FR2915691A3 - Treating residues from incineration smoke of household waste/residual waste containing heavy metals e.g. lead and salts e.g. sulfate in aqueous medium, comprises conditioning waste in aqueous suspension for maturing in lukewarm - Google Patents

Abstract

The process for treating a special industrial waste such as residues from the incineration smoke of household waste or residual waste containing heavy metals e.g. lead and salts e.g. sulfate in an aqueous medium, comprises conditioning the waste in an aqueous suspension for maturing in lukewarm to collect mature solid fraction, and subjecting the matured waste to repetitive solid/liquid washing-separation operation until the solid fraction reaches a desired level of non-harmful environment. The process for treating a special industrial waste such as residues from the incineration smoke of household waste or residual waste containing heavy metals e.g. lead and salts e.g. sulfate in an aqueous medium, comprises conditioning the waste in an aqueous suspension for maturing in lukewarm to collect mature solid fraction, and subjecting the matured waste to repetitive solid/liquid washing-separation operation until the solid fraction reaches a desired level of non-harmful environment. An accelerating agent such as sodium carbonate of less than 10 wt.% with respect to the waste to be treated is added to the fresh aqueous suspension for solubilizing kinetics of salts before maturing. The washing operation is carried out with water, where the cumulated weight ratio of repetitive solid/liquid washing-separation does not exceed 50. A prewash operation for the waste to be treated is carried out prior to the conditioning step. An independent claim is included for an installation for treating residues from the incineration smoke of household waste or residual waste containing heavy metals and salts in an aqueous medium.

Description

Stabilization treatment of REFIOM and other industrial waste

like.

