WO2001039902A1

WO2001039902A1 - Method and device for treating and conditioning an effluent for vitrification

Info

Publication number: WO2001039902A1
Application number: PCT/FR2000/003319
Authority: WO
Inventors: Jean Leybros; Jacques Lacombe
Original assignee: Commissariat A L'energie Atomique
Priority date: 1999-11-29
Filing date: 2000-11-28
Publication date: 2001-06-07
Also published as: FR2801521A1; EP1250197A1; JP2003515448A; FR2801521B1

Abstract

The invention concerns a method and a device for treating an effluent comprising heavy metal salts in view of its vitrification. The metal salts of said waste are water soluble, they can be easily carried by rain water and are not digestible in glass. They therefore constitute a source of pollution of soils and water tables. The method consists particularly in heating the effluent to be treated; recovering the gas products derived from heating including anions and cations of heavy metal salts; treating the gas products and re-introducing the heavy metals which they contain in digestible chemical form in a vitrifying matrix into the heated effluent, free of heavy metal salts, to be vitrified.

Description

PROCESS AND DEVICE FOR TREATING AND

PACKAGING OF AN EFFLUENT WITH A VIEW

OF A VITRIFICATION

DESCRIPTION

Technical field of the invention

The present invention relates to a method and a device for treating and conditioning an effluent comprising heavy metal salts with a view to its vitrification.

Different categories of effluents are produced for which there is no satisfactory disposal system from the point of view of environmental protection. The effluents in question are mainly inorganic waste containing various toxic pollutants, such as heavy metals and their salts, and very particularly, those having a soluble fraction large enough to prohibit their storage in landfill. These effluents can be liquid or solid. They can come from any effluent-generating process comprising salts of heavy metals.

Liquid effluents can come from, for example, chemical surface treatment processes. These effluents are generally acidic and highly charged with metals. Although widespread throughout the national territory, they represent a very large volume of pollution. For these effluents, the purification technique generally includes a conventional treatment of neutralization / precipitation which leads to the formation of sludge for storage in a Class I landfill. For the record, a medium-sized company practicing these processes can generate up to 1 tonne of sludge concentrated in metals per year.

Solid effluents can come from, for example, household waste incineration processes. These processes actually generate two categories of effluents: solid effluents and gaseous effluents or incineration fumes.

Solid effluents constitute the mineral fraction of the waste, and are basic in character due to the presence of certain metallic oxides such as alkali and alkaline earth metal oxides. These solid effluents are the so-called "under boiler" ashes and bottom ash. Certain bottom clinkers are considered non-toxic under the legislation in force, and can be stored in landfills or used without danger, for example in bitumens, after de-railing. These bottom ash represent approximately 30% by weight of the initial product. Ashes under boilers are very toxic powdery materials because they contain heavy metals and their salts, and must be stored carefully, after being stabilized, in protected sites awaiting possible reprocessing.

The gaseous effluents are more or less acidic in character due to the presence of acid gases such as HCl and HF and anhydrides of gaseous acids such as S0 and C0 ₂ , and they include toxic compounds such as heavy metals and their salts, and solid residues from incineration also called fly ash. These gaseous or smoke effluents must be filtered and treated to neutralize their acidity, to condense metals and their salts, and to retain fly ash before being released into the atmosphere. For example, the wet neutralization of these effluents leads to the formation of a more or less agglomerated pulverulent or particulate material called "filtration cake".

The fly ash and filter cake set constitutes a residue from the purification of household waste incineration fumes, also called REFIOM. It constitutes approximately 3% by weight of the initial waste. The composition of REFIOMs is very variable and depends on the techniques for cleaning the smoke and the incineration processes used. The following orders of magnitude can be retained for essential constituents in% by weight: calcium 10 to 30%, chlorine 10 to 25%, sulfate 15 to 25%, silicon 3 to 15%, aluminum 2 to 6%, potassium 1 to 7 %, sodium 1 to 4%, metals represent 3 to 4%. The polluting fraction which is essentially constituted by heavy metals therefore represents approximately 4% by weight of the total mass of REFIOM. Among the heavy metals, the most commonly encountered are zinc, lead, cadmium, nickel and chromium.

