Treatment of waste from the purification of incineration fumes by means of a thermoplastic polymer with a view to storing same

Abstract

The present invention relates to a method for treating a powder material, such as waste from the purification of incineration fumes, in order to obtain a solid composite product that is storable. The method has a markedly improved ecological footprint.

Description

Title: Treatment of Air Pollution Control Residues by means of a thermoplastic polymer with a view to storing same Technical field [1] This disclosure relates to the field concerning the treatment of products resulting from the incineration of waste so that they can be stored, and in particular to the treatment of air pollution control residues so that they can be stored. Prior art [2] The management of waste originating from residential, institutional, and commercial sources, as well as from agricultural waste and other waste streams such as sewage sludge, is a complex issue for which the solutions are constantly evolving. [3] Currently in France, incineration is the second most common method of waste disposal. The incineration process results in a reduction in the volume and mass of solid waste, although incineration generates flue gas containing acidic gases, fly ash, and gas cleaning residues, among other products. The flue gas must be purified before being released into the atmosphere, while the fly ash and the gas cleaning residues must be treated before being stored. [4] As illustrated in FIG. 1, an incineration facility comprises an incineration furnace 1, a fly ash storage unit 3, a cooling tower 5, a flue gas treatment unit 7, a storage unit 10, an optional catalytic treatment unit, and a stack (the latter two are not shown in FIG. 1), as well as other components. [5] The incineration furnace 1 incinerates the waste, produces fly ash, and emits flue gas. The recovered fly ash is conveyed to the fly ash storage unit 3 via a fly ash pipe 2. [6] The flue gas is conveyed via a pipe 4 to the cooling tower 5 in order to produce cooled flue gas. This cooled flue gas is conveyed via a cooled flue gas pipe 6 to the flue gas treatment unit 7, the goal being to ensure that the flue gas meets regulatory thresholds for atmospheric emissions. In this flue gas treatment unit 7, the cooled flue gas is brought into contact with a flue gas treatment material such as sodium bicarbonate or lime, in order to neutralize acidic gases such as SO2 and HCl, thereby producing purified flue gas and solid residues comprising soluble fractions such as NaCl, KCl, Na2SO4, K3Na(SO4)2, and CaCl(OH). [7] After separation using a bag filter, the purified flue gas is collected in the purified flue gas pipe 8 in order to be discharged into the atmosphere via the stack, while the solid residues are conveyed via a solid residue pipe 9 to the storage unit 10. [8] Prior to being discharged into the atmosphere, the purified flue gas may undergo an additional purification step in an optional catalytic treatment unit, to obtain highly purified flue gas which is then discharged into the atmosphere via the stack, and optional solid residues. These optional solid residues are then routed to the storage unit 10. The solid residues, and possibly the optional solid residues, stored in the storage unit 10 constitute the air pollution control residues (incineration flue gas cleaning residues). [9] Thus, an incineration facility may produce the following two different powdery materials: - fly ash, produced in the incineration furnace 1 and stored in the fly ash storage unit 3; and - air pollution control residues, produced in the flue gas treatment unit 7 and optionally in the catalytic treatment unit, and stored in the storage unit 10.

[10] Table 1 below presents the content, by weight, of the main salts in the soluble fraction present in three examples of air pollution control residues obtained by treatment with sodium bicarbonate or lime, and in one example of fly ash. Main salts are those which have a weight content of more than 4% relative to the total dry weight of the residue or fly ash.

[11] Table 1 highlights the fact that the composition of these two types of powdery materials is significantly different. Indeed, in cleaning residue, the weight content of the soluble fraction relative to the total dry weight of the residue is greater than 30%. In contrast, in fly ash, the weight content of the soluble fraction relative to the total dry weight of the fly ash is less than 20%. The weight content of the soluble fraction is calculated by adding the weight contents of each main salt present in the soluble fraction.

[12] Furthermore, a person skilled in the art knows that K3Na(SO4)2 and a high NaCl content are markers indicating a treatment with sodium bicarbonate, whereas CaCl(OH) is a marker indicating a treatment with lime.

[13] [Table 1] Main salts of the soluble fraction Examples of air pollution control residues obtained by treatment with sodium bicarbonate in a flue gas treatment unit 7 Example of air pollution control residues obtained by treatment with lime in a flue gas treatment unit 7 Fly ash obtained in the incineration furnace 1 NaCl 53.1% 53.4% 12.4% 10.0% KCl - 7.7% 7.2% 8.5% Na2SO4 4.8% - - - K3Na(SO4)2 10.8% 4.9% - - CaCl(OH) - - 38.2% -

[14] Two main directives establish the second tier of European legislation on waste and focus on the treatment operations for air pollution control residues: the Industrial Emissions Directive (waste incineration) and the Landfill Directive (storage). European Directive No. 1999 / 31 / EC of April 26, 1999 concerning the landfilling of waste introduces the concept of treatment prior to storage. The amended French Ministerial Order of December 30, 2002, concerning the storage of hazardous waste, imposes various limits on waste when entering storage. For example, it sets a limit of 10% for the soluble fraction, a limit of 1,000 mg / kg for Total Organic Carbon (TOC), a limit of 500 mg / kg for fluoride ions, a limit of 30 mg / kg for molybdenum, a limit of 70 mg / kg for chromium, and a limit of 50 mg / kg for lead in the leachate obtained from air pollution control residues.

