MXPA98007043A - Ceni inertitiation procedure - Google Patents

Abstract

An ash inerting process, according to which a reagent selected from phosphoric acid and the phosphates of the alacline metals is added to the ashes, the asphalt-containing phosphated mixture is subjected to a kneading with water and a hydraulic binder in order to form a mortar. hydraulic, and the mortar is subjected to setting and hardening

Description

ASH INERTIZATION PROCEDURE FIELD OF THE INVENTION The present invention relates to a method of inerting ash, in particular flue ash from urban incinerators.

BACKGROUND OF THE INVENTION Urban incinerators (which serve for the destruction of household waste and / or waste from hospitals) produce sometimes significant volumes of fly ash. The mineralogical composition of these ashes does not vary, whatever their origin, and in them they are generally found, although in proportions that can vary from a particular value to twice, or even more, alkali metal chlorides (NaCl and KC1), anhydrite, quartz, vitrified aluminosilicates, other relatively inert oxidized wastes in a chemical sense (Sn02 among them), heavy metals (particularly zinc, lead, cadmium, mercury and chromium), chlorinated, and unburned organic derivatives. Among the unburned ones, metallic aluminum is frequently found. The presence of water-soluble substances, heavy metals and toxic organic materials (dioxins, furans) can pose difficulties for the evacuation of these P1535 / 98MX fly ash and involves previously submitting them to an inertization procedure designed to render them harmless to the environment. Different procedures have been suggested to perform the inertization of ash from urban incinerators, with these procedures aimed at stabilizing heavy metals, mainly lead and cadmium. According to one of these methods (US Pat. No. 4,737,356), the fly ash is treated with a water and lime-soluble phosphate in order to insolubilize the ions of the heavy metals in the form of metal phosphates. According to a similar procedure (European patent application EP-A-568 903), the ashes are treated with water and phosphate ions in order to bring the pH to 6.9 and insolubilize the heavy metals to the state of metal phosphates, the phosphate ions in excess they are fixed by trivalent aluminum or iron ions and the reaction medium is made alkaline with the help of quicklime, CaO. According to the European patent application EP-A-534 231, fly ash collected from an acid fume treatment with lime is simply calcined at high temperature (between 375 and 800 ° C). With the known processes that have just been described, the inert products formed are powders, which may pose difficulties for their handling and their P1535 / 98MX storage. One means of avoiding this difficulty is to eliminate the fly ash in hydraulic mortars, with which solid and inert blocks are formed. For this purpose, in a known inertization process of a sludge contaminated by heavy metals, the mud is mixed with Portland cement and fly ash in order to form a solid, compact and inert block (ROY A. HEATON HC, CARTLEDGE FK and TITTLEBAUM ME "Solidification / Stabilization of a Heavy Metal Sludge by a Portland Cement / Fly Ash Binding Mixture" - Hazardous Waste &Hazardous Materials Vol. 8, No. 1, 1991, pages 33-41). The application of this known procedure to the inertisation of the fly ash from the fumes generated by the incineration of urban waste is not satisfactory, however. Indeed, the blocks obtained in this case are expanded by the presence of multiple gaseous inclusions, which considerably increases their volume and the space they occupy, and makes them friable and not very resistant to compression.

