 85 or 86, wherein the cubic capacity of each mould is more than 0.2 m³.

88. A method according to any of claims 85 to 87, further including the subsequent steps of removing the moulds to leave blocks of load bearing material and arranging the blocks in rows on top of one another to define a wall.

89. A load bearing material made from a method according to any of claims 69 to 88.

90. A load bearing material according to claim 90, wherein the material includes waste material that is bound into the load bearing material such that it does not leach from the material when exposed to water.