[15] Thus, prior to storage, the legislation mandates that air pollution control residues be stabilized, i.e. treated so that they satisfy the imposed limits. The resulting treated residues, commonly referred to as stabilized solid products, are then deposited in specifically designed cells at a temperature below 60°C, as required by current regulations.

[16] These air pollution control residues are generally stabilized by mixing them with a hydraulic binder, as described in the "Etude FNADE ADEME - retour d'experience sur la filiere frangaise - stabilisation / solidification - stockage de dechets dangereux" (FNADE ADEME Study - Report on the French Sector: Stabilization / Solidification - Storage of Hazardous Waste"), published in 2006. The hydraulic binder typically consists of a mixture of cement (approx. 15% by weight), metakaolin (approx. 15% by weight), blast furnace slag (approx. 15% by weight), and water (approx. 55% by weight).

[17] In France, the annual use of this hydraulic binder by hazardous waste storage facilities requires over 40,000 tonnes of cement, thereby generating more than 26,000 tonnes of CO2. Indeed, the production of one tonne of cement generates 650 kg of CO2. Furthermore, metakaolin - an artificial pozzolan derived from the calcination of kaolinite (AhO3-2SiO2-2H2O) - is produced via flash calcination at 900°C in gas-fired kilns. Blast furnace slag is a by-product of blast furnaces. The use of each of these three components in the hydraulic binder therefore generates significant amounts of CO2.

[18] The current method, which utilizes a hydraulic binder, therefore has a poor carbon footprint. In fact, the steady increase in atmospheric CO2 levels is widely held to be responsible for climate change and global warming via the greenhouse effect.

[19] It is therefore readily understood that reducing CO2 emissions remains a constant priority.

[20] Furthermore, air pollution control residues contain soluble chemical elements considered to be pollutants, such as molybdenum, lead, arsenic, antimony, fluorine, or selenium. The current method, which utilizes a hydraulic binder, is unable to effectively retain these harmful chemical elements.

[21] There is therefore a need to provide a method for treating air pollution control residues that has a lower carbon footprint than the poor carbon footprint of the current method which utilizes a hydraulic binder, while simultaneously optimally sequestering soluble chemical elements considered as pollutants. Summary

[22] This disclosure serves to improve this situation.

[23] A method is proposed for treating a powdery material with a thermoplastic polymer in order to obtain a solid composite product, the powdery material comprising at least 30% by weight of a soluble fraction relative to the total dry weight of the powdery material, the method comprising the following steps: a) bringing the powdery material and the thermoplastic polymer into contact at a temperature greater than or equal to the softening point of the thermoplastic polymer, in order to obtain a mixture; b) shaping the mixture; and c) solidifying the mixture to obtain the solid composite product.

[24] Advantageously, the method according to the invention makes it possible to stabilize the powdery material by efficiently encapsulating it within a thermoplastic polymer matrix, while having a lower carbon footprint than the poor carbon footprint of the current method which uses a hydraulic binder.

[25] Indeed, when the powdery material is air pollution control residue, the inventors have calculated that substituting thermoplastic polymer for the hydraulic binder prevents the emission of 1,100 to 1,700 kilograms of CO2 equivalent per tonne of powdery material encapsulated by using the method of the invention.

[26] Furthermore, the method of the invention serves to upcycle thermoplastic polymers that would otherwise have been incinerated. Indeed, plastic packaging is the primary source of thermoplastic polymers and these are generally incinerated. According to various studies, the incineration of plastic packaging generates approximately 2,400 kilograms of CO2 equivalent per tonne of plastic packaging. This upcycling advantageously serves to reduce the carbon footprint associated with the end-of-life phase of thermoplastic polymer packaging.

[27] Furthermore, the stability of the solid composite product obtained by the method of the invention is sufficient to: - prevent the soluble fraction of the powdery material from leaching; and - effectively sequester soluble chemical elements considered to be pollutants, such as molybdenum, lead, and chromium, as well as fluoride ions. The solid composite product also exhibits a TOC (Total Organic Carbon) content of less than 1000 mg / kg.

[28] The solid composite product obtained by the method of the invention can advantageously be stored in a landfill cell, as it complies with the storage facility acceptance limits imposed by the amended French Ministerial Decree of December 30, 2002, relating to the storage of hazardous waste.

