WO2014013515A1

WO2014013515A1 - Composition comprising bottom ash, and use thereof as secondary raw material

Info

Publication number: WO2014013515A1
Application number: PCT/IT2012/000222
Authority: WO
Inventors: Ercolino BERGAMINI; Dario ARENA; Filippo Arena
Original assignee: Basura S.R.L.
Priority date: 2012-07-17
Filing date: 2012-07-17
Publication date: 2014-01-23
Also published as: WO2014013429A2; EP2874963A1; EP2874964A2; WO2014013429A3; WO2014013515A9

Abstract

The present invention relates in general terms to a eomposition comprising bottom ash produced from the incineration of waste, in admixture with an alkali or alkaline earth silicate, and at least one compound selected from among: an alkali or alkaline earth sulphide and/or phosphate, and the use thereof as a secondary raw material, typically in the building sector, for example in the preparation of cement derivatives such as tiles, screeds and the like. When a ferromagnetic material is added to it, the present composition can be particularly useful in the preparation of dedicated paths for blind individuals.

Description

"COMPOSITION COMPRISING BOTTOM ASH, AND USE THEREOF AS

SECONDARY RAW MATERIAL"

Description

Technical Field

The present invention relates in general terms to a composition comprising bottom ash produced from the incineration of waste, in a mixture with an alkali or alkaline earth silicate, and at least one alkali or alkaline earth sulphide and/or phosphate, and the use thereof as secondary raw material (SRM), for example in the building sector in the preparation of cement derivatives.

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, the 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 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 and carbohydrates and compounds deriving from the thermal decomposition of organic materials, such as aliphatic and aromatic acids, styrene, polycyclic aromatic hydrocarbons, chloroorganics 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 special waste (above all because of the presence of heavy metals, lead and cadmium), the disposal thereof must take place in specific landfills for special 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 one micron to one centimetre.

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 use 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 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 used 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 originating from waste combustion are 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.

Summary of the invention

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

bottom ash, and

at least one stabilizing additive comprising: an alkali or alkaline earth silicate, and at least one alkali or alkaline earth sulphide and/or phosphate,

wherein said stabilizing additive is present in an amount of at least 2% by weight.

In another aspect, the present invention relates to a process for preparing the composition according to the preceding claims, said process comprising mixing, and subsequent grinding, if necessary, of the bottom ash with at least 2% of a stabilizing additive comprising: an alkali or alkaline earth silicate, and at least one alkali or alkaline earth sulphide and/or phosphate.

Finally, a further aspect of the invention consists in the use of the present composition as secondary raw material (SRM), preferably in the building sector, and even more preferably in the preparation of cement derivates, such as, for example, road bases, bricks, screeds, grouts and the like. When a ferromagnetic component is added to it, moreover, the present invention also relates to a composition useful for preparing dedicated paths for blind individuals.

Description of the drawings:

Figure 1 : tile obtained by mixing cement and the composition of the invention having a particle size of about 60μηι, comprising bottom ash and a stabilizing additive comprising: sodium silicate, calcium sulphide and calcium phosphate, said additive being present in total amount of 4% by weight relative to the total weight of the solid composition.

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 "alkali or alkaline earth" silicate, sulphide and phosphate mean a salt formed from the silicate anion (i.e. Si0₃ ^"), or sulphide anion (S^~") or phosphate anion (PO₄ ^""), or acid phosphate (HPO₄ ^"), or also hydrogen phosphate (H₂P0₄ ^"), 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. Said salts may be used in any of their hydrated forms, for example trihydrate.

