WO1993025716A1 - Method for detoxication of combustion residues by removing the movable toxic compounds and by binding and concentrating said compounds obtained from treatment solutions - Google Patents

Abstract

The invention relates to a method for stabilizing slag by removal of solubilizable metal fractions. It comprises leaching said slag with an aqueous leaching solution containing exchangeable elements in the form of chlorides with the cations of heavy metals present in said slag. The leaching solution is a dilute hydrochloric acid solution for the basic slag, or an alkali or alkali-earth metal chloride solution for neutral slag.

Description

METHOD FOR DETOXICATION OF COMBUSTION RESIDUES BY EXTRACTION OF MOBILE TOXIC COMPOUNDS AND FIXING CONCENTRATION OF THE SAME COMPOUNDS ARISING FROM TREATMENT SOLUTIONS

Slag is non-volatilized solid residue extracted from combustion stoves on industrial sites. Generally evacuated by a hydraulic flush to a receiving pit and then containing 3 to 30% of water, they have the appearance of black solid more or less divided and very heterogeneous.

In the context of the present description the expression "slag" must therefore be understood in the widest possible sense. It will relate to all combustion products and residues, for example clinkers likely to contain heavy metals more or less eligible for runoff or meteoric water. They may also consist of fly ash originating, for example, from the incineration of urban residue.

Slag is often characterized by a silico-aluminous gangue containing metallic oxides, essentially metallic oxides and lower contents, oxides of chromium, copper, nickel, zinc, even cobalt and lead (table 1 ) Their compositions can naturally vary considerably from one site to another.

This can be observed, for example the analysis in Table 1 below. It presents the results given as examples of multi elementary analyzes of slag obtained on three different industrial sites, in Strasbourg (ST 1), in Salais in the department of Isère (S II), and in Saint-Vulba in the department of Ain (SV 1). Table 1: Multi-element analysis of the slag from Tredi Strasbourg (ST 1), Tredi Salaise II (S II) and Tredi Saint-Vulbas (SV 1).

* Results in elementary form

Les scories provenant de l'incinération de déchet industriels doivent normalement être stockées dans de décharges ou centres techniques d'enfouissement (C.E.T.).

Slag from the incineration of industrial waste should normally be stored in landfills or technical landfill centers (TEC).

These slag can indeed present risks in particular when their contents of toxic heavy metals, in easily elutable forms, are still high. These heavy metals are concentrated in the slag according to various physicochemical mechanisms, and according to their natures, form various associations little known. This is the reason why these risks are the subject of assessments with the consequence of referrals to CE.T. which can be distinguished according to their respective capacities to authorize this burial under conditions meeting each faith to standards - when these have been defined - of appropriate security.

Selective extraction methods, used in pedology (soil science), make it possible to distinguish certain associations or certain specific constitutions (speciations) and provide information on the chemical forms and on the possible conditions for solubilization of metals. Knowledge of this data is important to assess the possibility of decontamination treatment.

The metals present in the slag can be water-soluble, exchangeable, associated with amorphous or crystallized oxides and hydroxides, or in the form of precipitates, such as carbonates or sulphides. Often the significant pollution to which slag can give rise, results from the extraction of these metals by solubilization in meteoric or runoff water. The "isotopically" exchangeable cations will be all the more quickly exchanged as the electrostatic forces on negatively charged sites will be weak.

More generally, these observations have led specialists to define the mobility of an element, that is to say the ability of this element to pass through compartments in the environment where it is less and less energetically retained, the ultimate compartment. etan represented by the liquid phase (solution).

Various standards exist to correlate the risk presented by the treated slag with the contents (o solubilizable quantities) of metals dissolved in the leachate or eluates obtained. For these standardized tests, these slags are leached by aqueous solutions simulating the action of meteoric waters. These leaching tests, carried out in the laboratory, allow an assessment of the real risks incurred during the controlled discharge of slag. They can specify the conditions under which certain clinkers can be used in public works (clinker circular of 8/04/92, see table 2 below). For example in France, the AFNOR standardized study protocol (X31210 1988) recommended by the Ministry of the Environment for the purpose of extracting soluble substances contained in crushed slag (diameter <4 mm) Other types of standards are under study by the competent services of the European Economic Community (EEC) In the different leachate categories, the analysis of soluble toxic metals makes it possible to locate the concentrations measured in relation to thresholds set by French and European standards. D this referencing will depend on the authorization for recovery (table 2) or for landfill in THIS. ad hoc, depending on whether the treated products obtained will be classified, for example, as "hazardous waste (CET of type Class I)," non-hazardous waste "(CET of type II), or" inert waste "(see table below ).

The operating mode of the AFNOR standard study protocol (X31210, 1988) is as follows:

- demineralized water saturated with air and CO ₂ pH 4.5 and with a resistivity of between 0.2 and 0.4 MΩ.c is mixed with 100 g of slag for 16 hours at ambient temperature with rotary stirring.

- The first leachate is obtained by filtration of the supernatant after centrifugation of the mixture (2000 for 15 minutes). The color, eye, conductivity and pH are then measured. The solid is then taken up for 2 new extractions with consequently the obtaining of two leachates (or additional eluates. At the end of these operations, the chemical oxygen demand (COD), the total organic carbon (TOC) and an analysis mineral are carried out on the eluates.

Similar trials have been developed in other countries or in the C.E.E.

They made it possible to define standards, as illustrated in Table 3, but subject to modification. The values presented define various "elution thresholds" corresponding to the sum of the maximum solubilizable quantities of each of the metals or other polluting constituents (for example soluble chlorides and cyanide) which can be tolerated, having regard to each of the categories or classes of waste. in question.

For polluting metallic elements, chlorides and cyanides, French standards and European (non-hazardous waste) moreover require that the quantities of each of the elements leached at the neck of the three successive extractions go in decreasing In the opposite case, that is to say the one where "increasing solubilizations" would be observed. certain metals in at least two successive leachates or eluates we could not conclude that the scori stabilized over time. We could indeed always fear the risk of pollution resulting from renewed exchanges between buried slag and runoff.

Tables 4, 5 and 6 which follow make it possible to appreciate what are the main polluting characteristics of slag, ST 1, SU and SV 1 considered as examples.

Table 2: Valuation of bottom ash from household waste incineration in public works concentration-thresholds given by the leachable fraction obtained by the standardized AFNOR test (x 31-210).

