EP2874964A2

EP2874964A2 - Use of a composition containing heavy ashes for the realization of a magnetic pathway

Info

Publication number: EP2874964A2
Application number: EP13767087.3A
Authority: EP
Inventors: Ercolino BERGAMINI; Dario ARENA; Filippo ARENA
Original assignee: IRIS AMBIENTE Srl UNIPERSONALE
Current assignee: IRIS AMBIENTE Srl UNIPERSONALE
Priority date: 2012-07-17
Filing date: 2013-07-16
Publication date: 2015-05-27
Also published as: WO2014013429A2; EP2874963A1; WO2014013515A1; WO2014013515A9; WO2014013429A3

Abstract

The present invention relates in general terms to the use of a composition comprising bottom ash produced from the incineration of waste, a magnetic component and a stabilizing additive comprising a silicate and at least an alkaline or an alkaline earth sulphide and/or phosphate, for the realization of dedicated magnetic paths. In this regard, the present composition can be particularly useful for preparing dedicated paths for blind individuals, said path being identifiable by using a guide stick provided with a magnet.

Description

USE OF A COMPOSITION CONTAINING HEAVY ASHES FOR THE REALIZATION OF A MAGNETIC PATHWAY

The present invention relates in general terms to a use of a composition comprising bottom ash containing a magnetic component, in admixture with an alkaline or an alkaline earth silicate, and at least an alkaline or an alkaline earth sulphide and/or phosphate, for the realization of magnetic paths, for example dedicated paths for blind individuals. The invention also relates to a guide instrument which can be used to detect said dedicated path, for example in the form of a stick.

Background art

Waste treatment is a complex process that includes a number of stages and procedures aimed at assuring that the waste has a minimal impact on the environment. In particular, waste management involves the collection, transport, treatment and also reuse of the waste materials in an attempt to reduce the effect thereof on human health and the environment . Among thermal waste treatment processes, incineration, which takes place in incinerators and waste-to-energy plants, undoubtedly represents the most widely used technique. However, incinerators used to reduce the volume of waste and recover part of the thermal energy thereof produce residual material of combustion (generally called ash) in an amount that may vary between 20% and 30% relative to the weight of the incinerated material. Said ash can generally be classified into bottom ash and fly ash. The former represents the most substantial fraction of waste produced by the incineration process, whereas the so- called fly ash represents the smaller fraction, and typically derives from purification treatments of the gaseous effluents and ash from boilers. The bottom ash obtained as a residual material of combustion mainly comprises: silicon, calcium, sodium, aluminium and iron oxides, as well as magnesium and potassium oxides. There can also be present traces of heavy metals and organic compounds such as lignin, amino acids, carbohydrates and compounds deriving from the thermal decomposition of organic materials, such as aliphatic and aromatic acids, styrene, polycyclic aromatic hydrocarbons, chloro- organics and the like.

By way of example, the residual material of combustion obtained at the end of a waste incineration process can contain the following components:

Generally speaking, the above-described residual material is collected at the bottom of the combustion chamber of an incinerator and cooled, for example using tanks, and transported by means of chain conveyors. The material thus cooled is then picked up and since it is classified as dedicated waste (above all because of the presence of heavy metals, lead and cadmium), the disposal thereof can take place in specific landfills for dedicated waste.

Alternatively, the residual material of combustion can be further treated by means of processing which comprises: sieving steps, for an initial selection of the materials based on their particle size; steps of extracting metals such as: iron (for example with electromagnets), aluminium and steel; and also steps of extracting other materials that may still be present, such as, for example, glass, ceramics, silicates and the like. At the end of this process one obtains a so-called "bottom ash", which appears as a solid material with a morphology similar to that of an ash or powder having a particle size that can vary from microns to centimetres. Notwithstanding the above-described processing steps, however, the bottom ash can still contain traces of metals or compounds of another nature (such as chlorides, for example), which make the reuse thereof problematic without further inertization treatments. In this regard, in fact, when evaluating the potential recovery of bottom ash, particular attention must be paid to the danger of polluting the soil, subsoil and water (underground and surface) due to the possible release of heavy metals and other substances that may be present in the ash. In particular, heavy metals (such as lead, cadmium and the like) pose a considerable degree of hazardousness which can depend, for example, on the total amounts present in the ash, the pH, the redox potential and other factors of the physicochemical environment in which they are to be found.

