BE1024612B1 - Process for producing a mass retaining a shape - Google Patents

Abstract

A method of producing a shape-retaining mass having a compressive strength, measured according to the standard ASTM D 698-12 test method, of at least 2 MPa, comprising the following steps: Step 1. mixing a composition binder (hereinafter, composition (B)) comprising at least one carbonating agent which is selected from the group consisting of potassium carbonate, potassium bicarbonate and hydrous magnesium carbonate hydroxide compounds of the general formula (I) : xMgCO3.yMg (OH) 2.zH2O where x is a number in the range of 3.5-4.5, y is a number in the range of 0.5-1.5 and z is a number in the range of range of 3.5 - 5.5, with at least one particulate material of steel slag thus forming a mixture (hereinafter mixed M) and wherein said particulate material of steel slag contains calcium silicate phases and at least chromium and is present in said mixture M in an amount of at least 50% in dry weight, based on the total dry weight of the mixture M, and Step 2. curing the mixture M, as obtained in Step 1., in the presence of water, thereby producing the mass retaining a shape.

Description

(73) Holder (s):

ORBIX SOLUTIONS 6240, FARCIENNES Belgium (72) Inventor (s):

DESCAMPS Philippe 6533 BIERCEE Belgium

BOUILLOT Frédérique

6110 MONTIGNY-LE-TILLEUL

Belgium (54) Method for producing a mass retaining a shape (57) Method for producing a mass retaining a shape and having a compressive strength, measured according to the standard test method ASTM D 698-12, d '' at least 2 MPa, comprising the following steps: Step 1. mix a binder composition (hereinafter, composition (B)) comprising at least one carbonating agent which is selected from the group consisting of potassium carbonate, bicarbonate potassium and hydrous magnesium carbonate hydroxide compounds of general formula (I): xMgCO3.yMg (OH) 2.zH2O in which x is a number in the range of 3.5 - 4.5, y is a number in the range of 0.5-1.5 and z is a number in the range of 3.5-5.5, with at least one particulate material of steel slag thus forming a mixture (hereinafter mixed M) and wherein said particulate steel slag material contains phases of calcium silicate and at least chromium me and is present in said mixture M in an amount of at least 50% by dry weight, relative to the total dry weight of mixture M, and Step 2. hardening of the mixture M, as obtained in Step 1., in the presence of water, thus producing the mass retaining a shape.

1425 ° C a ' _H

1177 ° C tl a ' _L

675 ° C

490 “C \

Fig.

BELGIAN INVENTION PATENT

FPS Economy, SMEs, Middle Classes & Energy

Publication number: 1024612 Deposit number: BE2015 / 5322

Intellectual Property Office International Classification: C04B 28/08 C04B 28/26 C04B 111/10 C04B 111/60

Issue date: 04/24/2018

The Minister of the Economy,

Having regard to the Paris Convention of March 20, 1883 for the Protection of Industrial Property;

Considering the law of March 28, 1984 on patents for invention, article 22, for patent applications introduced before September 22, 2014;

Given Title 1 “Patents for invention” of Book XI of the Code of Economic Law, article XI.24, for patent applications introduced from September 22, 2014;

Having regard to the Royal Decree of 2 December 1986 relating to the request, the issue and the maintenance in force of invention patents, article 28;

Considering the patent application received by the Intellectual Property Office on 05/22/2015.

Whereas for patent applications falling within the scope of Title 1, Book XI of the Code of Economic Law (hereinafter CDE), in accordance with article XI. 19, §4, paragraph 2, of the CDE, if the patent application has been the subject of a search report mentioning a lack of unity of invention within the meaning of the §ler of article XI.19 cited above and in the event that the applicant does not limit or file a divisional application in accordance with the results of the search report, the granted patent will be limited to the claims for which the search report has been drawn up.

Stopped :

First article. - It is issued to

ORBIX SOLUTIONS, Rue du Dria 46, 6240 FARCIENNES Belgium;

represented by

VAN REET Joseph, Holidaystraat 5, 1831, DIEGEM;

CAERS Raf, Holidaystraat 5, 1831, DIEGEM;

GEVERS PATENTS, Holidaystraat 5, 1831, DIEGEM;

a 20-year Belgian invention patent, subject to the payment of the annual fees referred to in article XI.48, §1 of the Code of Economic Law, for: Process for the production of a mass retaining a form .

INVENTOR (S):

DESCAMPS Philippe, Rue de la Ferme de la Folie 14, 6533, BIERCEE;

BOUILLOT Frédérique, Rue de la Montagne 297, 6110, MONTIGNY-LE-TILLEUL;

PRIORITY (S):

12/05/2014 EP PCT / EP2014 / 076771;

DIVISION:

divided from the basic application: filing date of the basic application:

Article 2. - This patent is granted without prior examination of the patentability of the invention, without guarantee of the merit of the invention or of the accuracy of the description thereof and at the risk and peril of the applicant (s) ( s).

Brussels, 04/24/2018, By special delegation:

B E2015 / 5322 “PROCESS FOR PRODUCING A MASS CONSERVING A SHAPE ¹ '

Field of the invention

The present invention relates to an environmentally friendly process for producing a mass retaining a shape and having a compressive strength of at least 2 MPa, in particular a foundation material, comprising the use of a particulate material of slag d 'steel. Said shape retaining mass has considerably reduced release behavior of heavy metals which are contained in the particulate material of steel slag.

Prior art of the invention

Steel slag materials are by-products that are generated during steel production.

Stainless steel slag from the production of stainless steel is a special group of slag. Stainless steel slag mainly consists of calcium oxide (CaO) and silicon dioxide (SiO ₂ ). For the production of stainless steel, chromium and often also nickel and / or molybdenum are used.

Therefore, stainless steel slag contains considerable quantities of heavy metals, such as in particular chromium and often also nickel and / or molybdenum, which are problematic because of their leaching behavior. According to certain laws, the dumping of these stainless steel slag as waste must be carried out under controlled conditions.

In order to avoid the environmental and hygienic problems linked to the dumping of these stainless steel slag as waste, attempts have already been made to develop methods for treating these stainless steel slag, ie processes for converting them into materials that have economic value and can be used in several technological fields such as road engineering, building engineering, construction and public works and soil stabilization.

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-2 For example, in EP-B-0837043, EP-B-1055647 and in EP-B1146022, the problems of leaching of stainless steel slag can be solved by crushing the steel slag, removing from it the valuable particles of stainless steel and applying the different fractions of the remaining crushed slag in limited applications. Specifically, the coarser fractions of the crushed stainless steel slag can be used in concrete or asphalt.

The use of stainless steel slag in concrete, A. Kortbaoui, A. Tagnit-Hamou, and P. C. A'itcin, Cement-Based Materials, p. 77-90, 1993, proposed a process for producing mortar or concrete comprising the step of mixing at least a fine fraction of steel slag particles, containing a significant amount of dicalcium silicate-γ, with at least a hydraulic binding agent and with water to produce said mortar or said concrete. However, the amount used was limited by the negative effect of this fine fraction on the workability of the cement mixture. Since the fine fraction of steel slag can absorb large amounts of water, the use of normal amounts of water in the mixture will result in a thick, almost solid paste. This negative impact on the workability of the cement mixture would in particular make it unsuitable for use in self-compacting concrete, as defined by the European Guidelines for Self-Compacting Concrete, published by the European Precast Concrete Organization, the European Cement Association , the European Ready-mix Concrete Organization, the European Federation of Concrete Admixture Associations and the European Federation of Specialist Construction Chemicals and Concrete Systems. The addition of more water will however have a negative impact on the strength of the concrete, since a film of water will form around each particle of steel slag which will leave a vacuum as soon as the concrete hardens. Attempts to compensate for this by adding plasticizer or cement will increase the cost.

