EP1404465A1

EP1404465A1 - Stabilisation treatment, in particular for waste incineration residues

Info

Publication number: EP1404465A1
Application number: EP02787142A
Authority: EP
Inventors: Jean-Pierre G. Hubert
Original assignee: Sagace Services En Administration Gestion Et Applications Au Conseil A L'environnement
Current assignee: Sagace Services En Administration Gestion Et Applications Au Conseil A L'environnement
Priority date: 2001-07-09
Filing date: 2002-07-03
Publication date: 2004-04-07
Also published as: FR2826887A1; WO2003008119A1; FR2826887B3

Abstract

The invention relates to a treatment method in cold liquid phase consisting essentially in first performing lixiviation-sulphuration in order to render the heavy metals therein inert by means of cementation (3) with a sulphuring agent (F), thereby enabling stable solid sulphurous compounds to be formed from their oxidised form and enabling the movement into the liquid fraction of chlorides and sulphates. Said liquid fraction is subsequently stabilised by means of precipitation with cementing materials (J) (preferably recovered, such as steel blast furnace slag). The solid fractions obtained after the treatment can be used as clinker or ore. The liquid phase (M) can be re-used in a new treatment cycle after desalination.

Description

STABILIZATION TREATMENT IN PARTICULAR OF RESIDUES RESULTING FROM THE INCINERATION OF WASTE

The invention relates to the "cold" hydro-chemical treatment of special industrial waste, intended to remove heavy metals and salts therefrom in a stabilized form which is not harmful to the environment and economically recoverable. The invention is more particularly concerned with the application of this type of treatment in the liquid phase at low temperature (approximately 80 ° C. for the hottest phases) to the incineration by-products of various fuels, in particular to residues of purification of household waste incineration fumes, hereinafter referred to as REFIOM.

As underlined by a report from the French Senate under reference 098/415 dating from 1998 on "recycling and recovery of household waste", chapter D, part 3 (Recovery methods linked to incineration, REFIOM recovery), and available between others on the Internet at: www.senat.fr/rap/o98-415/o98- 41516. tml, the incineration of household waste generates two types of waste: MIOM (Bottles of Household Waste Incineration) ) and REFIOMs (Household Waste Treatment Incineration Fumes). Under the term REFIOM are grouped ashes under boilers, fly ash and "filter cakes". The major part of these residues (up to 90% by weight) is made up of mineral substances without harmfulness (silica, lime, ...). The rest, on the other hand, is made up of metals, including heavy metals such as mercury, zinc, lead, copper, chromium, etc. The REFIOMs thus concentrate the pollutants contained in incinerated waste, such as metals heavy volatiles, chlorine, etc ...

Given their polluting characteristics, in particular their high content (up to 2% by weight and sometimes even beyond) in heavy metals easily entrained by water, REFIOMs are not mixed with bottom ash and obey a specific treatment stabilization. Classified in the category of "special industrial waste", REFIOMs are ultimate waste. They are therefore stored, before burial in landfill, to stabilize them and thus reduce their leachable action. They are then evacuated to class 1 ultimate waste storage centers (CSDUs), where they are received in silos. Then, they are, for example, mixed with hydraulic binders, and the concrete thus obtained, which constitutes a trapping for the polluting elements, is poured into specific cells.

Until recent years, this has been the only possible way to eliminate REFIOMs. Since then, treatment techniques intended to stabilize them have developed essentially along two axes. The methods of treatment by fusion of the ashes, or of vaporization after acid attack in a fluidized medium on one side, and on the other the hydro-chemical "cold" methods of stabilization with hydraulic binders, second category to which the treatment belongs according to the invention. These known techniques are however all based on the same principle of trapping heavy metals in a matrix with a rigid skeleton. However, as will be seen later, one of the remarkable aspects of the invention is to make these heavy metals inert with respect to the action of water, thus guaranteeing the durability of the depolluting action, durability which n 'is not ensured by the prior art, and to then be able to enhance the REFIOM.