Therefore, upstream of the process of recovery and reuse of bottom ash, deriving, that is, from bottom ash treatment deriving from waste incineration processes, further so-called inertization or stabilization treatments are necessary in order to convert the bottom ash into a "secondary raw material" (MPS), that is to say a stable material with physicochemical characteristics enabling the reuse thereof. In this regard, there are treatments known in the art which comprise, for example, bottom ash aging, stabilization, and vitrification processes, all aimed at obtaining a material that does not release any toxic or harmful compounds over time and which can be reused as a recycled material, for example as a component of road bases .

It is likewise known that the stabilization and inertization of bottom ash can also be achieved by using organic agents selected, for example, from among: thermoplastic substances, organic polymers and macro- encapsulating compounds in general. However, such stabilization processes have limited application on an industrial scale, due above all to the costs of implementing them.

The applicants have now found that when the bottom ash obtained by treating the residual material (bottom waste) originating from waste combustion is mixed with at least one specific inorganic stabilizing additive, an inert solid granular composition is obtained which is stable over time and can be conveniently reused as SRM. Moreover, since the stabilized bottom ash according to the invention contains a magnetic component, it is possible to obtain a final composition that can be used to realize magnetic paths, for example dedicated paths for blind individuals, detectable using a guide instrument, for example in the form of a stick fitted with a magnet. The magnetic component present in the bottom ash can originate from a high-efficiency magnetic process carried out on the ash itself in the initial stages of processing, so that a certain amount of magnetic material remains present in the ash obtained. Alternatively, or in addition, the magnetic component can be added (as an additional component) to the bottom ash obtained at the end of the processing of the residual material.

Summary of the invention

In a first aspect, the invention relates to the use of a composition comprising:

— bottom ash, and

— at least 2% by weight of a stabilizing additive comprising: an alkaline or an alkaline earth silicate, and an alkaline or alkaline earth sulphide and/or phosphate, and

— a magnetic component, preferably ferromagnetic or paramagnetic,

for the realization of magnetic paths, preferably for blind individuals.

Said magnetic component can be a paramagnetic or ferromagnetic component, and can be present in the bottom ash at the end of the steps of processing the residual material of combustion, or else, in accordance with one embodiment, it can be added as an additional component to the stabilized bottom ash.

In an additional aspect, the invention also relates to a guide instrument, preferably in the form of a stick or crutch for blind individuals, comprising a magnetic element for detecting said dedicated path.

Detailed description

Unless otherwise specified, the term "percentage by weight" of a component means the amount of the single component relative to the total weight of the composition .

The terms "alkaline or alkaline earth" silicate, sulphide and phosphate mean a salt formed from the silicate anion (i.e. S1O₃ ^~~) , or sulphide anion (S ) or phosphate anion (P0₄ ) , or acid phosphate (HP0₄ ^~~) , or also hydrogen phosphate (H₂PO₄ ) , respectively, with a metal in group I or II of the periodic table, such as, for example: sodium, lithium, potassium, calcium, magnesium, barium and strontium and the like. Said salts may be used in any of their hydrated forms, for example trihydrate .

The term "magnetic material or component" comprises in its meaning paramagnetic, diamagnetic or, preferably, ferromagnetic materials.

The term "paramagnetic material or component" indicates a material with a magnetization, in the presence of magnetic fields, having the same direction and orientation as that associated with the external field applied to the paramagnetic material itself. Examples of such components are aluminium and magnesium.

The term "ferromagnetic material or component" means a material, such as iron, which has the property of being very intensely magnetized under the action of an external magnetic field and remaining magnetized for a long time when the field is gone, thus becoming a magnet .