That being said, due to its higher content of gamma dicalcium silicate (C2S-y), the very fine fraction of these crushed steel slag having a particle size of 0 - 0.5 mm has absorption properties high in water and is therefore not suitable for use as a filler / fine aggregate in the manufacture of a mass retaining a shape such as in particular concrete or asphalt.

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In practice, these fines are generally separated from the coarser sand fraction (having a particle size greater than 0.5 mm) from stainless steel slag by a wet separation technique.

In WO 2009/090219, these fines are aggregated into larger grains so as to form a coarser granular material. Then, said coarser granular materials are carbonated at a relatively low pressure by means of carbon dioxide so as to produce a carbonated granular material. By the combination of the aggregation step and the carbonation step, a material can be obtained which has significantly less water absorption and therefore better workability when mixed with cement and water. Carbonation converts calcium and / or magnesium hydroxides into calcium and magnesium carbonate phases with bonding properties which fill micro cracks in fine particles of steel slag, which significantly reduces their demand for water and binds together in each grain, providing a coarser and harder material. The carbonated granular materials of WO 2009/090219 have the advantage of being able to be manufactured in advance and stored so that they can be mixed with cement and water in a conventional manner. However, granulation and carbonation equipment is required and the granulation and carbonation process is also time consuming and therefore relatively expensive. In addition, the carbonation process cannot be carried out on site, in order to produce the foundation layers, so that binder compositions are always required to produce the final product (concrete).

Another carbonation process for producing higher value building materials starting with crushed stainless steel slag fines which are between 0 and 0.5 mm in size is disclosed in WO-A-2009/133120. In this process, the fines are first molded in a press at a relatively high compaction pressure between 5 and 65 MPa and the tablet obtained is then carbonated at a relatively high temperature and pressure. In this way it is possible to produce larger carbonate tablets having a relatively high compressive strength in place of aggregates. By checking the porosity and the intrinsic permeability of the tablets and by carbonation for several hours (in particular for 18 hours at a pressure and a temperature

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-4accrues), compressive strengths between 26 and 66 MPa were obtained with a fine fraction of stainless steel slag of 0 - 500 pm which was press molded at a compaction pressure of 182 kg / cm ² (= 17.8 MPa). A disadvantage of this prior art method is that despite the fact that relatively small blocks were carbonated (62x62x32 mm and 120x55x46 mm), high gas pressures were required, which makes the process very expensive and could not be done on site to produce rigid foundation layers.

In other words, in all these processes, CO ₂ gas is used for the carbonation process which cannot be introduced into large volumes such as foundation layers or which is at least difficult to introduce so well, that Despite the fact that a formation and carbonation step has already been carried out, a binder is still necessary to produce the final product.

EP2,160,367 describes the use of stainless steel slag, specifically as fillers in construction materials, in particular asphalt or mortar or hydraulic concrete compositions which contain hydraulic or bituminous binding agents. The charge is produced by finely grinding a coarser fraction of crushed steel slag which preferably has a relatively high steel content (eg obtained by a magnetic separation process). The finely ground fractions obtained, for example having a particle size of less than 63 µm, have a lower gamma dicalcium silicate content than the fines described above, since they are produced by starting with a coarser fraction of the slag crushed steel so that they absorb significantly less water. However, these fillers are only used in small amounts in concrete and asphalt.

Therefore, it is still necessary to provide environmentally friendly and economically practical processes in which large quantities of waste, in particular the fine fractions of steel slag containing crushed chromium and / or steel slag containing ground chromium, can be used to produce materials of economic value, in particular foundation layers, and this in several technological fields such as road engineering, building engineering as well as construction and public works and according to which said materials have

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-5 considerably reduces the release of heavy metals and have compressive strengths of at least 2 MPa.

Summary of the invention

The applicant has noted with surprise that it is possible to provide a process that meets the needs mentioned above.

An object of the present invention is therefore a process for producing a mass retaining a shape and having a compressive strength, measured according to the standard test method ASTM D 698-12, of at least 2 MPa, comprising the following steps:

Step 1. Mix a binder composition [hereinafter, composition (B)] comprising at least one carbonation agent which is selected from a group consisting of potassium carbonate, potassium bicarbonate and compound of hydrated magnesium carbonate hydroxide of general formula (I): xMgCO ₃ .yMg (OH) ₂ .zH2O in which x is a number in the range of 3.5 - 4.5, y is a number in the range of 0.5 - 1.5 and z is a number in the range of 3.5 - 5.5, with at least one particulate material of steel slag thereby forming a mixture [hereinafter M mixture] and wherein said particulate material of steel slag contains phases of calcium silicate and at least chromium and is present in said mixture M in an amount of at least 50% by dry weight, relative to the total dry weight of mixture M, and

Step 2. hardening of the mixture M, as obtained in step 1., in the presence of water; thus producing the mass retaining a shape.

Another aspect of the present invention relates to a mass retaining a form prepared according to the method of the invention.

Another aspect of the present invention relates to the use of at least one carbonating agent which is selected from the group consisting of potassium carbonate, potassium bicarbonate and a hydrated magnesium carbonate hydroxide compound of general formula (I ): xMgCO ₃ .yMg (OH) ₂ .zH ₂ O in which x is a number in the range of 3.5 - 4.5, y is a number in the range of 0.5 - 1.5 and z is a number in the

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-6.5 - 5.5 range for carbonation of a particulate material of steel slag.

Detailed description of embodiments The particulate material of steel slag

In a preferred embodiment of the process according to the present invention, the percentage by dry weight of the particulate material of steel slag present in the mixture M of Step 1. is generally equal to or at least 20% by weight , preferably equal to or at least 40% by weight, better still equal to or at least 60% by weight, even better still equal to or at least 75% by weight, and ideally equal to or d '' at least 80% by weight, relative to the total dry weight of the mixture M of Step 1.

It is further understood that the dry weight percentage of the particulate material of steel slag present in the mixture M of Step 1. will generally be equal to or at most 99% by weight, better still equal to or d '' at most 95% by weight, even better still equal to or at most 90% by weight, ideally equal to or at most 88% by weight, relative to the total dry weight of the mixture M of Step 1 .

Good results have been obtained when the mixture M of Stage 1 comprised the particulate material of steel slag in an amount of 70% by dry weight - 95% by dry weight relative to the total dry weight of Stage 1 .

In the rest of the text, when percentages by weight are given in this specification, they are percentages by dry weight.

As specified above, in Step 1. of the process of the present invention, use is made of particulate materials of steel slag containing phases of calcium silicate and at least chromium.