* * * * * * * * * * * * * * * * * * * * * * * *

* i burned <5%

* soluble fraction <3%

* Hg <0.2 mg / Kg of dry matter

* Pb <4 mg / Kg of dry matter

* Cd <1 mg / Kg of dry matter

* Cu <20 mg / Kg of dry matter

* As <2 mg / Kg of dry matter

* CrVI <1 mg / Kg of dry matter

* sulfates <4000 mg / Kg of dry matter

* chlorides <2800 mg / Kg of dry matter

* TOC <1000 mg / Kg of dry matter * * * * * * * * * * * * * * * * * * * * * * * *

If the leachable fractions meet the above thresholds, the bottom ash is considered to have a low leachable fraction. The corresponding production can then be used in public works.

Reference: Clinker circular, Clean Technology and Waste Service

Ministry of the Environment, project 8/04/92. Table 3: Comparison of European and French standards on the landfill of waste. Threshold concentrations given for the leachable fraction obtained by the German test for European standards (100g of dry waste / Il of water) and by the Afnor standardized test for French standards (100g of gross waste / Il of water). The results are expressed in solubilizable quantities in mg / kg.

⁽¹⁾ in mg / kg of dry waste ⁽²⁾ in mg / kg of gross waste

REFERENCES

- Draft European Directive on the landfill of waste.

- Draft ministerial decree on the landfill of special industrial waste (Class I). Text from the Ministry of the Environment, ref DEPR / SEI / SDO / AN Feb-31, May 14, 1991.

- Circular on the landfill of solid residues from the purification of smoke from incineration plants for urban residues (Class II). Text from the Ministry of the Environment, ref DEPR / SEI / SM / STPD / APR / MBr, June 12, 1991.

TABLE 4: STANDARD LEACHING TEST (WITNESS)

Strasbourg slag (ST 1)

Analytical monitoring of extractions

* fly ash ashes from the incineration of urban waste. ⁰ ND: not dosable, MS: dry matter

Solubilization behavior

TABLE 5: STANDARD LEACHING TEST (WITNESS)

Salaise slag (S II)

Analytical monitoring of extractions

* fly ash ashes from the incineration of urban waste. ° ND: not dosable, MS: dry matter

Solubilization behavior

TABLEAU 6 : TEST DE LIXIVIATION NORMALISE (TÉMOIN)

TABLE 6: STANDARD LEACHING TEST (WITNESS)

Slag of Saint Vulbas (SV I)

Analytical monitoring of extractions

* relating to fly ash from the incineration of urban waste. ⁰ ND: not dosable, MS: dry matter

Solubilization behavior

La lecture des tableaux 4, 5 et 6 est facilitée dè lors que l'on tient compte des remarques suivantes, propos des quatre colonnes de droite des sous-tableau médians et des sous-tableaux inférieurs :

Reading tables 4, 5 and 6 is facilitated as soon as the following remarks are taken into account, concerning the four right columns of the middle and lower sub-tables:

- the "total quantity extracted from the raw waste" e "mg per kg" corresponds for each element to 10 times the sum of the quantities extracted by the three extraction solutions (or extractants) used to treat 100 g of the same waste. these numbers are to be compared with the standards which appear in the three right-hand columns of the median sub-tables (and which correspond to the values indicated in the columns "French standards class I" "French standards class II" in table 3 and "Valuation standard in Works public "in Table 2).

- these same numbers are, in the lower sub-tables, compared with the concentrations of the corresponding element "potentially dissolvable", which are none other than the values corresponding to the same slag and contents drawn from table 1.

From the examination of Tables 4, 5 and 6, we can therefore draw the following observations as to the possible polluting character of the slag examined by way of examples. The samples ST 1, SU and SV lead to colorless and odorless leachate. The chemical oxygen demand (COD), mineral and organic pollutio index, is 240 mg / kg for ST 1, 120 mg / kg for SU and 40 mg / kg for SV 1.

The soluble fraction of ST 1 slag (table 4 risks inducing pollution constituted by copper (total quantity extracted in mg / kg higher than class II norm and not in conformity with a recovery e public works), zinc, nickel and chloride (increasing solubilizations in successive eluates).

For the SU slag leachate (Table 5), all the metered elements have decreasing solubilization. But they have an elution threshold higher than European standards on non-hazardous waste for lead (8.72 mg / kg of dry waste), cadmium (1.1 mg / kg of dry waste), chromium ( 1.42 mg / kg of dry waste) and nickel (6.48 mg / kg of dry waste). Furthermore, these leachates do not comply with the legislation which provides for the recovery of bottom ash from public works (lead, cadmium, chromium and chlorides have too high threshold concentrations) The leachate nevertheless conforms to French class standards II.

The leachate obtained from the dried SV 1 slag complies with the aforementioned standards (Table 5).

It therefore follows from the above that some of these slag would come under a decontamination treatment before any storage, burial or recovery. It should also be the same for SV 1 slag, even if these already meet the standards tolerated to date, but which may not be in the future.

The object of the invention is precisely to fine-tune a process allowing the preservation of the environment while limiting the expensive storage of slag, especially in a class I landfill. It has particularly pleased a process for the stabilization of residues combustion, whatever its origin by extraction of the soluble metallic fraction The invention more particularly aims, e reference to French and European standards e force, to obtain in a particularly simple way the detoxification or "inertization" of the slag with the poin which they can then be stored in class II landfills as non-hazardous waste or even recycled.

According to a first essential provision of the invention, this consists in first carrying out o several leaching of the slag, if necessary previously ground to sufficiently small particle sizes, in particular at values less than 50 mm to allow sufficient contact between combustion residues and an aqueous solution or leach liquor, having a sufficient concentration of cations (K ⁺ , Na ⁺ , Ca ²⁺ ) or exchangeable protons in the form of chlorides with the heavy metal cations present in these residues. This leaching must be sufficient to ensure the transformation of at least part of the determined metals, in particular heavy metals contained in these slags, into soluble chlorides extractable by this leaching liquor, and their effective extraction in sufficient proportions so that: on the one hand, a standardized elutio test subsequently applied to the slag thus treated attests to the decrease in the successively solubilized quantities of each of these metals determined during repeated extraction tests carried out with a standardized leaching or elution solution in accordance with this test and, on the other hand, the sum of the quantities solubilized in the eluates resulting from the extractions with the aforesaid standardized solution, is situated at values corresponding to concentrations lower than the threshold concentrations also predetermined by the above standardized test for each of these metals.