The REFIOMs and the ashes under boilers previously described constitute materials currently considered as "ultimate waste". The metallic salts of these wastes, the heavy metals and their salts are soluble in water and can be easily washed away by rainwater and be dispersed in soils and groundwater.

Prior art

Vitrification appears to be the safest way at present to inert these final incineration materials or waste, for storage or even recovery. Indeed, these materials, which contain silica and alumina liquefy and form a fusion bath when subjected to temperatures above 1300 ° C. This molten bath when cooled forms a crystalline material or a solid amorphous glass, a true heavy metal retention matrix.

Many processes are known for treating these REFIOMs, associated or not with a vitrification process, which generally consist in precipitating or fixing the heavy metals by ion exchange from the liquid effluent itself or from a solution. for washing the REFIOM.

These known methods have many drawbacks. Among these, there may be mentioned in particular the large quantity of additives to be used which weighs on operating costs, the incomplete extraction of heavy metals, and the displacement of the pollution problem linked to heavy metals, the residue final not being sufficiently stabilized.

The vitrification processes generally lead to the use of flux additives such as boron oxide, sodium oxide, potassium oxide and / or network forming oxides such as silica which is most commonly used. These products often have the disadvantage of being expensive. On the other hand, all the elements present in these effluents are not digestible in the glass, which causes phase demixing.

The use of natural products as additives such as volcanic rocks is also known, but these products, although inexpensive, can cause problems linked to their supply or to their variability in composition.

In addition, vitrification processes do not generally accept waste in liquid or liquid-solid suspension form due to the high gassing produced during melting. This implies the installation, upstream of the vitrification process, of drying equipment such as filters or calciners.

Statement of the invention

The object of the present invention is in particular to overcome the aforementioned drawbacks and to reduce the overall flow of solid residues to be placed in landfill, by providing a process and a device for treating and conditioning an effluent comprising salts of heavy metals. .

The process of the invention is characterized in particular in that it comprises in this order: a) heating of the effluent to be treated so as to make the anions and cations of the salts gaseous volatile heavy metals which it contains and to evacuate them from the heated effluent, b) a step of recovery of the gaseous products resulting from the heating of the effluent, said gaseous products including the anions and cations of the volatile heavy metal salts, evacuated by heating the effluent, c) a step of treating said recovered gaseous products so as to isolate the heavy metals which they contain in a digestible chemical form in a vitrification matrix, d) a step of reintroducing said heavy metals , in said digestible chemical form, in the heated effluent of step a), to obtain a vitrifiable effluent, and optionally e) a vitrification step of the vitrifiable effluent.

The effluent can be one of those mentioned above. Thus, the method of the invention makes it possible to treat effluents from methods of surface treatment by chemical means, from method of incineration of household waste, or from any other method generating effluents comprising salts of heavy metals.

It makes it possible in particular to treat effluents, solids, sludge suspensions, decanted sludge, or liquids containing polluting metals, for example in the form of chlorides or any other volatile form under the effect of heating. It allows for example treating liquid solutions at the saturation limit with metallic salts.

The metals can be, for example, those mentioned above. They form the cations of heavy metal salts.

Step a) of the process of the present invention can be carried out for example in a melting furnace used for the melting of the abovementioned effluents. It makes it possible to make gaseous in particular the anions and cations of the volatile heavy metal salts contained in the effluent to be treated, and thus to evacuate, or distill, under the effect of heating, these heavy metal salts. It also makes it possible to remove the anions from these salts which are, for example of the chloride, fluoride, P0 ^" , S0 ₄ ^~ , etc. type, that is to say those which may be present in the effluents defined above. above .

This stage of the process makes it possible to distill almost all of the heavy metals present in the effluent to be treated, and also to eliminate in particular the chloride anions present in certain effluents, in order to make the fraction of the effluent remaining in the oven vitrifiable. , that is to say the non-volatile fraction at the heating temperature chosen for this step. In the prior art, whatever the solid or liquid residues treated, residues from the surface treatment industry or fly ash (REFIOM) from incineration processes, a preliminary dechlorination treatment was necessary. The absence of such preliminary treatment resulted in the departure of almost all of the heavy metals in gaseous form which would not allow their incorporation into the vitreous matrix.

