FR2714316A1 - Safe disposal of ash from the incineration of toxic waste - Google Patents

Abstract

Process for treatment of ash resulting from the incineration of toxic waste comprises dry mixing the ash with a wt. of cement equal to 0.2-0.70 times the wt. of ash, making a concrete by mixing the dry mixt. with aggregate, at least one fluidising agent and an amt. of water sufficient to wet the mixt. and to form a homogeneous mix, casting the mixt. into blocks and storing the resulting hardened concrete blocks.

Description

 The invention relates to a method for treating ash from combustion and fumes incineration of toxic waste such as household waste.

 The REFIOM (residues of purification of the fumes of incineration of garbage) are fly ash incorporating toxic products such as heavy metals, chlorides, cyanides, ... The problem arises thus to make these residues inert incorporating them into a stabilized solid product that is stored in a landfill or storage facility such as a controlled landfill. The solid product incorporating the ash must have good mechanical strength and be able to retain the toxic compounds.

 However, given the wide variety of compositions of these ashes that are from household waste whose nature itself varies considerably, their high reactivity and variable vis-à-vis hydraulic binders, their great propensity to absorb the water or their hydrophobic character, it is generally considered that their incorporation into a mixture based on hydraulic binder poses a problem.

 Therefore, the known processes for solidification and stabilization of REFIOM implement complex and expensive technologies and / or compounds (including binders) specific also expensive.

 Thus, in a first known type of process, a high proportion of REFIOM is mixed as little as possible (generally less than 10% by weight) of cement or hydraulic binder with a minimum amount of water (stoichiometric amount ), then the mixture is strongly compacted according to the method of limestone-sandstone. In this respect, it is generally considered that the lower the amount of water used, the more compacted product resulting is dense, impervious and better resistant to leaching. Such a process is complex and expensive to implement.

 In a second known type of process, the ashes are mixed with binders and / or specific additives. For example, FR-A-2,685,226 describes such a process in which the ash is incorporated in an aqueous binder formed mainly of a powder of a blast furnace slag product in the presence of magnesium oxide and a soluble sulfate, at a pH between 8 and 12. Nevertheless, it turns out that the results obtained by these methods vary considerably depending on the nature of the REFIOM implemented.

 Therefore, the specific prior laboratory study is necessary to verify the effectiveness of the process vis-à-vis the particular nature of the REFIOM to treat.

 In a third known type of process, the ashes are washed beforehand with water, then the washed ashes and / or the washings are treated according to one of the first two known types of process or in a treatment plant.

If it is easier to render the ash inert after washing, the problem of proper treatment of wash water arises. This third type of known process is therefore ultimately complex and expensive and requires the implementation of very different processes, in separate locations, and therefore the transport of dangerous products.

 The invention aims to overcome these drawbacks and to propose a process for treating the ashes of toxic waste that can be implemented with inexpensive traditional technologies and compounds, in particular without compacting and with a traditional binder such as Portland cement. .

 The invention also aims at providing such a method that can be fully implemented in a single place (production or storage site) in one step or series of steps, and that allows a complete treatment of the ashes by making them inert and transformed into stable and transportable products.

 The invention also aims at providing such a method providing solid products incorporating the ash and whose resistance to leaching remains almost constant and higher than the allowable values for storage in landfill or storage center (including controlled landfill) regardless of the origin and nature of the ashes of treated household waste.

 The invention also aims at providing such a method by which it is easy to indicate on the blocks obtained information relating to their content (nature, source, quantity of components, in particular incorporated waste) so that the storage can be reversible, blocks that can later be sorted and / or reprocessed.

 The invention also aims at providing such a method in which cement and additives are conventionally used, that is to say with a limited quantity of water, in particular less than 600 liters per cubic meter of solid product obtained, and without requiring the use of sophisticated and delicate mixing techniques or specific reagents determined according to the nature of the ashes.