[29] Moreover, the inventors have observed that, for the same mass proportion of powdery material, the volume of the solid composite product obtained by the method of the invention is smaller than the volume of a stabilized and solidified product obtained by the current method which utilizes a hydraulic binder. A landfill cell can therefore accommodate a larger amount of the solid composite product obtained by the method of the invention than the amount of stabilized and solidified products obtained by the current method which utilizes a hydraulic binder; this reduces the consumption of landfill void space associated with the storage of hazardous waste. Indeed, the preservation of landfill void space for hazardous waste storage constitutes a major challenge in the field of hazardous waste management in France.

[30] Furthermore, during step a), bringing the powdery material into contact with the thermoplastic polymer at a temperature greater than or equal to the softening point of the thermoplastic polymer makes it possible to have a homogeneous dispersion of the powdery material within the thermoplastic polymer.

[31] Indeed, but without wishing to be bound by any specific theory, the inventors are of the opinion that, due to its thermal conductivity, the soluble fraction of the powdery material acts as a heat conductor, thereby ensuring a homogeneous heating of the mixture comprising the powdery material and the thermoplastic polymer.

[32] This homogeneous dispersion is highly advantageous because it can impart stability to the solid composite product obtained via the method according to the invention, without the need to add a third component such as a wax, an anti-leaching agent, or a waterabsorbing agent, thereby enabling it to be stored in compliance with regulations.

[33] The fact that the addition of a third component is unnecessary is also advantageous, as it allows for an increased proportion of powdery material within the solid composite product.

[34] The method of the invention is also simple to implement on an industrial scale, to treat large quantities of waste. Indeed, the method of the invention can be implemented either downstream of or in parallel with a conventional waste storage facility.

[35] The method of the invention is also economical. Indeed, it does not require any heavy investment in equipment, as it can be implemented in a simple manner within existing facilities. Furthermore, the cost of thermoplastic polymer is low or even zero.

[36] In another aspect, a method is proposed for purifying flue gases resulting from waste incineration, which makes use of the treatment method as defined above and further comprises the following step: - bringing the incineration flue gases into contact with a flue gas treatment material to form an air pollution control residue, the air pollution control residue subsequently being utilized in step a) of the treatment method.

[37] Such a flue gas treatment material may be sodium bicarbonate, lime, or mixtures thereof.

[38] In another aspect, a solid composite product is proposed comprising particles of a powdery material dispersed within a thermoplastic polymer, the solid composite product comprising a leachable soluble fraction.

[39] Such a product is advantageous in that it allows the long-term storage of a high proportion of powdery materials exhibiting a high content of soluble fraction, while preventing the leaching phenomenon and effectively sequestering soluble chemical elements considered as pollutants, such as molybdenum, lead, and chromium, as well as fluoride ions. Brief description of drawings

[40] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, in which: Fig. 1

[41] [Fig. 1] shows a simplified diagram of a waste incineration facility. Fig. 2

[42] [Fig. 2] shows a photograph illustrating a solid composite product according to the invention. Detailed description

[43] A method is proposed for treating a powdery material with a thermoplastic polymer in order to obtain a solid composite product, the powdery material comprising at least 30% by weight of a soluble fraction relative to the total dry weight of the powdery material, the method comprising the following steps: a) bringing the powdery material and the thermoplastic polymer into contact at a temperature greater than or equal to the softening point of the thermoplastic polymer, in order to obtain a mixture; b) shaping the mixture; and c) solidifying the mixture to obtain the solid composite product.

[44] For the purposes of the invention, the singular forms "a," "an," and "the" also encompass the plural forms of the terms to which they refer, unless the context clearly indicates otherwise.

[45] Weight values are expressed as dry weights, unless otherwise specified.

[46] For the purposes of the invention, "powdery material" refers to a material in powder form.

[47] For example, the powdery material may be an air pollution control residues.

[48] For the purposes of the invention, " air pollution control residue" refers to a material: - obtained by treating incineration flue gases with a flue gas treatment material, such as sodium bicarbonate or lime, in particular sodium bicarbonate, and - comprising at least 40% by weight of a soluble fraction relative to the total dry weight of the air pollution control residue. In the present patent application, the air pollution control residue may be referred to as "cleaning residue."

[49] The composition of the cleaning residue obtained by treatment with sodium bicarbonate differs from the composition of the cleaning residue obtained by treatment with lime. In particular: - the weight content of the soluble fraction in the cleaning residue obtained by treatment with sodium bicarbonate is higher than the weight content of the soluble fraction in the cleaning residue obtained by treatment with lime, - the weight content of NaCl in the cleaning residue obtained by treatment with sodium bicarbonate is greater than 40%, whereas the weight content of NaCl in the cleaning residue obtained by treatment with lime is less than 40%, - the cleaning residue obtained by treatment with sodium bicarbonate comprises K3Na(SO4)2, whereas the cleaning residue obtained by treatment with lime comprises none of that compound, and - the cleaning residue obtained by treatment with lime comprises CaCl(OH), whereas the cleaning residue obtained by treatment with sodium bicarbonate comprises none of that compound.