For the sake of clarity of language, it has been made in the foregoing and will also be made in what follows, a distinction between: "leaching solutions", that is to say the extraction solutions containing the above cations o exchangeable protons and the "standardized elution solutions" corresponding to the solutions used in the above standardized tests.

The number of successive elution tests and the concentration thresholds (at least for those of metals which have already been the subject of special standards) are determined by existing or future standardized protocols. The standardized study protocol used in this study corresponds to the AFNOR standard (X31210, 1988), the detailed implementation of which has been recalled above.

In this case, the repeated elution tests with the standardized solution are then 3 and the standardized solutio is itself constituted by a demineralized ea saturated with air and CO ₂ at pH 4.5 and with a resistivity of between 0.2 and 0.4 MΩ.cm.

The elution tests with the standardized solution are then carried out by mixing with the treated slag (for example used in an amount of 100 g) for 1 hour and with stirring.

The cations or protons exchangeable in the form of chlorides from the liquor used for the initial leaching of the slag can be provided in any form allowing the goal to be achieved. The leach solution may consist of acid dilute hydrochloric acid, more particularly for the treatment of slag of a basic character, for example slag which, when it is suspended in water for a sufficient time, has the effect of bringing the pH to values of order of 9 to 10 For slag with a neutral character under the same conditions, it is preferred to use solutions of chlorides of alkali or alkaline earth metals, rather than hydrochloric acid. Experience shows indeed that hydrochloric acid, even in the diluted state, sometimes tends to attack, more than would be necessary the matrix or the gangue of slag with a neutral character. It will be immediately apparent to the skilled person that the concentration of solutions in exchangeable cations in the form of chlorides, or even the nature of the cation used (preferably potassium, calcium or another alkali or alkaline-earth metal) will most often have to be adjusted according to the slag treated, the nature of the metals heavy mobilizable.

In general, the hydrochloric acid concentrations of the acid solutions applicable to treatment in accordance with the invention will have molar concentrations most often comprised in intervals of 0.01 M to 1 M, while the metal chloride concentrations alkaline or alkaline earth solutions leaching corresponding will most often be included in the interval 0.01 M, especially 0.05 M, at 5 M.

As observed during experimentation carried out on various types of slag, a hydrochloric acid solutio 0.1 N is an RESPONSIVEN particularly suitable for the treatment of basic slag, while a solution of ^'potassiu 1 M or 0.01 to 2 M calcium chloride, in particular 0.09 M and 0.15 M, will allow the extraction of the mobilizable metals contained in the slag having a low acidity. This static or dynamic leaching (slag / extractant ratio 1.1) will be followed by a draining of the leachate to a storage tank. They may also be treated themselves as discussed below. Example: The slag from the Strasbourg incineration center (ST 1) was crushed, crushed and then divided to reconstitute a homogeneous average sample with a particle size of 0 to 2 mm. The Sain Vulbas slag (SV 1) was previously dried before being brought together as an average sample. The slag from Salais (SU) was treated as it was. The Strasbourg (ST 1), Salaise II (SU) and Saint-Vulba (SV 1) samples have a pH of 10.0, 7.6 and d 8.2, respectively.

Experimental device: extraction of exchangeable metals:

The extraction tests are carried out by leaching tests in a clogged column or in dynamic leaching (with stirring) on 100 g of slag. The reagents used (100 ml per 100 g of slag) are 0.1 N hydrochloric acid, potassium chloride 1 or calcium chloride 0.09 M and 0.15 M. They are left in contact from 2 to 24 hours with slag e can undergo 2 recycling (ie at least 3 times 2 hours of slag / extraction liquid contact). The pH, conductivity and chemical composition are determined on the leachate obtained. The slag sample is then rinsed with at most 2 times 100 m of distilled water and then the standardized leaching test is applied. Results:

The extractants used in the mobility tests form with the slag elements soluble metallic chloride, the speed of formation of which is a function of their solubility constant.

By way of examples, potassium chloride 1 results in a significant solubilization of calcium and copper in the slag ST 1. Potassium (excess reagent) and sodium, which were not assayed in these tests, proved to be found during the assays , be matrix elements having a negative impact on the analyzes (yellow emissio in the plasma). The solubilized trace elements are indicated in table 7. In the SU slag the most mobilizable elements are manganese and magnesium for the major elements, the trace elements being solubilized according to variable proportions (table 7). The analytical perturbation, due to a massive solubilization of alkaline earth elements is also noticed in these solutions coming from SU slag.

Hydrochloric acid more effectively mobilizes metals, in particular copper in ST 1 slag. The dissolution of the alkaline earths by this reaction leads to a disturbance in the dosage of calcium, whereas the yellow emission of the plasma is synonymous with a strong presence of sodium (Table 7).

Table 7: Determination of the mobility of 9 major elements and of 7 trace metals during leaching in a fouled column of 100 g of slag per 100 ml of extractant (3 successive passages). Analyzes of leachate obtained by assaying metallic elements in solution with a plasma emission spectrophotometer. Results expressed as a percentage by weight of the initial contents.

Tableau 8 : Détermination de la mobilité de 9 éléments majeurs et de 7 métaux traces au cours du rinçage (2 fois 100 ml d'eau distillée) des colonnes engorgées de 100g de scories après traitement par 100 ml d'extractant. Analyses des eaux obtenues par dosage des éléments métalliques en solution au spectrophotomètre d'émission plasma. Résultats exprimés en pourcentage pondéral des teneurs initiales.

Table 8: Determination of the mobility of 9 major elements and 7 trace metals during rinsing (2 times 100 ml of distilled water) of the columns engorged with 100g of slag after treatment with 100 ml of extractant. Analysis of water obtained by dosing metallic elements in solution with a plasma emission spectrophotometer. Results expressed as a percentage by weight of the initial contents.

Les eaux de rinçage ont pour but d'éliminer le excès de réactif avant la mise en oeuvre du tes normalisé de lixiviation. Au cours de cette opération une faible mobilité des éléments est à noter quelqu soient l'extractant et les scories considérés (tablea 8).

The purpose of the rinsing waters is to eliminate the excess of reagent before the implementation of the standardized leaching test. During this operation, a low mobility of the elements should be noted whatever the extractant and the slag considered (table 8).