The particulate material of steel slag containing phases of calcium silicate and at least chromium suitable for use in the process of the invention can comprise in particular the fine fractions of steel slag and cooled stainless steel slag relatively slowly, in particular special stainless steel slag produced during the production of chromium steel or chromium-nickel steel as described in particular in EP 2 160 367, EP 2 238 087 and WO 2009/090219, all of which content is incorporated into this document by reference.

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For the purposes of the present invention, the term “particulate material of steel slag” is defined in the present document as any material of steel slag which consists of loose particles. These particles can be of different sizes so that at least 50% by volume of the particulate material of steel slag has a particle size of less than 1.0 mm, preferably less than 0.8 mm, more preferably less than 0.5 mm. On the other hand, at least 50% by volume of the particulate material of steel slag preferably has a particle size greater than 1 µm, more preferably greater than 5 µm and ideally greater than 10 µm.

A particular embodiment of the invention will now be described by way of illustration, but not limitation, with reference to the figures which follow:

Fig. 1 is a diagram representing the phase transitions during the cooling of the dicalcium silicate;

Fig. 2 is a flow diagram showing a process for separating a fine fraction of stainless steel slag from the coarser fractions for use in the process of the present invention.

It is known that during the slow cooling of stainless steel slag particles which comprise crystals of dicalcium silicate (CaO) ₂ SiO ₂ in their two polymorphic states β and y, when the crystalline dicalcium silicate cools, it passes through several polymorphic forms as illustrated in fig. 1:

a with hexagonal crystal structure, a _H 'with orthorhombic crystal structure, a _L ' with orthorhombic crystal structure, β with monoclinic crystal structure, and γ with orthorhombic crystal structure.

With pure dicalcium silicate under laboratory conditions, the transition from dicalcium silicate-a _L 'to dicalcium silicate-ß will occur at 675 ° C, then will be followed by the transition from dicalcium silicate-ß to dicalcium silicate-γ at 490 ° vs. As the transition from dicalcium silicate-ß to dicalcium silicate-γ implies a 12% increase in volume due to their different crystal structure, it gives rise to high stresses and microcracks in the dicalcium silicate crystals of the orthorhombic γ polymorphic state. These microcracks explain the unfavorable water absorption properties that have been observed so far in the slag containing dicalcium silicate-γ, being

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Given that the water is absorbed by capillarity therein. The increase in volume in the transition from the polymorphic ß state to the polymorphic γ state does not only cause microcracks but even fracture and separation of the grains. Consequently, the fine fraction of the slag will be rich in comparatively soft dicalcium-γ silicate disproportionately. Due to the microcracks mentioned above and the associated capillarity, this fine fraction of slag will have a water absorption capacity of more than 20%. In addition, it can retain this water for longer periods of time.

In the separation process, as illustrated in fig. 2, molten slag is extracted from the stainless steel furnace 1 and brought to cooling pits 3. After cooling, the solidified slag will be extracted from these cooling pits 3 and loaded into a hopper 4. The hopper 4 comprises a grid to stop all the pieces 6 of oversized slag, in particular those larger than 300 mm. As oversized pieces could damage the shredders in the subsequent process, these oversized pieces 6 are removed for further special treatment, such as crushing with hammers and extracting large fragments of metal before being loaded back into the hopper 4.

Slag particles smaller than 300 mm pass through the hopper 4 and fall on a first conveyor belt. The first conveyor belt then transports them through a first cabin 8 for metal separation by hand to a first crusher 9 and a first screen 10. In cabin 8 for metal separation by hand, the operators eliminate the large 11 pieces of metal from the slag particles on the conveyor belt. After the slag particles have been crushed in the first crusher 9, they pass through the first screen 10 which separates them into three fractions: particles greater than 35 mm, particles between 14 and 35 mm and particles less than 14 mm. The fraction of particles greater than 35 mm is taken by a second conveyor belt through a second cabin 13 for metal separation by hand and a first magnetic strip 14 for metal separation where other pieces of metal 15 and 16 are removed. . The particles larger than 35 mm are then returned to the first crusher 9. The fraction of particles between 14 and 35 mm enters a second crusher 17 and a second screen 18 where, after being crushed again, it is

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-9separated into two fractions: a fraction of particles less than 14 mm and a fraction of particles greater than 14 mm. The fraction of particles larger than 14 mm is taken by a third conveyor belt through a second magnetic metal separation band 20 where more metal 21 is removed, and is brought back into the second crusher 17.

The fraction of particles less than 14 mm from the first screen 10 and the fraction of particles less than 14 mm from the second screen 18 combine and are brought together in the third screen 22 which separates them into a fraction 23 of particles less than 4 mm and a fraction of particles between 4 and 14 mm, this coarser fraction suitable for use, for example, in building materials.

In fraction 23 of particles smaller than 4 mm, a fine fraction 24 of particles smaller than 0.5 mm is particularly rich in dicalcium-γ silicate, as discussed above.

In a preferred embodiment of the process of the present invention, said fine fraction 24 of particles smaller than 0.5 mm is used in particular in the process according to the invention.

If desired, the larger particles can also be finely ground further to obtain a ground material having a particle size distribution which has a D ₁₀ value which is less than 100 µm, preferably less than 70 µm and more preferably less than 40 pm. Grinding said coarser fractions of the slag material to a smaller particle size makes it possible to recover more precious steel from the slag material, in particular stainless steel. Preferably, the steel slag material which is ground is a fraction of steel slag which contains a relatively large amount of stainless steel.

Therefore, the particulate material of steel slag as used in Step 1. of the process according to the present invention may have a relatively high dicalcium-γ silicate content, in particular at least 3% by weight, preferably at at least 5% by weight and better still at least 7% by weight of dicalcium-γ silicate and can therefore be formed by the fines separated from the particulate material of steel slag.

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The particulate material of steel slag as used in Step 1. of the process according to the present invention generally has a relatively high basicity.

For the purposes of the present invention, the term basicity is intended to mean the ratio between the calcium content, expressed as% by weight of CaO, as present in the particulate material of steel slag and the silicon content, expressed as% by weight of SiO ₂ , as present in the particulate material of steel slag. The basicity is more particularly generally greater than 1.2, in particular greater than 1.4 and often greater than 1.6.

It is because of this high basicity that the dicalcium silicates, as specified above, are formed during a slow cooling of the steel slag, which is also responsible for the (partial) disintegration of the steel slag, that is to say of what is called the smashing or spraying of steel slag.

The particulate material of steel slag as used in Step 1. of the process according to the present invention generally has a calcium content of at least 30%, in particular at least 40% by dry weight of CaO and a silicon content of at least 15%, in particular at least 20% by dry weight of SiO2 (the calcium and silicon contents are based on the respective molecular weights of CaO and SiO ₂ but it is generally understood that calcium and silicon must not be present in their oxide form but are in particular in other amorphous or crystalline phases, in particular in silicates.

The particulate material of steel slag as used in Step 1. of the process according to the present invention preferably comprises more than 50% by dry weight, better still more than 60% by dry weight and ideally more than 70% by dry weight of crystalline phases, the remaining phases being amorphous.

The particulate material of steel slag as used in Step 1. of the process according to the present invention generally has a pH of at least 8.5, in particular of at least 10, and even more particularly of at least 11.

The pH was measured after immersion of the mass retaining a form in demineralized water for 24 hours in a liquid / volume ratio of 10.