OBJECTS AND ADVANTAGES OF THE INVENTION The invention is aimed at remedying the aforementioned drawbacks of the known processes, by providing a method that performs a P1535 / 98MX effective inertization of ash comprising heavy metals and unburnt metallic aluminum, in solid, compact blocks and having good mechanical properties. The invention is particularly aimed at providing a method for evacuating fly ash from the fumes of urban incinerators, in compact, unexpanded blocks, which have a satisfactory resistance to compression and which comply with the standardized toxicity tests, particularly the TCLP toxicity test ("Toxicity Characteristic Leaching Procedure", E.U.A.). Accordingly, the invention relates to a process for inerting ash containing heavy metals and metallic aluminum, characterized in that a reagent selected from phosphoric acid and alkali metal phosphates is added to the ashes, the mixture is subjected to phosphated thus obtained to a kneading with water and a hydraulic binder in order to form a hydraulic mortar and subject the mortar to setting and hardening.EXPOSITION OF THE INVENTION Heavy metals are metals whose specific weight is at least 5 g / cm3, as well as beryllium, arsenic, selenium and antimony, in accordance with the P1535 / 98MX generally accepted definition (Heavy Metals in Wastewater and Sludge Treatment Processes, Vol. I, CRC Press, Inc., 1987, page 2). In the process according to the invention, a reagent selected from phosphoric acid and phosphates of the alkali metals (preferably sodium) is used. Orthophosphoric acid and sodium hexametaphosphate are satisfactory. The addition of the aforementioned reagent to the ashes must be carried out in the presence of a sufficient quantity of water in order to allow a homogeneous reaction mixture to be carried out rapidly, by simple mixing. Even if one does not wish to be bound by a theoretical explanation, the inventor thinks that one of the difficulties encountered, before the invention, in evacuating the fly ash from urban incinerators in hydraulic mortars was particularly attributable to the presence of metallic aluminum. in these ashes. In the process according to the invention, the aforementioned reagent has the function of converting metallic aluminum into aluminum phosphate. The amount of reagent that is necessary to use will therefore depend on the mineralogical composition of the ashes, in particular on their content of metallic aluminum and heavy metals, and it should be determined in each particular case a routine work in the P1535 / 98MX laboratory. In practice, weight quantities of 5 to 25% (preferably 8 to 15%) of said reagent relative to the weight of the ashes are satisfactory. The water and the hydraulic binder must be used in adequate quantities to form a hydraulic mortar with the phosphate mixture. It is important to efficiently knead the phosphate mixture with water and the hydraulic binder in order to produce a hydraulic mortar of homogeneous composition. At the end of the kneading, the mortar is subjected to ripening to cause its setting and hardening. Before subjecting it to setting and hardening, the mortar must be formed in a suitable form, which allows maintenance and effective storage, for example in the form of briquettes, prismatic blocks or spherical agglomerates. Setting and hardening can be carried out in a humid or dry atmosphere. They are usually done in the presence of atmospheric air. The hydraulic binder is advantageously selected from Portland cement and Portland cement clinker. Even though Portland cement provides satisfactory results, Portland cement clincher is preferred. The amount of hydraulic binder to be used will depend on various parameters, in particular the binder P1535 / 98MX selected hydraulic, the composition of the ashes and the properties sought for the products collected from the inertization process, in particular their mechanical resistance and their behavior in the toxicity tests (for example the TCLP test defined above). In practice, it is recommended to use a weight amount of hydraulic binder greater than 10% (preferably at least equal to 20%) of the weight of the ashes. It has no interest that the weight of the hydraulic binder employed exceeds 100% (usually 50%) of the weight of the ashes. Particularly recommended are the weight quantities of hydraulic binder located between 20 (preferably 25)% and 50 (preferably 40)% of the weight of the ash. At the end of the setting and hardening treatment, which can last several days, a solid and compact mass is collected, which is substantially inert against atmospheric agents and meets the toxicity standards, in particular those defined by the TCLP test defined above. The shape of this solid mass is that in which the mortar has been formed, and may comprise, for example, briquettes or spherical or prismatic blocks. Said mass is compact, substantially free of gaseous inclusions, and due to this it has good mechanical properties, particularly a hardness and a P1535 / 98MX resistance to shocks and abrasion sufficient to allow handling and storage without difficulty. In an advantageous embodiment of the method according to the invention, setting and hardening of the mortar are carried out in a humid atmosphere, preferably saturated with water vapor. This embodiment of the process according to the invention has proved to be particularly advantageous in the case of ash containing valence chromium 6. Indeed, it has been observed that, keeping all the remaining conditions equal, said embodiment significantly improves the inertization of chromium in the solid mass collected at the end of the procedure. In a further advantageous embodiment of the process according to the invention, an additive selected from iron, manganese, iron (II) compounds, manganese (II) compounds and alkali metal-reducing salts (preferably from alkaline metals) is incorporated into the mixing water. sodium), in a quantity by weight of 0.3 to 1% of the weight of the mortar. In this embodiment of the invention, the additive is advantageously selected from ferrous sulfate, manganous sulfate, sodium nitrite, sodium sulfite