"Bottom ash" means the solid residual, typically having a morphology similar to a powder or ash, obtained by treating the residual material of combustion (bottom waste) deriving from the incineration of solid waste. Typically, said treatment comprises steps of sieving, removing metals such as iron, aluminium and steel and removing other materials such as ceramics and glass. At the end of such treatment a granular material is obtained, with particles of variable size, comprised from 0.1 mm to 10 mm, known to the person skilled in the art as bottom ash. The applicants have now found that when the above-described bottom ash is mixed with at least the 2% of a stabilizing additive comprising an alkaline or an alkaline earth silicate and at least an alkaline or an alkaline earth sulphide and/or phosphate, in the presence of a magnetic element or compound, the composition thus obtained is stable, easy to handle and reusable as a secondary raw material, for example for the realization of dedicated paths for the blind individuals. Said additive, in fact, surprisingly acts even in small amounts as a stabilizing agent, preventing the release of metals or of any toxic substances present in the bottom ash, whereas the magnetic, preferably ferromagnetic, component renders the path realized with the composition detectable by means of an instrument capable of interacting magnetically with said component, such as, for example, a magnet or the like. Therefore, it follows that the composition of the invention can be conveniently used as a recycled material, or secondary raw material (SRM) , in extreme safety, as an environmentally compatible product, and at a low cost of production .

In a preferred embodiment, the stabilizing additive of the present composition comprises an alkaline or alkaline earth silicate selected from among: sodium silicate, potassium silicate, calcium silicate and magnesium silicate, sodium silicate (Na2SiC>3, CAS No. 6834-92-0) being particularly preferred. In addition to the silicate, the stabilizing additive preferably comprises at least a sulphide in a mixture with an alkaline or alkaline earth phosphate, possibly in a mono- or polyhydrated form. In this regard, examples of preferred sulphides and phosphates are salts of: sodium, potassium, magnesium and, even more preferably, sodium and calcium. Sodium or calcium acid phosphates (HPO₄ or H₂PO ) are equally preferred. In one embodiment, the stabilizing additive of the invention comprises: an alkaline or an alkaline earth silicate, preferably of sodium (Na₂SiC>3) , and at least a calcium or sodium sulphide and phosphate, possibly in a mixture with an acid phosphate, preferably of sodium or calcium.

The alkaline or alkaline earth sulphide and/or phosphate can be present in a total amount comprised from 1% to 10% relative to the amount of silicate used.

In any case, the percentage of stabilizing additive present in a mixture with the bottom ash of the composition of the invention is equal to at least 2% of the total weight of the composition, preferably in a percentage amount by weight of up to 20%, preferably comprised from 5% to 10%, even more preferably comprised from 2% to 5%. It has been noted, in fact, that amounts exceeding 20% can result in an undesired increase in the costs of preparing the composition, whereas percentages below 2% could lead to a degree of inertization of the ash that is too low to enable it to be used according to the present invention. The stabilizing additive can be previously prepared and added to the bottom ash containing the selected magnetic component, or, in case, it can be prepared in situ, i.e. by mixing all of the components of the present composition together in a single step.

The bottom ash of the present invention can derive from the residual material of combustion obtained from the incineration of municipal solid waste (MSW) , or from the non-degradable fraction of separately collected waste (SCW) or also from the incineration of industrial waste, such as sludge. It can also derive from the residue originating from the combustion of waste in waste-to- energy plants in general or the combustion residue from thermoelectric plants.

Preferably, the bottom ash of the present composition is obtained from the incineration of municipal solid waste (MSW) . The composition of the invention is moreover characterized in that it contains a certain amount of a magnetic component or material. Preferably, the latter is selected from among: rust, iron oxides, metallic iron, ferrite, magnetite or also mixtures or alloys thereof. More preferably, said component is selected from among: rust, iron oxides and, even more preferably, metallic iron, on their own or in a mixture.

The magnetic component can be in the form of granules, powder or flakes, with a size preferably comprised from 10 microns (|Im) and 3 mm.

It can be present in an amount comprised from 20% to the 90%, more preferably comprised from 65% to 75% relative to the total weight of the ash. Advantageously, the presence of the magnetic material imparts to the composition of the invention magnetic properties which can be useful in particular practical applications, as described and claimed hereunder.

In one embodiment, the composition of the invention can optionally also comprise further components, such as, for example: surfactants, colourants, fluidifying agents, carboxylic polyamine complexing agents, such as EDTA and the like, zeolites and/or bentonites. When present, said further components are preferably used in a percentage by weight comprised from 5 to 20% by weight, preferably comprised from 10 to 15% by weight. Preferably said component is EDTA

(ethylenediaminetetraacetic acid) .