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The particulate material of steel slag from the process according to the present invention generally contains substantial quantities of heavy metals such as chromium, in particular chromium IV in the form CrO ₄ ' ² and Cr2O7' ² and often also molybdenum in anionic form such as MnO4 ² , which is a big environmental and public health problem.

The molybdenum (Mo) and chromium (Cr) present in the particulate material of steel slag can be very mobile and can therefore be subject to prompt leaching from the slag. Consequently, slag cannot be disposed of in ordinary landfills; they should be treated as special waste, which makes their disposal more expensive.

The inventors have surprisingly found that the method according to the invention is particularly effective in immobilizing Cr and Mo, if they are present in the particulate material of steel slag, in the final mass retaining a shape, in particular in materials of road construction.

Advantageously, the particulate material of steel slag can in particular comprise at least 1000 ppm, more particularly at least 3000 ppm and even more particularly at least 5000 ppm of chromium.

Advantageously, the particulate material of steel slag can in particular comprise at least 100 ppm, in particular at least 1000 ppm and more particularly at least 2500 ppm of molybdenum.

The steel slag particulate material of the present invention may include nickel (Ni). Typically, the particulate material of steel slag can comprise at least 300 ppm of nickel, in particular at least 400 ppm of nickel and more particularly at least 500 ppm of nickel.

The composition (B)

In a preferred embodiment of the process according to the present invention, the percentage by dry weight of the composition (B) present in the mixture M of Step 1. is generally at least 1% by weight, preferably of at least 5% by weight, preferably at least 8% by weight, better still at least 10% by weight and even better still at least 12% by weight, relative to the total dry weight of the mixture M from Step 1.

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It is further understood that the percentage by dry weight of the composition (B) present in the mixture M of Step 1. is generally at most 45% by weight, better still at most 35% by weight , better still at most 30% by weight, even better still at most 25% by weight, relative to the total dry weight of the mixture M of Step 1.

Good results have been obtained when the mixture M of Stage 1 comprises composition (B) in an amount of 5% by dry weight - 30% by dry weight relative to the total dry weight of the mixture M of Stage 1 .

In the rest of the text, the expression carbonation agent is understood, for the purposes of the invention, in the plural and in the singular, that is to say that the composition (B) may comprise one or more of an agent carbonation.

In one embodiment of the method according to the present invention, the composition (B) mixed with the particulate material of steel slag in Step 1. consists essentially of the carbonating agent, as specified above.

For the purposes of the present invention, the expression consists essentially of is intended to indicate that any additional ingredient different from the carbonating agent, as specified above, is present in an amount of at most 1% by weight, over the base of the total weight of the carbonating agent in composition (B).

In another embodiment of the present invention, the composition (B) mixed with the particulate material of steel slag in Step 1. of the process of the present invention comprises a carbonating agent in an amount advantageously greater than 1 % by weight, better still greater than 5% by weight, better still greater than 10% by weight, better still greater than 15% by weight,%; better still greater than 20% by weight, better still greater than 25% by weight, based on the total weight of the composition (B). It is further understood that the percentage by weight of the carbonating agent in the composition (B) will generally be at most 99% by weight, preferably at most 95% by weight, preferably at most 90% by weight, better still at most 80% by weight, better still at most 75% by weight, based on the total weight of the composition (B).

Good results have been obtained when the mixture M of Step 1. included the carbonating agent in an amount of at least 1% by weight

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-13sec, preferably at least 2% by dry weight, better still at least 3% by dry weight, relative to the total dry weight of the mixture M of Step 1.

According to certain preferred embodiments of the process according to the present invention, the carbonating agent comprises a hydrated magnesium carbonate hydroxide compound of general formula (I): xMgCO ₃ .yMg (OH) ₂ .zH ₂ O in which x is a number in the range of 3.5 - 4.5, x is preferably 4, y is a number in the range of 0.5 - 1.5, y is preferably 1 and z is a number in the range 3.5 - 5.5, z is preferably 4 or 5.

The preferred hydrated magnesium carbonate hydroxide compounds are chosen from hydromagnesite (i.e. 4MgCO ₃ .Mg (OH) ₂ .4H ₂ O) and dypingite (i.e. 4MgCO ₃ .Mg (OH) ₂ .5H ₂ O).

The hydrous magnesium carbonate hydroxide compounds of general formula (I) are known in the art. They can be produced by methods known in the art. In general, they can be produced by exposure of magnesium compounds, for example MgO or Mg (OH) ₂ (or mixtures thereof) to CO ₂ under various conditions.

For example, EP 2 508 496 describes the use of these hydrated magnesium carbonate compounds (I) of formula (I) in binders which are based on the formation of magnesium silicate hydrates (MSH) and used to form concrete, mortar or plaster and other construction chemicals. These binders can be used to replace known binders Portland cement, molten cement and the like. According to the teachings of EP 2 508 496, the amount of additional calcium, for example Ca (OH) ₂ and / or CaO, must be limited, because these calcium ions form calcite in the presence of hydromagnesite (i.e. i.e. 4MgCO ₃ .Mg (OH) ₂ .4H ₂ O), which results in a decrease in its effectiveness.

The inventors have now surprisingly found that, despite the high CaO content of the steel slag particulate material, as specified above, the hydrated magnesium carbonate compounds of formula (I) can act as very effective carbonation and reduce leaching of heavy metals, especially chromium and molybdenum in the final mass retaining a shape.

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-14WO 2009/156740 also describes the use of these hydrated magnesium carbonate compounds of formula I with the addition of magnesia as a binder composition used to manufacture construction products.

The inventors have now found that, in comparison with Portland cement, these binder compositions improve the leaching behavior of heavy metals, in particular chromium and molybdenum, despite the fact that they have a much lower pH than Portland cement.

Comparative tests in which various quantities of different cements (CEM I, CEM II and CEM Mb) were mixed with fines of stainless steel slag (0 - 0.5 mm) were also carried out. At the natural pH of these mixtures, that is to say at a pH of around 12.8, it took large quantities of cement (cement-aggregate ratios of 0.5 or even more) to keep the leaching of the chromium below the limit of 0.10 mg / l and the leaching of molybdenum below the limit of 0.15 mg / l. The tests also revealed that when the water used to make these leaching tests is acidified so that the final pH approaches pH 12, the leaching of chromium and molybdenum increases considerably. With the process of the present invention, on the contrary, low leaching values have been obtained for lower final pH values.

According to another preferred embodiment of the process according to the present invention, the carbonating agent comprises potassium carbonate and / or potassium bicarbonate.

According to a preferred embodiment of the process according to the present invention, the carbonation agent in Step 1. may also comprise a carbonation-improving compound selected from the group consisting of magnesium oxide (MgO), calcium oxide ( CaO), calcium and magnesium oxide (i.e. calcined dolomite) and mixtures thereof, preferably MgO.

The molar ratio of said carbonation enhancing compound is advantageously at least 1.0, preferably at least 1.5, more preferably at least 3.0. It is further understood that the molar ratio of said carbonation-improving compound to the carbonation agent will generally be at most 10, preferably at most 8 and better still at most 6.

