FR3040009A1 - MINERAL VITRIFICATION PROCESS AT LOW TEMPERATURE - Google Patents

Abstract

Low temperature mineral vitrification process for dry and wet inorganic and powdery products which contain divalent or multivalent metals in a form available in water. It is characterized by the succession of 2 distinct phases: a) An aqueous solution of alkali silicate is contacted with or sprayed on the mineral product, in an amount sufficient to agglomerate it in the form of granules, in a powder / powder mixer. liquid capable of producing this granulation. b) The granulate obtained is dried and completely dehydrated, that is to say by eliminating at least 95% of the water present in the granule obtained in step a), and preferably 99%, bringing it to a temperature of between 100 ° C. and 400 ° C., in an industrial drying apparatus capable of carrying out this operation, so as to obtain a totally insoluble, glassy or amorphous product, in which the alkali silicate is chemically combined with all the multivalent metals present in the powdered mineral product. The low-temperature inorganic vitrification process for mineral products relates more particularly to waste products, such as household waste incineration wastewater treatment residues (REFIOM), mining residues, residues from the manufacture of aluminum, fly ash, sediment recovered from port facilities and dams, as long as they contain multivalent metals in available form in water. The invention also relates to the use of the method for vitrifying, inerter, immobilize all forms of solid or powdery mineral waste, dry or wet, of a toxic or dangerous nature.

Description

MINERAL VITRIFICATION PROCESS AT LOW TEMPERATURE

OF RESIDUAL PRODUCTS, AND ITS INDUSTRIAL APPLICATIONS, IN PARTICULAR FOR THE INERTAGE OF TOXIC SOLID WASTE

The low temperature inorganic vitrification process of mineral waste products according to the present invention is directed to dry or wet mineral products, which contain divalent or multivalent metals in a form available in water, and is characterized by the succession of 2 distinct phases: a) An aqueous solution of alkali silicate, in an amount sufficient to agglomerate it in the form of granules, is brought into contact with or sprayed onto the inorganic product in a powder / liquid mixer capable of producing this granulation. b) The granulate obtained is dried and completely dehydrated, that is to say by removing at least 95% of the water present in the granule obtained in step a), and preferably at least 99%, in the at a temperature of between 100 ° C. and 400 ° C., in an industrial drying apparatus suitable for carrying out this operation, so as to obtain a completely insoluble, vitreous or amorphous product, in which the alkali silicate is chemically combined with the set of multivalent metals present in the residual mineral product.

By form available in water for divalent or multivalent metals is meant all metals that can be measured in the filtrate of a conventional leaching test, usually performed on waste or waste products from industrial processes. For the details of this standardized test, reference will be made to standard NF EN-12457 of December 2002. Briefly described, this test consists in introducing into an excess of distilled water the product to be analyzed, to leave the mixture in contact under stirring, then filtering the mixture and assaying the metal elements in the filtrate by any conventional analysis technique, including spectroscopic measurement techniques such as atomic absorption spectrometry (AAS), emission spectroscopy (ICP-OES ) or ultra-sensitive detection coupling of ICP to a mass spectrometer (ICP-MS).

The method according to the invention can be applied to all kinds of solid or powdery mineral products, dry or wet, insofar as these products contain multivalent metals, but it relates more particularly to inerting by vitrification at low temperature of mineral residues. containing toxic metals in an available form and in solid, divided, pulverulent form. Generally, toxic metals are referred to generically as "heavy metals". The concept of metallic trace elements, or ETM, tends to replace that of heavy metals, which is a relatively imprecise definition.

In one of these previous patents, BF 00495, or WO 2011095702 A1 which has been granted, the Applicant claims a "low temperature asbestos amorphization process".

The means used to obtain this amorphization are similar to those of the present application, but of course, the purpose is totally different and the physicochemical concept exploited is also totally different.

In the case of amorphization of asbestos, the process makes it possible to transform an organized crystalline structure into an amorphous structure that no longer poses a risk to human health. This transformation is explained by the property of alkali silicates to add to silicic structures and also to break these silicic chains thanks to their alkalinity.

In the present application, it is a question of integrating the toxic metals, available, into an insoluble vitreous structure obtained at low temperature. This capture of toxic metals is carried out thanks to the double property, very particular of the alkali silicates in solution to bind first to multivalent metals and then return to a completely insoluble vitreous state by completely removing the water from the solution of the solution. alkali silicate.

Many industrial sectors produce waste, which is highly toxic because of its heavy metal content. These residues come either from incineration processes (household waste, for example), industrial processes (process for obtaining aluminas and aluminum), or the recovery of bulky sediments, for example dams or port installations. ...