Indeed, the implementation of vitrification requires compliance with a number of criteria. Among these: α) The elements must be digestible in the glass so as to avoid the unmixed phases or the precipitates in large quantities. The aforementioned anions are thus the most troublesome elements due to their poor solubility in glass which causes phase demixing. The materials obtained are then non-homogeneous and of poor quality, the molten salt phase which is not vitrified extracting a non-negligible proportion of toxic cations. In addition, these phases being lighter than glass, the fairly high volatility of the salts is further exacerbated by their contact with the gaseous atmosphere. β) Waste, glass and its by-products must be compatible with the technological materials used for the parts of the oven in contact with them. Indeed, the anions Cl ^" and S0 ₄ ^{2 ~ in} particular can be aggressive vis-à-vis certain refractories.

The process of the present invention has the advantage of being free from this preliminary treatment since the chlorides are eliminated during step a) of heating the effluent, and that of being able to incorporate the heavy metals into the vitreous matrix by example from the heating of the effluent. The process of the present invention makes it possible in particular to eliminate the anions Cl ^" and S0 ₄ ^~ and to provide a vitrifiable effluent meeting the above criteria.

When the effluent is liquid, or contains liquids, step a) also makes it possible to evacuate the liquid phase in the form of vapors or mist recovered with the aforementioned gaseous products. These liquids can for example be water, organic solvents, etc. The amount of water present is only limiting by the overconsumption of energy which it induces for its evaporation.

For a liquid effluent, the heating can be carried out for example in several stages, or gradually, to first evacuate the liquid phase of the effluent so as to obtain a solid residue. This solid residue can then be heated to a temperature sufficient to remove the heavy metal salts which it contains.

Heavy metal salts are volatile from around 1000 ° C. The heating temperature of the effluent is preferably at least at this temperature.

The effluent, or the residue, can be heated until it melts, that is to say to the vitrification temperatures. The heating temperature in this step also depends on the nature of the effluent, it can for example be from 1200 ° C. to temperatures above 1500 ° C. for effluents such as those mentioned above. In addition, the heating temperature may depend on the possible addition of vitrification additives to the heated effluent as set out below. The heating can be carried out by means of an energy source which can be for example plasma, arc plasma, resistance or induction. The combustion of any fuels contained in the treated effluents can contribute to the heating of the effluent.

In the case of REFIOMs, heating them to a temperature allowing vitrification results in a loss in mass of the material to be vitrified corresponding to at least 60% of the material introduced into the oven.

In step b), the gaseous products from step a) of heating are recovered. The recovery of these gaseous products including the anions and cations of the heavy metal salts can be done by a pipe allowing a collection of gases and fumes from the oven. These gaseous products are preferably maintained at a sufficient temperature, generally at 400 ° C. or more, to avoid condensation of the volatile heavy metal salts which they contain, until the stage of treatment of said gaseous products.

Step c) of treatment of the recovered gaseous products can for example comprise a first washing of the gaseous products so as to block the heavy metal salts in a solution, a precipitation of the metals in a digestible chemical form in a vitrification matrix, a filtration, and possibly a second washing of heavy metals in said digestible form. The first washing allows the gaseous metal salts from the oven to be dissolved or blocked, and recover all the soluble fraction containing all the metals. Washing can for example be carried out in a gas / liquid reactor, or in a packed tower or any other equipment making it possible to perform this function. Advantageously, this operation is carried out with water.

The solution obtained with this washing is more or less acidic depending on the initial composition of the solid or effluent residue treated. This solution can then be adjusted in acidity in a precipitation apparatus of the ripener-thickener type to precipitate the metals in a digestible chemical form in a glass matrix and preferably insoluble in water, for example in the form of metal carbonate, for example by means of sodium carbonate or calcium carbonate.

These metal carbonates are insoluble. This chemical form, which is digestible in a glass matrix, is suitable for vitrification. In this example, it may be powdered sodium carbonate or in solution at 200 g / l, or powdered calcium carbonate. These precipitate quantitatively the metals and very particularly the most troublesome such as cadmium, nickel, lead and zinc.

The precipitation can be carried out for example at a pH of less than about 10, for example between 8 and 10, for example at a pH of 9. This makes it possible in particular to limit the redissolution of the aluminum and chromium oxides which may be present in these gaseous products. The precipitation can be carried out hot, for example at a temperature ranging from approximately 40 to approximately 60 ° C., for example at approximately 50 ° C., which increases the rate of formation and of maturation of the precipitate and makes it possible to avoid the untimely precipitation of lead chloride for certain effluents.