"Bottom ash" means the solid residual, typically having a morphology similar to a powder or ash, obtained by treating the residual material of combustion 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 between 0.1 mm and 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 admixed with at least 2% of a stabilizing additive comprising an alkali or alkaline earth silicate and at least one alkali or alkaline earth sulphide and/or phosphate, the composition thus obtained is stable, easy to handle and reusable as a secondary raw material in a series of industrial applications, such as, for example, in building and geotechnical applications. 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, obtained, for example, after treating the residual material of combustion originating from the incineration of municipal solid waste (MSW). Therefore, the composition of the invention can be 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 alkali or alkaline earth silicate selected from the group consisting of: sodium silicate, potassium silicate, calcium silicate and magnesium silicate, being sodium silicate (Na₂Si0₃, CAS No. 6834-92-0) particularly preferred. In addition to the alkali or alkaline earth silicate, the stabilizing additive comprises at least one alkali or alkaline earth sulphide and/or 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 (ΗΡ0₄ ^"' or H₂P0₄ ^") are equally preferred. In a particularly advantageous embodiment, the stabilizing additive of the invention comprises: an alkali or alkaline earth silicate, preferably sodium silicate (Na₂Si0₃), and at least one calcium or sodium sulphide and/or phosphate, possibly in mixture with an acid phosphate, preferably sodium or calcium phosphate.

The alkali or alkaline earth sulphide and/or phosphate can be present in an amount comprised between 1% and 10% relative to the amount of alkali or alkaline earth 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 between 5% and 10%, even more preferably comprised between 2% and 5%. It has been noted, in fact, that amounts exceeding 20% can result in an undesired increase in the costs for preparing the composition, whereas percentages below 2% could lead to a degree of inertization of the ash that is too low to enable its use, for example, in the preparation of cement or building derivatives for civil purposes. The stabilizing additive comprising silicate and at least one sulphide and/or phosphate as described above can be previously prepared and added to the bottom ash, or even 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, or 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).

In an additional embodiment, the bottom ash can also contain a certain amount of a ferromagnetic material. The term "ferromagnetic material" comprises in its meaning all materials capable of producing their own magnetic field, which also persists in the absence of an externally applied magnetic field.

Preferably, said ferromagnetic component is selected from: rust, iron oxides, metallic iron, ferrite, magnetite and mixtures or alloys thereof. Said material can be present in the form of granules, powder or flakes, with a size preferably comprised between 10 microns (μη ) and 3 mm.

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

In one embodiment, the composition of the invention can optionally also comprise further components, such as, for example: surfactants, colourants, fluidifying agents, polyamino carboxylic chelating agents, such as EDTA and the like, zeolites and/or bentonites, typically according to the use for which the composition is intended. When present, said further components are preferably used in a percentage 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. Therefore, in an additional aspect, the invention relates to a process for preparing the composition of the invention, said process comprising mixing and, if necessary, grinding, preferably dry grinding, the bottom ash, having a particle size comprised between 0.1 mm and 10 mm, preferably comprised between 0.1 mm and 6 mm, with at least 2% of a stabilizing additive comprising an alkali or alkaline earth silicate and at least one alkali or alkaline earth sulphide and/or phosphate, possibly in the presence of further components as indicated above. Said mixing can take place using a low-cost dynamic mixer of the paddle or blade type, easily applicable on an industrial scale. In a preferred embodiment, the mixing of the bottom ash with the stabilizing additive is followed by a rest step for the composition thus obtained. Said rest step, which preferably takes place after mixing and before grinding, can be carried out by leaving the composition at a temperature comprised between 15° C and 40° C, typically for a period of several days, preferably comprised between 5 and 10 days, in order to enable the 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, as demonstrated by the leaching tests included hereunder in the experimental part. After said rest step, the composition undergoes grinding in order to obtain a product with a defined particle size, particularly useful as a secondary raw material. Grinding can typically take place using machineries known in the art, such as, for example, presses, mills or the like. Preferably, the particle size of the composition (here intended as the average diameter of the particles making up the solid composition of the invention) is at least 30 microns (μηι), preferably comprised between 30 and 50 microns, even more preferably comprised between 60 and 100 microns. Depending on the particle size, in fact, the present composition can have different practical applications as a secondary raw material, as described and claimed hereunder.

