EP4081492A1

EP4081492A1 - Method for treating soil contaminated by sulphates

Info

Publication number: EP4081492A1
Application number: EP20839098.9A
Authority: EP
Inventors: Blandine ALBERT; Véronique BROYER; Ivan SERCLERAT; Vincent Meyer; Mickaël RUIZ
Original assignee: Holcim Technology Ltd
Current assignee: Holcim Technology Ltd
Priority date: 2019-12-23
Filing date: 2020-12-23
Publication date: 2022-11-02
Also published as: WO2021130327A1; FR3105032B1; FR3105032A1

Abstract

The present invention relates to a method for treating contaminated soil, comprising at least a step of treating the soil with, by weight relative to the weight of the dry soil: - between 1.5% and 5.0% of a first belite sulfoaluminate clinker-type mineral binder, - between 2.0% and 5.0% of lime, and characterised in that the soil is also treated with an additional component chosen from: - a second mineral binder that is different from the first mineral binder and preferably chosen from a calcium aluminate cement, a blast furnace slag or a combination thereof at a content ranging from 1.5% to 5.0% by weight relative to the weight of the dry soil, - an alkanolamine at a content ranging from 0.001 to 0.050% by weight relative to the weight of the dry soil, - a hexavalent chromium salt reducing agent at a content ranging from 0.01 to 3.00% by weight relative to the weight of the dry soil, and - combinations thereof, and in that the lime is added to the contaminated soil in proportions greater than 30% by weight relative to the total weight of the first mineral binder, lime and, where appropriate, the second mineral binder.

Description

Title: PROCESS FOR TREATMENT OF SOIL POLLUTED BY SULPHATES

Technical field The present invention relates to a process for treating soil polluted, in particular with anions such as sulfate ions and with heavy metal cations, characterized in that it comprises at least the treatment of the soil with a first mineral binder of sulfoaluminous clinker type, lime and an additional component chosen from a second inorganic binder different from the first inorganic binder, an alkanolamine, a reducing agent of a hexavalent chromium salt and their combination (s). A subject of the present invention is also the product capable of being obtained by said process as well as a composition for treating polluted soil comprising a first inorganic binder of sulfoaluminous clinker type, lime, and an additional component chosen from a second binder. mineral different from the first inorganic binder, an alkanolamine, a reducing agent of a hexavalent chromium salt and their combination (s), and the use of said composition for the treatment of a polluted soil.

Soil decontamination is a growing demand and comes with major challenges in terms of public health and environmental protection.

In particular, during construction work, the builder is required to treat the excavated soil before putting it in landfill.

The release of soluble pollutants following their contact with water exposes a significant potential pollution risk to the environment during short-term or final storage, or the reuse of contaminated soils.

To limit this risk, the landfill of contaminated soils first requires lowering the dangerousness class of these soils, which amounts to lowering the level of leachable pollutants in the water.

Lowering the hazard class can also make it possible to reuse soils treated in this way, for example in road sub-layers or in embankments. Recently, solutions based on more or less belitic sulfoaluminous cement (WO2013 / 171418 and WO2019 / 162605) and on aluminous cement (WO2018 / 065447) have been proposed. Anionic pollutants, such as sulphates, or heavy metals, present in contaminated soil, can be trapped during the hydration process of a hydraulic binder mixed with the soil to be treated and with water. These elements can be trapped in hydrates of the CSH (hydrated calcium silicate) or sulphoaluminous type. of the ettringite or calcium monosulfoaluminate type. Some elements can also be stabilized in the form of hydroxides.

In particular, in patent application WO 2013/171418, the Ciments Français company describes the use of a composition comprising a specific sulphoaluminous clinker and lime for the treatment of soils polluted with sulphates.

In patent application WO 2019/162605, the Vicat company describes the use of a composition comprising another type of belitic sulphoaluminous clinker optionally doped with iron and lime for the treatment of soils polluted with sulphates and / or metals. heavy.

These solutions have the advantage of being effective quickly, after just a few days of treatment. However, it is essential that the soil, once treated and classified as inert, remains so. The storage and use conditions of inert soil being different from that of non-inert soil, significant risks for the environment are to be feared in the event of soil evolution. It is therefore a question of stabilizing the release of sulphates also in the long term, in particular at 2 months, advantageously at 6 months.

In addition to the questionable durability of solutions based on sulphoaluminous cement, a major drawback is the risk of release of hexavalent chromium, a mobile and toxic form of chromium, which comes from the mineral binder used for the treatment of sulphates. The presence of lime in the binder according to the solution proposed in WO2019 / 162605 seems to solve this problem. Indeed, the values of chromate released are low enough for the soil to be considered inert. But the durability of this solution limiting the release of chromates is not guaranteed. Soil can evolve into non-inert and polluting soil.

However, it has been observed that the amount of sulfate or hexavalent chromium released increases over time. Thus, the durability of the solutions proposed in the prior art is not guaranteed. Surprisingly, it has been discovered that the addition to these compositions in particular of an additional component chosen from a second inorganic binder different from the first inorganic binder, an alkanolamine, a reducing agent of a hexavalent chromium salt and their (s) combination (s) make it possible to prolong the trapping of sulphates and hexavalent chromium over the long term.