The percentage of metals which can be mobilized from the slag could not be precisely assessed, but the partial analyzes carried out during successive passages of reagents suggested that only a contact of 2 24 hours slag / extractant and a single rinse would be necessary to obtain an effective stabilization. of this waste. This simplification by limiting the number of operations initially planned demonstrates the advantage of a single leaching and constitutes an optimization of this process.

Standard leaching test

Given the objectives set in the context of these examples, the leaching tests must obey French class II standards and European standards on non-hazardous waste or standards for the recovery of bottom ash in public works.

At the end of the two treatments applied to the slag from Strasbourg (ST 1) and from Salaise II (SU), l standardized leaching tests lead to the formati of lixiviates having a higher resistivity compared to the controls, therefore to less effluents loaded with mineral elements (Figures 1 and 2).

The reduction in chemical oxygen demand (DC is 23% after treatment with potassium chloride on slag from Salaise II (SU), it is 100 for all other treatments and whatever the slag considered (Figure 3 ). It is noted that in FIGS. 1 and relating to the standardized leaching test on the slag from Strasbourg (ST 1) and Salais II (SU) respectively, the variation in the resistivity of the leachate before and after treatment with the liquor has been illustrated. leaching, by showing what the resistivities expressed in ohm / cm were on the ordinate axes after application of the standardized test (norm AFNOR X31210, 1988), directly on the slag in question (TN), on the pre-slag treated with a solution of potassium chloride (KC1), and on the slag previously treated with the solution of hydrochloric acid (HC1).

In Figure 3, the COD abatements (COD% on the ordinate axis following the treatment applied to the slag from Strasbourg (ST 1) and from Salaise II (SU) are also illustrated.

For polluting metallic elements, chlorides and cyanides, the standards require decreasing solubilization and / or an elution threshold. The determination of these parameters for the highly basic slag from Strasbourg (ST 1) shows the following results: treatment with potassium chloride solution is manifested by strong extraction of polluting metals; but we observe that several metals (lead, copper and chromium) as well as chlorides give rise to increasing solubilizations (table 9), on the other hand, the treatment with hydrochloric acid (table 10) accentuates the solubility of pollutants , but the elution threshold imposed with decreasing solubilization remains in accordance with the standards French and European standards on non-hazardous waste. The corresponding clinker production would also be suitable for public works.

Tables 11 and 12 illustrate the results obtained under similar conditions, in standardized leaching tests after treatment of the slag, S after treatment with potassium chloride (table 11) and hydrochloric acid (table 12).

TABLE 9: STANDARD LEACHING TEST AFTER KCL TREATMENT

Strasbourg slag (ST I)

Analytical monitoring of extractions

* relating to fly ash from the incineration of urban waste. ⁰ ND: not dosable, MS: dry matter

Solubilization behavior

TABLEAU 10 : TEST DE LIXIVIATION NORMALISE APRÈS TRAITEMENT AU HCL

TABLE 10: STANDARDIZED LEACHATION TEST AFTER HCL TREATMENT

Strasbourg slag (ST I)

Analytical monitoring of extractions

* fly ash ashes from the incineration of urban waste. ⁰ ND: not dosable, MS: dry matter

Solubilization behavior

TABLEAU 11 : TEST DE LIXIVIATION NORMALISE APRÈS TRAITEMENT AU KCL

TABLE 11: STANDARDIZED LEACHATION TEST AFTER KCL TREATMENT

Salaise slag (S II)

Analytical monitoring of extractions

* Relauves the fly ash from ^the incinérauon urban waste. ⁰ ND: not dosable, MS: dry matter

Solubilization behavior

TABLEAU 12 : TEST DE LIXIVIATION NORMALISE APRÈS TRAITEMENT AU HCL

TABLE 12: STANDARDIZED LEACHATION TEST AFTER HCL TREATMENT

Salaise slag (S II)

Analytical monitoring of extractions

* fly ash lifers from 1 urban waste incinerauon. ° ND: not dosable, MS: dry mauers

Solubilization behavior

CONCLUSIONS:

CONCLUSIONS:

Depending on the leaching tests carried out on the slag and on its foreseeable storage in class II or its recycling, the following conclusions (Table 13) can be drawn from the previous experiments, after application to the treated or "inertized" slag, of the protocol for study according to the above AFNOR standard: Strasbourg slag (ST I) without prior treatment generates eluates whose toxicity thresholds are higher than French class II standards, in addition to European standards. These eluates are, moreover, not in conformity with the legislation which provides for the recovery of slag in public works. After prior treatment of the slag with hydrochloric acid, the eluates produced comply with French class II standards, with European standards on non-hazardous waste, the treated slag can also be recycled in public works. Salaise II slag (S II) without prior treatment generates eluates whose toxicity thresholds are lower than French class II standards but higher than European standards for non-hazardous waste and recovery standards in public works. After treatment with potassium chloride, the eluates produced comply with European standards and the standards for recycling bottom ash.

Table 13: Summary of the results obtained during the treatment of slag. Comparison of the results of their leaching to European and French standards on the landfill of waste. Threshold concentrations given for the leachable fraction obtained by the German ballast for European standards (100g of dry waste / I l of water) and by the standardized Afnor test for French standards (100g of raw waste / l of water) . The results are expressed in solubilizable quantities in mg / kg.

The leachate resulting from the application of the leaching procedure contains metal chloride salts as well as an excess of extractant. The average composition of leachate and rinsing water for all treatments, obtained during no experiments on 100 g of slag, is given in table 14.

Table 14: Chemical analysis of leachate and rinsing water. Average composition obtained from the different treatments performed on the slag from Strasbourg (ST 1) and Salaise II (S π).

RINSING WATER LEXIVIATES

£ ÏL 1.86 to 9.37 4.30 to 8.94

Leaching has been extended to other reagents under different conditions. The transformation of slag into inert rubble taking place under the influence of exchangeable cations or protons, investigations have focused on the use for reactional purposes of saline and acid discharges from incineration centers.

Experimental extraction device

The leaching was carried out under agitatio (dynamic leaching) in 2-liter bottles with at most 1 liter of extractant in the presence of 100 g of slag. In view of the preliminary experiments, the incubation was maintained for 2 hours at room temperature. A single rinse with at most u liter of distilled water is carried out after treatment. The solid / liquid separation is carried out by centrifugation at 2000 g. For analytical purposes, filtration is carried out on Millipore membranes with a diameter of 0.45 m.