 To do this, the invention relates to a process for treating ash such as REFIOMs from the incineration of toxic waste in which they are incorporated in a mixture comprising a powdery binder from which a stabilized solid product resistant to lixiviation that can be stored directly in a storage center, characterized in that the dry ash is added to a weight of cement between 0.20 and 0.70 times the weight of ash, then a concrete is made into kneading these dry products (ash and cement) with aggregates, at least one fluidifying agent and a weight of water for wetting the entire mixture and to obtain a homogeneous paste, and then solidified blocks made with this concrete are stored.

 Advantageously and according to the invention, the weight of water is the minimum weight which wets the mixture, and is in particular between 0.4 and 0.7 times the total weight of ash and cement. And the ash is mixed with a cement weight of between 0.45 and 0.70, in particular of the order of 0.6 times the weight of ash.

 According to the invention, the aggregates consist of sand and are used from 0 to 600 kg of aggregates per cubic meter of concrete. Advantageously and according to the invention, a proportion of fluidizing agent of between 2% and 3% by weight of the amount of cement is used. The fluidizing agent used may be a known plasticizer in the manufacture of concretes, in particular a naphthalene derivative. In a process according to the invention, it is also possible to use at least one plasticizer.

 The inventor has indeed noted with surprise that, contrary to what was considered until then, it is thus possible to stabilize the ashes by incorporating them into a concrete made simply from cement such as artificial Portland cement in the manner concrete construction, without specific reagent, and although the products obtained are not intended for construction but only for their disposal in landfill.

 The method according to the invention thus makes it possible to obtain solid blocks intended to be stored in a landfill incorporating stabilized ash resulting from the incineration of toxic waste, characterized in that they consist of a concrete obtained from a weight of cement between 0.20 and 0.70 times the weight of ash mixed with a weight of water of between 0.4 and 0.7 times the total weight of ashes and cement with aggregates and at least a fluidifying agent. According to the invention, a cubic meter of solid block thus obtained can incorporate between 400 and 1000 kg of REFIOM, between 200 and 400 kg of cement, and between 0 and 600 kg of aggregates such as sand. A solid block according to the invention comprises between 25 and 60% of ash such as REFIOM, between 10 and 30% of cement, and between 0 and 15% of sand.

 The invention also relates to a treatment method comprising in combination all or some of the characteristics mentioned above or below.

 Other features and advantages of the invention will appear on reading the following description of an installation for implementing a method according to the invention shown schematically in the attached figure, and examples of implementation of the invention. process according to the invention.

 The installation shown in the figure comprises a rocker 1 receiving ash from a tank 2 and the cement of a tank 3. The installation comprises a mixer 4 receiving the dry products from the rocker 1. This mixer 4 is fed in water through a pipe 5, in admixtures (fluidizing agent and / or plasticizer) through a pipe 6 connected to the water supply pipe 5. It is also fed with aggregates such as sand from a tank 8 and a rocker 7 with aggregates. The mixer 4 may be a vertical axis mixer of a type known for the manufacture of building concretes. The concrete resulting from this mixer 4 is molded into block molds 10 which, after solidification, can be stored in a discharge.

EXAMPLE 1
Cement 1 was mixed in the mixer 1
Artificial Portland 55 of Martre Tolosane with ashes of garbage (including REFIOMs) taken from
December 1992 according to a proportion by weight of cement on the ash weight of 0.6. In the second mixer 4, from this dry mix, a concrete was produced whose composition per cubic meter was as follows
- ash: 500 kg,
sand 0/6: 200 kg,
- 6/10 gravel: 200 kg,
- CPA 55 cement from Martre Tolosane: 300 kg,
- water: 520 liters,
- reducing fluidizer of water: 15 kg,
deflocculating plasticizer: 0.9 kg.

Three prismatic specimens were cut from a block made of this concrete after setting, which was subjected to lixiviation and compression tests, the results of which are given in the following table.