As mentioned above, the composition of the invention can be conveniently prepared by mixing and, if necessary, grinding the various components, for example by means of techniques and processes known in the art. In one embodiment, the mixing of the bottom ash, containing a selected magnetic element, with the stabilizing additive is followed by a step in which the composition thus obtained is allowed to rest. Said rest step can be carried out by leaving the composition at a temperature comprised from 15 to 40° C, typically for a period of several days, preferably comprised from 5 to 10 days, in order to enable a complete interaction between the stabilizing additive and the bottom ash, intimately mixed with each other. In this manner it is possible to ensure complete stabilization and inertization of the present composition. After the rest step, the composition undergoes grinding in order to obtain a product with a defined particle size, particularly useful as a secondary raw material for the present use. Grinding can typically take place using machinery known in the art, such as, for example, presses, mills or the like. Preferably, the final particle size of the composition (understood as the average diameter of the particles making up the solid composition of the invention) is at least 30 microns (pm) , preferably comprised from 30 to 50 microns, even more preferably comprised from 60 to 100 microns.

The water leach tests have demonstrated that the present composition is characterized by a high degree of retention of the analyzed substances, which are thus not released into the eluate. This means a high degree of stabilization and inertization of the bottom ash, which therefore satisfies the requirements imposed by current laws and regulations concerning the reuse of substances as SRM.

The present composition, preferably with a particle size comprised from 30 to 100 microns (um) , can be conveniently used as a recycled material for the preparation of magnetic paths, for example in the form of: tiles, road edges, paving, surfaces of squares, road bases, street curbs, grouts, plasters and the like. In this case, in fact, it has been noted that, thanks to its hygroscopic and aggregating properties, the present composition can be used in combination with cement as a replacement (even total) of sand. Surprisingly in this case, simply by mixing the composition and cement in water one obtains a cement derivative material that exhibits a magnetic, preferably paramagnetic or ferromagnetic, character, and a greater elasticity than a corresponding cement material that does not contain the present composition. This greater elasticity further allows to reduce (and substantially to eliminate) the break phenomena or crack formation that usually occurs over time for cement materials commonly used.

Therefore, when the present composition, comprising stabilized bottom ash and at least a magnetic component as described here in detail, is mixed with cement and possibly sand, a magnetic cement-based material can be obtained which is potentially useful for preparing magnetic paths, preferably dedicated paths for blind individuals. In this regard, in one embodiment the present invention relates to the use of the composition as defined above, further comprising cement and/or sand, for the realization of magnetic paths, preferably guide paths for blind individuals, even more preferably in the form of: tiles, road edges, surfaces of squares, paving, road bases, street curbs, or also grouts, plasters and claddings. In fact, the presence of the magnetic material makes it possible to impart, for example to a road base, magnetic properties which differ from those of a road base commonly used. Therefore, the use of a stick or, more generally speaking, of a guide instrument comprising an element capable of interacting with the selected magnetic component, for example by generating a magnetic field, makes it possible to physically identify dedicated paths obtained with the present composition and specifically realized for individuals with sight impairments who need to use guide instruments such as sticks and the like. Said element is preferably positioned at the lower extremity (i.e. at the end that can come into contact with the base comprising the composition of the invention) , and even more preferably it is an element selected from among: a magnet and an electromagnet, preferably a magnet.

Therefore, in an additional aspect, the invention relates to an instrument in the form of a stick or crutch comprising an element capable of generating a magnetic field, useful as a guide instrument for magnetic paths realized according to the present invention .

In particular, said instrument comprises at least a handgrip and an element, preferably a magnet, capable of magnetically interacting with the magnetic composition of the invention, for example in the form of a road edge or base. In one embodiment, said guide instrument is a stick comprising at least a handgrip and a magnet positioned at the lower end of the stick, understood as the distal end relative to the handgrip, suitable for coming into contact with a ferromagnetic path obtained with the composition of the invention. Said instrument can be realized using methods and materials known in the art for the manufacture of articles of this kind.

The cement-based material of the invention can likewise be conveniently prepared according to methods known in the art and wholly similar to traditional processes, and used, for example, in tile form.