Treatment by saline discharges of slag from the incineration of chlorinated waste

Dynamic leaching of SU slag; leachate and waters

Leaching was carried out on S slag by Rhône effluents-discharges from the TREDI Saint-Vulbas center (Ain), this extraction reagent corresponds to an instant sample taken in January 1992 at the outlet of the clarifier (Table 15 ).

SU slag was also extracted using a reconstituted calcium effluent (calcium chloride 10g / l, which corresponds to a molar concentration of 0.09M). They were also leached with 1M potassium chloride.

Results The use of saline discharges in accordance with the regulations as an extraction reagent leads to a considerable reduction in the elutio thresholds compared to the control test (Table 16). This dynamic leaching significantly mobilizes nickel. Chromium, despite its abundance in waste, remains insoluble. The COD remains unchanged while the CO decreases by 50%, this being caused by adsorption of organic matter on the slag (Table 17).

The use of a reconstituted calcium effluent leads, under identical conditions, to similar results (Table 18).

Treatment with potassium chloride results in less nickel extraction but more efficient mobilization of copper (Table 19).

The rinsing water leads in all the treatments to eliminate the residual solubilized elements and to remove the excess of reagent (Tables 17 to 19).

Demonstration of slag stability

Salaise II slag from saline or reconstituted discharges see their soluble fraction decrease to become consistent with a recovery in public works The COD of leachate is lowered, as well as the solubilization of chlorides, while the sulphate content reaches a lower concentration at the threshold values of the public works standard (as modified in 1992). The decreasing solubilization of nickel is also established (Tables 20 and 21).

The Salaise II slag leached by KC1 1 presents, as before, values for the sulphates in accordance with a recovery in public works (Table 22). In all cases, the treatment of slag p leaching, thanks to an extraction of the polluting fraction, leads to a notable increase in resistivity of the leachate of the standardized test.

It follows from the above tests that both potassium chloride and calcium chloride allow significant displacements of heavy meta out of the slag, even if the observed ta would be different. In all cases, it will be up to the specialist to determine the salt of choice in order to operate the successive leachings according to the extractability contents of each type of slag in the heavy dic cations vis-à-vis which "inertization" is sought. It is remarkable that the calcium chlorides often also allow stabilization of treated slag.

It has indeed been observed for various treated slag, in particular for SU slag, that the quantity of calcium exchanged is greater than the cation exchange capacity calculated experimentally, moreover this quantity exceeds the contents of heavy meta extracted during successive leachings .

Indeed, the treated slag, 18 months after sampling (Table 20), see their quality improve in terms of the soluble fraction, solubilization of nickel, chlorides and sulfates.

This test repeated 3 months after this treatment on c slag stored at room temperature demonstrates that c last, under the effect of treatment with calcium chloride solution, have stabilized [decrease in the soluble fraction, and above all, the elution threshold d chlorides and sulfates (Table 23)]. In addition, no destabilization of the slag matrix appeared. This stability phenomenon could be explained as follows.

The mineral analysis of SU slag carried out under the same conditions on the control and on the treated residue, 3 months after the leaching operation, showed an enrichment in carbonate of the slag treated with calcium. Thus, the control slag contains 1.83 carbon in the form of carbonates while the treated slag has a concentration of 2.38%, that is to say a 30% increase in the carbonate content.

The calcium exchanged during leaching with heavy metals would therefore have accelerated the natural carbonation of the slag to give them better stability. Such a result is of particular interest, for example for clinkers from household waste incineration plants when these have an intermediate leachable fraction, e when these clinkers are subject to prolonged storage at 'outdoors.

TABLE 15: Study of the composition of the Rhône effluent-discharge from the TREDI Saint-Vulbas center. Analysis carried out on 01/13/92 by plasma emission and / or atomic absorption spectrophometry.

Rhone effluent-discharge parameters

* detection limits and (raw values)

SALAISE slag (SU)

Characteristics Results Standards Standards Valonsauon physical waste class I * Class II ** Public works (TP)

Spit coat (on dry waste) 4.5% <10% <5% <3%

Fire bead (at 550 ° C on dry) <5% <5%

C.O.T (dry) pH 7.6 4 <pH <13

Dryness 73.6%> 35% raised to slag standards before stabilization ^; relauves the fly ash from the ^incineration of municipal waste

Analytical monitoring of extractions

Lead 0.443 0.116 0.052 6.11 <100 <30 8.30 <15

Cadmium 0.058 0.015 <0.010 0.73 - 0.83 <50 <5 0.99 - 1.13 <1

Zinc 0.093 <0.050 <0.050 0.93 - 1.93 <500 1.26 - 2.62

Copper 0.088 0.066 <0.050 1.54 - 2.04 <20 2.10 - 2.77

Nickel 0.338 0.085 <0.050 4.23 - 4.73 <100 5.74 - 6.42

Chrome 0.100 <0.010 <0.010 1.00 - 1.20 <100 1.36 - 1.63 <]

Mercury <0.001 <0.001 <0.001 <0.03 <10 <0.2 <0.04 <0.2

Cyanides ND ^{* 1} ND ND <10

Arsenic <0.010 <0.010 <0.010 <0.30 <10 <2 <0.40

Chlorurcs 338 86 9 4 330 <10 000 5 883

Sulfate. 1650 250 68 19680 26739 <7000

° ND. not dosable

Solubilization behavior

Behaviour

Elements Dissolution Solubilization Solubilization Total solubilization of increasing stagnant TOissanic

Lead X

Cadmium X

Copper X

Nickel X

Chrome x

Chloride. X

TABLEAU l-7 : Suivi des lixiviats et des eaux de rinçage au cours du traitement des scories de Salaise II (SU) par l'effluent - rejet Rhône.Sulfaic; X

TABLE l-7: Monitoring of leachate and rinsing water during treatment of Salaise II slag (SU) with effluent - Rhône discharge.

Parameters Leachate Rinse water pH 7.5 7.1

Resistivity (Ohm.cm) 94 925 D.C.O mg O2 / I 414 0 C.O.T me / 1 6 7

Elements Concentration mg / 1 * Concentration mg / 1 *

Lead

Cadmium

Zinc

Copper

Nickel

Chromium

Calcium

limites de détection et (valeurs brutes). Chlorides

detection limits and (raw values).

TABLE 18: Monitoring of leachate and rinsing water during the treatment of Salaise II slag (SU) with CaCl at 10g / l.