In an advantageous embodiment of the present invention, the composition (B) mixed with the particulate material of slag

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The steel in Step 1. of the process of the present invention further comprises a binder composition forming a gel in an amount advantageously greater than 1% by weight, preferably greater than 10% by weight, better still greater than 20% by weight, better still greater than 30% by weight, based on the total weight of the composition (B). It is further understood that the percentage by weight of the gel-forming binder composition in composition (B) will generally be at most 99% by weight, preferably at most 95% by weight, better still at most 80% by weight, better still at most 70% by weight, based on the total weight of the composition (B).

The gel-forming binder composition comprises a glass compound and said glass compound contains more than 50% by dry weight of SiO ₂ .

Alternatively, the gel-forming binder composition consists of the glass compound.

Non-limiting examples of glass compounds may include, but are not limited to, industrial silicate glass, such as hollow glasses (of bottles, cups, etc.) or flat glass, different from natural silicate glasses (such as pozzolan , tuff, pumice) or any other industrial silicate glass (in particular such as blast furnace slag, silica smoke, fly ash from thermal power stations) as described in particular in EP 1250397 B1, all of its content being incorporated into this document by reference.

In an advantageous embodiment of the method according to the present invention, the glass compound however comprises glass powder, in particular soda-lime glass powder. The glass powder preferably comprises particles of ground cullet.

Cullet is a waste product comprising industrial silicate glass and flat and hollow glass (container) which cannot be introduced into an oven to be recovered. The glass powder used in the process according to the present invention preferably comprises more than 60%, better still more than 65% by dry weight of SiO ₂ .

In another advantageous embodiment of the method according to the present invention, the glass compound is silica smoke. Silica fume is an amorphous polymorph of silicon dioxide. It's a powder

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-16ultrafine containing more than 85% by dry weight of SiO ₂ . As it contains little or no CaO, only silica gel is formed in the absence of CaO.

In another advantageous embodiment of the method according to the present invention, the glass compound is fly ash, such as fly ash of class C and of class F.

It is known that under alkaline conditions, these glass compounds are activated thereby producing a silica gei material which provides high mechanical strength to a finished product. Due to the alkaline nature of the particulate steel slag material of the present invention, as noted above, the production of said silica gel material may also take place upon mixing with said particulate steel slag material forming thus a finished product with high mechanical strength. However, such a finished product suffers dramatically from the leaching of heavy metals, in particular chromium and molybdenum.

The inventors have now found that the combined use of the binding capacity of an inexpensive binder composition forming a gel with the carbonating agent, in particular a hydrated magnesium carbonate hydroxide compound of general formula ( I) provides a less expensive process for producing a final mass which retains its shape and always has an appropriate mechanical strength and which exhibits greatly reduced leaching of heavy metals, in particular chromium and molybdenum.

If desired, the gel-forming binder composition, as specified above, is completed by adding to the glass compound at least one basic reagent suitable for activating the glass compound before it is mixed with the particulate material. steel slag in Step 1. of the process of the present invention and / or after it has been mixed with the particulate material of steel slag in Step 1. of the process of the present invention. This is particularly advantageous when the particulate material of steel slag has a reduced pH, for example exposed to the action of air for a certain time, that is to say by natural carbonation.

Advantageously, the dry weight ratio of the glass compound to the basic reagent is greater than 3, preferably greater than 4, better still greater than 5.

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Non-limiting examples of suitable basic reagent may include, but are not limited to, sodium and / or potassium hydroxide, lime, cement, in particular blast furnace cement.

In another preferred embodiment of the process according to the present invention, the composition (B) mixed with the particulate material of steel slag in Step 1. consists essentially of the carbonating agent, as specified above, and the gel-forming binder composition, as specified above.

For the purposes of the present invention, the expression consists essentially of is intended to indicate that any additional ingredient different from the carbonating agent, as specified above, and the glass compound, as specified above, is present in a amount of at most 1% by weight, based on the total weight of the carbonating agent in composition (B).

The inventors have therefore found that the presence of the gel-forming binder composition makes it possible to obtain appropriate mechanical strength and that the carbonation agent makes it possible to control the leaching, over time, of the heavy metals contained in the preserving mass. a shape. In addition, the combination of the gel-forming binder composition with the carbonating agent makes it possible to reduce the amount of carbonating agent in the mixture without affecting the final properties of the mass retaining a shape in terms of resistance to compression and leaching.

Reducing agent

According to certain embodiments, it is possible to add, in Step 1. of the method according to the present invention, a reducing agent, in particular a chromium reducing agent capable of transforming hexavalent chromium into a trivalent chromic form by giving one or more electrons.

The applicant has found that the addition of reducing agents in Step 1. of the process of the invention further improves the retention of chromium in the final mass retaining a shape, that is to say the finished product.

Said reducing agent may be added to composition (B), as specified above, before mixing with the particulate materials of steel slag or may be added to the particulate materials of steel slag, such as

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Specified above, before mixing with composition (B) or can be added to mixture M formed in Step 1 before hardening of said mixture M. Non-limiting examples of suitable reducing agents may in particular include ferrous sulfate ( FeSO ₄ ), in particular ferrous sulfate heptahydrate (FeSO ₄ .7H ₂ O), stannous chloride (SnCI ₂ ), stannous sulfate (SnSO ₄ ), stannous oxide (SnO), stannous hydroxide (Sn ( OH) ₂ ), iron sulfide (FeS) and / or ferrous chloride (FeCI ₂ ), in particular ferrous chloride tetrahydrate (FeCI ₂ .4H ₂ O) and combinations thereof. Preferred reducing agents are FeSO ₄ .7H ₂ O, SnSO ₄ , SnCI ₂ , SnO, Sn (OH) ₂ and combinations thereof.

The percentage by dry weight of the reducing agent in the mixture M is generally at least 0.01% by weight, preferably at least 0.03% by weight, better still at least 0.25% by weight, even more preferably at least 0.50% by weight, more preferably at least 1.00% by weight, based on the total dry weight of the steel slag particulate material.

It is further understood that the percentage by dry weight of the reducing agent in the mixture M will generally be at most 8.0. % by weight, more preferably at most 6.0% by weight, more preferably at most 5.0% by weight, based on the total dry weight of the steel slag particulate material.

Good results have been obtained when the mixture M comprises the reducing agent in an amount of 0.03% by weight - 5.00% by weight, based on the total dry weight of the particulate material of steel slag.

Other ingredients

According to certain embodiments, other ingredients can be added in Step 1. of the process according to the present invention to further improve the final properties of the mass retaining a shape as a function of the desired end use.

Said other ingredients can be added to composition (B), as specified above, before mixing with the particulate material of steel slag or can be added to the particulate material of steel slag, as specified above, before mixing with composition (B) or may

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Be added to the mixture M formed in Step 1. before hardening of said mixture M in Step 2. The other suitable ingredients may in particular include, without being limited thereto, (i) fine and / or coarse aggregates having a particle size larger than the particle size of the particulate material of steel slag such as in particular sand, natural gravel, pebbles and the like; (ii) an inert charge.

The percentage by dry weight of the other ingredients in the mixture M is generally equal to or at least 0.01% by weight, preferably equal to or at least 0.03% by weight, better still equal to or d '' at least 0.25% by weight, even better still equal to or at least 0.50% by weight, ideally equal to or at least 1.00% by weight, based on the total dry weight of the mix M.