For these reasons, they can be in various physical forms, for example dry, powdery and insoluble for incineration residues, either wet or in the form of concentrated suspensions for industrial processes or the recovery of sediments hindering the port facilities or dam reservoirs.

Among these sectors of activity, the incineration of household garbage produces residues of purification of household waste incineration fumes (REFIOM) whose toxicity and dangerousness are due at the same time to their content of "heavy" metals ( including Lead, Cadmium, Chrome 6+, Nickel, Arsenic or even Mercury ...) and their powderiness leading to the formation of very fine dust during their handling. Residues from the purification of incineration fumes from industrial waste or REFIDI present the same type of problem.

In the prior art, several inerting processes are used to condition these toxic residues prior to their discharge, such as incorporation into hydraulic binders, for example, or into bitumens that are previously melted or softened.

But the process of the prior art unanimously recognized as the best is certainly vitrification at high temperature, which allows to obtain a "glass" completely inert and insoluble in the form of blocks of high mechanical hardness, which permanently immobilizes pollutants contained in the toxic residue.

Indeed the analysis of the REFIOM shows that their composition corresponds quite well to that of the glasses and that therefore, a high temperature treatment of the order of 1500 to 1600 ° C, possibly in the presence of a flux additive, will lead to obtaining a totally insoluble glass, by melting the mixture.

Unfortunately vitrification processes at high temperature are extremely expensive which prevents their development on a scale that could correspond to the volumes of REFIOM to treat (400 000 tons / year for France). In addition, the installed capacities, in France in particular, are very small relative to the volumes to be treated and are generally reserved for the inerting of the most dangerous waste, like the friable friends.

The low temperature mineral vitrification process according to the invention makes it possible to solve this problem and to obtain the best results of inerting and long-term immobilization of toxic heavy metals at a much lower cost.

The table below, which gives an overview of the composition of some types of glass, will provide a better understanding of the concept of the invention and the "cold" vitrification process:

The components that are always present in all cases of glass formulation are two in number: Si02 silica is the main component en masse: In the language of glassmakers, it is called element "network trainer". The second indispensable element is a very alkaline product, which is either soda in the form of sodium oxide Na 2 O or potash in the form of potassium oxide K 2 O, these alkalis can be introduced into the process in the form of carbonates. The other alkaline bases that could be used are those based on the other alkaline elements of the Mendeleyev table, notably Lithium. These alkalis are qualified by the glass makers of the term "flux", or network breaker.

The other components of the different glasses are divalent or multivalent metals, in the form of oxides which give the vitreous products obtained particular properties. Since they are divalent or multivalent, they will also participate in the amorphous structure of the glass obtained as network formers, by creating bonds of the type -O-Si-O-Me-O-Si-O, which may have a three-dimensional character, Me being a divalent or multivalent metal. These strong bonds help to make the glasses completely insoluble in water. Figure 1 in the appendix shows schematically in a plan view, but which may be three-dimensional, the insertion of lead (b) available in the structure of an alkali silicate (a), insertion accompanied by a bridging reinforcing the insoluble glassy structure . Lead, in this case, is a substitute for two Si-ONa terminations, or possibly Si-OH terminations when the medium is not anhydrous.

The table below already mentioned mentions calcium, magnesium, aluminum, lead, but we can easily add heavy metals or transition metals such as cadmium, nickel, chromium, iron, copper. ..

Si02 B203 AI203 Na2O K20 CaO MgO PbO

Flat glass 72 2 12 10 3

Glass bottles 73 1 15 10

Glass type

Pyrex 81 12.5 2.5 4 1

Fiberglass 55 8 15 0.5 18 4.5

Crystal glass 55 12 33

Glass of lamps 73 1 16 1 5 4

In the usual way, to obtain products with a glassy structure, it is necessary to melt the mixtures of these various elements at a very high temperature, of the order of 1400 to 1800 ° C.

The process according to the invention makes it possible to obtain an amorphous, insoluble and closed structure without resorting to such high temperatures, by employing an alkali silicate in aqueous solution, said aqueous solution being added or sprayed onto a mineral product, insoluble, dry or wet, containing divalent or multivalent metals, and then by dehydrating the solid mixture to such a degree as to extract practically all the water which is brought by the alkaline silicate solution; say at least 95%, and preferably 99%.

Temperatures between 100 and 400 ° C are sufficient to effect this dehydration.

Indeed, the alkali silicate in solution (also called in the language of those skilled in the art "soluble glass") provides in the process, the silica and the alkaline element melting, but in a form already solubilized in water and available for the formation of a glass by an aqueous route,

And the insoluble, mineral product containing divalent or multivalent metals provides the metal elements necessary to obtain a "vitreous" structure that is definitely insoluble after dehydration.