Leachate parameters Rinsing water

7.5

1030

635

6

Elements Concentration mg / 1 * Concentration mg / 1 *

Lead

Cadmium

Zinc

Copper

Nickel

Chromium

Calcium

limiter de détection et (valeurs brutes) Chlorides

limit detection and (raw values)

TABLE 19: Monitoring of leachate and rinsing water during the treatment of Salaise II slag (SII) with KCl IM.

* detection limits and (raw values).

TABLE: STANDARDIZED LEACHATION TEST AFTER TREATMENT WITH RHONE RELEASE

UNDER AGITATION SALAISE II Slag (SU)

Physical characteristics of the waste

Soluble fraction (on dry dcchei)

Pearl fire (at __0 ° C on dry)

C.O.T (on dry) pH

relatives aux normes sur les scories avant stabilisation ' relatives aux cendres volantes provenant de l'incinération de résidus urbainsDryness

relating to standards on slag before stabilization 'relating to fly ash from the incineration of urban waste

Analytical monitoring of extractions

ND: non dosable

ND: not dosable

Solubilization behavior

Behaviour

Elements Dissolution Solubilization Solubilization Total solubilization decreasing if increasing

Copper X

Nickel X

Chloride ¹ - X

TABLEAU : TEST A AL S A RES TRAITEMENT PAR EFFLUENT RECONSTITUESulfate-. X

TABLE: TEST AT ITS RES TREATMENT WITH RECONSTITUTED EFFLUENT

(CaCI ₂ at lOg / l) SUB-AGITATION Slag from S ALAIS E (S II)

Characteristics Results Standards Standards Standards physical recovery of waste Class I * Class II ** Public works (TP)

Fracuon soluble (on dry waste) 1, 4% <10% <5% <3%

Loss on ignition (at ₅₅ 0 ° C on dry) <5% <5%

C.O.T (on dry)

PH 7.8 4 <pH <13

Dryness 66.7%> 35%

* relating to the standards on the stabilizer front scoπes

** on fly ash from the ^incineration of municipal waste

Analytical monitoring of extractions

⁰ ND: not dosable

Solubilization behavior

Behaviour

Elements Dissolution Solubilization Solubilization Total solubilization decreasing stagnant increasing

TABLEAU 22 : TEST DE LIXIVIATION NORMALISE APRES TRAITEMENT PAR KCL IM SOUS AGITATIONNickel X Chloride. X Sulfate-. X

TABLE 22: NORMALIZED LEACHING TEST AFTER TREATMENT WITH KCL IM WITH AGITATION

SALAISE slag (S II)

* relating to standards on slag before stabilization

• * on fly ash from the ^incineration of municipal waste

Analytical monitoring of extractions

ND: not dosable

Solubilization behavior

Behaviour

Elements Dissolution Solubilization Solubilization Total solubilization decreasing stagnant increasing

Nickel X

Chlorides X

:Sulfates X

:

STUDY DF THE STABILITY SALT slag (SU)

* upgrades to slag standards before stabilization

** relating to fly ash from the incineration of urban waste

Analytical monitoring of extractions

ND: non dosable

ND: not dosable

Solubilization behavior

Behaviour

Elements Dissolution Solubilization Solubilization Total solubilization decreasing stagnant increasing

Nickel X

Chlorides X

Cependant —et selon une disposition supplémentair préférée de l'invention— on procède à la biosorptio préalable de ces métaux hors de ces lixiviats. En effet ces métaux s'y trouvent sous une forme très accessible un certain nombre de biosorbantε. En d'autres termes l procédé selon 1'invention est avantageusement complét par une étape supplémentaire de biosorption des métau lixiviés hors des scories traitées, comme cela a ét décrit plus haut.Sulfates X

However - and according to a preferred additional provision of the invention - one proceeds to the prior biosorptio of these metals out of these leachates. Indeed these metals are found in a very accessible form a number of biosorbents. In other words, the process according to the invention is advantageously supplemented by an additional step of biosorption of the metals leached out of the treated slag, as has been described above.

In this regard, it is recalled that biosorption is the sequestration of metal ions by solid material of natural origin. This general term brings together very diverse mechanisms: ingestion of particles active transport of ions, complexation, adsorption and inorganic precipitation on the biosorbent.

A biosorbent whose use seems particularly advantageous is chitosan.

Chitosan is the main derivative of chitin (poly N-acetyl D-glucosamine). It is a saccharide polymer consisting of a long linear polymer chain with glucosamine units, linked by (1-4) glucosidic bridges.

Little present in nature, chitosan is obtained by deacetylation of chitin, itself extracted from the exoskeleton of crustaceans, myriapods and other arthropods or even microorganisms, fungi.

From the diversity of sources of chitin, there arises a wide variety of potential qualities of chitosan.

The deacetylation rate ranging from 80 to 100% and the average molecular mass from 5,000 to 1,000,000 have the consequence of fixing the turbidity, viscosity and solubility of the solutions. This solubility of chitosan, with a low degree of N-acetylation, is only obtained in an acid medium diluted in the pH range <6 It is linked to the presence of amino functions on the C- glucoside units, conferring on this polymer u weak polybase behavior.

Several authors admit that the use of chitosan in water treatment is indeed a way of the future. A product seems to be currently developed in Europe in this sense, it is PRO FLOC (Protan). Its characteristics are the following flakes / powder; free amino form (-NH ₂ ), medium purity. In Japan, chitosan (chitosan beads, Fujib Inc, Shizuo a) is used in the treatment of domestic and industrial water. Another form of usable chitosan (which was used in the preliminary tests reported below) is the SIGM chitosan (ref: C.0792). However, other biosorbents can be used in place of chitosan. We could for example use some of the biosorbent identified below. Their biosorption characteristics do not always coincide with those of chitosan. The choice of the most suitable biosorbent will often result from the contents of the leachate obtained by applying the first part of the process according to the invention to the slag which was to be treated.

Preliminary tests have been carried out with different biosorbents capable of fixing metals: chiti Sigma ^R (ref: C.3387), chitosan Sigma ^R (ref: C.0792) fungal biomass with walls made up of chitosa (Rhizopus arrhizus), bacterial biomass (Zooglo ramigera) and feather meal. Methodology: In 250 ml plasma bottles, we introduce 100 ml of a saline solution (Cobalt: Co (N0 ₃ ) 2 ^o Chromium: Cr (N03) 2. 9H ₂ O or Copper: CuS0 ₄ , 5H ₂ 0 or Zinc ZnS0 ₄ , 5H2O or Cadmium: 3CdS0 ₄ , 8H2O or Lead (Pb (N0 ₃ ) ₂ at 100mg / l adjusted to pH 4.0 and 100 mg of biosorbents (either lg / 1) as is or ground.