  The invention relates to the treatment of industrial waste. More precisely, the treatments of the type under consideration are those of a hydrometallurgical nature, enabling the separation of the treated material into two fractions, one of which is produced in a stabilized form that is not harmful to the environment and is therefore potentially recoverable by recycling. in industry. The invention relates more particularly to the application of this type of treatment to special waste, such as the by-products of incineration of various fuels, in particular residues of purification of household refuse incineration fumes. , commonly referred to as REFIOM. It is recalled that the term "REFIOM" generally refers to fly ash, sub-boiler ash or filtration "cakes" generated by the incineration of household waste followed by a spraying of lime in the counterflow chimney fumes. They are generally in fragmented or divided form, in powder or granules. Although consisting mainly of mineral substances without harmfulness, the REFIOM concentrates however pollutants contained in waste incinerated, such as heavy metals (lead, chromium, cadmium, zinc ...) or salts (sulphates and chlorides) mainly). Given their high content of pollutants easily driveable to water, the REFIOMs must be buried in class I storage centers. This storage contributes to protecting the environment but bears a high recurrent cost (more than 200%). t currently in France for example), which is added to the cost of a prior stabilization treatment, while paradoxically these materials contain a certain economic potential. For this purpose, the document EPA 1 499 458 proposes a hydrometallurgical treatment of the REFIOMs which, after having fragmented them if necessary, consists firstly in wetting them with water and kneading them in order to form an aqueous suspension which is made ripen to warm. Once matured, the solid fraction is extracted to be washed according to a protocol with several repetitive washing sequences followed by solid / liquid separation until it meets the high level of non-harmfulness requirement for the environment that allows it to be storable in the natural state or recoverable in various industries, including road engineering. The washing water is reused in a loop after being treated to be cleaned. This type of wet treatment, whose major advantage is that it can be used at low temperatures, however, has the disadvantage of requiring large amounts of water. The washes to be performed also require water contact times with the relatively large amount of waste to be treated, of the order of twenty hours each wash. These constraints represent handicaps that can affect the economic profitability of the treatment operation. The object of the invention is to answer this problem. To this end, the subject of the invention is a process for the treatment in aqueous medium of special industrial waste containing heavy metals and salts, such as REFIOMs, according to which, the waste being supplied in divided form, they are packaged in one form. aqueous slurry (or pulp) which is heated to warm before collecting a matured solid fraction which is subjected to washing, by repeated solid-liquid washing-separation operations, until said solid fraction meets a desired level of requirement of non-harmfulness to the environment, characterized in that is added to said suspension, preferably before ripening, if not before washing, an accelerator of the solubilization kinetics salts, preferably an alkali metal carbonate, advantageously sodium carbonate in a Na 2 CO 3 / waste weight ratio of less than about 30%, and preferably about 25% by weight. In accordance with the invention, the washing is carried out in several repetitive washing-solid / liquid separation sequences in a cumulative liquid / solid weight ratio which does not exceed 50. In a first variant, the washing is carried out in four repetitive sequences in a liquid / solid weight ratio of 10 each. In a second variant, the washing is carried out in five repetitive sequences in a liquid / solid weight ratio of 5 each. According to a preferred embodiment of the invention, the waste undergoes a prewashing operation before wetting. Preferably, this prewash is carried out with water in a liquid / solid weight ratio of 5 over a period of about 2 hours (more or less about 1 hour). The Na 2 CO 3 / waste ratio is then chosen preferentially less than 10%. The subject of the invention is also a REFIOM treatment installation comprising, in the chronological treatment direction, a pulping unit followed by a washing unit, the pulping unit comprising a wetting tank provided with brewing means and connected to to a maturation tank equipped with heating means, characterized in that the pulping unit is further provided with means for supplying the divided carbonated material. According to a variant, the plant also comprises, located upstream of the pulverizing unit, a prewashing tank provided at the outlet of a solid liquid separator whose solid path is connected to the inlet of the washing unit. As will probably have already been understood, the invention essentially consists in combining the thermal ripening of the starting suspension with the addition to the waste to be treated of an accelerating agent of the kinetics of solubilization of the contained salts which it is able, on the one hand, to move the sulphates from their alkaline earth cation (Ca ++ in the great majority) to alkaline cations, and on the other, to precipitate a species containing this alkaline earth cation. Sodium carbonate (Na2CO3) will be retained as the preferred accelerator because of its commercial availability at an acceptable price. However, any other soluble agent in a basic medium and capable of solubilizing the sulfates may also be suitable, such as potassium carbonate (K2CO3) or magnesium carbonate (Mg2CO3) hydrated. Laboratory tests by upward percolation have indeed made it possible to better determine the parameters related to the solubilization of the constituents of the REFIOMs. It has thus been demonstrated that the salts present in the REFIOMs show between them very different aqueous solubilization kinetics. Chlorides, mainly present as CaCl 2, are very soluble but reach their solubility limit very quickly. Sulphates, on the other hand, mainly present as CaSO4, have much slower dissolution kinetics in water, but with a higher equilibrium dissolution rate. In other words, it was realized that the consequent periods of washing used until now for the solubilization of the constituents of the REFIOM found in fact their reason for being in the need to solubilize the sulphates. The reagent added, sodium carbonate for example, will thus significantly increase the solubilization kinetics of the sulphates and reduce the washing times accordingly. Schematically, the main reaction that takes place can be expressed as follows: CaSO4 + Na2CO3 → CaCO3 + Na2SO4 The calcium carbonate formed will precipitate and the sodium sulfate, which itself is soluble (solubility 455 g / l to 100 C) is entrained in solution. It is thus possible to divide the necessary contact time of the waste with the washing water by almost ten compared to the known practice, which makes the implementation of the industrial treatment much easier and compatible with the economic requirements of profitability. the stabilization treatment of the REFIOMs as a whole. It should be noted that the document WO 98-56464 already discloses a treatment of REFIOMs using sodium carbonate twice: firstly to wash the REFIOMs in order to extract the salts, then to increase the pH of the REFIOM to promote the solubilization of heavy metals.

  According to the invention, sodium carbonate is used, not for extracting and removing salts and heavy metals, but conversely, and in synergy with the heat treatment, to improve their retention in non-leachable form by encapsulation within a REFIOM transformed by ripening.