The alkali silicate that can be used in the low temperature inorganic vitrification process of inorganic products is understood to mean an alkali silicate in solution such as sodium, potassium or lithium (Me) silicate, but preferably sodium silicate, which has a molar SiO 2 / Me 2 O ratio of between 0.5 and 4, and preferably between 2 and 3.5, and which is in solution in water in an alkali silicate / water proportion of between 1 and 55%, and preferably between 30 and 45%.

The low-temperature mineral vitrification process of dry or wet mineral products according to the invention can be implemented in any industrial mixing apparatus in which the alkali silicate in solution is brought into contact with or sprayed on the mineral product, for example rotating apparatus or granulation apparatus.

The process according to the invention is also characterized in that the weight ratio between the alkali silicate in solution and the mineral product, expressed as dry product, brought into contact with step a) of the process is between 5 and 60%, this proportion being adjustable according to the physical characteristics of specific surface and porosity of the mineral product, possibly residual, to be treated.

The low temperature mineral vitrification process of dry or wet mineral products according to the invention is characterized in that the industrial drying apparatus used for step b) of the process is a rotary kiln or an optionally rotary dryer, heated by any form of direct or indirect energy possible and capable of bringing the solid mixture from step a) to a temperature between 100 and 400 ° C.

The low-temperature inorganic vitrification process of mineral and pulverulent products, dry or wet, according to the invention, is finally characterized in that the products are waste products, such as residues for the purification of incineration fumes from household waste. (REFIOM), mining residues, residues from aluminum production, fly ash, mineral residues from decongestion of ports or dams known as "port vessels", insofar as they contain multivalent metals in available form in water.

The present invention also relates to the use of the method according to claim 1 for vitrifying, inerter, immobilize all forms of solid and powdery inorganic waste having a toxic or dangerous character.

The process according to the invention makes it possible, for example, to obtain a vitrification of the REFIOMs and their definitive inerting at low temperature, ie at a temperature of between 100 and 400 ° C. The typical chemical analysis of a REFIOM is approximately as follows: - SiO 2: 22% by weight - CaO: 29% by weight - Al 2 O 3: 13% by weight - MgO: 3% by weight, ie around 65-70% by weight total mass of the REFIOM.

The remainder consists of NaCl, KCl, sulphate, carbonate or bicarbonate chlorides and other related compounds, of which about 6% are heavy metal oxides (Pb, Zn, Cu, and to a lesser extent Cd, Ba). , Cr, Sn ...).

The process according to the invention consists in wetting, granulating and then coating the REFIOM, which is a pulverulent and dry product by its method of production, with an alkali silicate in solution, silicate of formula nSiO 2, Me 2 O, with n between 0.5 and 3.5, and Me = Na, K, or Li, then heat-treated the granulate obtained so as to eliminate almost completely the water of the aggregate.

In fact, the solutions of alkaline silicates generate, by drying, either products which are soluble at room temperature, if 20% of water is retained after drying, or insoluble products regressing into a completely insoluble vitreous product if they are dried harder while only preserving them. between 0 and 5% water.

But of course the vitrification result and the total insolubilization are even better if the drying is done in the presence of multivalent metals, which participate in the condensation of alkali silicates by multiple bypasses between the ionic silicic units present in the aqueous silicate solutions , which is precisely the case for REFIOMs.

The heavy metals present in the REFIOMs are therefore valued by their ability to react with the alkaline silicates in solution by forming insoluble glassy networks. The heavy metals responsible for the toxicity are therefore doubly "immobilized" because they are chemically related to the glass structure and also occluded in this vitreous matrix, which is a mechanism of capture much greater than the simple physical coating in a matrix more or less porous.

Example 1

In a laboratory granulator mixer of the Lodige type, 10 kg of REFIOM having the composition stated above is placed.

The mixer is started and 4.5 kg of a solution of sodium silicate of formula 3.5 SiO 2, Na 2 O, containing 34% solids, is slowly sprayed.

First, the fine particles of REFIOM are granulated to a size of 1 to 2 mm, then, if the addition of silicate in solution is continued, they are coated with a slightly sticky silicate liquid film.

The mixture is then introduced into a rotary drier and dried with hot air at 250-300 ° C until the residual product mass is 11.55 kg.

The product obtained is a very hard dense granulate, insoluble in water, with a vitreous nature in which the silicate in solution has been transformed into a vitreous product by the reaction with the multivalent metals present in the REFIOM and by drying with less 0.5% residual water relative to the liquid silicate introduced into the granulation process.

The leaching tests, even prolonged, show no entrainment of heavy metals, which are therefore completely "immobilized".