and metallic iron. For the application of the procedure according to P1535 / 98MX invention, the origin of the ashes is not critical. However, the invention is especially adapted to fly ash collected from the fumes of urban incinerators, such as household waste incinerators and hospital waste incinerators. Fly ash from the fumes generated by urban incinerators usually comprises, in addition to heavy metals and metallic aluminum, undesirable organic matters (in particular chlorinated organic substances such as dioxins and furans), water-soluble compounds, for example alkali metal chlorides, as well as unburned. In a particular embodiment of the method according to the invention, in the case where the ashes contain water-soluble compounds, they are subjected to a wash with alkaline water, before adding them the reagent mentioned above, selected from phosphoric acid and phosphates of the alkali metals. In this embodiment of the process according to the invention, the washing of the ashes with water is aimed at eliminating the water-soluble compounds, in particular the sodium and potassium salts (mainly sodium chloride, potassium chloride and potassium chloride). sodium sulfate) and a part of the anhydrite. For washing the P1535 / 98MX Ashes, it is necessary to use an alkaline water, in order to insolubilize the heavy metals. In practice, the washing of the ashes (particularly the pH of the water used and the contact time between the water and the ash) must be regulated so that the aqueous medium collected from the washing is alkaline and preferably has a pH value. higher than 8, recommending the values at least equal to 9.5. In this way, a solubilization of the heavy metals is prevented, which therefore remains in the residual solid phase collected from the washing. If necessary, it may be necessary to add a reagent to the wash water to bring the pH to the desired value, for example lime. At the end of the wash, an aqueous suspension is collected which is subjected to a filtration or equivalent mechanical separation (for example sedimentation or centrifugation) to separate solid, undissolved materials from it, to which the reagent mentioned is then added. above, according to the method according to the invention. In another embodiment of the method according to the invention, in the case where the ashes contain organic and / or unburned matter, the aforementioned phosphate mixture is subjected to calcination before the water and the hydraulic binder are added thereto. In this embodiment of the method according to the invention, P153.5 / 98MX the calcination is carried out in an oxidizing atmosphere (usually in ambient air). This calcination has as its objective the destruction of the unburned ones and the elimination of the organic matters. Calcination is generally carried out at a temperature above 600 ° C, preferably at least equal to 700 ° C. It is advisable to avoid excessive temperature, which would result in vaporizing a part of the heavy metals. In practice, the calcination temperature is preferably below 1000 ° C and, advantageously, does not exceed 800 ° C. Temperatures of 600 to 800 ° C are especially recommended. The invention is illustrated by the following description of the single figure of the attached drawing, which represents the scheme of an installation using a particular embodiment of the method according to the invention. The installation schematized in the figure is intended for the treatment of inertization of ashes 1, comprising heavy metals, metallic aluminum, water-soluble compounds, organic and unburned materials. It comprises a washing chamber 2 in which ashes 1 and water 3 are introduced. The amount of water 3 introduced into chamber 2 is regulated to dissolve all the water-soluble compounds of the ashes 1, in particular the chloride of water. sodium, potassium chloride and P1535 / 98 X the sodium sulfate. On the other hand, a pH value higher than 8, for example from 9.5 to 14, is adjusted in chamber 2 in order to insolubilize the heavy metals. If necessary, to adjust the desired pH value, hydrochloric acid or sodium hydroxide is added to the washing water 3. An aqueous suspension 4 is collected from the washing chamber 2, which is immediately treated in a filter 5. It is discarded the filtrate 6 and the filtration cake 7 is collected, which is sent to a reaction chamber 8. In the reaction chamber 8, a sufficient amount of phosphoric acid 9 and water 10 are added to the filtration cake 7 to form , by kneading, a pumpable mass 11 in which all the metallic aluminum of the ashes is in the aluminum orthophosphate state (as an alternative, part or all of the phosphoric acid is replaced by an alkali metal phosphate, with sodium hexametaphosphate preference). The pumpable mass is removed from the reaction chamber 2 and introduced into a calcination furnace 12, in which the same is heated to a temperature of 700 to 800 ° C, for a sufficient time to decompose the organic matters and destroy the unburned. The calcined material 13, extracted from the furnace 12, is transferred to a kneading chamber 14, in which water 15 and a hydraulic binder 16 (for example Portland cement clinker) are added in quantities P1535 / 98MX adjusted to form, by kneading with the calcined material 13, a hydraulic mortar. The hydraulic mortar 17 collected from the kneading chamber 14 is treated in a rotating drum 18, to conform it to the state of spherical agglomerates 19 which are stored for several days in an enclosure 20, hermetically sealed and filled with air sensibly saturated with water vapor , at room temperature of approximately 20 ° C and at atmospheric pressure. The duration of the maturation treatment in the enclosure 20 is adjusted to achieve the setting and complete hardening of the spherical mortar agglomerates 19. At the end of the maturation treatment in the enclosure 20, spherical agglomerates are collected 21 hard, compact and inert in front of the environment and the atmospheric agents, in such a way that they can be evacuated to a waste products dump. The examples whose description follows will make the interest of the invention appear.