In a preferred embodiment, the composition of the invention is obtained by mixing the hash with the selected stabilizing additive, the latter being added in the form of an aqueous solution. In this regard, the stabilizing additive can be conveniently obtained by preparing an aqueous solution of an alkali or alkaline earth silicate and adding the selected sulphide and/or phosphate thereto. In a further embodiment, the aqueous solution of silicate, preferably sodium silicate, has a concentration comprised from 15 to 35%, preferably comprised from 28 to 32%, whereas the sulphide and/or the phosphate, both preferably of sodium or calcium, are added to said aqueous solution in an amount comprised from 1 to 10%, preferably comprised from 1 to 4 %. The aqueous solution comprising the above-described additive is then mixed with the bottom ash, allowed to rest, and then ground so as to obtain the composition of the invention, which can be preserved or used directly as SRMs. In this regard, the water leaching 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. Moreover, thanks to its high stability and inert character, the composition of the invention can also be stored or conveyed without any particular devices or environmental risks.

In a preferred embodiment, the process for the preparation of the composition of the invention comprises mixing the bottom ash with at least 2% of a stabilizing additive, preferably in an aqueous solution as defined above, followed by a rest period of around 8 days, and subsequent grinding, using a tube mill with a horizontal axis, to a particle size comprised between 30 and 100 μιη. After grinding one obtains the composition of the invention with the desired particle size, stabilized by the additive, which is practically incorporated and absorbed by the initial bottom ash. Therefore, in a further aspect, the invention relates to the use of the present composition as a secondary raw material (SRM), preferably as a recycled material for building use, even more preferably in a mixture with cement for the preparation of cement derivatives.

The present composition, preferably with a particle size comprised between 30 and 100 microns (μηι), can be conveniently used as a recycled material for the preparation of: mortars, concrete, tiles, edges, 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 the sand. Surprisingly in this case, simply by mixing the composition and cement in water, a cement derivative material can be obtained, displaying a greater elasticity than a corresponding cement material not containing the present composition. This greater elasticity makes it possible to reduce (and substantially eliminate) the phenomenon of breakage or crack formation, which often occurs over the time by commonly used cementitious materials.

Furthermore, the applicants have now found that cement derivatives, for example in the form of tiles, obtained by mixing the present composition with cement, have a decidedly lower weight than the same product prepared using raw materials that are typically employed for the purpose, such as sand. The present composition, besides ensuring high stability and a low environmental impact, if suitably mixed with water, cement and/or sand, makes it possible to obtain a final cement derivative having excellent mechanical strength, greater elasticity and a weight that is as much as 30% lower compared to the same material prepared without the composition of the invention. In this regard, figure 1 represents a possible cement derivative of the invention, in the form of a parallelepiped tile, obtained by mixing, in water: cement (in an amount of about 22% by weight), and the composition of the invention having a particle size of about 50 microns (in an amount of about 78% by weight), comprising bottom ash and a stabilizing additive (about 4% by weight)^' comprising sodium silicate, calcium sulphide and calcium phosphate. Therefore, the subject matter of the invention relates to a cementitious material comprising at least: cement, the present composition and possibly sand, preferably present in amounts of:

cement: 15-30%

composition of the invention: 70-85%,

sand: 0-15%.

Said cementitious material can also be in the form of a powder with an appearance and consistency that are wholly similar to that of the cement powder commonly used in the building sector. With the addition of suitable amounts of water, the cementitious material comprising the composition of the invention can be easily worked up, offering the further advantage of having rapid drying times.

Furthermore, it has been observed that the present composition comprising bottom ash and at least 2% of a stabilizing additive comprising an alkali or alkaline earth silicate and at least one alkali or alkaline earth sulphide and/or phosphate, can also be used as a fluidifying agent for concrete. It is known, in fact, that concrete displays poor fluidity, which at times can negatively affect its handling, for example when large amounts are transferred. The applicants have now found that when the composition of the invention is used as a pumping aid for concrete, preferably in amounts comprised from about 2% to about 10%, preferably comprised from 4 to 6%, one can obtain a material which maintains the characteristics of solidity and stability that are typical of concrete while showing increased fluidity and better handling.

In a further application, the present composition, thanks to its hygroscopic and binding properties, can be used as a stabilizer of clayey and sandy soils.