[50] For the purposes of the invention, "solid composite product" refers to a material comprising particles of powdery material dispersed in a thermoplastic polymer, the powdery material comprising a soluble fraction. In the present patent application, the solid composite product may also be referred to as "composite product".

[51] For the purposes of the invention, "soluble fraction" refers to a fraction comprising at least one soluble salt selected among salts where: - the anion is chloride, sulfate, hydroxychloride, or combinations thereof, and - the cation is sodium, potassium, calcium, or combinations thereof.

[52] For example, the soluble fraction may comprise a salt selected among NaCl, KCl, Na2SO4, K3Na(SO4)2, CaCl(OH), and mixtures thereof, in particular a mixture of NaCl and KCl, a mixture of NaCl and Na2SO4, a mixture of NaCl and K3Na(SO4)2, a mixture of NaCl and CaCl(OH), a mixture of KCl and K3Na(SO4)2, a mixture of KCl and CaCl(OH), a mixture of Na2SO4 and K3Na(SO4)2, and mixtures thereof, particularly a mixture of NaCl, Na2SO4, and K3Na(SO4)2, a mixture of NaCl, KCl, and K3Na(SO4)2, and a mixture of NaCl, KCl, and CaCl(OH), even more particularly a mixture of NaCl, Na2SO4, and K3Na(SO4)2 and a mixture of NaCl, KCl, and K3Na(SO4)2.

[53] The mixture of NaCl, Na2SO4, and K3Na(SO4)2, or the mixture of NaCl, KCl, and K3Na(SO4)2, can be characteristic of a cleaning residue obtained by treatment with sodium bicarbonate.

[54] The mixture of NaCl, KCl, and CaCl(OH) can be characteristic of a cleaning residue obtained by treatment with lime.

[55] The powdery material may comprise at least 40% by weight of sodium chloride (NaCl) relative to the total dry weight of the powdery material, preferably between 45% and 75%, more preferably between 50% and 60%.

[56] The powdery material may, for example, comprise between 1% and 50% by weight of KCl relative to the total dry weight of the powdery material, preferably between 1% and 15%, more preferably between 5% and 10%.

[57] The powdery material may comprise between 1% and 50% by weight of Na2SO4 relative to the total dry weight of the powdery material, preferably between 1% and 15%, more preferably between 1% and 5%.

[58] The powdery material may comprise between 1% and 50% by weight of K3Na(SO4)2 relative to the total dry weight of the powdery material, preferably between 1% and 25%, more preferably between 1% and 20%.

[59] The powdery material may comprise between 1% and 50% by weight of CaCl(OH) relative to the total dry weight of the powdery material, preferably between 30% and 45%, more preferably between 35% and 40%.

[60] The powdery material may comprise at least 40% by weight of NaCl relative to the total dry weight of the powdery material, preferably between 45% and 75%, more preferably between 50% and 60%, and, optionally: - between 1% and 50% by weight of KCl relative to the total dry weight of the powdery material, preferably between 1% and 15%, more preferably between 5% and 10%, - between 1% and 50% by weight of Na2SO4 relative to the total dry weight of the powdery material, preferably between 1% and 15%, more preferably between 1% and 5%, - between 1% and 50% by weight of K3Na(SO4)2 relative to the total dry weight of the powdery material, preferably between 1% and 25%, more preferably between 1% and 20%, or mixtures thereof.

[61] The powdery material may comprise: - between 50% and 60% by weight of NaCl relative to the total dry weight of the powdery material, - between 1% and 20% by weight of K3Na(SO4)2 relative to the total dry weight of the powdery material, and - between 5% and 10% by weight of KCl relative to the total dry weight of the powdery material, or between 1% and 5% by weight of Na2SO4 relative to the total dry weight of the powdery material.

[62] The powdery material may comprise: - between 10% and 15% by weight of NaCl relative to the total dry weight of the powdery material, - between 1% and 20% by weight of KCl relative to the total dry weight of the powdery material, preferably between 5% and 15%, and - between 30% and 45% by weight of CaCl(OH), more preferably between 35% and 40%, relative to the total dry weight of the powdery material.

[63] The sum of the weight contents of the salt or salts of the soluble fraction, relative to the total dry weight of the powdery material, cannot exceed 100%.

[64] The powdery material may comprise between 30% and 90% by weight of the soluble fraction relative to the total dry weight of the powdery material, preferably between 35% and 80%, more preferably between 40% and 70%, even more preferably between 50% and 70%.