<tb><SEP><SEP> limit value
<tb><SEP> Test specimen <SEP> Specimen <SEP> Qualifying specimen <SEP>
<tb><SEP> Sample <SEP> for <SEP> Storage
<tb><SEP> n0 <SEP> 1 <SEP> n <SEP> 2 <SEP> n <SEP> 3 <SEP> (standard
<tb><SEP> AFNOR)
<tb><SEP> Color <SEP> colorless <SEP> colorless <SEP> colorless
<tb><SEP> Weight <SEP> 242 <SEP> g <SEP> 211 <SEP> g <SEP> 211g <SEP>
<tb> Moecuremg / kg <SEP><<SEP> 0.015 <SEP><SEP> 0.015 <SEP><SEP> 0.015 <SEP> 0.3
<tb> Cadmium <SEP> mg / kg <SEP><<SEP> 0.3 <SEP><<SEP> 0.3 <SEP><<SEP> 0.3 <SEP> 5
<tb><SEP> Lead <SEP> mg / kg <SEP><SEP> 1.5 <SEP><SEP> 1.5 <SEP><SEP> 1.5 <SEP> 30
<tb> Arsenic <SEP> mg / kg <SEP><<SEP> 0.15 <SEP><<SEP> 0.15 <SEP><<SEP> 0.15 <SEP> 2
<tb> chloniemg / kg <SEQ> 3181 <SEQ> 3135 <SEP> 3075 <SEP> 25 <SEP> 000 <SEP>
<tb><SEP> Resistance
<tb><SEP> compression
<tb><SEP> 3months <SEP> 4.2 <SEP> 4.6 <SEP> 4.3 <SEP> 1
<tb><SEP> solidification
<tb><SEP> MPa
<Tb>
The leaching tests were carried out in accordance with the AFNOR X31-210 standard with demineralized water in a mass ratio of water relative to the weight of the test tube of 10. The test pieces were brought into contact in the water. with reciprocating agitation.

After stirring for 16 hours, the leachate is separated from the residual waste and the leaching of 16 hours followed by separation is repeated twice with residual waste. Quantities of toxic compounds are analyzed in leachates and expressed as weight of compound per kilogram of concrete. The values obtained are to be compared with the limit values defined in the standard
AFNOR X31-210.

EXAMPLE 2
A concrete was made in a manner similar to the previous example from ashes of winter household waste (including REFIOM) harvested on December 30, 1992, the composition of which was as follows
- ash: 500 kg,
- sand 0/2: 400 kg,
- artificial Portland cement 55 de Martre
Tolosane: 300 kg,
- water required for wetting: 536 liters, (0.67 times the weight ash + cement),
- water reducing fluidizer: 9 kg.

The lixiviation and compression tests carried out after taking on three prismatic test pieces cut from a block molded with this concrete gave the following results:

<tb><SEP> Value
<tb><SEP> ijinle <SEP>
<tb><SEP> Test specimen <SEP> Specimen <SEP> Qualifying specimen <SEP>
<tb><SEP> specimen <SEP> Average <SEP> for
<tb><SEP> n0 <SEP> i <SEP> n <SEP> 2 <SEP> n <SEP> 3 <SEP> Storage
<tb><SEP> (nun <SEP>
<tb><SEP> AFNOR)
<tb><SEP> Weight (g) <SEP> 190 <SEP> 192 <SEQ> 194 <SEP> 192
<tb><SEP> Carbon <SEP>
<tb><SEP> Organic <SEP> 51 <SEP> 69 <SEP> 69 <SEP> 63 <SEP> 400
<tb><SEP> total <SEP> (mg / kg)
<tb> Manne <SEP> (mg / kg) <SEP><<SEP> 0.015 <SEP><SEP> 0.015 <SEP><SEP> 0.015 <SEP><SEP> 0.015 <SEP> 0.3
<tb><SEP> Cadmium
<tb><SEP> (mg / kg) <SEP><<SEP> 0.3 <SEP><<SEP> 0.3 <SEP><SEP> 0.3 <SEP><SEP> 0.3 <SEP> 5
<tb> Lead <SEP> (mgtk <SEP><SEP> 1.5 <SEP><SEP> 1.5 <SEP><SEP> 1.5 <SEP><SEP> 1.5 <SEP> 30
<tb> Arsenic <SEP> (mg / kg) <SEP><<SEP> 0.15 <SEP><<SEP> 0.15 <SEP><<SEP> 0.15 <SEP><<SEP> 0.15 <SEP> 2
<tb><SEP> Chloride <SEP>
<tb><SEP> (mg / kg) <SEP> 6 <SEP> 540 <SEP> 6 <SEP> 840 <SEP> 7 <SEP> 920 <SEP> 7 <SEP> 110 <SEP> 25 <SEP> 000
<tb><SEP> Extract <SEP> sec
<tb><SEP> (mg / kg) <SEP> 16 <SEP> 800 <SEP> 18 <SEP> 420 <SEP> 19 <SEP> 680 <SEP> 18 <SEP> 300 <SEP> 50 <SEP> 000
<tb><SEP> to <SEP> 1030 <SEP> C <SEP>
<Tb>
The concrete had a slow hold, left traces of moisture in the mold and the block had a concave upper surface and its volume increased during setting. The compressive strength of the concrete measured according to standard NF-P-18406 was 11.8 MPa. The weight of dry extract obtained at 10 ° C. from the treated leachate is indicated in the table based on the weight of the initial concrete specimen.