First series of tests In the examples 1 to 5 whose description follows, ashes removed from a household waste incinerator have been treated. The weight composition of the ash is reported in Table 1 below.

P1535 / 98MX Table 1 / 98MX Example 1 (not according to the invention) 108 g of ash were washed with 1000 ml of water. After 1 hour, the pH of the reaction medium is set to 10.9. The aqueous suspension thus formed was filtered and the filter cake was collected, after having previously washed it with 100 ml of water. A sufficient amount of water has been added to the filter cake to form a malleable paste containing about 40% water. To the paste thus obtained, 11.8 g of an aqueous solution of phosphoric acid (concentration: 85% by weight) have been added, keeping the pulp in permanent agitation. The addition of phosphoric acid has been accompanied by a moderate heat release. The homogenous pasty mass thus obtained has been placed in a refractory porcelain capsule, which has been introduced in a cold oven. The furnace was then heated to progressively bring its temperature to 800 ° C, in the course of about 1 hour. This temperature of 800 ° C has been maintained for 1 hour, then the material has been removed from the oven and allowed to cool to room temperature. The calcined powder, collected from the furnace, has been subjected as such to a toxicity test according to the TCLP standard defined above. To this effect, 2 liters of a reaction have been added to 100 grams of the calcined powder P1535 / 98MX water containing 6 g of acetic acid and 2.57 g of sodium hydroxide per liter. The mixture has been homogenized, then filtered on a glass fiber filter of 0.6 to 0.8 μm and the content of the filtrate in heavy metals from the powder subjected to the test has been determined. The results are listed below in table 2.