The precipitate obtained can be filtered, for example, on a continuous filter of the rotary or belt type, or any other equivalent equipment, and optionally undergo a second washing during filtration, for example with water.

According to the invention, the filtration water can be recovered and concentrated by evaporation, which allows, on the one hand, to recover water usable for the first washing of the gases from the melting furnace and for the second washing during filtration during step c), and, on the other hand, recovering the alkaline and alkaline earth salts.

This makes it possible, on the one hand, to separate the polluting metals from a complex effluent, and to make them vitrifiable with a view to their storage, and, on the other hand, to recover inert salts with respect to the environment and usable for example in road engineering. This embodiment also has the advantage of allowing recycling of the water inside the treatment unit.

In stage d), the washed precipitate, that is to say the heavy metals in a digestible chemical form in a vitrification matrix, is reintroduced into the heated effluent of stage a) free of metal salts heavy. In this step, when the salts of metals have been precipitated as carbonates, the metal carbonates decompose into metal oxides with emission of carbon dioxide.

According to a first embodiment, the heating step a) can be carried out in a first chamber, and the step d) can be carried out in a second chamber, the first and the second chambers being separated, a passage being provided between the two chambers so that the heated effluent can pass from the first to the second chamber when it is free of volatile heavy metal salts.

According to this first embodiment, the introduction of the metals in the digestible chemical form into a glass matrix in the second chamber makes it possible to avoid possible recombinations of the metals, for example with the chlorine present in the gaseous emissions from the heating of the effluent from step a), in the first chamber.

According to a second embodiment of the present invention, steps a) and d) can be carried out in a single heating and melting chamber for vitrification of the treated effluent.

According to this second embodiment, the implementation of the method of the invention can be used to recover metals in a digestible chemical form in a glass matrix after treatment of sludges containing metal salts for later use such as recovery of a recoverable metal, for example chromium, copper, etc. According to a third embodiment, the furnace chamber can be with a separate atmosphere. This mode of embodiment is shown diagrammatically in FIG. 4 and explained in the examples below.

In step e), the effluent assembly free of volatile heavy metal salts contained in the furnace and metals in said digestible chemical form in a glass matrix, called vitrifiable effluent, is vitrified. As explained below, some effluents require the addition of a vitrification additive for this, others do not. This step e) is intended to render these treated effluents inert by trapping them in a glass matrix which can be stored safely. It is optional. Indeed, the treated effluent and the metals in said digestible chemical form can be stored, or put on standby, before proceeding to their vitrification or to be used for other purposes.

According to the invention, step e) of vitrification can be carried out in said oven. According to the invention, a vitrification additive can be added to the effluent, for example in the case where the effluent does not include, or not enough, fluxes or oxides forming endogenous networks allowing its vitrification. This additive can be one of those known to those skilled in the art.

As a reminder, the average composition of a common industrial glass is as follows: Vitrifying Si0 ₂ + B ₂ 0 ₃ + Al ₂ 0 ₃ 72 to 74% by weight

Fondants Na ₂ 0 + K ₂ 0 10 to 16% by weight CaO + MgO stabilizer 10 to 14% by weight

Other constituents P ₂ 0 ₅ , PbO 0.2 to 5% by weight The vitrification additive includes these elements and is added, if necessary, to the effluent to be vitrified in an amount sufficient to reach the abovementioned percentages. The amount of additive can range, for example, up to 90% by weight of the mixture comprising the additive and the effluent to be treated.

For example, REFIOMs can have a high concentration of silica, the main component of glass, of the order of 30 to 35% by weight. They therefore do not necessarily require the addition of vitrification additives.

This additive can be added to any process step of the invention when necessary. The heating of the effluent can be adapted in particular according to the presence of additive.

For example, with an additive, the melting temperature can be between 1200 ° C. and 1350 ° C., preferably around 1300 ° C. Without additive, the melting temperature can be higher than 1500 ° C and the volatile metals are largely released.

The process can be carried out in a "batch" system, or continuously.