[65] The content of soluble fraction in the powdery material may be determined using the following protocol: - carrying out a leaching test on the powdery material in accordance with standard NF EN 12 457-2 dated December 2002, to obtain an eluate, and - analyzing the eluate in accordance with standard NF T 90-029 dated August 2002, to determine the content of soluble fraction in the powdery material.

[66] The content of each soluble salt present in the soluble fraction of the powdery material may be determined by this protocol and by analysis of the eluate in accordance with standard NF EN ISO 11885 dated November 2009, which measures cations and Cl and S anions.

[67] The solid composite product may have a content of soluble fraction that is between 20% and 80% relative to the total dry weight of the composite product, preferably between 25% and 70%, and more preferably between 30% and 65%.

[68] A portion of the soluble fraction of the solid composite product is leachable. The solid composite product may thus have a content of leachable soluble fraction that is less than 10% by weight relative to the total dry weight of the solid composite product, in particular less than 7% by weight, and more particularly at least 0.5%.

[69] For the purposes of the invention, "leachable soluble fraction" refers to the portion of the soluble fraction present in an eluate obtained via a leaching test performed on the solid composite product in accordance with standard NF X 31-211:2012. The content of leachable soluble fraction within the solid composite product may be determined by analyzing the eluate in accordance with standard NF T 90-029 of August 2002.

[70] The median diameter in the particle size distribution (d50) of the powdery material employed in the method according to the invention may be less than or equal to 100 pm, preferably between 8 pm and 70 pm, and more preferably between 25 pm and 60 pm. The d50 value may be determined via liquid-phase laser diffraction analysis in distilled water using a Malvern Mastersizer 2000 laser particle size analyzer equipped with a 120 ml "small volume" cell; the signal is treated using the Mie mathematical model.

[71] Advantageously, a particle size distribution within the above ranges serves to increase the contact surface area between the powdery material and the thermoplastic polymer. This facilitates the homogeneous mixing of these two compounds and therefore the production of the composite product.

[72] Advantageously, the method according to the invention makes it possible to obtain the composite product without needing to add a third compound, such as a wax, an antileaching agent, a hydraulic binder, or a water-absorbing agent. The implementation of step a) of the method is therefore facilitated, as it may not require managing a ternary mixture.

[73] The composite product may comprise less than 1% by weight of wax relative to the total dry weight of the composite product, preferably less than 0.5% by weight of wax, and preferably is completely free of wax.

[74] The composite product may comprise less than 1% by weight of an anti-leaching additive relative to the total dry weight of the composite product, preferably less than 0.5% by weight of anti-leaching additive, and preferably is completely free of anti-leaching additive.

[75] The anti-leaching agent may be selected among calcium hydroxide, sodium hydroxide, magnesium hydroxide, sodium sulfide, and mixtures thereof.

[76] The composite product may comprise less than 1% by weight of a water-absorbing agent relative to the total dry weight of the composite product, preferably less than 0.5% by weight of water-absorbing agent, and preferably is completely free of water-absorbing agent.

[77] The water-absorbing agent may be selected among clay, Na-Ca borosilicates, expanded silicates, and mixtures thereof.

[78] The method according to the invention is advantageous in that it allows obtaining a composite product having a water content that is less than 7% by weight relative to the total weight of the composite product, preferably less than 3% by weight, without the addition of a water-absorbing agent.

[79] The composite product may comprise between 40% and 80% by weight of powdery material relative to the total dry weight of the composite product, preferably between 50% and 75%, and more preferably between 55% and 70%.

[80] This amount of powdery material is greater than or equal to the amount introduced in a conventional method which utilizes a hydraulic binder. Thus, within the same landfill cell volume, it is possible to store a larger mass of waste treated by encapsulation than is possible using the conventional method which utilizes a hydraulic binder.

[81] Without wishing to be bound by any theory, the inventors are of the opinion that, for the same volume, the mass proportion of powdery materials contained in the composite product obtained by the method according to the invention is greater than the mass proportion of powdery materials contained in the stabilized and solidified product obtained by the conventional method which utilizes a hydraulic binder.

[82] The composite product may comprise between 20% and 60% by weight of thermoplastic polymer relative to the total dry weight of the composite product, preferably between 25% and 50%, and more preferably between 30% and 45%.

[83] In the composite product, the sum of the content of powdery material and of thermoplastic polymer cannot exceed 100% by weight relative to the total dry weight of the composite product.

[84] The composite product may comprise between 20% and 80% by weight of a soluble fraction relative to the total dry weight of the composite product, preferably between 25% and 70%, more preferably between 30% and 65%.

[85] The thermoplastic polymer may be a polymer having working temperatures between 80°C and 300°C, particularly between 100°C and 275°C, and more particularly between 140°C and 250°C.