Stabilization with hydraulic binders is a technique which is based on two processes which develop jointly during the treatment (see for example the edition n ° 136 of the journal Environnement et Technique / Info-Déchets dating from May 1994). On the one hand, precipitation of the chlorides and sulfates present takes place by 1 complexation in the form of stable solid salts (Ettringite, chloroaluminates). On the other hand, a solidification of the whole occurs, generated by the hydraulic setting of the binder which creates a solid matrix which is not very permeable to water and which embeds the minerals carrying elements likely to go into solution. This route is very widespread in France and abroad for the treatment of special industrial waste (or assimilated as such). However, its use is based on the choice of the best binder (s) according to the nature of the waste, in particular according to their heavy metal content. Since REFIOMs are by nature of variable composition, the application of such a solution may require, for the optimization of the stabilization formula, numerous prior laboratory tests.

The state of the art also discloses processes for cleaning up waste containing either heavy metals or salts.

Thus, the steel industry has already envisaged using a hydrometallurgical process for the sulfur treatment of certain electric steel dust with high lead, zinc, cadmium and chromium contents. The sulfurization of this dust using solutions of sodium sulfides or polysulfides (Na S) or calcium (CaS) would have made it possible to reduce the quantities of heavy metals by transforming their oxides into insoluble solid sulfides, therefore stable.

To the knowledge of the applicant, the transposition of this route to the treatment of REFIOMs has not so far been implemented due, no doubt, to the high content of the latter in salts harmful to the environment, in particular chlorides and sulfates, in the presence of which sulfides have no marked action.

A treatment of solutions strongly loaded with salts, such as nitrates, chlorides and sulfates, is also known from EP-A-0 494 836. This process, implemented in particular for the treatment of slurry or water polluted, such as urban waste water and factory effluents, consists of precipitating these salts by adding hydraulic binders made up of tricalcium aluminates (Al ₂ O ₃ -3CaO). However, its application to the treatment of REFIOM would join the stabilization processes mentioned above, with the problems already mentioned, in particular with regard to the sustainability of depolluting action on heavy metals, or optimization of the stabilization formula.

The object of the invention is to provide a treatment for REFIOMs, or other similar special wastes containing heavy metals and salts, a treatment which differs from those usually used in the sense that the heavy metals are not "trapped" in a rigid skeleton, but rendered inert and eliminated.

To this end, the invention provides a depolluting treatment process, by physico-chemical means in an aqueous medium, of special waste containing salts and heavy metals, such as the incineration by-products of various fuels, and in particular the REFIOM, for the implementation of which:

- First, a leachate-sulphurization step is carried out, which breaks down into two successive phases, not necessarily taken in this order: a heavy metal precipitation phase by carburizing with a sulfurizing agent; and a phase of dissolving the soluble species by aqueous leaching; the solid fraction and the liquid fraction are then separated from the suspension obtained,

- Then, on said liquid fraction, a salt precipitation step is carried out with hydraulic binders, and the solid fraction thus created is again separated from the liquid fraction.

According to a preferred implementation of the invention, during the leaching-sulfurization step, the phase of carburizing heavy metals with a sulfurizing agent occurs before the phase of dissolution of the soluble species by aqueous leaching. In accordance with a preferred embodiment, the hydraulic binders used contain tricalcium aluminate.

According to another preferred embodiment, the sulfurizing agent used is a polysulphide, preferably calcium polysulphide. As a variant, if the aqueous leaching of the soluble species takes place before the sulfurization and if one proceeds at the end of this leaching to a solid / liquid separation, the solid and liquid fractions thus separated are treated separately with a sulfurizing agent.

The subject of the invention is also an installation for implementing the above method, characterized in that it comprises successively, and linked together in series,

- a leach-sulfurization stage comprising a cementation unit by sulfurization and a leaching unit, and provided with a liquid / solid separator at the outlet,

- And mounted on the "liquid" outlet of the leach-sulfurization stage, a salt precipitation stage provided with a distributor of hydraulic binders and equipped at its outlet with a liquid / solid separator.