Table 2 Example 2 (according to the invention) A batch of the ash defined in table 1 has been treated as in example 1 and the calcined powder, collected from the furnace and cooled to room temperature has been intimately mixed with Portland cement clinker ( to P1535 / 98MX ratio of 1 part weight of clinquer to 5 parts by weight of the calcined powder). To the obtained mixture, mixing water has been added at a rate of 30 ml of water for 100 g of said mixture, kneading to form a homogeneous mortar. This was then shaped into spherical agglomerates that have been stored in the air for 5 days, to cause the setting and hardening of the mortar. The spherical agglomerates collected at the end of setting and hardening of the mortar were subjected to the TCLP toxicity test as in example 1. For this purpose, the spherical agglomerates have been crushed to a size smaller than 1 mm in diameter (diameter defined by sieving) and, to 100 g of the crushed matter thus obtained, 2 liters of an aqueous solution containing 6 g of acetic acid and 2.57 g of sodium hydroxide per liter were added. The mixture was homogenized, then filtered on a glass fiber filter from 0.6 to 0.8 μm and the content of the heavy metal filtrate from the powder subjected to the test was determined. The results are listed below in table 3.

P1535 / 98MX Table 3 A comparison of the results shown in tables 2 and 3 immediately shows the progress made by the invention, as regards the inertization of the heavy metals in the ash.

Example 3 (according to the invention) In this example, the operation was as in the example 2, but the spherical agglomerates collected at the end of setting and hardening of the mortar have been subjected to a different toxicity test from the TCLP test. In this test, the spherical agglomerates have been crushed to a size less than 1 mm (diameter defined by sieving) and the crushed material has been subjected to a triple leaching with demineralized water, in a liquid / solid ratio equal to 10.

P1535 / 98MX At the end of each leaching, the content in the washing liquid of the heavy metals of the powder subjected to the test has been determined. The results are listed below in table 4.

P1535 / 98MX Table 4 / 98MX Example 4 (according to the invention) The test of example 2 was repeated, under the same conditions, with the only exception that the Portland cement clinker has been replaced by Portland cement. The results of the TCLP test are reproduced in table 5.

Table 5 Example 5 (according to the invention) The test conditions of example 3 have been repeated, with the only exception that the Portland cement clinker has been replaced by Portland cement. The results of the triple leaching test are reproduced in table 6.

P1535 / 98MX Table 6 / 98MX Second series of tests In the examples 6 to 17 whose description follows, ashes having the weight composition of table 7 have been treated.

P1535 / 98MX Table 7 / 98MX Example 6 (not according to the invention) 136 g of ash were washed with 1300 ml of water. After 1 hour, the pH of the reaction medium is set to 11.0. The aqueous suspension thus formed was filtered and the filter cake was collected, after having previously washed it with 100 ml of water. The operation was then carried out as in Example 1. The results of the toxicity test (TCLP test) are reported in Table 8 below.

Table 8 Example 7 (according to the invention) A batch of the ashes defined in table 7 has been treated as in example 6 and the calcined powder collected from the calcination furnace and cooled to the P1535 / 98MX Room temperature has been mixed with Portland cement clinquer, at a rate of one part weight of clinquer for four parts by weight of calcined ash. To the homogeneous mixture obtained, kneading water has been added in an amount equal to 30 ml for 100 g of mixture, and it has been kneaded to form a mortar. The obtained hydraulic mortar has been formed into spherical agglomerates that have been stored in the air for 5 days, to cause the setting and hardening of the mortar. The spherical agglomerates collected at the end of setting and hardening of the mortar have been subjected to the TCLP toxicity test. For this purpose, the spherical agglomerates have been crushed to a size less than 1 mm in diameter (diameter defined by sieving) and, to 100 g of the crushed material thus obtained, 2 liters of a 0.1 M aqueous solution have been added. of acetic acid. The mixture was homogenized, then filtered on a glass fiber filter of 0.6 to 0.8 μm and the content of the filtrate in the heavy metals of the powder subjected to the test was measured. The results are reported in table 9 below.

P1535 / 98MX Table 9 Example 8 (according to the invention) The test of example 7 has been repeated, with the only difference that the TCLP toxicity test has been replaced by the triple leaching test described in example 3. The results of the test are reported to continuation in table 10.