[86] The polymer may be selected among polyolefins, polyvinyls, polystyrenes, poly(meth)acrylics, polyamides, polycarbonates, linear polyesters, fluoropolymers, polyacetals, polysulfones, cellulose-based polymers, and mixtures thereof. Preferably, the polymer may be selected among polyolefins, poly(meth)acrylics, polyvinyls, polyamides, and linear polyesters.

[87] The fluoropolymers may be polyfluoroethylenes.

[88] An example of a polysulfone is polyphenylene sulfide.

[89] For example, the polymer may be polyethylene (including high-density polyethylene (HDPE) and low-density polyethylene (LDPE)), polypropylene, acrylic, polyvinyl acetate, polyvinyl chloride (PVC), polystyrene, nylon, polybutadiene, and mixtures thereof.

[90] Polyolefins are preferred as they are advantageously present in abundance in plastic waste.

[91] Some or all of the thermoplastic polymer, in particular all, may originate from plastic waste, preferably non-biodegradable plastic waste, non-recyclable plastic waste, or plastic waste that is both non-biodegradable and non-recyclable.

[92] For the purposes of the invention, "non-biodegradable plastic waste" refers to waste that does not spontaneously and naturally undergo degradation under the action of a natural environment, for example an environment comprising living organisms and / or air and / or water, or that undergoes such degradation too slowly. Non-biodegradable plastic waste is, in particular, unsuitable for inclusion in the formation of compost via composting.

[93] For the purposes of the invention, "non-recyclable plastic waste" refers to waste that does not meet the criteria enabling it to be treated within a traditional recycling stream. Such waste is generally landfilled or incinerated, which generates CO2 and consumes landfill space.

[94] The method is therefore advantageous in that it allows putting waste to good use without generating CO2, which would not be the case had the waste been incinerated. The utilization of such a thermoplastic polymer thus serves to further reduce the carbon footprint of the method according to the invention.

[95] For example, the thermoplastic polymer may originate, at least partially or entirely, from waste such as packaging, an object, or both. The waste may be clean or soiled.

[96] The packaging may take the form of a bag, a food tray, a yogurt pot, a cream jar, a gas can, a container, or mixtures thereof.

[97] The object may take the form of disposable tableware, a food container, a piece of furniture, a tarp, or mixtures thereof.

[98] In the composite product, the thermoplastic polymer may comprise one or more thermoplastic polymers.

[99] The thermoplastic polymer may be supplied as crushed particles having a particle size that is between 1 and 10 mm, preferably between 2 and 6 mm.

[100] Such a particle size advantageously facilitates good mixing between the powdery material and the thermoplastic polymer, and therefore better dispersion of the powdery material during step a).

[101] Bringing the powdery material and the thermoplastic polymer into contact with each other in step a) of the method may be carried out at a temperature between 80°C and 300°C, particularly between 100°C and 275°C, and more particularly between 140°C and 250°C.

[102] A temperature below 80°C does not ensure proper dispersion of the cleaning residue in the thermoplastic polymer. A temperature above 300°C could degrade the thermoplastic polymer and impair its elastic and plastic properties.

[103] The length of time that the cleaning residue and the thermoplastic polymer are placed in contact with each other in step a) of the method depends on the cleaning residue and thermoplastic polymer used; however, a person skilled in the art will know how to adapt this. For example, the time may be between 3 minutes and 20 minutes, preferably between 5 minutes and 10 minutes.

[104] A shorter length of time would not enable the powdery material and the thermoplastic polymer to become homogeneous: the resulting mixture could have heterogeneous areas. A longer time would involve significant energy expenditure and a decreased costeffectiveness of the method.

[105] Step a) may be carried out in a kneader.

[106] The use of a kneader is advantageous because it is a device that operates semi-continuously and allows maintaining a constant temperature and viscosity during mixing. Furthermore, hot mixing in a kneader produces a paste that can then easily be shaped, for example by extrusion. The kneader serves primarily to mix and homogenize various materials. Preferably, the kneading is performed using a Z-blade kneader.

[107] The powdery material, the thermoplastic polymer, or mixtures thereof may be preheated to a temperature greater than or equal to the softening point of the polymer. In particular, the powdery material and the thermoplastic polymer may be preheated separately to a temperature greater than or equal to the softening point of the polymer, prior to mixing them together.

[108] The powdery material may be preheated, prior to contact step a), to a temperature higher than ambient temperature and less than or equal to the temperature at which step a) is carried out. For example, the powdery material may be preheated to a temperature between 50°C and 300°C, particularly between 60°C and 250°C, and more particularly between 80°C and 200°C.

[109] The thermoplastic polymer may be preheated, prior to contact step a), to a temperature higher than ambient temperature and less than or equal to the temperature at which step a) is carried out. For example, the thermoplastic polymer may be preheated to a temperature between 20°C and 100°C, particularly between 30°C and 90°C, and more particularly between 40°C and 80°C.