It is further understood that the percentage by dry weight of the other ingredients in the mixture M will generally be equal to or at most 79% by weight, preferably equal to or at most 50% by weight, better still equal to or at most 30.0% by weight, ideally equal to or at most 10% by weight, based on the total dry weight of the mixture M.

In step 1. of the process according to the present invention, the particulate material of steel slag, as specified above, the carbonating agent, as specified above, optionally the binder composition forming a gel, such as specified above, optionally the reducing agent, as specified above, and possibly other ingredients are mixed so as to obtain a homogeneous mixture M according to the practice known in the art.

Before Step 2., it is preferable to compact the mixture (M) by means of a compactor, in particular by means of a compactor roller (that is to say of what is called a steamroller) . The mixture (M) is first spread in a layer and this layer is then compacted before it has hardened.

In step 2. of the process of the present invention, the hardening of the mixture (M), as obtained in Step 1., takes place in the presence of water and the amount of water relative to the dry weight total of the mixture M is advantageously equal to or at least 5% by weight, preferably equal to or at least 10% by weight, better still equal to or at least 15% by weight. %.

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When the particulate material of steel slag as used in the process according to the invention is too dry, then additional water can be added to the particulate material of steel slag, as specified above, or can be added to composition (B), as specified above, before it is mixed with the particulate materials of steel slag or can be added to mixture M.

Alternatively, when the particulate steel slag material as used in the process according to the invention has too high a water content, then the particulate steel slag material can be dried according to methods known in the art. art.

The mass retaining a shape

As mentioned, another aspect of the present invention relates to a mass retaining a form prepared according to the method of the invention, as described in detail above.

The mass retaining a shape according to the invention advantageously has a compressive strength greater than 2 MPa, a compressive strength greater than 3 MPa being preferred and a compressive strength greater than 4 MPa being particularly preferred, a resistance to compression being measured according to the standard test method ASTM D 698-12. It has, advantageously, a compressive strength lying in the range between 2 MPa and 50 MPa.

The mass retaining a form according to the invention advantageously has a leaching of Cr and / or Ni of less than 0.5 mg / L, preferably less than 0.30 mg / L, better still less than 0.20 mg / L, even better still less than 0.10 mg / L, the mass leaching test retaining a shape being measured according to DIN 38414-S4 / EN 12457-4.

The mass retaining a form according to the invention advantageously has a leaching of Mo of less than 1.0 mg / L, preferably of less than 0.50 mg / L, better still of less than 0.20 mg / L, even better still less than 0.10 mg / L, the leaching test of the mass retaining a form being measured according to DI N 38414-S4 / EN 12457-4.

A preferred use of a mass retaining a shape according to the invention is as a building material, in particular building material.

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-21 road construction such as foundation and sub-foundation depending on the compressive strength obtained.

The inventors have surprisingly found that the mass retaining a form of the invention comprises calcite (CaCO ₃ ).

Without being bound by this theory, the formation of calcite could be the result of the reaction of the amorphous phases of the particulate material of steel slag with the carbonating agent of the present invention. In addition, in addition to this production of calcite, they observed with surprise that multiple crystalline phases are also produced, including in particular the newly formed phases magnesiochromite and hydrates of magnesium carbonate and chromium. The presence of these crystalline phases could make it possible to fix certain heavy metals, in particular chromium, better still chromium and / or nickel, in the structure of these. In this way, the leaching of the mass retaining a shape can be sufficiently controlled over time, since the heavy metals are fixed in the crystal structures.

Experimental test results

The invention will now be described in more detail with reference to the following examples, the aim of which is purely illustrative and is not intended to limit the scope of the invention.

General procedure for producing a mass retaining a shape

A shape-retaining mass was produced by mixing the particulate material from steel slag (i.e. stainless steel slag fines (0 - 0.5 mm)) with a carbonating agent, optionally a reducing agent, optionally a gel-forming binder composition, optionally other ingredients and water. The quantities of the various ingredients are summarized in Tables 1 to 3. Specimens were made from this mixture by compacting it in a mold having an internal diameter of 54.8 mm and a height of 50 mm, at a pressure of 10 MPa.

The addition of water makes it possible to reach the required water / solid ratio and to obtain a homogeneous mixture.

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The Proctor values of the various mixtures have been determined, that is to say the water content at which the maximum dry density is obtained in a Proctor test. Moisture contents that were close to this Proctor value were used in all experimental trials, as summarized in Tables 1 - 3.

The compressive strength of all the pellets of all comparative examples C1, C2, C23 and C24 and of examples 2 -22, 25 and 26 was measured after 21 days with a Controlab hydraulic press of type E0160S and according to the method d standard test ASTM D 698-12.

All the mass leachate analysis tests retaining a form of all the comparative examples C1, C2, C23 and C24 and examples 2 22, 25 and 26 were measured according to DIN 38418-S4

All experimental results are summarized in the tables

1,2 and 3.

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Table 1:

CO T “ m T “ xr " τ— CN T “ Τ- Ο 0) 00 <0 IO Xf Q O 4-> S Φ O) vs m o E 3 T3 uo CO in ïï E IO o o_ (AT .2 Έ 0 (J (AT Φ TJ 'S where ο Ιο Ιο Ιο I ο I ο | 0.1 11 | 5 | o | 1 | 0.25 | 0.03 | 0.03 | 0.03 | 0.5 | Molar ratio I 3.43 33.3 1 O 66.7 glass binder LO CT) 0 0 0 m o '* 12.1 I 16.2 I 20.6 I 20.8 I 21.9 I 18.1 I 17.8 I 18.7 | 19.9 | 18.0 | ? | 18.0 | 18.0 | 18.0 | 18.0 | 18.0 | MPa the- in CT) xf O) 'T CN m CN co CO CN CN < CO oo CO 1-- ^ · CO h- ‘ T “ 'ί in nt r-_ -T 00 CT) O CN o V <0.1 I I <0.1 I I 10.7 I O) 85 I m CO co VS 0 ‘35 0 33.3 1 O 66.7 95 | 0 0 0 LO <0.1 o V <0.1] I 10.9 CN m 00 LO ’T“ 3.43 33.3 1 0 66.7 95 | 0 0 m o o CO o o V ί <0.1 I 111.0 1 12.6 l 85 I m 3.43 33.3 d O 66.7 95 | 0 tn 0 o I 0.26 o V ! <0.1 I 10.9 I 12.5 85 I w 3.43 33.3 1 O 66.7 m CT) 0 in 0 o 0.23 o V I <o, i ! 10.9 I 12.0 85 I LO 3.43 33.3 1 O 66.7 95 1 0 IO 0 o I <0.1 o V I <o, i 11.4 T ^- cm T 85 | m 3.43 33.3 1 O 66.7 95 d 0 LO 0 o 0.34 o V <0.1 11.1 V “ CM v 85 | U0 3.43 0 0 O 0 0 0 0 0 o o V o V o V 11.7 | 85 | w V “ 3.43 0 0 O 0 0 0 0 0 o V “ where T— o V I <0.1 CN O) m 00 IO 3.43 0 0 O 0 0 0 0 0 o o o V I <o, i <q <q 85 I tn 3.43 0 0 O 0 0 0 0 0 o 0.2 o V I 0.3 CO 11.8 88.3 I 11.7 I CO co 0 14.5 I 85.5 95 I 0 10 0 o I 0.16 I 0.25 I ί <0.1 CO 12.7 88.3 I 11.7 I 3.43 E 0 o (Q 14.5 I 0 85.5 95 I 0 10 0 o 0.18 0.27 <0.1 b- 12.5 00 CN O Τ- Ο not o 4-> U Φ w <A TJ Ö f | 88.3 I r- 0 Φ Ό " O 4-, (AT TJ Ö 0 14.5 I 0 85.5 % by total weight of 95 1 0 tn 0 o 0.17 I 0.25 Ί <o, i I tn 12.5 85 I tn 0 0 0 100 85 I m 0 0 o I 2.80 I ί 1.40 l 1 12.8 VS Φ o ** 100 I o 0 vs Φ 'S where 0 0 0 0 0 0 0 o I 0.67 [0.51 I 0.3 t Example number I Mix M Slag (0 - 0.5 mm) Composition (B) Reducing agent 0 CN £ d w Φ LL Composition (B) 0 CN X in ?! O ra Zo oo σ> & 0 CN T IC5 CN X 0 ro 2 CO O 0 05 2 Ν ’ + O 05 2 0 CM X LO ^ CN X 0 'S co 0 0 O) M- + 0 CO O Gel-forming binder composition Gel-forming binder composition Cullet NaOH CN X 0 "F 0 I CEM Cement 1 I CEM Cement III A Humidity Real water / solid ratio Compressive strength of the mass □ _# o V “& I Leachate content (mg / L) O O Z pH mix M pH final mass