The present invention relates to a composition for the treatment of polluted soils and to a process for the treatment of polluted soils using such a composition making it possible to obtain both short-term efficiency, with trapping of sulphates from 1 day. , and durability over time of this trap, including more than 2 months after treatment. The release of chromate ions in the short term and in the long term (2 months or 6 months) is also controlled and improved within the framework of the invention.

Definitions

In cement language, the primary compounds are represented by C for CaO, S for S1O ₂ , A for AI ₂ O ₃ , $ for SO ₃ , F for Fe ₂ C> ₃ , T for T1O ₂ , which will be used in the throughout this text, unless otherwise indicated.

By the term "clinker" is meant according to the invention the product obtained after cooking (clinkerization) of a mixture (raw) composed, inter alia, for example of limestone and for example of clay for Portland clinker.

The sulfoaluminate phase, optionally doped with iron, has the formula C4AxFy $ z with x varying from 2 to 3, y varying from 0 to 0.5 and z varying from 0.8 to 1, 2. In particular, the yeelimite or ye'elimite is a sulfoaluminate phase. It is a calcium sulfoaluminate of formula Ca ₄ (AI0 ₂ ) ₆ SC> ₃ (hereinafter referred to as “C4A3 $”).

Belite is a dicalcium silicate of formula Ca2SiC> 4 (hereinafter referred to as “C2S”). Belite exhibits different varieties of polymorphisms: C2S (a ’), orthorombic crystal, C2S (a), hexagonal crystal, 028 (b), monoclinic crystal, C2S (y), orthorombic crystal. For the purposes of the invention, unless otherwise indicated, the term "belite" refers to any crystalline form of belite.

Ferrites are phases comprising iron oxide. In particular, the ferrites are a calcium aluminoferrite phase corresponding to the general formula C2Ax'F (1-x '), with x' ranging from 0.2 to 0.8. The ferrites preferably comprise a brownmillerite phase. The brownmillerite is a ferro-aluminate tetracalcium of formula Ca ₄ Al ₂ Fe ₂ 0io (hereinafter referred to as "C 4 AF") The ferrites may also comprise a so-called ferroperovskite phase. Ferroperovskite is a perovskite phase integrating iron, which gives a compound of variable composition, in particular of formula C3FT.

Mayenite is an anhydrous calcium aluminate of formula 12Ca0.7Al ₂ C> ₃ (hereinafter referred to as "C12A7") and exhibits a crystal structure composed of three-dimensionally bonded voids (cages) comprising "free oxygen ions". These free oxygen ions can be substituted by anions at room temperature. Thus, within the meaning of the present invention, the C12A7 phase encompasses any isotype structure of C12A7, such as for example C11A7.CaF2 (F here denotes fluorine) whose structure results from a substitution of O 2 - ions by F - ions. . In the rest of the description, by C12A7, it is necessary to understand C12A7 or any isotype structure in particular C11A7.CaF2 (F here denotes fluorine) and C11A7.CaCl2.

Quicklime is the direct product of the thermolysis or calcination of limestone. It mainly contains calcium oxide (CaO).

Slaked lime is obtained after hydration of quicklime. It includes calcium hydroxide Ca (OH) 2.

A mineral binder is a mineral material having the property of solidifying and then of hardening while acquiring mechanical characteristics. In particular, according to the invention, a mineral binder can be a hydraulic binder and / or a latent hydraulic binder and / or a binder having pozzolanic properties.

A hydraulic binder is a material having the property of hydrating in the presence of water and the hydration of which makes it possible to obtain a solid with mechanical characteristics. A latent hydraulic binder and a pozzolanic binder have the property of hydrating in the joint presence of water and lime.

According to the invention, "long term" corresponds to "at least 2 months", advantageously "at least 6 months".

According to the invention, "short term" corresponds to "from 1 to 7 days".

The subject of the invention is a method for treating polluted soil comprising at least treating the soil with, by weight relative to the weight of said dry soil:

- from 1.5% to 5.0% of a first inorganic binder of the belitic sulphoaluminous clinker type,

- from 2.0% to 5.0% lime, and characterized in that the soil is also treated with an additional component chosen from:

- a second mineral binder different from the first mineral binder, preferably chosen from a cement of calcium aluminates, a blast furnace slag or their combination, in a content ranging from 1.5% to 5.0% by weight relative to the weight of said dry soil,

- an alkanolamine in a content ranging from 0.001 to 0.050% by weight relative to the weight of said dry soil,

- a reducing agent of a hexavalent chromium salt in a content ranging from 0.01 to 3.00% by weight relative to the weight of said dry soil, and

- Their combination (s), and in that lime is added to the polluted soil in proportions greater than 30% by weight relative to the total weight of the first mineral binder, lime and optionally second mineral binder. Belitic sulfoaluminous clinker

A belitic sulfoaluminous clinker is a clinker comprising at least one sulfoaluminate phase, in particular C4A3 $ yeelimite, and a C2S belite phase in proportions in these two phases of more than 60% by weight relative to the total weight of said belitic sulfoaluminous clinker.

