GB2529876A

GB2529876A - Reuse of by-products from metallurgical processes

Info

Publication number: GB2529876A
Application number: GB1415736.6A
Authority: GB
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: 2014-09-05
Publication date: 2016-03-09
Also published as: GB201415736D0

Abstract

The present invention provides a method of treating contaminated slag 202 from a steelmaking process. The method comprises: separating the slag by particle size; subjecting at least part of the slag to attrition while it is in a flow of water; and magnetically separating 240 at least part of the slag that has been subjected to attrition. In particular the present invention may be used to treat slag produced during Basic Oxygen Steelmaking. Suitably, the method includes carrying out an air blowing separation step on the contaminated slag, for example in an air screen separator 236. The method may also comprise performing a flotation step 220 and/or an eddy current flotation step 248 on the contaminated slag. The step of separating the contaminated slag by particle size can comprise the use of a mesh screen 204. A rotatable shaft comprising an Archimedes screw and/or paddles may be utilised in the attrition step. The present invention may separate out reusable components of the contaminated slag.

Description

Reuse of by-products from metallurgical processes

Field of the Invention

The present invention concerns the re-use of metallurgical process by-products. More particularly, but not exclusively, this inventicn concerns the reuse of by-products generated from steel production.

Background cf the Invention

During the handling of molten material in industrial metallurgical process plants, there is liable to be some spillage. In steelmaking processes, fcr 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 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 sguare 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. 4Smm-l7Smm 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 (flights"), 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-45rnm 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 eguipment, 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 exampTh, dust fines, wood, paper and/cr plastic, may float to the surface of the water.

The light and/or low density materials may be mechanically remcved or flow over a weir under the influence cf 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 partioes of contaminated stag, 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 divine 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.

Throughout this specification where proportions of

materials are given whether as percentages or parts ratios, those proportions are by mass.

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 subseguent 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; BUS slag aggregate may be crushed and further dc-metalled; large particles of BUS 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 described in relation to the method of the present invention may be incorporated into the apparatus of the present 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: -10 -Figure 1 shows a schematio diagram showing the steps taken / flow of material in relation to a method aocording to a first embodiment of the invention;

Detailed Description

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

Unprocessed BOS refuse 202 (contaminated slag from a 305 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 subseguently sent for separation by an excavator and magnet into components including skulls (l75rnm+), plate (l75rum+), refractory (175mm-I-) and non-metallic (l75rnm+) The (Ornm-175mm) BOS refuse particles are passed beneath an overband magnet 208. The overband magnet 208 attracts and removes (Omm-l75rnm) ferrous particles 210 having a significant ferrous metal content.

The remaining (Ornm-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 305 refuse particles 214 having a particle size smaller than 6mm; small BUS refuse particles 216 having a particle size from 6mm to 45mm; and large BUS refuse particles 218 having a particle size from 45mm to 175mm.

-11 -The fine (Orum-6mra) BOS refuse particles 214 are collected for use as a flux replacement.

The large (45rarn-175mm) BOS refuse particles 213 are fed into a flotation system 220 and wash screen. The flotation system 220 comprises a water filled tank which receives the large EQS 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 45rnm-175mm BUS refuse particles, sink to the bottom of the tank and are removed from there.

The small (6mm-45irrm) 305 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 305 refuse particles 216 are received in a receiving portion of the HIAU 226 where the small BUS 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 -12 -against each other. The attrition may break up some of the small EQS refuse particles 216 and help remove oils and other contaminants on the surfaces of the particles, thereby substantially cleaning the small EQS refuse particles 216.

The Archimedes screws will transport the high density components 230 of the small EQS refuse 216, in a first direction along the length of the HIAU 226.

Low density components 228 of the small EQS refuse 216, including dust fines, wood, paper and plastic, float or are substantially suspended in the water in the lUAU 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 lUAU 226 at the opposite end to the end which the high density components 230 exit.

The EQS 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 Omm-3mm flux replacement material, and 3mm-6mm waste material.

The EQS 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 EQS refuse. The HIAS 236 removes and collects light components 238 of the clean 6mm-45rnm EQS refuse contaminated slag, such as wood, paper, plastics and fines, by blowing them from the remaining BQS slag.

-13 -The remaining clean 6iimn-45mm BOS refuse is subsequently magnetically separated by passing it under an overband magnet 240. Particles of 6mm-45mrn BOS refuse substantially comprising ferrous material (E-scrap) 242 are removed by the overband magnet 240.

A third screening unit 244 separates out 6mm-25rrau 305 refuse 246, which typically comprises 6mm-25rum 305 slag aggregate -The remaining 25rnm-45rnm EQS refuse is fed into an eddy current separator 246. The eddy current separator 248 separates the remaining 25rnm-45rnm BOS refuse into: 25rnm-45rmn high-ferrous material 250, 25mm-45imn non-ferrous/low-ferrous metallic material 252, and 25mm-45mm non-metallic material 254.

whilst 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.

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 -14 -benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

-15 -Claims 1. 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.
2. A method according to any preceding claim, wherein the contaminated slag is dirty slag, clean-up slag, steel making sweepings, slag rubble and/or slag refuse.
3. A method according to any preceding claim, wherein the contaminated slag comprises EQS slag produced in a Basic Oxygen Steelmaking process.
4. A method according to any preceding claim, wherein the method includes carrying out an air blowing separation step on at least part of the contaminated slag.
5. A method according to claim 4, wherein the air blowing separation step comprises carrying out air blowing separation in an air screen separator.

-16 -
6. A method according to any preceding claim, wherein the method includes carrying out a flotation step on at least part of the ccntaminated slag.
7. A method according to any preceding claim, wherein the method includes carrying out an eddy current separation step on at least part of the contaminated slag.
8. A method according to any preceding claim, wherein low density components of the contaminated slag are separated from high density components of the contaminated slag.
9. A method according to claim 8 wherein the low density materials include at least one of: dust fines, wood, paper and/or plastic.
10. A method according to claim 8 wherein the high density materials include at least one of: slag aggregate, refractory material and/or metallic material.
11. A method according to any preceding claim, 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.
12. A method according to any preceding claim, 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.

-17 -
13. A method according to any preceding claim, wherein the contaminated slag is separated Into materials including a material for flux replacement.
14. A method according to any preceding claim, wherein the contaminated slag is separated intc materials including a material comprising more than 401 ferrous metal.
15. A method according to any preceding claim, wherein the contaminated slag is separated into materials including a material comprising more than 601 ferrous metal.
16. A method according to any precedIng claIm, wherein the contaminated slag is separated into materials including slag aggregate.
17. An apparatus for carrying out a method according to any preceding claim.