 Another block of concrete was also made with sand 0/6 instead of sand 0/2 and 520 liters of water allowed to wet the mixture (0.65 times the weight ash + cement). The beginning of the setting was more pronounced and there was a withdrawal instead of an increase in volume. The compressive strength was 11.1 MPa.

EXAMPLE 3
The same tests were carried out as in the previous example from ashes of summer household waste (including REFIOM) harvested on May 28, 1993.

 With the same proportions as in the previous example and fine sand 0/2, the mixture could be wetted with 528 liters of water (0.66 times the weight ash + cement).

 As in Example 2, the leaching tests failed to reach detectable values for mercury, cadmium, lead and arsenic.

The following table gives the values obtained for chlorides, total organic carbon and dry extract.

<tb><SEP> Value
<tb><SEP> limit <SEP>
<tb><SEP> specimen <SEP> Summer <SEP> Qualified <SEP> Louvre <SEP>
<tb><SEP> Specimen <SEP> Average <SEP> for <SEP>
<tb><SEP> n <SEP> 1 <SEP> n <SEP> 2 <SEP> n <SEP> 3 <SEP> Storage <SEP>
<tb><SEP> AFNOR)
<tb><SEP> Weight (g) <SEP> 204 <SEP> 187 <SEQ> 194 <SEP> 195
<tb><SEP> Carbon
<tb><SEP> Organic <SEP> 60 <SEP> 63 <SEP> 69 <SEP> 63.9 <SEP> 400
<tb> total <SEP> (mg / kg)
<tb><SEP> Chloride <SEP>
<tb><SEP> (mg / kg) <SEP> 7 <SEP> 260 <SEP> 9 <SEP> 840 <SEP> 9 <SEP> 960 <SEP> 8 <SEP> 970 <SEP> 25 <SEP> 000
<tb><SEP> Extllit <SEP> sec <SEP>
<tb><SEP> (mg / kg) <SEP> 17 <SEP> 340 <SEP> 22 <SEP> 800 <SEP> 22980 <SEP> 20 <SEP> 970 <SEP> 50 <SEP> 000
<tb><SEP> to <SEP> 103 <SEP> C <SEP>
<Tb>

 The compressive strength of the concrete was 12.4 MPa.

EXAMPLE 4
The same tests as in Example 3 were carried out with ashes of summer household waste (including REFIOM) harvested on June 03, 1993 and using sand of 0/6 particle size.

 The mixture could be wet with 392 liters of water (0.49 times the weight ash + cement). The concrete was put in place by stitching. After molding, there was a rise of water on the surface and the mold was wet.

The leaching tests did not detect traces of heavy metals. The following table gives the results for chlorides, organic carbon and dry extract.