In the context of the invention, the belitic sulfoaluminous clinker preferably comprises at least 30% by weight relative to the total weight of said sulfoaluminate phase clinker, in particular yeelimite, more preferably at least 35%. It comprises in particular at least 15% by weight relative to the total weight of said belite phase clinker, more particularly at least 20% by weight.

In particular, the belitic sulfoaluminous clinker comprises less than 65%, preferably less than 60%, more preferably less than 50%, by weight relative to the total weight of said clinker of sulfoaluminate phase, advantageously yeelimite. More particularly, the belitic sulfoaluminous clinker comprises between 30 and 65%, preferably between 30% and 60%, more preferably between 35% and 50%, by weight relative to the total weight of said sulfoaluminate phase clinker, such as yeelimite.

In particular, the belitic sulfoaluminous clinker also comprises more than 15% by weight relative to the total weight of said belite phase clinker. Preferably, the belitic sulfoaluminous clinker comprises at least 2% by weight relative to the total weight of said belite phase clinker in alpha ’form. Thus, it is understood that the belitic sulfoaluminous clinker comprises at least 2% by weight relative to the total weight of said belite phase clinker in alpha ’form and the belite phase complement in another form. More particularly, the belitic sulfoaluminous clinker comprises between 15 and 35%, preferably between 20% and 35%, by weight relative to the total weight of said belite phase clinker, including in particular at least 2% by weight relative to the total weight of said belite phase clinker in alpha 'form.

Advantageously, the belitic sulfoaluminous clinker further comprises more than 12% by weight, more preferably more than 15% by weight, more preferably more than 20% by weight relative to the total weight of the ferrite clinker, more preferably between 20% and 40%. %.

Preferably, the belitic sulfoaluminous clinker comprises, by weight relative to the total weight of said clinker:

- more than 60%, of sulfoaluminate phase, preferably yeelimite (C4A3 $), and of belite phase (C2S), preferably including at least 2% of belite phase in alpha 'form, - More than 15% of ferrites. Preferably, the belitic sulfoaluminous clinker comprises, by weight relative to the total weight of said clinker:

- from 30% to less than 60%, preferably from 30% to less than 50%, of sulfoaluminate phase, preferably yeelimite (C4A3 $), - More than 15% of belite phase (C2S), preferably including at least 2% of the belite phase in alpha 'form,

- More than 20% of ferrites.

Other minority phases may be present in the belitic sulphoaluminous clinker, in particular chosen from calcium sulphates, gehenite or mayenite, and their combinations.

Preferably, the belitic sulfoaluminous clinker comprises less than 5% by weight relative to the total weight of said mayenite clinker. In particular, the belitic sulfoaluminous clinker does not include a mayenite phase detectable by Rietveld analysis of the X-ray diffraction spectrum of the clinker. In particular, the belitic sulfoaluminous clinker comprises at least 80% by weight relative to the total weight of said clinker of sulfoaluminate phases, preferably yeelimite C4A3 $, belite C2S and ferrites, preferably at least 90%, more preferably at least 95%.

Compared to sulfoaluminous clinkers with high sulfoaluminate phase contents and limited belite and ferrite contents, this type of clinker has on the one hand the advantage of having lower chromium contents (because their manufacture requires less bauxite, which is the raw material which provides the most chromium in the clinker) and on the other hand to have sufficient reactive constituents in the short term (yeelimite) and long term (belite and ferrite). As examples of clinkers particularly suitable for the process according to the invention, one can in particular describe the clinkers B1, B2 and B3 having the following mineralogy:

[Table 1]

ND: not detected.

In particular, the Blaine specific surface area of the belitic sulfoaluminous clinker according to the invention is between 2500 cm ² / g and 6000 cm ² / g. Belitic sulfoaluminous clinker is mixed with the polluted soil in proportions varying from 1.5 to 5% by weight relative to the weight of the dry soil, preferably from 1.5 to 4%, more preferably from 1.5 to 3%.

These low proportions lead to an economical formulation and make it possible to limit the intake of chromates by limiting the quantity of belitic sulfoaluminous clinker added to the soil.

Lime

In the context of the invention, the lime can be free lime (CaO), slaked lime (Ca (OH) 2), or a mixture of free lime and slaked lime in any proportion. In one embodiment, the lime is slaked lime.

The use of slaked lime makes it possible to limit the consumption of free water, and not to penalize the reactions of clinker with the sulphates in the soil. The presence of lime is key.

It allows: - to limit the quantity of leachable chromates when the treatment is carried out with a belitic sulphoaluminous clinker,

- to optimize the quantity of free sulphates which react with the belitic sulphoaluminous clinker and therefore to have a more effective binder in the short term,

- to guarantee the durability of the treatment. In the context of the invention, the lime is mixed with the polluted soil in proportions varying from 2.0 to 5.0% by weight relative to the weight of the dry soil, preferably from 3 to 5%.

Lime is added in proportions greater than 30% by weight relative to the total weight of the first inorganic binder, lime, and optionally of the second inorganic binder, preferably greater than 50%, and more preferably up to 80 %.

Indeed, below 30% by weight, the durability of the treatment is less because it must be taken into account that part of the lime will interact with the soil (cationic exchanges between Ca ²⁺ which comes from the lime and the ions present in the interfoliar space of clay minerals present in the soil). Part of the lime will therefore not be available to react with the clinkers and sulphates.