[110] Advantageously, this preheating step, applied to the powdery material, the thermoplastic polymer, or both, facilitates good mixing of the powdery material and thermoplastic polymer by preventing the formation of a "cold spot" at the point of contact between the powdery material and the thermoplastic polymer during step a).

[111] Furthermore, these preheating steps serve to reduce the time required during contact step a), as at least one of the components of the mixture is already at the treatment temperature required for step a).

[112] The shaping step b) may be selected among extrusion, injection molding, molding, thermoforming, rotational molding, compression, calendering, metal fabrication, pultrusion, and combinations thereof; preferably, it is selected among extrusion, molding, calendering, and combinations thereof.

[113] The term "extrusion" refers to preparing a polymer in a desired shape, starting with a material in granular or powder form and using an extruder.

[114] The primary function of the extruder is to pass a mixture through a die located at its end, by the application of temperature and pressure. Typically, an extruder consists of: one or more heated barrels featuring different temperature zones; one or two Archimedes screws that serve to transport the material along the barrel; a hopper that feeds the material to be extruded, at various points; and a die of varying complexity located at the end of the barrel and which imparts the desired shape and size to the continuously emerging material. Preferably, the extrusion step is carried out using a twin-screw extruder.

[115] Performing step b) by extrusion is particularly well-suited for a step a) implemented using a kneader. Indeed, this allows steps a) and b) to be performed using a single device known to the skilled person as a kneader-extruder.

[116] Molding may be carried out using an extruder screw, for example a worm screw, to inject the mixture into a closed mold.

[117] The resulting composite product may have a cylindrical structure with a diameter of less than 100 mm, and preferably 40 mm.

[118] In another aspect, a method is also proposed for purifying flue gases resulting from waste incineration, which makes use of the treatment method as defined above and further comprises the following step: - bringing the incineration flue gases into contact with a flue gas treatment material to form an air pollution control residue, the air pollution control residue then being utilized in step a) of the treatment method.

[119] The flue gas treatment material may be sodium bicarbonate, lime, or mixtures thereof.

[120] The step of bringing the incineration flue gases into contact with the flue gas treatment material is a step well known to the person skilled in the art, who will know how to implement it.

[121] Preferably, the incineration flue gases are gases resulting from the incineration of household waste or industrial waste.

[122] According to another aspect, a solid composite product is proposed comprising particles of a powdery material dispersed within a thermoplastic polymer, the solid composite product comprising a leachable soluble fraction.

[123] The powdery material, the thermoplastic polymer, and the leachable soluble fraction are as defined above in connection with the treatment method of the invention.

[124] For example, the content of the leachable soluble fraction in the solid composite product may be less than 10% by weight relative to the total dry weight of the solid composite product, in particular less than 7% by weight, more particularly at least 2%.

[125] Thus, in accordance with current regulations, the solid composite product is waste, or even waste classified as hazardous waste, that can be stored in a landfill cell, as it complies with the storage facility acceptance limits imposed by the amended French Ministerial Decree of December 30, 2002, relating to the storage of hazardous waste.

[126] The powdery material and the thermoplastic polymer are as described above in relation to the treatment method of the invention.

[127] The solid composite product is obtainable by means of the treatment method of the invention as described above.

[128] The solid composite product may have a density between 1.5 and 2, preferably between 1.6 and 1.8.

[129] The solid composite product may comprise between 20% and 60% by weight of thermoplastic polymer relative to the total dry weight of the solid composite product, preferably between 25% and 50%, more preferably between 30% and 45%.

[130] The solid composite product may comprise between 40% and 80% by weight of powdery material relative to the total dry weight of the solid composite product, preferably between 50% and 75%, more preferably between 55% and 70%.

[131] Advantageously, this allows better integration of the powdery material into the solid 5 composite product, whereas, until now, prior art methods based on hydraulic binders did not allow including, in a stabilized and solidified product, more than 30% of powdery material having a high soluble fraction.

[132] According to another aspect, a solid composite product is provided comprising particles of a powdery material dispersed in a thermoplastic polymer, the powdery material 10 comprising a soluble fraction, the solid composite product having a content of soluble fraction that is between 20% and 80% relative to the total dry weight of the composite product, preferably between 25% and 70%, more preferably between 30% and 65%. 15 Examples

[133] Example 1 - Obtaining solid composite products

[134] Starting materials

[135] Two different air pollution control residues are used in this example.

[136] The first, designated REF BICAR, results from a sodium bicarbonate treatment of flue gases generated by the incineration of hazardous waste, and has a d50 value of 32 pm.

[137] The second, designated REF CALCIQ, results from a lime treatment of flue gases generated by the incineration of hazardous waste, and has a d50 value of 56 pm.

[138] Each of the two residues - REF BICAR and REF CALCIQ - is subjected to a leaching test in accordance with standard NF EN 12 457-2, dated December 2002, to obtain an eluate.