Preferably, the installation further comprises, mounted on the liquid outlet of the solid / liquid separator associated with the saline precipitation stage, means for purifying salts from a saline solution. It will be understood, on reading this definition, that the invention essentially consists in first of all practicing a sulfurization of the heavy metals contained in the REFIOMs, and in terminating the treatment by precipitation of the salts previously dissolved in solidified in a hydraulic binder. For the sake of clarity of the description which follows, it is advisable to give a first schematic vision of the process, which comprises three main stages: a) leaching-sulfurization, the objective of which is the inerting of heavy metals by cementation with a sulfurizing agent which makes it possible to form, from their oxidized form, solid solid sulfur compounds, and the displacement in the liquid fraction of the soluble species with a view to their treatment, b) a solid / liquid separation c) precipitation with hydraulic binders (of recovery preferably, like slag from the steel blast furnace) of chlorides and sulfates in a cement with hydraulic setting on the liquid fraction. The leaching-sulfurization stage is broken down into hardening of heavy metals with a sulfurizing agent in order to make them inert with respect to the action of water, and into a leaching intended to separate the soluble species from the fine clinker.

Regarding the hardening of heavy metals, the sulfurizing agent used is advantageously a polysulphide, which will preferably be chosen in the form of calcium polysulphide, this because of its excellent qualities of sulphurizing agent, on the one hand, and its ease of industrial production, on the other hand.

Indeed, the preparation of calcium polysulfide (CaS4) is done from a lime milk obtained by adding dehydrated lime to water. The mixture is heated to boiling, then the sulfur is added slowly. The poly sulfide concentration of this stock solution is adjusted to the needs of the treatment by adding volume to volume water. The two main reagents used to obtain calcium polysulfide are not necessarily of high purity. One can, for example, take the same lime as that used for the treatment of incineration fumes and recovered sulfur from operations for desulfurization of coke oven gases. Leaching can be carried out by means of several successive water washes (for example three), using a battery of mixing tanks mounted in cascade. It can take place before or after the sulfurization treatment depending on whether or not it is desired to extract the metals from the clinker obtained at the end of this stage with a view to their recovery as ore. When the leaching is carried out before the sulfurization, it will be advantageous to carry out a "lukewarm" washing. Bringing the temperature of the leaching to a value around 60 to 70 ° C makes it possible to accelerate the solubilization of soluble species and to precondition the heavy metals to prevent them from remaining in the solid state (essentially in the form of oxides) thanks to an acceleration of the lowering desired pH, which is thus dropped to around 10, or even less. The applicant's work has shown, in fact, that a pH reduced to 9 or 10 (instead of 12 or 13 initially) had a marked impact on the passage into the liquid phase of certain heavy metals, lead for example. The liquid phase loaded with salts and heavy metals will then be separated from the solid phase before being treated with a sulfurizing agent.

It will of course be advantageous to use a pH test on the suspension in order to determine the state of progress of the dissolution of the species which have to move in the liquid phase. Thus, it will be advantageous to consider the solubilization of the species as complete when the pH of the solution resulting from the last wash, or the leachate extracted, has reached a value close to 9 or 10, or a reduction of approximately 4 points.

In a preferred implementation of the invention, the leaching takes place, not before, but after the sulfurization of heavy metals. It operates as before. The liquid phase thus obtained will not contain heavy metals which will then be present in stable, solid and non-soluble sulfurized form. It will however be advantageous to add water before the sulfurization reaction which takes place in an aqueous medium. The quantity of water to be brought in for sulfurization is around a quarter of the water required for leaching.

According to the invention, a solid / liquid separation takes place between the steps of leaching and sulfurization and precipitation with hydraulic binders so that said precipitation of the salts takes place only on the liquid fraction. If stabilization by precipitation with hydraulic binders was carried out on the suspension obtained at the end of the leaching-sulfurization step, this would result in the formation of a concrete in which the solid fraction would play the role of aggregate. Although, strictly speaking, obtaining such concrete does not harm the sustainability of the depolluting action with regard to heavy metals (since these have been previously rendered inert), nor does it require optimization of the composition of hydraulic binders compared to heavy metals, it would however require an optimization of the water supply and would not be compatible with the REFIOM recovery objectives targeted by the invention, unless immediate use is made of the concrete produced. At the end of the third step of the process, namely that of precipitation of the salts with hydraulic binders, the formation of an Ettringite type compound will be favored by using a hydraulic binder containing tricalcium aluminate C3A (where C represents CaO and A represents AI2O3). This calcium aluminate is conventionally present in the liquid state. A preferred implementation of the invention will retain a mixture consisting of C3A and C12A7. The precipitation of chlorides and sulfates will be considered complete when the pH of the liquid phase has reached a value close to 7 or 8. This liquid phase, recovered at the end of the operating cycle, then contains only a low concentration of calcium, sodium and potassium. It can therefore be returned to the natural environment without special precautions. It can also be advantageously reused for a new treatment cycle, in order to reduce the costs generated by the large amount of water to be used. In this case, and in order to avoid a progressive enrichment in calcium, sodium and potassium, all or part of this water can be treated before being reintegrated into the circuit. This water treatment can be done by nanofiltration, by reaction with spent acids such as H ₂ SO ₄ or by production of brine by means of a CMN (Mechanical Steam Compression) unit.