The invention also relates to a device for implementing the method of the present invention, said device comprising:

- An oven for heating the effluent to be treated, said oven comprising a heating means, a means for entering the effluent to be treated into the oven, a means for recovering the products gaseous from the heating of the effluent to be treated in the oven, and a means for removing the treated effluent from the oven,

a means for treating the recovered gaseous products, and isolating the heavy metals in a digestible chemical form in a vitrification matrix, said means for treating gaseous products being connected with the means for recovering these products from the oven, and a means for reintroduction into the furnace of heavy metals in said digestible chemical form in the heated effluent free of heavy metal salts.

The heating means may for example be one of those mentioned above. The means for entering the effluent to be treated makes it possible to introduce the effluent into the oven and the means for discharging the treated effluent makes it possible to evacuate the treated effluent, possibly vitrified from the oven. For continuous treatment, these inlet and outlet means can be regulated so as to optimize the process of the present invention.

The means for recovering the gaseous products from the heating of the effluent can for example be one of those mentioned above, for example a pipe. It may further comprise a system for maintaining the temperature of the gaseous products, for example a heat-insulating system, a system for heating the pipes, in-line heat exchangers, etc., so as to maintain the gaseous products at a temperature sufficient to limit the condensation of volatile metals between the oven and the means for treating gaseous products.

This means for recovering gaseous products is connected with the means for treating these products. The means for treating gaseous products and isolating heavy metals can be one of the above. It can comprise, for example, a precipitation apparatus, for example of the ripener-precipitator type, and a filter, for example a continuous filter, for example of the rotary or belt type.

The oven, as described above, can be separate chambers or a single chamber.

According to the first embodiment of the present invention, the device comprises an oven with separate chambers as described above allowing primary treatment of the effluent to be vitrified in the first chamber with departure of the volatile heavy metals, and then the addition 1 incorporation in the glass for example of heavy metal carbonates in the second chamber.

According to the third embodiment, the oven is with a separate atmosphere as described in FIG. 4 and in the examples.

According to this first or this third embodiment, the means for reintroducing metals in a digestible form into the furnace, in the heated effluent free of heavy metal salts, is preferably connected to the second chamber of the furnace.

According to the second embodiment of the present invention, the installation comprises a single chamber melting furnace allowing the treatment primary of the effluent to be vitrified and the simultaneous incorporation into glass of heavy metals in a digestible chemical form in a glass matrix, for example in the form of carbonates of heavy metals. The means for reintroducing heavy metals in said digestible chemical form can be constituted, for example, by a screw, belt, vibration, etc. conveyor.

The device according to the invention may further comprise an evaporation system for concentrating the washing water from the treatment of gaseous products.

Other characteristics and advantages of the present invention may also appear on reading the description which follows, with reference to the accompanying drawings.

Brief description of the figures

FIG. 1 is a diagram illustrating the steps of the method of the present invention according to the first embodiment, that is to say in which steps a) and d) are carried out in two separate chambers,

FIG. 2 is a diagram illustrating the steps of the method of the present invention according to the second embodiment, that is to say in which steps a) and d) are carried out in a single chamber,

FIG. 3 is a diagram illustrating an oven usable in the second embodiment of the present invention, and - Figure 4 is a diagram illustrating an oven usable in the third embodiment of the present invention.

Examples

Example 1: Device for implementing the method of the invention according to the first embodiment As illustrated in FIG. 1, the device comprises six chemical equipments, referenced F and 2 to 5, adapted to the different steps of the method of 1 invention.

It includes a melting furnace F for heating the effluent to be treated, comprising two chambers 1 and 1 ′ of separate atmospheres, the total volume and the heating power of which are adaptable to the flow rate of ffluent to be treated, the liquid effluents or solids being introduced continuously by the inlet means 11 of the effluent to be treated in the chamber 1 of the furnace F.

Reference 13 indicates a supply line for vitrification additive.

A means 15, 17 in the form of a pipe, for recovering the gaseous products resulting from the heating of the effluent, allows the collection of the gaseous products formed during step a) of the process containing the volatile metals and the fumes. It includes a temperature maintenance system 6 for the gaseous products collected which makes it possible to maintain the temperature of these products and fumes in line 21 supplying the means T for processing the recovered gaseous products.