Additional component

The additional component is chosen from a second inorganic binder different from the first inorganic binder, an alkanolamine, a reducing agent of a hexavalent chromium salt, and their combination (s).

It makes it possible to stabilize the leachable sulphates in the long term, or even in particular to reduce the release of sulphates in the long term. It can also help control the release of chromate ions in the short term or even in the long term.

Mineral binder

The additional component can be an inorganic binder different from the first inorganic binder. In the context of the invention, the second inorganic binder, different from the first inorganic binder, is preferably a hydraulic binder and / or a latent hydraulic binder and / or a binder having pozzolanic activity. It can be a calcium aluminate cement or a mineral addition chosen from a blast furnace slag, fly ash, calcined clays and their combinations, or the combination of a calcium aluminate cement and said mineral addition. . More particularly, the second inorganic binder is calcium aluminate cement or blast furnace slag or a combination thereof.

The second inorganic binder is mixed with the polluted soil in proportions varying from 1.5 to 5% by weight relative to the weight of the dry soil, preferably from 1.5 to 4%, more preferably from 1.5 to 3%.

In particular, according to the invention, the mass proportion between first and second mineral binder mixed with the polluted soil is between 30/70 and 70/30, more particularly 40/60 and 60/40, preferably 50/50. In particular, the second inorganic binder is a calcium aluminate cement.

A calcium aluminate cement is a cement comprising at least one phase chosen from C3A, CA, C12A7, C11A7CaF2, C4A3 $ (yeelemite), C2A (1-x) Fx (with x belongs to] 0, 1]), hydraulic amorphous phases having a C / A molar ratio of between 0.3 and 15 and such that the cumulative Al ₂ O ₃ contents of these phases are between 3 and 70% by total weight of the calcium aluminate cement, preferably between 7 and 50% by weight and better still between 20 and 30% by weight. In the context of the invention, the calcium aluminate cement comprises more than 60%, preferably more than 80%, by mass of Mayenite C12A7 phase or of a Mayenite isotype.

Advantageously, the calcium aluminate cement of the invention comprises, as the sole aluminate phase, the Mayenite C12A7 phase.

The calcium aluminate cement advantageously comprises more than 85% by mass of Mayenite phase, more advantageously more than 90% by mass of Mayenite phase, even more advantageously more than 95% by mass of Mayenite phase.

The calcium aluminate cement can comprise up to 99% by mass of Mayenite phase, or even 100% by mass. Clinkers richer in C12A7 allow more ettringite to be formed.

The calcium aluminate cement of the invention is advantageously obtained by melting or sintering between 1250 and 1300 ° C approximately of a mixture of white bauxite and limestone. Low levels of silica and iron in the raw materials guarantee an optimal level of C12A7. Advantageously, the cumulative content of iron and silica is less than 30%, even more advantageously less than 20%, by weight relative to the total weight of the raw materials.

Alternatively, the second mineral binder is a mineral addition chosen from a blast furnace slag, fly ash, calcined clay, and their combinations, in particular a blast furnace slag.

A blast furnace slag is a by-product of smelting resulting from the reduction of iron ores by coke. It is a mixture composed essentially of silicates, aluminates and lime, with various metal oxides, with the exception of iron oxides. It is as defined in the “Cement” standard NF EN 197-1 paragraph 5.2.2 of April 2012. Preferably, in the context of the invention, the blast furnace slag is ground with a particle size of between 3 and 50 pm.

Fly ash is siliceous or calcic in nature. They are obtained by precipitation of pulverulent particles in the flue gases of the boilers supplied with pulverized coal. They are as defined in the “Cement” standard NF EN 197-1 paragraph 5.2.4 of April 2012.

Calcined clay is produced in a kiln at a temperature of around 800 ° C. It is as defined in the “Cement” standard NF EN 197-1 of April 2012.

Alcanolamine

The additional component can also be an alkanolamine.

An alkanolamine is an alkane comprising at least one amine function and at least one alcohol function. In particular, the alkane is a C2-C6 alkane, preferably a C3-C5 alkane.

Advantageously, the alkanolamine is selected from the group comprising N, N bis- (2-hydroxyethyl) -2-propanolamine) (DIEPA), N, N bis- (2-hydroxypropyl) -N- (hydroxyethyl) amine ( EDIPA), diethanolamine (DEA), triethanolamine (TEA), triisopropanolamine (TIPA), N- (hydroxyethyl) diethylenetriamine (HEDETA), aminoethylethanolamine (AEEA) and their combination (s).

In particular, the alkanolamine is a tri (hydroxyalkyl) amine, more particularly, a tri (hydroxyalkyl) amine having at least one hydroxyalkyl group comprising 3 to 5 carbon atoms.

Preferably, the alkanolamine is chosen from triethanolamine, triisopropanolamine and their combination.

The possible presence in the binder of such a component makes it possible to increase the effectiveness of the treatment in the medium and long term by optimizing the reactivity of the aluminate phases. The alkanolamine is preferably mixed with the polluted soil at a dosage by weight relative to the weight of said dry soil of between 0.001 and 0.050%.