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-24Table 2:

Example number 17 18 19 20 21 22 Mix M % by total dry weight of the total mixture M Slag (0 - 0.5 mm) 85 85 85 86 86 87.5 Composition (B) 15 15 15 14 14 12.5 Reducing agent % scor es (0 - 0.5 mm) FeSO ₄ .7H ₂ O 0 0 0 0.25 0 0 SnSO ₄ 0.5 0 0 0 0 0.05 SnCI ₂ 0 0 0 0 0.05 0 Sn (OH) ₂ 0 0.25 0 0 0 0 SnO 0 0 0.25 0 0 0 Composition (B) Molar ratio (MgO) 1 4MgCO ₃ .Mg (OH) ₂ .5H ₂ O 3.43 3.43 3.43 3.43 3.43 3.43 % by total weight of the composition (B) MgO + 4MgCO ₃ .Mg (OH) ₂ .5H ₂ O 33.3 33.3 33.3 28.6 28.6 20.0 Gel-forming binder composition 66.7 66.7 66.7 71.4 71.4 80.0 Gel-forming binder composition % by total weight of the glass binder Calci n 95 95 95 95 95 95 NaOH 0 0 0 0 0 0 Ca (OH) 2 5 5 5 0 5 0 CEM cement 1 0 0 0 0 0 0 CEM Cement Ili A 0 0 0 5 0 5 Humidity % Real water / solid ratio 18.0 18.0 18.0 17.0 17.0 17.0 Compressive strength of the mass MPa oc (21 days) 5.9 3.6 3.0 4.0 3.7 3.3 Leachate content (mg / L) Cr <0.1 <0.1 <0.1 0.17 0.17 <0.1 Mo <0.1 <0.1 <0.1 0.13 0.21 0.24 Or <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 pH mix M 10.7 10.8 10.8 11.2 11.3 11.7 pH final mass 12.0 12.0 12.1 12.3 12.0 12.3

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-25Table 3:

Example number C23 C24 | 25 26 Mix M % by total dry weight of the total mixture M Slag (0 - 0.5 mm) 85 85 85 85 Composition (B) 15 15 15 15 Reducing agent % slag (0 - 0.5 mm) FeSO ₄ .7H ₂ O 0 5 5 I 1 Composition (B) % by total weight of the composition (B) MgO + K ₂ CO ₃ ^a 0 0 100 0 MgO + NaHCO ₃ ^a 33.3 100 0 0 MgO + 4MgCO ₃ .Mg (OH) ₂ .5H ₂ O ^a 0 0 100 Limestone charge 0 0 0 4.5 Binder composition forming a gel 66.7 0 0 0 Gel-forming binder composition % by total weight of the glass binder Cullet 85 0 0 0 NaOH 15 0 0 0 Ca (OH) 2 0 0 0 0 CEM Cement I 0 0 0 0 CEM III A cement 0 0 0 0 Humidity % Actual water / solid ratio 16.2 | 18.0 | 16.1 | 18.0 Compressive strength of the mass MPa oc (21 days) 8.3 1.1 5.3 6.0 Leachate content (mg / L) Cr 2.7 0.1 0.1 <0.1 Mo 1.4 0.7 1.0 <0.1 Or - <0.1 <0.1 <0.1 pH mix M - 12.1 11.7 10.8 pH final mass 12.9 12.3 12.4 12.2

^a The molar ratio of MgO to K ₂ CO ₃ , NaHCO ₃ or 4MgCO ₃ .Mg (OH) ₂ .5H ₂ O is 3.43

Experiment 27

A mineralogical analysis was performed by XRD (5 X-ray diffraction) for the mass retaining a shape of Example 9 and for particulate stainless steel slag (i.e. slag (0 / 0.5 mm)) used for the production of said mass retaining a shape. The results are summarized in Table 4.

Table 4: semi-quantitative mineralogical analysis of slag (0 / 0.5) before mixing and of the mass retaining a form of Example 9.

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Compounds Chemical formula Slag (0 / 0.5 mm) (%) Ex. 9 (%) Amorphous / 25 10 Akermanite-Gehlenite Ca2 (AI.25Mg.75) ((AI.25Si.75) O7) 5 / Brédigite Ca ₁₄ Mg ₂ (SiO4) ₈ 14 14 Brownmillerite Ca ₂ (AI, Fe ⁺³ ) ₂ O ₅ <5 / Brucite Mg (OH) ₂ / <5 Calcio-olivine CaSiO ₄ 10 11 Calcite CaCO ₃ <5 17 Calcium sulfate and hydrated aluminum Ca4Al2O ₆ SO ₄ .14H ₂ O / <5 Cuspidine Ca ₄ Si ₂ O ₇ F 2 11 / Enstatite MgSiO ₃ / 6 Iron enstatite Fe. ₁₅₅ Mg.845SiO ₃ / / Ferrinatrite Na ₃ Fe (SO _{4) 3} .12 (H ₂ O) / / Gypsum Ca (SO ₄ ) .2 (H ₂ O) <5 <5 Magnesiochromite Fe.i3Mg.87Cr ₂ O ₄ / <5 Magnesiochromite iron (Mg.8Fe. ₂ ) Cr ₂ O ₄ <5 / Carbonate magnesium and hydrated chromium MgCr (CO ₃ ) ₂ .3 (H ₂ O) / <5 Manganilvaite (Ca.98Mn.02) Fe2 (Mn.72Fe.28 (Si ₂ O7) O (OH) / <5 Mayenite Cai ₂ AI ₁₄ O ₃₃ <5 / Melilite Ca2Mg.75Af5Si1.75O7 / 5 Merwinite Ca ₃ Mg (SiO ₄ ) ₂ 17 13 Periclase MgO <5 <5 Quartz SiO2 <5 <5 Rutile TiO ₂ <5 / Aluminate silicate Na1.04AI2Si48O99.52 / /

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sodium Wollastonite CaSiO ₃ <5 /

As can be seen in Table 4, the invention found that chromium is located in stable structures such as magnesiochromite, magnesium carbonate and hydrated chromium during carbonation with the carbonating agent of the present invention thus preventing actually the leaching of chromium. In addition, the calcite content increases from an amount of less than 5% to an amount of 17%, while the amount of amorphous phases decreases from 25 to 10% thus providing good mechanical properties.