<tb><SEP> Value <SEP>
<tb><SEP> limit <SEP>
<tb><SEP> Epmuvette <SEP> Specimen <SEP><SEP> Eprowate <SEP> Admissible <SEP>
<tb> Specimen <SEP> Average <SEP> for
<tb><SEP> n0 <SEP> 1 <SEP> n <SEP> 2 <SEP> n <SEP> 3 <SEP> Storage
<tb><SEP> (standard <SEP>
<tb><SEP> AFNOR)
<tb><SEP> Weight <SEP> (g) <SEP> 207 <SEQ> 214 <SEQ> 205 <SEP> 208.6 <SEP>
<tb><SEP> Carbon
<tb><SEP> organic <SEP> 51 <SEP> 48 <SEP> 51 <SEP> 51 <SEP>
<tb> total <SEP> (mg / kg)
<tb><SEP> Chloride
<tb><SEP> (mg / kg) <SEP> 7 <SEP> 110 <SEP> 7 <SEP> 050 <SEP> 9 <SEP> 090 <SEP> 7 <SEP> 740 <SEP> 25 <SEP> 000 <SEP>
<tb><SEP> Extract <SEP> sec
<tb><SEP> (mg / kg) <SEP> 19 <SEP> 260 <SEP> 14 <SEP> 400 <SEP> 16 <SEP> 620 <SEP> 16 <SEP> 740 <SEP> 50 <SEP> 000
<tb><SEP> to <SEP> 1030 <SEP> C <SEP>
<Tb>

 The compressive strength of the concrete was 16.6 MPa.

EXAMPLE 5
With the same ashes in the previous example, the Portland cement was replaced by fused aluminous cement. The mixture was wet with 416 liters of water (0.52 times the cement + ash weight), but the concrete, very dry, did not take.

EXAMPLE 6
Several concretes were made as in Examples 1 and 2, but with the following proportions (per cubic meter of concrete)

<tb><SEP> BETON <SEP> 1 <SEP> BETON <SEP> 2 <SEP> BETON <SEP> 3 <SEP> BETON <SEP> 4
<tb> Ash <SEP> (kg) <SEP> 500 <SEP> 630 <SEP> 1 <SEP> 000 <SEP> 730
<tb> Cement <SEP> (kg) <SEP> 300 <SEP> 235 <SEP> 200 <SEP> 146
<tb> Sand <SEP> 0/6 <SEP> (kg) <SEP> 400 <SEP> 315 <SEP> - <SEP> 292
<tb><SEP> Water <SEP> (l) <SEP> 392 <SEP> 417 <SEQ> 588 <SEP> 429
<tb> Fluidifier <SEP> (kg) <SEP> 9 <SEP> 7.09 <SEP> 6 <SEP> 6
<Tb>
All the concretes took in eight days and had a compressive strength greater than 1 MPa. Concrete 3 had some cracks.

Claims (9)

 1 / - Process for treating ashes resulting from the incineration of toxic waste in which they are incorporated in a mixture comprising a powdery binder from which a stabilized solid product resistant to lixiviation is formed which can be stored directly in the center storage system, characterized in that the dry ash is added to a weight of cement between 0.2 and 0.70 times the weight of the ash, and a concrete is made by mixing these dry products with aggregates, at least a fluidifying agent and a weight of water for wetting the entire mixture and to obtain a homogeneous paste, and then solidified blocks made with this concrete are stored.  2 / - Method according to claim 1, characterized in that the weight of water is the minimum weight to wet the mixture.  3 / - Method according to one of claims 1 and 2, characterized in that the weight of water is between 0.4 and 0.7 the total weight of ash and cement.  4 / - Method according to one of claims 1 to 3, characterized in that the ash is added to a cement weight between 0.45 and 0.70, in particular of the order of 0.6 times the weight of ashes.  5 / - Method according to one of claims 1 to 4, characterized in that one uses from 200 to 500 kg of aggregates per cubic meter of concrete.  6 / - Method according to one of claims 1 to 5, characterized in that the aggregates consist of sand.  7 / - Method according to one of claims 1 to 6, characterized in that a proportion of fluidizing agent of between 2% and 3% by weight of the amount of cement.  8 / - Method according to one of claims 1 to 7, characterized in that the fluidizing agent is a naphthalene derivative.  9 / - Method according to one of claims 1 to 5, characterized in that one uses, in addition, at least one plasticizer.