  In a first embodiment of the invention, the amount of sodium carbonate to be added is of the order of 30% and preferably 25% (ie 250 kg per tonne of waste to be treated). This salt solubilizing agent may be added to the aqueous suspension either fresh (preferably) or thermally matured, that is, either before or after the heat treatment. It should be noted that better results have been obtained when the agent is added to the fresh suspension. It is therefore this protocol that will be the preferred according to the invention. In general, it can be said that the addition of sodium carbonate influences the overall efficiency of the process by allowing better extraction of pollutants. In addition, the tests carried out made it possible to demonstrate that the chloride content of the REFIOMs had an effect on the solubilization of the sulphates. It appears in fact that the more the REFIOMs are rich in chlorides, the more the solubilization of the sulphates 15 is slowed down. An explanation could be found in the fact that the chlorides also react with sodium carbonate according to the following reaction: CaCl 2 + Na 2 CO 3 -> CaCO 3 + 2 NaCl As already stated, the chlorides are very soluble, but they quickly reach their limit of solubility (of the order of 190 g / l under the conditions of the test). In order to limit their influence on the solubilization kinetics of the sulphates, the invention proposes to take advantage of this easy solubilization by subjecting the waste to a first washing operation prior to the curing stage with the addition of sodium carbonate. This first wash (hereinafter referred to as "prewash" to avoid confusion with the repetitive wash sequences that follow the ripening step) can be performed in a liquid / solid ratio of 10 and last for two hours. It makes it possible to significantly reduce the concentration of chlorides in the waste to be treated. As a result, a substantial fraction of the products which can be reacted with the sodium carbonate is thus removed, and the latter can be added in a reduced amount. The necessary quantity of reagent to be added is then of the order of 10% and preferably 8.5% (ie 85 kg per ton of waste to be treated). This dechlorination prewash allows up to a reduction of consumption by three. in sodium carbonate. It will thus constitute a preferred variant of implementation of the invention. The invention will be better understood and other aspects and advantages will become more apparent from the following description of the exemplary embodiments given with reference to the accompanying drawing plates in which: FIG. 1 shows the general block diagram of the processing of FIG. Waste - Figure 2 shows the block diagram of treatment with prewash waste. First alternative embodiment of the invention (FIG. 1): Simple treatment with sodium carbonate. The REFIOM A is introduced in divided form in a mixing tank 3 equipped with stirring means 4 in an aqueous suspension unit (or pulpage) 1 further comprising an autoclave tank 5. It is mixed with a solution aqueous B, which advantageously will simply be clear water, in a liquid / solid weight ratio of 2, but may go well beyond (up to 5 for example) depending on the nature of the REFIOM to be treated. At the same time, sodium carbonate C is added to the tank at the rate of 25% by weight of reagent on the raw mass of REFIOM to be treated. It should be noted that the sodium carbonate may, alternatively, be added after the curing heat treatment which will be specified below. The pulp D once obtained is directed to an autoclave cuvette 5 with an electric resistance heating wall 6 and closed by a hermetic cover 7 to prevent loss of liquid by evaporation. In known manner, this vessel is provided with a measuring cell 8 which continuously monitors the electrical conductance of the material in the tank 5 in order to compare it with a predetermined reference value representative of the conductance of a matured reference pulp. to allow dynamic control of the ripening step if desired. To fix the ideas, however, this thermal ripening is done "warm", that is to say at the boiling temperature of the suspension under atmospheric pressure (110 C for example) for a period of between 16 and 24 hours. At the end of this ripening step, the solid fraction E once collected from the treated suspension is directed to a washing unit 2. This unit consists of a washing tank 9 (or a battery of successive bins of which one consider in this case that only the latter is shown in the figure). Each wash tank is equipped with a liquid / solid separator. This separation can be done by centrifugation, by press, or by any other suitable means. The wash tank 9 is supplied with a washing solution F, which may simply be water. Preferably, the liquid / solid weight ratio accumulated during these successive washing operations will not exceed 50. However, washing may be carried out in different ways. For example, it is possible to carry out 5 successive washes with a liquid / solid ratio of 5 or 4 successive washes with a liquid / solid ratio of 10, or any other mixture, provided, however, that the principle of a sequence of repetitive washes is maintained. The wash solution / REFIOM contact time is of the order of 2 to 3 hours for each wash sequence. A final liquid / solid separation of the suspension G obtained at the end of the washing operation makes it possible to extract the inert solid fraction H with a view to its valorization as a fine of clinker of category V, applicable in road techniques for example .