As above illustrated in detail, the composition of the invention comprising bottom ash obtained from the incineration of waste, in a mixture with an additive comprising an alkaline or an alkaline earth silicate and an alkaline or alkaline earth sulphide and/or phosphate and a magnetic component, enables the use thereof as a secondary raw material for realizing magnetic paths, while ensuring excellent characteristics in terms of stability, weight, mechanical strength and elasticity. Finally, the simplicity of the process of preparation thereof ensures cost savings, advantageous above all in cases where it is necessary to prepare and use large amounts of the finished product.

The present invention will now be described in the following experimental part, without limiting the scope thereof in any way. Experimental part.

Example 1 :

Preparation of the composition of the invention:

A sample of bottom ash containing approximately 50% of a ferromagnetic component comprising iron oxides and metallic iron is mixed in a dynamic paddle mixer with an aqueous solution containing 30% sodium silicate, to which sodium sulphide and sodium acid phosphate (2% by weight) are added.

After mixing, the composition is allowed to rest at room temperature for 8 days. After that period has elapsed, the composition undergoes dry grinding in a horizontal axis tubular mill. Grinding takes place in a closed circuit, i.e. after grinding the ash exits from the opposite side of the mill and, via a conveyor system made up of screws and a bucket elevator, is delivered to an air separator, in which the finer part is separated, whereas the part that is still too coarse returns to the mill for further grinding. At the end of the grinding process one obtains the composition of the invention, having a particle size of 50 pm, which is mixed with cement and water to form a cement-based material useful for constructing a magnetic road edge or base.

Claims

1. A use of a composition comprising:

— bottom ash, and

— at least 2% by weight of a stabilizing additive comprising: an alkaline or an alkaline earth silicate, an alkaline or alkaline earth sulphide and/or phosphate, and

— a magnetic component,

for the realization of magnetic paths, preferably for blind individuals.

2. The use according to claim 1, wherein said magnetic component is a paramagnetic or, preferably, ferromagnetic component.

3. The use of the composition according to claim 1 or 2, having a particle size comprised from 30μπι to ΙΟΟμπι, preferably comprised from 30μπι to 60μπι.

4. The use of the composition according to claim 3, having a particle size comprised from 60μπι to ΙΟΟμπι.

5. The use of the composition according to any one of the preceding claims, wherein said alkaline or alkaline earth silicate is sodium or calcium silicate.

6. The use of the composition according to any one of the preceding claims, comprising an alkaline or alkaline earth sulphide and phosphate.

7. The use of the composition according to any one of the preceding claims, comprising a sodium or calcium sulphide and/or phosphate.

8. The use of the composition according to any one of the preceding claims, wherein said stabilizing additive is present in an amount comprised from 2 to 20%.

9. The use of the composition according to claim 8, wherein said stabilizing additive is present in an amount comprised from 2% to 5%.

10. The use of the composition according to the preceding claims, wherein said magnetic component is selected from among: rust, iron oxides, metallic iron, ferrite, magnetite and mixtures or alloys thereof.

11. The use of the composition according to claim 10 wherein said magnetic component is metallic iron.

12. The use of the composition according to the preceding claims, wherein said magnetic component is present in an amount comprised from 20% to 90% by weight .

13. The use according to claim 11, wherein said magnetic component is present in an amount comprised from 65% to 75% by weight .

14. The use of the composition according to the preceding claims, moreover comprising: surfactants, colourants, fluidifying agents, zeolites and/or bentonites .

15. The use of the composition according to the preceding claims, further comprising cement and, optionally, sand.

16. The use of the composition according to the preceding claims, for preparing magnetic paths, preferably for blind individuals, in the form of: tiles, road edges, surfaces of square, paving, road bases, street curbs, grouts or plasters.

17. A guide instrument per blind individuals, preferably in the form of a stick or crutch, comprising a magnetic element for detecting a magnetic path obtained according to claims 1-16.

18. The guide instrument according to claim 17 in the form of a stick, comprising at least a handgrip and a magnetic element positioned at the lower end of the stick, understood as the distal end relative to the handgrip .

19. The instrument according to claim 17 or 18, wherein said magnetic element is a magnet.