Moreover, in an additional aspect of the invention, the applicants have surprisingly found that when the present composition comprising bottom ash and also containing a ferromagnetic component as described here in detail is mixed with cement, it is possible to obtain a ferromagnetic cementitious material, potentially useful in the preparation of dedicated paths for the blind. In this regard, in a preferred embodiment the present composition also comprising a ferromagnetic component is used in the preparation of the road base or edges for dedicated lanes or paths for the blind. The presence of the ferromagnetic material enables different magnetic properties to be imparted, for example, to the road base as compared to the road base commonly used. Therefore, the use, for example, of a magnetic stick or a means comprising an element capable of generating a magnetic field, e.g. a magnet, on the lower end (i.e. at the end which can come into contact with the magnetic base comprising the composition of the invention and the ferromagnetic material) would make it possible to practically identify dedicated paths specifically realized for people with vision problems, who need to use supporting instruments such as walking sticks and the like.

Therefore, in an additional aspect, the invention relates to an instrument, preferably in the form of a walking stick or a crutch, useful as a guide instrument for blind individuals for dedicated magnetic paths, characterized in that it comprises at least one element capable of generating a magnetic field.

In particular, said instrument comprises a grip and at least one magnet capable of interacting with said ferromagnetic material.

In a preferred embodiment, said instrument is a walking stick comprising a magnet positioned at the lower end of the stick, understood as the tip distal to the grip, suitable for coming into contact with the material comprising the ferromagnetic composition of the invention, understood as a characterizing element of the magnetic path.

Constituting a further aspect of the invention is a cementitious material comprising at least: cement, the composition of the invention, a ferrous, preferably ferromagnetic component, and optionally sand. Preferably, said ferromagnetic component is selected from: rust, iron oxides and metallic iron, on their own or mixed together, present in the form of a powder, granules or flakes. The ferromagnetic cementitious material of the invention can be conveniently prepared according to methods known in the art which are wholly similar to traditional procedures, and used for example in the form of a tile.

As amply described in detail above, the composition of the invention comprising bottom ash obtained from the incineration of waste, in admixture with at least one additive comprising an alkali or alkaline earth silicate and at least one alkali or alkaline earth sulphide and/or phosphate, wherein said additive is present in an amount of at least 2% by weight, enables the use thereof as a secondary raw material in a vast range of potential applications, such as, for example in the production of solid cementitious materials for building use, or, when a ferromagnetic component is added thereto, also in the realization of dedicated paths for blind individuals. In any case, the versatility of the present composition is associated with excellent characteristics in terms of stability, weight, mechanical strength and elasticity. Finally, the simplicity of the process of the preparation thereof ensures cost savings, particularly advantageous 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 is mixed in a dynamic paddle mixer with an aqueous solution containing 30% sodium silicate, to which sodium sulphide and sodium acid phosphate are added (2% by weight).

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 tube mill with a horizontal axis. 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 μπι, which is subjected to the leaching test as indicated in the following example 2b.

Leaching tests

Leach experiments were conducted on the present composition and on non-stabilized bottom ash by contact with water, as reported for the following experiments 2a and 2b, carried out in line with the European standard UNI ENV 12920.

Leaching (or solid-liquid extraction) refers to a process consisting in the separation of one or more soluble components from a solid mass by water.

Example 2a: leaching test on non-stabilized bottom ash.

A sample of lOOg of bottom ash obtained after treatment of the residual material of the combustion of MSW was subjected to a leach test with water in accordance with European standard UNIENV 12920, with an analysis of the amount of substances released by the ash and present in the eluate. The results are summed up in Table 2a, in relation to the required limits set by laws and regulations for the use of ash as a secondary raw material (SRM):

Table 2a: water leaching tests of non-stabilized bottom ash.