Incubation is carried out at 25 ° C with gentle shaking; The samples are taken after 3, 6, 12 24, 48 and 72 hours of contact.

Analysis of the elements in solution is carried out by plasma emission spectrophotometry.

Figures 4 to 9 provide relative curves, the kinetics of adsorption of lead, copper, chromium, cobalt, zinc and cadmium respectively on different biosorbents.

The following salts were used respectively: lead nitrate (Figure 4), copper sulfate (Figure 5), chromium nitrate (Figure 6), cobalt nitrate (Figure 7), zinc sulfate (Figure 8), cadmium sulfate (Figure 9).

The figures are representative of the respective variations of the absorbed metal (in% of the initial content on the ordinate axis) as a function of time (in hours [H]) on the abscissa axis. Results:

By choosing initial conditions eg favorable for biosorption (initial pH: 4.0), the different metals tested at a salt / biosorbent weight ratio of 0.1 gave the following results: the lead is quickly fixed by Zoop; loea will ramify at a rate of 75% in 5 hours; chitin and feather meal accumulate up to 30% then the fixation stops for the rest of the kinetics. R.arrhizus regularly fixes this metal to reach 80% after 7 hours.

Chitosan does not seem to immobilize lead in the conditions of the experiment (Figure 4). copper has a very similar behavior towards chitin, fungal and bacterial biomass and feather meal; its immobilization is close to 10 and remains practically constant. Chitosan is the best copper adsorbent and takes on a colored hue in its presence, 50% of copper sulphate is chelated in 72 hours (Figure 5). chromium alone has an affinity for chitosan and its adsorption reaches 6% in 72 hours of incubation (Figure 6). cobalt has an alternate adsorption and desorption profile for all of the biosorbents tested. The percentage fixed varies between 2 and 8% (figur

7). zinc has a good affinity for Rhizopu arrhizus and chitosan (10% adsorbed in 72 hours of incubation). The other polymers do not chelate the zin either at the chosen concentrations or at the parameters set (FIG. 8). cadmium is fixed by chitosan at a rate of 20% after 72 hours of incubation. Other biosorbents do not accumulate this metal (Figure 9). it follows from the comparative examination of the above-mentioned curves that it is possible, by the choice of biosorbent used in these preliminary tests, to cope with treatment of all leachates obtained resulting from the treatment of slag with a solution containing chloride ions, whatever their respective polluting metal contents.

We can also note that some of the biosorbents used may be weakly active in certain conditions, but become so in others. This is the case, for example, for chitosan with regard to lead and copper.

Some of the biosorbents are of particular interest, especially when they can be regenerated. In this regard, chitosan is particularly effective. The tests briefly reported below demonstrate the capacity of chitosan to be regenerated by treatment with an exchange reagent or an acid.

Another parameter can in particular reside in the presence of larger quantities of biosorbents with respect to the element to be extracted. This is also the case for lead and zinc. Under the conditions of the experiment carried out as indicated below, the quantity of lead absorbed can increase considerably when the relative proportion of the biosorbent increases with respect to the concentration of metal to be adsorbed. Methodologies:

In 250 ml flasks, on the one hand, 100 ml of saline solution are introduced (metals tested: CUSO ₄ , 5H ₂ 0; ZnS0 ₄ , 5H ₂ 0; CdS0 ₄ , 8H ₂ 0; Pb (N0 ₃ ) ₂ ; NiS0 ₄ , 6H2O), either adjusted to pH 4.0 (with the acid corresponding to the conjugate base), or left at its own pH, e on the other hand, respectively 100, 200, 400 and 800 mg of chitosan. After 24 hours of incubation at 25 ° C under gentle agitation, the preparation is centrifuged and 20 m of the supernatant are removed for assay at plasma emission spectrophotometer. The 800 mg pellet is kept to measure desorption.

On this, 20 ml of distilled water are added and the whole is stirred for 1 hour before being centrifuged. The supernatant is analyzed and the residue reprized in a solution of 0.1 M ammonium sulphate and / o of hydrochloric acid IN. After a new agitation, the analysis of the supernatant is repeated. Results:

Copper is the element with the best affinity for chitosan; with a salt / biosorbent ratio of 0.8 the metal chelation is practically complete in 24 hours of contact, the value of the initial pH does not seem to influence the fixing capacity of the biosorbent, however its basic power tends to orient the pH of the medium towards values close to 7 where the competition for protons becomes less.

Desorption using ammonium sulphate is weak, thus proving that the fixed metal is difficult to exchange. The modification of the pH by addition of hydrochloric acid tends to ionize the intervening groups and lead to the release of the chelated metal Having not taken into account the losses during the experiment the percentage of recovery is around 80%. P moreover, the hydrochloric acid used to shift the balance of the reaction seems to have ^* - ^** ~ er the chitosan structure because a slight disaggregation of the product has been observed. According to the data in the literature, sulfuric acid could be effective in shifting the chemical balance of the reaction without dissolving chitosan.

Zinc, another element tested, has a lower affinity compared to copper and its percentage of fixati reaches 60% in 24 hours for a salt / biosorban ratio of 0.8. The pH of the medium changes in an identical manner to the experiments with copper.

Desorption with water seems to be washing rather than active desorption. Zinc is slightly exchangeable but mobilization becomes effective by addition of acid.

Among the elements tested, cadmium has a behavior similar to zinc, its degree of fixation reaches 60% in 24 hours for an identical salt / biosorban ratio.

With the exchange reagent, the cadmium is strongly desorbed; its desorption becomes complete by adding hydrochloric acid. The use of acid as the sole desorption reagent does not seem sufficient to extract all of the fixed metal.

Lead is adsorbed at 91% for a salt / biosorbent ratio of 0.8. This metal is weakly exchangeable, it is partly mobilized by adding hydrochloric acid.

Nickel has a lower affinity for chitosan, its percentage of fixation reaches 60% in 2 hours for a salt / biosorbent ratio of 0.8. Desorption is effective (78%) following displacement of the reaction equilibrium by addition of hydrochloric acid.