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Claims (24)

1. A method for producing a mass retaining a shape and having a compressive strength, measured according to the standard test method ASTM D 698-12, of at least 2 MPa, comprising the following steps: Step 1. Mix a binder composition [hereinafter, composition (B)] comprising at least one carbonation agent which is selected from the group consisting of potassium carbonate, potassium bicarbonate and compound of hydrated magnesium carbonate hydroxide of general formula (I): xMgCO ₃ .yMg (OH) ₂ .zH2O in which x is a number in the range of 3.5 - 4.5, y is a number in the range of 0.5 - 1.5 and z is a number in the range of 3.5 - 5.5, with at least one particulate material of steel slag thereby forming a mixture [hereinafter M mixture] and wherein said particulate material of steel slag contains calcium silicate phases and at least chromium and is present in said mixture M in an amount of at least 50% by dry weight, relative to the total dry weight of mixture M, and Step 2. hardening of the mixture M, as obtained in step 1., in the presence of water, thus producing the mass retaining a shape. 2. Method according to claim 1, characterized in that the particulate material of steel slag is present in an amount of 70 - 95% by dry weight based on the total dry weight of the mixture M. 3. Method according to claim 1 or claim 2, characterized in that at least 50% by volume of the particulate material of steel slag has a particle size less than 1.0 mm. 4. Method according to any one of claims 1 to 3, characterized in that the particulate material of steel slag comprises dicalcium-γ silicate in an amount of at least 3% by weight relative to the total dry weight of the particulate material of steel slag. 5. Method according to any one of claims 1 to 4, characterized in that the particulate material of steel slag has a content of B E2015 / 5322 -29calcium, expressed as% CaO, of at least 30% by dry weight and a silicon content, expressed as% of SiO ₂ , of at least 15% by dry weight. 6. Method according to any one of claims 1 to 5, characterized in that the particulate material of steel slag has a pH of at least 8.5. 7. Method according to any one of claims 1 to 6, characterized in that the particulate material of steel slag has a chromium content of at least 1000 ppm, more particularly at least 3000 ppm, even more particularly at least 5000 ppm. 8. Method according to any one of claims 1 to 7, characterized in that the particulate material of steel slag has a molybdenum content of at least 100 ppm, in particular at least 1000 ppm, and more particularly at least 2500 ppm. 9. Method according to any one of claims 1 to 8, characterized in that the particulate material of steel slag has a nickel content of at least 300 ppm, in particular of at least 400 ppm, and more particularly at least 500 ppm. 10. Method according to any one of claims 1 to 9, characterized in that the composition (B) is present in the mixture M in an amount of at least 1% by weight, preferably at least 5% by weight, more preferably at least 10% by weight and the composition (B) is preferably present in the mixture M in an amount of at most 45% by weight, more preferably at most 35% by weight, the basis of the total dry weight of the mixture M. 11. Method according to any one of claims 1 to 10, characterized in that the composition (B) consists essentially of the carbonating agent or comprises the carbonating agent in an amount greater than 1% by weight, preferably greater than 5% by weight, better still greater than 10% by weight, based on the total weight of the composition (B). 12. Method according to any one of claims 1 to 11, characterized in that the carbonation agent comprises at least one hydrated magnesium carbonate hydroxide compound of general formula (I): xMgCO ₃ .yMg (OH) 2.zH ₂ O in which x is 4, y is 1 and z is 4 or 5. B E2015 / 5322 -BE. Process according to any one of Claims 1 to 12, characterized in that the carbonating agent comprises potassium carbonate and / or potassium bicarbonate. 14. Method according to any one of claims 12 to 13, characterized in that the carbonation agent further comprises a carbonation improving compound selected from the group consisting of magnesium oxide (MgO), calcium oxide (CaO) , calcium and magnesium oxide (i.e. calcined dolomite) and mixtures thereof, preferably MgO. 15. The method of claim 14, characterized in that the molar ratio of said carbonation-improving compound to the carbonation agent is advantageously at least 1.0, preferably at least 1.5, better still at least 3.0. 16. Method according to any one of claims 1 to 15, characterized in that the composition (B) further comprises a binder composition forming a gel in an amount greater than 1% by weight, preferably greater than 10% by weight, more preferably greater than 20% by weight and the composition (B) preferably comprises said binder composition forming a gel in an amount of at most 99% by weight, preferably at most 95% by weight, better still at most 80% by weight, based on the total weight of the composition (B). 17. The method of claim 16, characterized in that the gel-forming binder composition comprises a glass compound which contains more than 50% by dry weight of SiO ₂ . 18. The method of claim 17, characterized in that the glass compound comprises glass powder, in particular a soda-lime glass powder. 19. Method according to any one of claims 1 to 18, characterized in that a reducing agent capable of transforming hexavalent chromium into a trivalent chromic form by giving one or more electrons is added in Step 1. and said agent reducing agent is preferably selected from the group consisting of ferrous sulfate (FeSO ₄ ), in particular ferrous sulfate heptahydrate (FeSO ₄ .7H ₂ O), stannous chloride (SnCI ₂ ), stannous sulfate (SnSO ₄ ), stannous oxide, (SnO ), stannous hydroxide (Sn (OH) ₂ ), sulfate B E2015 / 5322 -31 stannous manganese, iron sulfide (FeS) and / or ferrous chloride (FeCI ₂ ), in particular ferrous chloride tetrahydrate (FeCI ₂ .4H ₂ O) and combinations thereof. 20. Method according to any one of claims 1 to 19, characterized in that before Step 2., the mixture (M) is compacted by means of a compactor, in particular by means of a roller compactor . 21. Mass retaining a form prepared according to the method according to any one of claims 1 to 20. 22. mass retaining a shape according to claim 21, said mass retaining a shape having a compressive strength greater than 2 MPa, preferably greater than 3 MPa, better still greater than 4 MPa, the value of compressive strength being measured according to the standard test method ASTM D 698-12. 23. A mass retaining a form according to claim 21 or 22, wherein the leaching of Cr and / or Ni from the mass retaining a form is less than 0.5 mg / L, preferably less than 0.30 mg / L, better still less than 0.20 mg / L, even better still less than 0.10 mg / L, the mass leaching test retaining its shape being measured according to DIN 38414S4 / EN 12457-4 . 24. A form retaining mass according to any one of claims 21 to 23, wherein the leaching of Mo from the form retaining mass is less than 1.0 mg / L, preferably less than 0.50 mg / L, better still less than 0.20 mg / L, even better still less than 0.10 mg / L, the mass leaching test retaining its shape being measured according to DIN 38414-S4 / EN 12457 -4. 25. Foundation or sub-foundation layer comprising the mass retaining a shape according to any one of claims 21 to 24. B E2015 / 5322