This means T comprises a system 2 for purifying the fumes, a line 22 for extracting the purified gaseous residues and directing them towards the atmosphere, a line 23 for the arrival of a smoke washing solution, a line 24 making it possible to collect the smoke washing solution to direct it to a system 3 for precipitation / washing of metals in their digestible chemical form in a glass matrix. A reagent intended to transform the heavy metals into a digestible chemical form in a glass matrix, for example a sodium or calcium carbonate, is introduced via line 31 into the system 3.

A pipe 32 makes it possible to collect the heavy metals in said digestible form, generally in the form of a precipitate, from the system 3 to direct them to a system 4 for filtration / washing of the metals in their digestible chemical form. The mother liquors for filtration and washing are collected via a pipe 41 for recycling. The heavy metals in said digestible form are reintroduced via line 12 into the effluent free of heavy metal salts present in the chamber 1 'and coming from chamber 1.

Figure 4 is a diagram of an oven (II) usable in the third embodiment of the present invention. The same references as in Figure 1 indicate the same things. This oven (II) has a separate atmosphere or partitioned sky. Indeed, it includes a partition 56 which prevents fogging and volatile metals are in contact with the part of the furnace in which the heavy digestible metals are reintroduced into the effluent. This oven (II) is provided with the lines 11, 12, 13, 14, 15 and 16 mentioned above. The reference 54 indicates a heating means and the reference E the molten effluent.

In the example according to which the heavy metals are in the form of carbonates of digestible heavy metals in a glass matrix, when they are reintroduced into the effluent free of heated heavy metal salts, there is emission of fumes of dioxide of carbon. A pipe 16 makes it possible to collect this smoke, and to lead them into the pipe 17.

A line 14 allows the continuous elimination of the solidified glasses and products formed in the furnace F towards a discharge Dl. This oven allows continuous discharge of the vitrified product.

The mother liquors for filtration and washing are collected from the system 4 by a line 41 which ensures their elimination or their orientation towards an optional system 5 for evaporation and concentration of these mother liquors.

The alkaline salts of the mother liquors of filtration are collected at 51 towards a discharge D2. The water of evaporation is collected by a line 52 for recycling in the process to lines 42 and 23 of water inlet for the first and second washes in the treatment of gaseous products. Example 2: Device for implementing the method of the invention according to the second embodiment

This second embodiment is shown diagrammatically in FIGS. 2 and 3. The references identical to those of FIG. 1 indicate the same things.

In Figure 2, the furnace (I) consists of a single chamber I whose volume and heating power are adapted to the flow of effluent to be treated. Solid or liquid effluents are introduced through line 11 into the furnace. A line 12 allows the heavy metals to be reintroduced in the digestible chemical form into the furnace F '. Reference 13 indicates an inlet pipe for a vitrification additive. A pipe 15 collects the fumes and brings them to the system for treating, or purifying, gaseous products. A single chamber furnace (I) is shown diagrammatically in FIG. 3 in which the furnace 1 is provided with the lines 11, 12, 13, 14 and 15 mentioned above. It includes a heating means 54. The molten effluent is referenced E.

The other elements have been described in Example 1 above.

Example 3: Treatment of a solid effluent

In an installation similar to that which has just been described in Example 2, a REFIOM is treated in a direct induction furnace in a cold crucible, without adding any additive. The REFIOM treated has the following composition in percentage by weight: anionic charge: [Cl ^" ] = 20.34% [S0 ^" ] = 13, 19% Heavy metals = 10% of which

Zn = 5.3% Pb = 2.3% Sn = 0.6% Cu = 0.2% Cd = 0.01%

It also presents the following composition of vitrifiable elements in percentage by weight: [Si] = 4.41% [Ca] = 8.88%

[Na] = 9.7% [K] = 10.3%

[Al] = 2.7%

For a ton of REFIOM treated, 430 kg of glass are obtained, for an electrical consumption of 1.2 kWh / kg.

The heating temperature was about 1600 ° C.

The treatment of fogging requires 170 kg of powdered sodium carbonate. Analysis of the products, glass-filtrates-gases during the process, shows that all of the above-mentioned heavy metals have been incorporated into the vitrified mass.