  The liquid fraction I is collected for further processing. In a known manner, this liquid fraction I will advantageously be packaged into a brine J by means of a desalination unit 11. This unit may consist of a commercial CMV (Mechanical Vapor Compression) equipment followed by a vacuum evaporator. or by nanofiltration membranes for example. The purified water collected K may advantageously be redirected to the pulverization unit 1 or to the washing unit 2. The brine J may, for its part, be treated according to the known techniques for stabilizing / consolidating the REFIOMs with hydraulic binders. and polysulfides for storage as waste.

  Two samples were treated with the process according to the invention by adding 25% by weight of sodium carbonate to the raw mass of REFIOM to be treated. For the sample R1, this addition was carried out at the level of the fresh aqueous suspension, before heat treatment of maturing, therefore. For sample R2, this addition is done at the level of the suspension once matured, but before the first wash.

  The example given below gives the quantities released by the solid fraction H recovered at the end of the process, expressed in mg / kg of dry matter for a liquid / solid ratio of 10 determined by application of the leaching test NF EN 12457-3. Example 1 Test reference R1 R2 Heat treatment 22 h at boiling L / S = 4 Thresholds Na2CO3 added (in kg / t MB) Class III 250 0 Wash 4 washes at 10 = 10 for 3 h Na2CO3 added in first wash (in kg / t MB) 0 250 Chlorides 70 760 800 Sulphates 260 410 1000 Chromium 0.6 0.5 0.5 Lead <0.1 0.3 0.5 Zinc <0.5 0.8 4.0 Copper <0.5 <0.5 2.0 As regards the salts, which are the primary target of the invention, it should be noted that the results obtained on the two samples are satisfactory since they are below the threshold values of class III in the last column, and should not be exceeded. These are the limit values applicable for waste in storage centers according to Decision No 2003/33 / CF of 19 December 2002. For heavy metals, the results are generally satisfactory except for chromium. in the sample R1. In such a case, its treatment will require special attention that goes beyond the scope of the present invention.

  It will be noted that, with regard to salts, the results obtained in terms of encapsulation of potentially leachable pollutants are much better when the ripening of the aqueous suspension takes place in the presence of sodium carbonate. The effect is particularly striking with regard to the chlorides whose salting out decreases by a ratio of 10 when passing from the sample R1 to the sample R2. Second variant of the implementation of the invention (FIG 2): Prewash of dechlorination and treatment with sodium carbonate. The REFIOM A are introduced in divided form in a pre-washing tank 13 placed upstream of the treatment unit 1. They are mixed therein for approximately two hours with an aqueous aqueous solution B, advantageously clear water, in a liquid / solid ratio by weight of 10. The prewashing tank is provided at its output with a liquid / solid separator 14 for separating the pre-washed REFIOMs L from the washing liquid loaded with chlorides M. The pre-washed REFIOMs L are then introduced within the actual processing unit to undergo the operations of aqueous suspension (or pulpage), curing and washes described previously. Note however that in this prewash variant, the sodium carbonate will be added by weight at a rate of 8.5% of reagent per gross mass (MB) of REFIOM to be treated. The method was applied to the R3 sample. The reagent was added during the formation of the fresh aqueous suspension. The example given below gives the quantities released by the solid fraction H recovered at the end of the process, expressed in mg / kg of dry matter for a liquid / solid ratio of 10 determined by application of the leaching test NF EN 12457-3. Example 2 Test reference R3 Prewash L / S = 10 for 2 hours Thresholds Class III Na2CO3 added (in kg / t MB) 85 Heat treatment 22 hours at boiling L / S = 4 Washings 5 washes at L / S = 5 for 2h Chlorides 90 800 Sulphates 500 1000 Chromium <0.1 0.5 Lead 29 0.5 Zinc 15 4 Copper 1.2 2 Fraction soluble 19100 n 4000 Prewash allows a reduction in the amount of sodium carbonate to add to the level of the heat treatment step, since, as regards the treatment of salts, the values obtained are correct. The high soluble fraction remaining at the end of treatment, as well as the lead and zinc values still too high may be the subject of another treatment outside the precise scope of the present invention. The higher release of the heavy metals in Example R3 compared with the results obtained in Examples R1 and R2 could be due, but it remains to be confirmed, to an action of the chlorides in the ripening of the aqueous suspension and in obtaining effective encapsulation of heavy metals within the final solid fraction (the treated REFIOMs), or the fact that the tests were carried out on different REFIOMs. As already pointed out, the invention finds a privileged application in the field of treatment of REFIOM for which it was also initially designed.