Bottom ash Required limits mg/1 mg/1

COD (*) 161 30

Chlorides 453 100

pH 12.2 12

Barium 1.6 1

Chromium 0.1 0.05

Lead 0.8 0.05 Mercury o:o75 0.001

Copper 1.7 0.5

Zinc 5 3

Fluorides 0.8 1.5

(*) COD: chemical oxygen demand

As may be seen from the data in Table 2a, the non-stabilized bottom ash shows values of components in the eluate which do not comply with the limits imposed by current laws and regulations.

Example 2b: water leaching test of the stabilized bottom ash according to the present invention

A sample of 100 g of bottom ash of the above example 1 was subjected to a leach test as described in example 2a. The results are shown in Table 2b.

Table 2b: water leaching test of a sample of stabilized ash according to the present invention.

Stabilized ash Limits

(present

composition)

mg/1 mg/1

COD (*) < 30 30

Chlorides 90 100

pH 11.2 12

Barium 0.2 1

Chromium <0.001 0.05

Lead <0.1 0.05

Mercury O.001 0.001 Copper Oil 0.5

Zinc 0.25 3

Fluorides 0.3 1.5

(*) COD: chemical oxygen demand

As can be seen, the results obtained demonstrate that the composition of the invention complies with the required limits set by laws and regulations and can thus be considered inert and reusable in the production cycle as SRM.

Claims

1. A composition comprising:

bottom ash, and

2. The composition according to claim 1, having a particle size of at least 30 μιη, preferably comprised from 30 to 60μπι, even more preferably comprised from 60 to ΙΟΟμπι.

3. The composition according to claim 1 or 2, wherein said bottom ash is obtained by treating the residual material of combustion deriving from the incineration of municipal solid waste.

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

5. The composition according to any one of the preceding claims, wherein said alkali or alkaline earth sulphide and/or phosphate is a sodium or calcium sulphide and/or phosphate.

6. The composition according to any one of the preceding claims, optionally in the presence of a sodium or calcium acid phosphate.

7. The composition according to any one of the preceding claims, wherein said stabilizing additive is present in an amount comprised from 2 to 20%, preferably comprised from 5% to 10%, even more preferably comprised from 2% to 5%.

8. The composition according to any one of the preceding claims, wherein said bottom ash further comprises a ferromagnetic component.

9. The composition according to claim 8, wherein said ferromagnetic component is selected from the group consisting of: rust, iron oxides, metallic iron and mixtures thereof, preferably present in an amount comprised from 20% to 90% by weight.

10. The composition according to any one of the preceding claims, further comprising: surfactants, colourants, fluidifying agents, zeolites and/or bentonites.

11. A process for preparing the composition according to the preceding claims, said process comprising mixing and grinding, preferably dry grinding, the bottom ash with at least 2% of a stabilizing additive comprising: an alkali or alkaline earth silicate, and at least one alkali or alkaline earth sulphide and/or phosphate.

12. The process according to claim 11, wherein after mixing and before grinding the composition is allowed to rest, preferably for a period comprised between 5 and 10 days.

13. The process according to claim 11 or 12, wherein said stabilizing additive is an aqueous solution of an alkali or alkaline earth silicate, preferably sodium silicate, comprising an alkali or alkaline earth sulphide and/or phosphate, preferably of sodium or calcium.

14. The process according to claims 11-13, wherein said mixing takes place by a dynamic paddle or blade mixer and the grinding takes place using a tube mill with a horizontal axis.

15. A use of the composition in accordance with each of the claims 1 to 10 as a secondary raw material (SRM), preferably in the building sector, even more preferably for the preparation of a cement derivative.

16. A use of the composition as defined in any one of claims 1-10, as a fluidifier for concrete.

17. A use of the composition as defined in any one of claims 1-10, as a stabilizer of clayey and sandy soils.

18. A cement derivative comprising: cement, the composition as defined in any one of claims 1-10, and eventually sand.

19. A use of the composition as defined in any one of claims 8-10, for the preparation of dedicated paths for blind individuals.

20. An instrument, preferably in the form of a stick or crutch, comprising a grip and at least one element capable of generating a magnetic field, preferably a magnet, for use as a guide instrument for blind individuals for dedicated ferromagnetic paths.