The solid fractions obtained during the implementation of the method according to the invention can advantageously be used as clinker. It is recalled that to be industrially recoverable, bottom ash must belong to the so-called "N" category, by analogy to the term "recovery" (circular DIPPR / SEI / BPSEID n ° 94-IN-l of May 9, 1994). The category "V is that of bottom ash with low leachable fraction. The membership of a batch in a category is fixed on the basis of a pollutant potential test. This test includes three successive leachings with a liquid / solid ratio of 10 / 1 on samples representative of the 100 g lot To be classified in category "V", clinker must not release, among other things, more than 1.5 mg of chromium and more than 10 mg of lead per kg.

The method according to the invention is remarkable in that the depolluting treatment of REFIOMs at the level of heavy metals consists in inerting them and not in their encapsulation in a rigid skeleton of which it cannot be certified that there is no risk of subsequent release.

It will be clearly understood that the order of succession of the three operating phases constituting the treatment as just described must be scrupulously observed: leaching and sulfurization first, then liquid / solid separation, then precipitation with hydraulic binders.

The method according to the invention makes it possible to treat REFIOMs whatever their initial chemical composition. One of the problems encountered by the prior art arose precisely from the fact that REFIOMs are by nature of variable composition. During the implementation of the method according to the invention, the controls are carried out at the end of treatment on the products obtained. It is not necessary to adjust the composition of the reagents involved in order to obtain optimal treatment of the waste.

Another remarkable advantage of the process according to the invention is that all the treatment is carried out "cold" or "lukewarm", which limits energy expenditure and facilitates its implementation on an industrial level.

The invention is also remarkable from an ecological point of view in that it produces no secondary pollution on the one hand, and that, on the other hand, all the products obtained are industrially recoverable. It will be noted that the process according to the invention can offer a recovery outlet for waste from other industries as as reactants (lime, sulfur, steel slag). In addition, the water used can, without inconvenience, after possible treatment, be discharged into the wild or reused for a new operating cycle.

The invention will be well understood and other aspects and advantages will appear more clearly in the light of the description of the examples which follow, given with reference to the accompanying drawing plates, giving the functional diagrams of the treatment, and in which:

FIG. 1 represents the functional diagram of the process when the heavy metals are cemented with a sulfurizing agent before the dissolution of the soluble species by aqueous leaching during the leaching step;

- Figure 2 shows the block diagram of the process when the heavy metals are cemented with a sulfurizing agent after the dissolution of soluble species by aqueous leaching during the leaching step.

Example 1 (Figure 1):

At a flow rate of approximately 1 ton / h, the REFIOM A are introduced in the divided state (granules or powder) into a sulfurization tank 3 where they are mixed with a sulfurizing agent F, for example calcium polysulphide, under a flow rate of approximately 3 m ³ / h and with an aqueous solution B, or simply water, at a flow rate of approximately 75 m ³ / h. An increase in temperature (from 60 to 70 ° C. for example) using the electrical resistance 13, as well as continuous homogenization by stirring of the mixture makes it possible to increase the rate of precipitation of the sulfides. The mixture P thus obtained can be stored, if necessary, until the end of the sulfurization reactions in a holding tank, not shown. The mixture P is then introduced into a leaching tank 1 (or a battery of tanks cascaded in the case of successive washings) receiving, moreover, an aqueous washing solution B, or simply water, introduced under a flow rate of 225 to 300 m ³ / h, allowing the solubilization of the various soluble species still present in the REFIOMs, in particular the salts. A solid / liquid separation 2 of the suspension Q thus obtained, by filter press for example, makes it possible to extract a solid fraction R, containing the heavy metals inert to polysulphides, with a view to its recovery as a clinker fine.