Reducing agent of a hexavalent chromium salt

The additional component may also be a reducing agent for a hexavalent chromium salt, in particular calcium nitrite, or a reducing agent for a hexavalent chromium salt based on antimony.

In one embodiment, the reducing agent for a hexavalent chromium salt is calcium nitrite.

In another embodiment, the reducing agent for a hexavalent chromium salt is a reducing agent for an antimony-based hexavalent chromium salt.

The reducing agent of a hexavalent chromium salt is mixed with the polluted soil at a dosage of between 0.01% and 3.0% by weight relative to the weight of said dry soil. In fact, in the presence of belitic sulfoaluminous clinker, it is not easy to control the release of chromate ions. It is therefore possible to use components which make it possible to reduce the part of chromium VI in chromium III which is stable and non- toxic. Sulphate-based reducing agents such as FeSCL and SnSCL are not recommended, so as not to provide additional sulphates. Other chlorine-based reducing agents should be avoided because they interfere with the action of the sulfoaluminous belitic clinker and greatly reduce the effectiveness of the treatment. Antimony-based reducing agents perform well in this regard.

The additional component can be a combination of an inorganic binder other than the first binder, an alkanolamine and / or a reducing agent of a hexavalent chromium salt.

Thus, in particular, the additional component can be a combination of an inorganic binder different from the first binder and of an alkanolamine. The additional component can also be a combination of an inorganic binder different from the first binder and a reducing agent of a hexavalent chromium salt.

Other

The effectiveness of the treatment can be significantly improved in the short and long term by adding water during the treatment.

To optimize the formation of ettringite in the material to be treated, the binder is evenly distributed and the amount of water in the soil to be treated is sufficient to optimize the formation of ettringite. This results in practice by a water content which can be between 5% and 40% by weight, more advantageously 15% and 40%, relative to the weight of the dry soil, depending on its nature. If necessary, water can be added to the soil. The amounts of water are sufficient to allow the hydration reaction, and can easily be determined by one skilled in the art.

Process

The soil to be treated is non-inert and naturally or artificially contains leachable sulphates (from 1000 to 15000 ppm). It is taken as is, and usually has a humidity of 10 to 40%.

The constituents of the treatment, namely the first mineral binder, lime and the additional component chosen from a second mineral binder different from the first mineral binder, an alkanolamine, a reducing agent of a hexavalent chromium salt and their combination (s) ( s) can be added simultaneously, consecutively or sequentially and separately to the polluted soil to be treated. In one embodiment, a composition comprising the first inorganic binder, the additional component chosen from a second inorganic binder different from the first inorganic binder, an alkanolamine, a reducing agent of a hexavalent chromium salt and their combination (s) ) and optionally the lime can be prepared beforehand and then added to the polluted soil to be treated. The composition can be prepared by separate grinding of each of its constituents and then mixing all the constituents or by mixing the constituents and then co-grinding all the constituents.

The hydraulic binder can be ground and / or separated from the lime in order to obtain a binder having a Blaine specific surface area of between 2500 cm ² / g and 6000 cm ² / g.

Water can be added to the soil or be introduced at the same time or after addition of the constituents of the treatment. In particular, the soil is also mixed with water at a dosage of between 1% and 15% by weight based on the weight of the dry soil.

In an advantageous embodiment, the soil is mixed with each of the constituents of the treatment.

Thus, the method of treating polluted soil comprising at least one step of mixing the soil with, by weight relative to the weight of said dry soil:

- from 2.0% to 5.0% lime, characterized in that the soil is also treated with an additional component chosen from:

- a second mineral binder different from the first mineral binder in a content ranging from 1.5% to 5.0% by weight relative to the weight of said dry soil,

- Their combination (s), and in that lime is added to the polluted soil in proportions greater than 30% by weight relative to the total weight of the first mineral binder, lime and optionally second mineral binder.

The soil is mixed with the constituents of the treatment for a sufficient time in any suitable container. The mixing can be carried out continuously or discontinuously, in particular the mixing is carried out continuously. Mixing can be carried out with an open or closed type mixer. For the purposes of the invention, the terms “mixed” and “mixed” are used interchangeably.

Use of the process

The present invention also relates to the use of the process according to the invention for the stabilization in situ or before storage of soil polluted in particular by sulphate anions and / or heavy metal cations, in particular in the long term, more particularly in the long term. short and long term.

Composition for the treatment of polluted soil

The present invention also relates to a composition for the treatment of polluted soil, comprising, in percentage by mass:

- from 7.5 to 70% of a mineral binder of the belitic sulphoaluminous clinker type,

- from 10 to 70% lime,

- an additional component chosen from: from 7.5 to 70% of a second mineral binder different from the first mineral binder, preferably chosen from a calcium aluminate cement, a blast furnace slag or a combination thereof from 0.005 to 0 , 70% of an alkanolamine, from 0.05 to 42% of a reducing agent of a hexavalent chromium salt and their combination (s), and in that the lime is in proportions greater than 30 % by weight relative to the total weight of the first inorganic binder, lime and, where appropriate, the second inorganic binder. Preferably, the composition for the treatment of polluted soil, comprising, in percentage by mass:

- from 10 to 60% of a mineral binder of the belitic sulphoaluminous clinker type,

- from 10 to 70% lime,

- an additional component chosen from: from 10 to 60% of a second mineral binder different from the first mineral binder, from 0.01 to 0.5% of an alkanolamine, from 0.1 to 30% of a reducing agent of a hexavalent chromium salt and their combination (s), and in that the lime is in proportions greater than 30% by weight relative to the total weight of the first mineral binder, lime and optionally second binder mineral. The components of this composition are as described above. In particular, the belitic sulfoaluminous clinker comprises more than 12% by weight relative to the total weight of the ferrite clinker, preferably more than 15%, preferably more than 20%, more advantageously between 20% and 40%.