P1535 / 98MX Table 10 / 98MX Example 9 (according to the invention) The test of Example 7 was repeated, with the only exception that the storage of the spherical agglomerates, at the end of the kneading, was carried out in a hermetically sealed enclosure, filled with steam-saturated air. of water (100% relative humidity) for 8 days. The spherical agglomerates collected from the enclosure were dried in the air for 2 days and then subjected to the TCLP test of Example 8. In the TCLP test, a hexavalent chromium content of 42 μg / 1 was determined in the filtrate.

Examples 10. 11 12 (according to the invention) These examples relate to three tests that have been carried out under the same conditions as in example 9, with the only exception that an additive has been added to the mixing water. In the test of Example 10, this additive consisted of ferrous sulfate heptahydrate (used in a weight amount equal to 1% of the weight of the mortar); in the test of Example 11, said additive consisted of manganous sulfate monohydrate (used in a weight amount equal to 0.7% of the weight of the mortar); and in the test of Example 12, the additive consisted of an iron powder (used in a weight amount equal to 0.3% of the weight of the mortar).

P1535 / 98MX In the TCLP assay, it was determined that the content of hexavalent chromium in the filtrate, in each of the three examples, was less than 10 μg / 1).

Examples 13, 14 15, 16 and 17 (according to the invention) The test of example 9 was repeated with an amount of ashes sufficient to be able to prepare, from the mortar, five prismatic test pieces of 4 x 4 x 16 cm. The test pieces were kept for 28 days in an atmosphere saturated with water vapor, at room temperature to cause the setting and hardening of the mortar. The five trials have differed from each other in the weight ratios between the amount of ash and the amount of clinker used. After setting and hardening of the mortar, the test pieces were subjected to a mechanical strength test, which consisted in measuring their resistance to bending and their resistance to compression under the conditions of the Belgian standard NBN 196 1 (1991) . The results of the tests are mentioned in table 11 below.

P1535 / 98MX Table 11 P1535 / 98MX

Claims (11)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. A method of inertization of ashes containing heavy metals and metallic aluminum, characterized in that a reagent selected from phosphoric acid and phosphates of the alkali metals is added to the ashes, the phosphated mixture thus obtained is subjected to mixing with water and with a hydraulic binder in order to form a hydraulic mortar and the mortar is subjected to a setting and a hardening.
2. 2. A process according to claim 1, characterized in that the reagent comprises sodium hexametaphosphate.
3. 3. A process according to claim 1 or 2, characterized in that the hydraulic binder is selected from Portland cement and Portland cement clinker.
4. 4. A process according to any one of claims 1 to 3, characterized in that the reagent mentioned above is used in a weight amount of 8 to 15% by weight of the ash.
5. 5. A procedure according to any one of the P1535 / 98MX claims 1 to 4, characterized in that the hydraulic binder is used in a weight amount of 25 to 40% by weight of the ash.
6. 6. A process according to any one of claims 1 to 5, characterized in that setting and hardening are carried out in an atmosphere saturated with water vapor.
7. A process according to any one of claims 1 to 6, characterized in that an additive selected from iron, manganese, iron (II) compounds, manganese (II) compounds and alkali metal reducing salts is incorporated into the mixing water. , in a quantity by weight of 0.3 to 1% of the weight of the mortar.
8. 8. A process according to claim 7, characterized in that the additive is selected from ferrous sulfate, manganous sulfate, sodium nitrite, sodium sulfite and metallic iron.
9. 9. A process according to any one of claims 1 to 8, characterized in that, in the case in which the ashes contain water-soluble compounds, they are subjected to a wash with alkaline water, before adding the phosphoric acid thereto.
10. 10. A process according to any one of claims 1 to 9, characterized in that, in the case where the ashes contain organic matters and / or P1535 / 98MX unburned, the above-mentioned phosphatic mixture is subjected to a calcination before the water and the hydraulic binder are added thereto.
11. 11. A method according to any one of claims 1 to 10, characterized in that the ashes comprise fly ash from a smoke coming from the incineration of urban waste. P1535 / 98MX