The liquid underflow I obtained, which contains the salts of the sulphate and chloride type, arrives in a saline precipitation tank 5 to undergo treatment therewith with hydraulic binders J. This is done by adding blast furnace slag steel, or tricalcium aluminate (CA), which will precipitate the salts in the form of complexes and lead to the production of a solid phase comprising calcium monochloroaluminates (by precipitation of chlorides) and Ettringite ( through precipitation of sulfates). This solid phase L is then extracted from the suspension K thus formed by a solid / liquid separation 6.

The material L thus collected can be used industrially as clinker and, as such, mixed with the clinker fine R obtained previously at the end of the leachate-sulfurization step.

The liquid fraction M, then containing a low content of calcium, sodium and potassium salts, can, after possible treatment, be discharged, using a valve 14, into the natural environment without harm to the environment .

As a variant, the solution M can be recirculated in the leaching tank 1 in order to reuse it for a new cycle as washing solution B. In this case, in order to avoid a progressive enrichment of the solution B in calcium, sodium and potassium which would eventually lead to blockage of the treatment installation, the solution M may advantageously be subjected beforehand to a thorough desalination treatment on all or on an adjusted fraction of its total volume. A three-way valve 7 will advantageously be provided at the outlet of the saline precipitation unit 5 by hydraulic binder in order to allow the adjustment of the flow rates for reuse of the final aqueous solution M in the leach mixer 1, with or without elimination. preliminary residual salts.

The prior elimination of the residual salinity from the solution M can take place, for example, in a CMN 8 (Mechanical Steam Compression) unit subsequently comprising a vacuum evaporator 11 producing a brine Ν to be eliminated, and a capacitor 12 delivering purified water O. Nanofiltration can also be considered in place of CMV, or treatment with used acids (H ₂ S0 ₄ for example). Note also the advantageous presence of probes 15 and 10 making it possible to measure the pH of the suspension Q and of the liquid fraction K at the outlet of the leach tanks 1 and of saline precipitation 5 respectively. These pH measurements will make it possible to determine the state of progress of the reactions implemented in the process and will serve as fundamental indicators for continuous operation with loop recycling of the process.

Example 2 (Figure 2):

At a flow rate of approximately 1 ton / h, the REFIOM A are introduced into a leaching tank 1 (or a battery of tanks cascaded in the case of successive washes) also receiving an aqueous washing solution B, or simply water, introduced at a flow rate of the order of 300 m ³ / h. An increase in temperature (from 60 to 70 ° C. for example) using the electrical resistance 13 makes it possible to increase the speed of solubilization of the various soluble species, the metal oxides and the salts in particular. A solid / liquid separation 2 of the suspension .C thus obtained makes it possible to extract a solid fraction D with a view to its recovery as a clinker fine. It may be advantageous, for example, to carry out this solid / liquid separation on a washer-filter, such as a band filter, to best wring out the solid fraction of its interstitial liquid loaded with soluble species and which is collected. for further processing.

The liquid fraction E, thus made clear, but charged with metals and dissolved salts, then arrives in a sulphurization tank 3 in which the displacement of heavy metals, such as lead, cadmium, zinc, etc. , by cementation with polysulphides. The precipitated sulfides thus obtained are very slightly soluble in water. The sulfurizing agent F, for example calcium polysulphide, is introduced into tank 3 in the liquid state and in an amount sufficient to allow the metal displacement reactions to be complete, ie of the order of 1% by weight approximately, which is equivalent in the example considered to a quantity of the order of 1 m ³ / h for the 100 m ³ / h of solution E to be treated. The mixture G obtained may be stored, if necessary, until the end of the sulfurization reactions in a holding tank, not shown. The metallic precipitate H, containing the heavy metals inert to the polysulphides, is then extracted by a second solid / liquid separation 4. It can be upgraded industrially in the form of ore. The liquid underflow I obtained being treated in the same way as in Example 1 described above. The three solid fractions (D, H and L) successively resulting from such a treatment can be upgraded industrially, the first D and the last L can moreover be advantageously mixed together to form a bottom ash that can be upgraded in road engineering.