In particular, the belitic sulfoaluminous clinker comprises at most 5% by weight relative to the total weight of the Mayenite clinker. In particular, the belitic sulfoaluminous clinker does not include a Mayenite phase detectable by Rietveld analysis of the X-ray diffraction spectrum of the clinker.

In particular, the second inorganic binder is a calcium aluminate cement or a mineral addition chosen from a blast furnace slag, fly ash, calcined clays and their combinations, or the combination of a calcium aluminate cement. and said mineral addition. More particularly, the second inorganic binder is calcium aluminate cement or blast furnace slag or a combination thereof.

According to a first variant, the second inorganic binder is a calcium aluminate cement, preferably comprising more than 60%, preferably more than 80%, by mass of Mayenite C12A7 phase or of a Mayenite isotype.

According to a second variant, the second mineral binder is a mineral addition chosen from a blast furnace slag, fly ash, calcined clays and their combinations, in particular a blast furnace slag.

Advantageously, the alkanolamine is a tri (hydroxyalkyl) amine, more advantageously chosen from triethanolamine, triisopropanolamine and their combinations.

Preferably, the reducing agent for a hexavalent chromium salt is selected from calcium nitrite, a reducing agent for a hexavalent chromium salt based on antimony, and combinations thereof.

Lime is present in the composition in proportions greater than 30% by weight relative to the total weight of the first inorganic binder, lime, and optionally of the second inorganic binder, preferably greater than 50%, and more preferably up to 'to 80%.

In particular lime is slaked lime, or a mixture of free lime and slaked lime in any proportion. In one embodiment, the lime is slaked lime.

Use of composition The present invention also relates to the use of the composition as defined above for the treatment of soils polluted with anions, in particular sulphates, and with heavy metal cations, in particular hexavalent chromium salts, and their mixture.

Examples

Experimental protocols

Mineralogical analysis of a clinker:

The quantitative mineralogical analysis of a clinker is carried out by Rietveld analysis of the X-ray diffraction spectrum of this clinker. The clinker sample to be analyzed is finely ground to provide a sample in which all the particles pass through a sieve with a mesh size of 63 µm. The reference X-ray diffraction spectra of the crystal phases present in the sample to be analyzed (except for the glass phase which does not have a well-defined spectrum) are obtained from pure samples of these phases.

Leaching tests:

The tests were all carried out according to the recommendations of standard NF EN-12457-2, December 2002.

The tests are carried out on a material in which at least 95% of the particles (by mass) have a size of less than 4 mm.

For analyzes and leaching tests, the mass of dry matter (DM) of the sample is determined after passing in an oven at 105 ° C ± 5 ° C until constant weight in accordance with ISO 11465, August 1994. The difference between the masses of the sample before and after the passage in the oven corresponds to the moisture content of the soil or water content, which is expressed in relation to the mass of dry soil, as defined in standard NF EN 12457-2: 2002.

From the test sample, a test portion of a total wet mass containing exactly 0.090 kg ± 0.005 kg (measured with an accuracy of 0.1 g) of dry matter is prepared.

The leaching test is carried out at room temperature, i.e. 20 ° C ± 5 ° C.

The wet test portion with a total mass corresponding to 0.090 kg ± 0.005 kg of dry matter is placed in a flask, then a quantity of lixiviant is added (distilled water, demineralized water, deionized water or water of equivalent purity having a pH between 5 and 7.5, conductivity less than 0.5 mS / m) allowing a liquid-solid ratio of 10 L / kg ± 2% to be obtained. The stoppered vial is placed in a stirring device (as defined in the standard) is stirred at about 10 rpm for 24 hours ± 0.5 h. To achieve a good chemical balance between the solid and the solution, during the extraction it is important to avoid the settling of the solids.

In addition to the samples, leach “blanks” are also prepared.

After stopping the stirring, the suspended solids are decanted for 15 minutes ± 5 min, then vacuum filtered through a 0.45 μm membrane filter.

If filtration is made too difficult, the eluate can be centrifuged at 2000g for 30 minutes to prevent clogging of the 0.45 µm filter. The conditions are specified in standard NF EN-12457-2, December 2002.

The eluate is then divided into an appropriate number of sub-samples for the various chemical analyzes and stored according to standard EN ISO 5667-3.

Analysis of the eluate produced by the leaching test provides the concentration of the constituents in the eluates expressed in mg / L. The final results are expressed as the quantity of constituent leached relative to the total mass of the sample, in mg / kg of dry matter.