The results obtained make it possible to envisage the industrialization of the stage of biosorption of the meta-pollutants contained in the leachate obtained at the end of the stages of "inertization" of the initial slag.

FIG. 10 is a block diagram of an industrial device which can be envisaged for this purpose. The leachate will be directed to a reactor containing the chitosan or to a mixed device comprising da a separate reactor or a mixture of another biosorban (eg stabilized biomass). This will be provided with a recycling loop in order to obtain a complete water treatment. This metal-free water can be discharged into the river or possibly recycled as slag rinse water.

By analogy to ion exchange resins, the chitosan will be regenerated by desorption of the metals using an acid eluent, an operation possibly followed by reconditiόnnement of the biosorbent by adding sodium hydroxide. Regeneration will be carried out alternately on one of the treatment chains (route I or II). The acid eluate will be sent to a storage tank before final solidification, but the recovery of metals and the recycling of water may be envisaged later.

Very similar results can be obtained with other biosorbents, for example with fungal biomass (particularly effective for the treatment of calcium leachate).

Treatment of leachate with fungal biomass

Operating conditions

The biosorption tests are carried out with stirring for 2 hours at 25 ° C. and without pH control 100 ml of an effluent of composition similar to the slag leachate are placed in the presence of 50, 100 or 250 mg of fungal biomass (Rhizopus arrhizus ) cultivated in the laboratory. The determination of the mineral elements is then carried out on the solutions obtained after filtration on millipore membranes with a diameter of 3 m then 0.45 m. Results

The results recorded in table 24 and FIG. 11 show that Rhizopus arrhizuε are particularly effective in removing heavy metals in trace amounts from a calcium matrix.

Leachate treatment (Figure 12)

In practice, the effluents or leachate can be treated continuously in a device comprising a stirred bath fed with the effluents to be treated and the biomass and a decanter for the solid / liquid separation. The liquid supernatants are eliminated and the solid materials (biomass) are either recycled into the food as soon as they are not yet saturated with metals, or to a purge when they are saturated. They are then concentrated (ultimate waste) and, possibly destroyed, for example by incineration, or solidified, for example by vitrification for storage.

Table 24 is representative of the results obtained. FIG. 11 provides an illustration of results obtained in tests involving three different concentrations of "Rhizopus arrhizus (study of the adsorption of different metals contained in effluents. Calculation of the percentage of elimination and confidence interval at 5% after a hour contact with stirring in the presence of Rhizopus arrhizus).

Table 24: Biosorption of heavy metals. Study of the composition of effluents before and after treatment on fungal biomass. 3 repetitions per test. Concentration in μg / 1 and confidence interval at 5%.

Scuii of detection in μg / l for the mineral elements assayed: Pb <25; Cd <10; Zn <50, Cu <50; Nκl00: Cr <10.

All of these results eloquently demonstrate the effectiveness of the entire process according to the invention. The schematic diagram of one of its preferred methods _of implementation appears in FIG. 1 ₃ .

It therefore follows from the above that the process according to the invention leads to fuel residues which, after treatment, conform to the definition of inert European waste and / or conform to values leading to a product which can be recycled in public works.

On the other hand, the mobile fraction of heavy metals initially contained in the residues was concentrated in a mass very much less than the initial mass of slag.

Finally, the treatment does not lead to pollution transfer into the natural environment.

Claims

1. Method for stabilizing combustion residues, in particular slag whatever its origin, and in particular by extracting dissolvable metal fractions, characterized by carrying out one or more leaching of the slag beforehand if necessary, ground to particle size sufficiently low, in particular at values less than 50 mm, to allow sufficient contact between the combustion residues and an aqueous or liquefied leach solution, having a sufficient concentration of elements, ie cations (K ⁺ , Na ⁺ , Ca ²⁺ ) , or proto exchangeable in the form of chlorides with the heavy metal cations present in these residues, this leaching must be sufficient to ensure transformation of at least part of the determined meta, in particular heavy metals contained in the combustion residues, into soluble chlorides and which are extractable by this leach liquor, and the effective extraction in proportions sufficient for: on the one hand, a standardized eluti test subsequently applied to the slag thus treated attests to the decrease in the successively solubilized quantities of each of these metals determined at the necks of repeated extraction tests carried out with a standardized solution of elution in accordance with this test and, on the other hand, the sum of the quantities solubilized in the eluates resulting from the extractions with the above normalized solution, is at values corresponding to concentrations lower than the threshold concentrations also predetermined for each of these metals e for the other parameters set by the standards. 2. Method according to claim 1, characterized in that the above standardized elution test comprises three extraction tests carried out with ι. * ^** e standardized solutio itself consisting of demineralized water saturated with air and CO2 at pH 4.5 and resistivity between 0.2 and 0.4 MΩ.cm. 3. Method according to claim 1 or claim 2, characterized in that the leaching solution or treatment consists of a dilute hydrochloric acid solution, particularly for the treatment of slag basic character. 4. Method according to claim 3, characterized in that the hydrochloric acid concentration of the slag leach solution has a molar concentration in the range of 0.01 M to 1 M, in particular of the order of 0.1 Mr. 5. Method according to claim 1 or claim 2, characterized in that the leaching or treatment solution consists of a chloride solution of an alkali or alkaline earth metal, more particularly for the treatment of slag of neutral nature. 6. Method according to claim 5, characterized in that the leaching solution or treatment are constituted by a potassium chloride solution. 7. Method according to claim 6, characterized in that the concentration of alkali or alkaline earth metal chloride in the leaching or treatment solution is in the range 0.01 M, in particular 0.05 M, to 5 M . 8. Method according to claim 7, characterized in that the alkali metal chloride is potassium chloride, and that its concentration is of the order of 1 M. 9. The method of claim 7, characterized in that the alkali metal chloride is calcium chloride, and that its concentration is in the range of 0.01 M, especially 0.05, to 5 M, especially is d around 0.09 M and 0.15 M. 10. The method of claim 7, characterized in that the alkaline earth metal chloride is calcium chloride, and that its concentration is of the order of 0.09M. 11. Method according to any one of claims 1 to 10, characterized in that the leaching solutions collected from the treated slag are subject to a biosorption with biosorbents capable of sequestering at least a large part of the metal ions heavy metals extracted from this slag. 12. Method according to claim 11, characterized in that the biosorbent is based on chitosan. 13. The method of claim 11, characterized in that the biosorbents are biomass, in particular fungi or bacteria, from cultures or biological fermentations.