It will be noted, as in the previous example, the advantageous presence of probes 9 and 10 making it possible to measure the pH of the suspension C and of the liquid fraction K at the outlet of the leach tanks 1 and of saline precipitation 5 respectively. These pH measurements will make it possible to determine the state of progress of the reactions implemented in the process and will serve as fundamental indicators for continuous operation with loop recycling of the process. A person skilled in the art can envisage, in certain circumstances, an additional treatment of the solid fraction D resulting from leaching 1 with a sulfurizing agent in order to guarantee the classification of the clinker obtained in category "V.

As already pointed out, the invention finds a preferred application in the field of treatment of REFIOMs. However, it remains generally applicable to all by-products of incineration of various fuels and more generally to all special industrial waste or polluted soil containing a high content of salts and / or heavy metals in a mobile form which pollutes the environment.

It goes without saying that the invention is not limited to the exemplary embodiments described above, but extends to multiple variants or equivalents insofar as is respected its definition given by the appended claims. Thus, for example, a person skilled in the art may use, during the step of carburizing heavy metals with a sulfurizing agent, rather than calcium polysulphide, sodium polysulphide or simple sulphides used in industry.

Claims

1. A depolluting treatment process, by physico-chemical route in an aqueous medium, of special industrial waste containing salts and heavy metals, such as the incineration by-products of various fuels, in particular REFIOMs, characterized in that:

a leaching-sulfurization step (I) is first carried out, comprising two successive phases, not necessarily carried out in this order: a phase (3) of precipitation of the heavy metals by cementation with a sulfurizing agent (F), and a phase (1) of dissolving the soluble species by aqueous leaching (B);

- Then separating (II) the solid fraction (R, H) and the liquid fraction (I) from the suspension obtained; - Then, on said liquid fraction (I) thus obtained, a salt precipitation step (III) is carried out with hydraulic binders (J), and the solid fraction (L) and the fraction are again separated from the pulp obtained (K). liquid (M).

2. Method according to claim 1 characterized in that during the leaching-sulfurization step (I), the phase (3) of precipitation of heavy metals by cementation with a sulfurizing agent (F) occurs before phase (1) for dissolving soluble species by aqueous leaching (B).

3. Method according to claim 1 characterized in that during the leaching-sulfurization step (I), the phase (1) of dissolving the soluble species by aqueous leaching (B) occurs before the phase (3) of precipitation of heavy metals by cementation with a sulfurizing agent (F), and in that a solid-liquid separation (2) is carried out at the exit of the leaching phase (1) so as not to treat with a sulfurizing agent by precipitation phase (3) than the liquid fraction (E).

4. Method according to claims 1, 2 or 3, characterized in that one carries out "lukewarm" the leaching-sulfurization step (I).

5. Method according to claims 1, 2 or 3, characterized in that the hydraulic binders (J) used contain tricalcium aluminate.

6. Method according to claim 1 characterized in that the solution (M) obtained at the end of the salt precipitation step (III) is reused for a new treatment cycle.

7. Method according to claim 6 characterized in that the solution is subjected

(M) to be reused in a prior purification operation (8) intended to precipitate the salts which would still be contained therein in residual form.

8. Method according to claim 3 characterized in that, following the solid liquid separation (2), the liquid fraction is treated with a sulfurizing agent

(E)) and the solid fraction (D)) separately.

9. Method according to claims 1, 2, 3 or 7, characterized in that the sulfurizing agent (F) used is a polysulphide

10. Method according to claim 9, characterized in that the polysulfide is a calcium polysulfide.

11. Method according to claims 1, 3 or 7, characterized in that the solid fractions (D, L) obtained respectively during the leaching-sulfurization step

(I) and the salt precipitation step (III) are combined together to obtain a recoverable clinker.

12. Installation for implementing the method according to claim 1, characterized in that it comprises successively, and linked together in series,

- a leach-sulfurization stage (I) composed, not necessarily in this order, of a cementation unit by sulfurization (3) and a leaching unit (1),

- a solid / liquid separation unit (II) (4), and a salt precipitation stage (III) with hydraulic binders (J) provided with a liquid / solid separator (6) at the outlet.

13. Installation according to claim 12, characterized in that it further comprises, mounted on the liquid outlet (M) of the solid / liquid separator (6) associated with the saline precipitation stage (III), means (8 ) purification of salts from a saline solution.