The amount of a constituent leached from the material, based on the dry mass of the original material, is calculated using the following formula:

A = C x [(L / MS) + (TH / 100)] (1) where:

A is the release of a constituent for L / S = 10 (expressed in milligrams per kilogram of dry matter);

C is the concentration of a particular constituent in the eluate (expressed in milligrams per liter);

L is the volume of leachate used (expressed in liters);

TH is the moisture content, expressed as a percentage of dry mass (4.3.2) and calculated as follows: TH = 100 (MH-MS) / MS

MS is the mass of the dry test portion expressed in kilograms MH is the mass of the non-dried test portion expressed in kilograms Anion analysis

The anion analysis is carried out by ion chromatography eluting with solutions of 1 mM NaHCCh and 3.5 mM Na2CC> 3. Standard solutions for the F, Cl, NO, NO3, Br, PO4 ² , and SO4 ² ions are prepared.

The effectiveness in stabilizing sulfates is measured after 1 day of treatment for up to 2 or 6 months.

Heavy metal analysis: The analysis of the elements (heavy metals) is carried out by ICP-AES analysis (Atomic Emission Spectrometry coupled to an induced plasma).

RF power: 1.3 kW Plasma flow rate: 15 L / min Auxiliary flow rate: 2.25 L / min Nebulizer flow rate: 0.8 L / min Reading time per replica: 20 s

The following non-restrictive examples illustrate exemplary embodiments of the invention.

Unless otherwise indicated, all percentages are percentages by weight. In all tables:

DM = dry matter

ND: Not Detectable, i.e. below the detection threshold of the measurement NM: Not measured

The effectiveness of the treatment is discussed on the basis of the quantities of stabilized sulphates, and compliance with the limit values mentioned in the French legislative document (Decree of 12/12/2014 relating to the conditions for the admission of inert waste in installations falling under the sections 2515, 2516, 2517 and in inert waste storage facilities under heading 2760 of the nomenclature of classified installations (consolidated version of 08/11/2018)).

The overall effectiveness of the treatment is also discussed on whether or not the limit values mentioned in this decree are respected for other substances whose release must be limited.

Ideally, we look for a solution that will have a quantity of leached sulphates less than 1000 ppm and chromates less than 0.5 ppm (max 1.5 ppm), without the release of other compounds.

Unless otherwise indicated, all the percentages indicated in the tables below are expressed as a percentage by mass of dry soil.

Non-inert soil to be treated

The two soils, noted Sol 1 and Sol 2, are loamy soils from the Paris region near Guerville, and naturally contain sulphates (between 9000 to 12000 ppm leachable sulphates according to the NF EN 12457-2 leaching test with a liquid / solid ratio (L / S) of 10). Their water content is 20% compared to dry soil. List of constituents

[Table 2]

* ROLAC-OB contains 72% blast furnace slag, 25% Portland clinker and 3% secondary constituents authorized according to standard NF EN 197-1.

Mineralogy of the clinkers tested [Table 3]

Total chromium content in binders

[Table 4] Treatment process

The contaminated soil samples are treated by the method according to the invention by the formulas noted in the tables below according to the following protocol:

- A quantity of wet soil equivalent to 600 g of dry soil is introduced into a Perrier type mixer. - By wet we mean the natural soil moisture possibly adjusted to optimize the hydration of the binder (amount of water extractable by evaporation during baking at 105 ° C to constant weight). The water content can be between 5% and 40% of the weight of the soil, depending on its nature.

- The formula for the treatment is introduced on the surface and then the whole is mixed, at low speed, for at least 2 minutes until a mixture is obtained which is homogeneous in color and texture.

- All of the treated material is extracted from the bowl and then stored for 1 hour in an airtight bag.

- After an hour, the whole is passed through a 4 mm sieve. The residue is broken off by hand or with a tool to pass all of the processed material through a 4mm sieve.

- All of the sieved material is returned to the airtight bag to prevent any drying of the material.

The maturation of the treated soil is carried out over a period of 2 hours, 1 day, 7 days, 1 month, 2 months or 6 months at room temperature. 1 / Solution based on sulphoaluminous belitic clinker, calcium aluminate cement and lime

[Table 5]

Example 1.1 is a control test.

Examples 1.2 and 1.4 are comparative tests.

Examples 1.3 and 1.5 are tests according to the invention.

The treatment with the combination of a sulphoaluminous belitic clinker, lime and a calcium aluminate cement (1.3 and 1.5) improves the long-term performance of the treatment compared to a combination of a belitic sulphoaluminous clinker. and lime (1.2 and 1.4) whether for the release of sulfate ions or the release of chromate ions.

21 Solution based on belitic sulfoaluminous clinker, lime and alkanolamine (TEA or Tl PA)

[Table 6]

Example 2.0 is a control test. Example 2.1 is a comparative test.

Examples 2.2 to 2.7 are tests according to the invention.

Stabilization of sulfates can be significantly improved with the addition of Tl PA or TEA to the binder. Their presence also has a surprisingly positive impact in limiting the release of chromium.

3 / Solution based on sulphoaluminous belitic clinker, lime and reducing agents of hexavalent chromium salt

[Table 7]

Example 3.0 is a control test.