Example 2

In Example 2 is described another form of the invention, not preferred, but which can however be implemented to inert toxic waste products which still contain significant amounts of process water, and which can be in the form of sludge, slurry or filter cakes

In such cases, the process according to the invention may be unsuitable for a cost reason, because the amount of water evaporated to result in vitrification at low temperature by total dehydration of the mixture obtained in step a) will be such that the amount of calories to be implemented will be too high.

This other, non preferred form of the invention consists in using alkali silicates, or rather sodium silicates in their solid form, which are soluble in water at room temperature, which avoids the use of a product in solution. which provides an undesirable water supplement the solid and soluble sodium silicates, powder or granules, contain about 20% water, instead of 55 to 65% water for the sodium silicates in solution. These water contents of about 20% preserved at the time of drying ensure good solubilization in water.

Also, solid and water-soluble sodium silicates are commercially available in the form of co-granules Silicate / sodium carbonate, and may be used in the non-preferred context of the invention, the presence of carbonate being able to provide vis-a-vis of the so-called "heavy" metals an insolubilization supplement in the form of carbonate of divalent or multivalent metals, thus insoluble. Example 2 relates more specifically to the inerting of the residual products of aluminum metallurgy, which are commonly known as "red mud".

The industrial waste product used in Example 2 has the following approximate composition:

Si02 5.5% AI203 10%

Fe203 35%

CaO 2%

0.5% MgO

Ti02 1.0% P205 2.0% C02 10%

Water 35.5%

It is a "red mud" resulting from the manufacture of aluminum, thickened by filtration or by partial evaporation of the process water.

1000 g of this "sludge" are introduced into a laboratory mixer, and 300 g of a granular commercial product containing sodium silicate in soluble form and sodium carbonate are added, the trade name of this product being Nabion, sold in France by the company Novabion. This product contains some water in the form of sodium silicate, but provides much less water in the system than a sodium silicate in aqueous solution.

After mixing at room temperature for 10 minutes, a slightly sticky granular product is obtained, which is subjected to a heat treatment at 280 ° C. for 2 hours in a laboratory rotary kiln heated by electric resistances.

After the heat treatment, the product obtained is a hard granulate, which contains less than 1% water (measured by the loss at 550 ° C for 2 hours) completely insoluble in water. The leaching test carried out according to standard NF EN-12457 shows that there is less than 5 mg / liter of divalent metals which are entrained in water.

Claims (7)

1) Process for low-temperature mineral vitrification of dry or wet mineral products, containing multivalent metals in a form available in water, characterized in that: a) a solution is contacted with or sprayed on the mineral product; aqueous alkali silicate, in an amount sufficient to agglomerate in the form of granules, in a powder / liquid mixer capable of producing this granulation. b) The granulate obtained is dried and completely dehydrated, that is to say by eliminating at least 95% of the water present in the granule obtained in step a), and preferably at least 99%, by carrying it at a temperature of between 100 ° C. and 400 ° C., in an industrial drying apparatus capable of carrying out this operation, so as to obtain a totally insoluble, glassy or amorphous product, in which the alkali silicate is chemically combined with the whole multivalent metals present in the powdered mineral product. 2) Process for low-temperature mineral vitrification of dry or wet mineral products according to claim 1, characterized in that the alkali silicate in solution is a sodium, potassium or lithium (Me) silicate, but preferably a silicate of sodium which has a molar SiO 2 / Me 2 O ratio of between 0.5 and 4, and preferably between 2 and 3.5, and which is in solution in water in an alkali silicate / water content of between 1 and 55% and preferably between 30 and 45%. 3) Process for low temperature mineral vitrification of dry or wet mineral products according to claim 1, characterized in that the mixing apparatus in which the alkali silicate in solution is sprayed on the mineral product to be treated is a rotary apparatus or a granulation apparatus. 4) Process for the low-temperature mineral vitrification of dry or wet mineral residual products according to claim 1, characterized in that the weight ratio between the alkali silicate in solution and the mineral product, expressed as dry product, is between 5 and 60 %, these proportions being adjustable according to the physical characteristics of specific surface and porosity of the mineral product. 5) Process for low temperature mineral vitrification of dry or wet mineral products, according to claim 1, characterized in that the industrial drying apparatus is a rotary kiln heated by any possible form of energy and capable of carrying the mixture to a temperature of between 100 and 400 ° C. 6) Process for low-temperature mineral vitrification of dry or wet mineral products, according to claim 1), characterized in that the mineral products are waste products, such as residues for the purification of waste incineration fumes (REFIOM) , tailings, residues from the manufacture of aluminum, fly ash, mineral residues from the decongestion of ports or dams known as "port vessels", in so far as they contain multivalent metals in the form available in the water. 7) Use of the method according to claim 1 for vitrifying, inerter, immobilize all forms of mineral waste, dry or wet of toxic or dangerous character.