Example 4 Treatment of an Effluent in the Form of Wet Sludge

In the same installation as that used in the previous example, the treatment of wet sludge containing 50% by weight of water and loaded with heavy metals results in an energy consumption close to 2.5 kWh / kg. The effluent was heated to a temperature of about 1300 ° C. The heavy metal composition of these sludges was as follows in percentage by weight: [Cl ^" ] = 5% [SO ₄ ^" ] = 0.5%

[If] = 3.3% [Ca] = l% [Na] = 0.01% [K] = 0 _f 02%

[A1] = 0.03%

Heavy metals = 8.6% of which Fe = 1.5%, Cr = 1.3%, Co = 0.2%, Zn = 5.3%, Cu = 0.3% A vitrification additive, at a rate of 60% by weight relative to the total weight of treated effluent and additive was added. This additive contained in percentage by weight was basalt.

Analysis of the products, glass-filtrates-gases during the process, shows that all of the above-mentioned heavy metals have been incorporated into the vitrified mass.

Claims

1. Process for treating an effluent comprising salts of heavy metals, characterized in that it comprises, in this order:

(a) heating the effluent to be treated so as to make the anions and cations of the volatile heavy metal salts which it contains gaseous and to remove them from the heated effluent,

(b) a step of recovering the gaseous products resulting from the heating of the effluent, said gaseous products including the anions and cations of the volatile heavy metal salts removed by the heating of the effluent,

(c) a step of treating said recovered gaseous products, so as to isolate the heavy metals which they contain in a digestible chemical form in a vitrification matrix,

(d) a step of reintroducing said heavy metals, in said digestible chemical form, into the heated effluent of step a), in order to obtain a vitrifiable effluent, and optionally,

(e) a vitrification step of the vitrifiable effluent.

2. Method according to claim 1, wherein the effluent is heated until fusion.

3. Method according to claim 1, in which step c) of treatment of the recovered gaseous products comprises a first washing of the gaseous products so as to block the heavy metal salts in a solution, a precipitation of the metals in a digestible chemical form. in a vitrification matrix, filtration, and, optionally, a second washing of the heavy metals in said digestible form.

4. The method of claim 3, wherein the metals are precipitated in the form of metal carbonates.

5. Method according to claim 3, in which the metals are precipitated in the form of carbonates by means of sodium carbonate or calcium carbonate.

6. The method of claim 3, wherein the precipitation is carried out at a pH between 8 and 10.

7. The method of claim 3, wherein the precipitation is carried out hot.

8. The method of claim 1, wherein step a) of heating is carried out in a first chamber, and wherein step d) is carried out in a second chamber, the first and second chambers being separated, a passage being provided between the two chambers in such a way that the heated effluent can go from the first to the second chamber when it is free from heavy metal salts.

9. The method of claim 2, wherein steps a) and d) are carried out in a single heating and melting chamber for vitrification of the treated effluent.

10. The method of claim 9, wherein step e) of vitrification is carried out in said chamber.

11. The method of claim 1, wherein the effluent is chosen from an effluent from methods of incineration of household waste, a liquid effluent from methods of surface treatment by chemical means.

12. The method of claim 1, wherein a vitrification additive is added to the effluent.

13. Method according to any one of claims l to 11, wherein said method is carried out continuously.

14. Device for implementing the method of claim 1 comprising:

- An oven for heating the effluent to be treated, said oven comprising a heating means, a means for entering the effluent to be treated into the oven, a means for recovering the products gaseous from heating the effluent to be treated in the oven, and a means for removing the treated effluent from the oven, - a means for treating the recovered gaseous products, and isolating the heavy metals in a digestible chemical form in a matrix of vitrification, said means for treating gaseous products being connected with the means for recovering these products from the furnace, and - a means for reintroducing heavy metals in the said digestible chemical form into the heated effluent free of heavy metal salts.

15. Device according to claim 14, wherein the means for recovering the gaseous products from heating the effluent comprises a system for maintaining the temperature of the gaseous products.

16. Device according to claim 14 or 15, wherein the means for treating the gaseous products comprises a precipitation apparatus and a filter.

17. Device according to any one of claims 14 to 16, in which the oven is an oven comprising a first chamber and a second separate chamber, a passage being provided between the first and the second chamber so that the effluent is heated. in the first chamber can pass into the second chamber when it is free of heavy metal salts, said means for reintroducing into the metal furnace in a digestible form, in the heated effluent free of heavy metal salts, being connected to the second chamber of the furnace.