Example 3.1 is a comparative test.

Examples 3.2 and 3.3 are tests according to the invention. The treatment with the combination of a sulphoaluminous belitic clinker, lime and a reducing agent of a hexavalent chromium salt (3.2 and 3.3) makes it possible to reduce the release of sulphate ions and chromate ions at 1 month and 2 month.

4 / Solution based on sulphoaluminous belitic clinker, blast furnace slag and lime

[Table 8]

Example 4.0 is a control test.

Examples 4.1, 4.5 and 4.6 are comparative tests.

Examples 4.2, 4.3, 4.4, 4.7 and 4.8 are tests according to the invention. The performance of the treatment is significantly improved with the addition of blast furnace slag with 2.5% B3 clinker mixed with 3.33% slaked lime (4.2 vs 4.1), or 3% B3 clinker. mixed with 4% slaked lime (4.7 vs 4.6). The stabilization of sulphates is improved, and the amounts of chromium released are much less than 0.5 ppm up to 2 months. The slag is effective whether it is added as it is or in a road binder (4.4). The addition of water during the treatment makes it possible to further improve the efficiency of the treatment (4.3 and 4.8).

Claims

1. A method of treating polluted soil comprising at least treating the soil with, by weight relative to the weight of said dry soil:

- from 1.5% to 5.0% of a first inorganic binder of the belitic sulphoaluminous clinker type

- from 2.0% to 5.0% lime, and characterized in that the soil is also treated with an additional component chosen from: a second mineral binder different from the first mineral binder chosen from a calcium aluminate cement, a blast furnace slag or their combination in a content ranging from 1.5% to 5.0% by weight relative to the weight of said dry soil, an alkanolamine in a content ranging from 0.001 to 0.050% by weight relative to the weight of said dry soil, a reducing agent of a hexavalent chromium salt in a content ranging from 0.01 to 3.00% by weight relative to the weight of said dry soil, and their combination (s), and in that lime is added to the polluted soil in proportions greater than 30% by weight relative to the total weight as the first inorganic binder, lime and, where appropriate, the second inorganic binder.

2. Method according to claim 1, characterized in that the soil is polluted with anions, such as sulfate ions or heavy metal cations, such as a hexavalent chromium salt, or a mixture of the two.

3. Method according to claim 1 or 2, characterized in that the belitic sulfoaluminous clinker comprises by weight relative to the total weight of said clinker:

- from 30% to less than 60% of sulfoaluminate phase C4AxFy $ z with x varying from 2 to 3, y varying from 0 to 0.5 and z varying from 0.8 to 1, 2, - more than 15% phase C2S belite including at least 2% of belite phase in alpha 'form, more than 20% of ferrites.

4. Method according to any one of the preceding claims, characterized in that the lime is quicklime or slaked lime, or a mixture of the two, preferably slaked lime.

5. Method according to any one of the preceding claims, characterized in that the lime is added to the polluted soil in proportions greater than 50% by weight relative to the total weight of the first mineral binder, lime and optionally second mineral binder .

6. Method according to any one of the preceding claims, characterized in that the second inorganic binder is a calcium aluminate cement, preferably comprising more than 60% by mass of Mayenite C12A7 phase or of a Mayenite isotype.

7. Method according to any one of claims 1 to 5, characterized in that the second inorganic binder is a blast furnace slag.

8. Method according to any one of claims 1 to 7, characterized in that the alkanolamine is chosen from triethanolamine, triisopropanolamine and their combination.

9. Method according to any one of the preceding claims, characterized in that the reducing agent of a hexavalent chromium salt is chosen from sodium nitrite, a reducing agent of a hexavalent chromium salt based on antimony and their combination.

10. Method according to any one of the preceding claims, characterized in that water is also added to the soil during the treatment at a dosage of between 1% and 15% by weight relative to the weight of the dry soil.

11. Method according to any one of the preceding claims, characterized in that the treatment comprises mixing, advantageously continuously, the soil with the first inorganic binder, lime and the additional component.

12. Composition for the treatment of polluted soil, comprising, in percentage by mass:

- from 10 to 70% lime, an additional component chosen from: from 7.5 to 70% of a second mineral binder different from the first mineral binder chosen from a calcium aluminate cement, a blast furnace slag or their combination, from 0.005 to 0.70% of an alkanolamine, from 0.05 to 42% of a reducing agent of a hexavalent chromium salt and their combination (s), and in that the lime is in proportions greater than 30% by weight relative to the total weight of the first inorganic binder, lime and, where appropriate, the second inorganic binder.

13. Composition for the treatment of a soil according to the preceding claim, characterized in that the belitic sulfoaluminous clinker comprises more than 12% by weight relative to the total weight of the ferrite clinker, preferably more than 15%, preferably more by 20%, more preferably between 20% and 40%.

14. Use of the composition as defined in claim 12 or 13 for the treatment of soil polluted with anions, in particular sulphates, and heavy metal cations, in particular hexavalent chromium salts, and their mixture.

15. Use of the process according to any one of claims 1 to 11 for in situ stabilization or before storage of soil polluted in particular by sulfate anions and / or heavy metal cations.