  However, it remains applicable to all residues of thermal processes containing salts that make them unstabilized or evolving in the state, so leachable naturally. It goes without saying that the invention is not limited to the embodiments described above, but extends to multiple variants or equivalents to the extent that its definition is fulfilled given in the appended claims.

  In particular, as already mentioned, any other reagent than calcium carbonate, insofar as it is soluble in basic medium and capable of solubilizing sulphates may also do the trick. This is the case, for example, of potassium carbonate (K 2 CO 3) whose solubility at 100 ° C. is 1560 g / l and which, by reaction with calcium sulphate, forms soluble potassium sulphate up to 241 g / l. at said temperature and precipitated calcium carbonate. It is also the case of hydrated magnesium carbonate (Mg2CO3), whose hot solubility is 375 g / 1 and which reacts with calcium sulphate to form hot-soluble magnesium sulphate up to 738 g / l and precipitated calcium carbonate.

Claims (1)

CLAIMS 1 - Treatment process in aqueous waste medium   special industrial products containing heavy metals and salts, such as REFIOMs, according to which, the waste being supplied in divided form, they are conditioned into an aqueous suspension which is warmed to maturity before collecting a mature solid fraction which is repeated solid-liquid washing-separation operations are carried out until said solid fraction satisfies a desired level of non-harmfulness to the environment, characterized in that it is added to said aqueous suspension an accelerating agent for the kinetics of solubilization of salts. 2. Process according to claim 1, characterized in that said solubilizing agent for the salts is added to the fresh aqueous suspension before maturing. 3 - Process according to claim 1 or 2 characterized in that said agent for solubilizing the added salts is an alkali carbonate. 4 - Process according to claim 3 characterized in that said alkali carbonate is sodium carbonate. 5 - Process according to claim 4 characterized in that said sodium carbonate is added in a weight ratio Na2CO3 / waste to be treated less than about 30%. 6 - Process according to claim 1 characterized in that the washing operations are carried out in water in several repetitive solid / liquid washing-separation sequences whose combined liquid / solid weight ratio does not exceed 50. 35 7 - Process according to claim 1 characterized in that, prior to their conditioning in an aqueous suspension, the waste to be treated undergo a prewash operation. 408 - Process according to claims 7 and 3 characterized in that the sodium carbonate is added in a weight ratio Na2CO3 / waste to be treated less than 10% approximately. 9 - Processing plant for carrying out the process according to claim 1 comprising, in the direction of the progress of the treatment, - a pulper unit equipped with a wetting tank (3) provided with stirring means (4) and a curing pan (5) provided with heating means (6), followed by a solid-liquid washing-separation unit (2), characterized in that said pulverizing unit (1) is provided with means supply of divided material in said tank (3) or in said tank (5) 10 - Installation according to claim 9 characterized in that it further comprises, located upstream of the pulverizing unit (1), a prewash unit (13).