[139] Each eluate is analyzed in accordance with standards NF T 90-029 of August 2002, NF EN ISO 11885 of November 2009, NF ISO 10359-1 of December 1992, and NF EN 1484 of July 1997, to determine, respectively: -the content of soluble fraction in the residue, -the content of metals present in the eluate, -the content of fluoride ions present in the eluate, and -the Total Organic Carbon (TOC) value of the eluate.

[140] Table 2 shows the results of these analyses.

[141] [Table 2] Soluble fraction content Metals exceeding regulatory thresholds (content) Fluoride ion content Total organic carbon REF BICAR residue 79 % Molybdenum (248 mg / kg) Chromium (161 mg / kg) 2040 mg / kg 1620 mg / kg REF CALCIQ residue 35 % Lead (141 mg / kg) < LoQ <LoQ LoQ: Limit of quantitation

[142] Three thermoplastic polymers are utilized in this example.

[143] The first, designated THERMO SOFT, is a mixture of soft thermoplastic polymers derived, for example, from flexible tarps and rolls of pallet wrap film.

[144] The second, designated THERMO HARD, is a mixture of hard thermoplastic polymers derived, for example, from containers.

[145] The third, designated THERMO HDPE, is obtained from high-density polyethylene waste.

[146] Operating Procedure

[147] Various solid composite products, presented in Table 3 below, are obtained using the following operating procedure: The thermoplastic polymer is ground to a particle size of approximately 4 mm. The ground thermoplastic polymer is then introduced into a kneader. Inside the kneader, it is subjected to a temperature ranging from 220°C to 250°C, which causes it to soften. In the kneader, the cleaning residue is added to the softened thermoplastic polymer. The solid composite product is obtained at the outlet of the kneader which is equipped with an extrusion screw.

[148] FIG. 2 is a photograph of the solid composite product 3.

[149] Example 2: Characterization of solid composite products

[150] Each of the various solid composite products obtained is subjected to a leaching test in accordance with standard NF X 31 211:2012, to obtain an eluate.

[151] Each eluate is analyzed in accordance with standards NF T 90-029 of August 2002, NF EN ISO 11885 of November 2009, NF ISO 10359-1 of December 1992, and NF EN 1484 of July 1997, to determine, respectively: - the content of leachable soluble fraction in the solid composite product, - the content of metals present in the eluate, - the content of fluoride ions present in the eluate, and - the Total Organic Carbon (TOC) value of the eluate.

[152] Table 3 presents the results of these analyses.

[153] As demonstrated in Table 3, all of the solid composite products exhibit, in compliance with regulations: - a content of leachable soluble fraction of less than 10%, - no metal content exceeding the regulations, - a fluoride ion content of less than 500 mg / kg, and - a Total Organic Carbon (TOC) value of less than 1000 mg / kg.

[154] In accordance with current regulations, these solid composite products can therefore be placed in storage.

[155] [Table 3] Solid composite product Cleaning residue Thermoplastic polymer Mass of solid composite product obtained Cleaning residue incorporation rate Leachable soluble fraction content Metals at concentrations exceeding regulatory thresholds Fluoride ion content Total Organic Carbon 1 REF BICAR THERMO SOFT 2735 g 50% 1% None 28 mg / kg 100 mg / kg 2 REF BICAR THERMO SOFT 2163 g 60% 1.8 % None 39 mg / kg 70 mg / kg 3 REF BICAR THERMO HARD 3290 g 64 % 3.9 % None 84 mg / kg 170 mg / kg 4 REF BICAR THERMO SOFT 2585 g 70 % 5.7 % None 125 mg / kg 150 mg / kg 5 REF BICAR THERMO SOFT 3004 g 72 % 5.8 % None 107 mg / kg 100 mg / kg 6 REF BICAR THERMO HDPE 4700 g 75% 8.6 % None 180 mg / kg 150 mg / kg 7 REF CALC IQ THERMO HDPE 4474 g 80% 1.2 % None <LoQ 20 mg / kg LoQ: Limit of quantitation -20-

Claims

1. A method for treating a powdery material with a thermoplastic polymer in order to obtain a solid composite product, the powdery material comprising at least 30% by weight of a soluble fraction relative to the total dry weight of the powdery material, the method comprising the following steps:a) bringing the powdery material and the thermoplastic polymer into contact at a temperature greater than or equal to the softening point of the thermoplastic polymer, in order to obtain a mixture;b) shaping the mixture; andc) solidifying the mixture to obtain the solid composite product.

2. Method according to claim 1, wherein the soluble fraction comprises a salt selected among sodium chloride (NaCl), potassium chloride (KCl), sodium sulfate (Na2SO4), potassium sulfate (K3Na(SO4)2), calcium hydroxychloride (CaCl(OH)), and mixtures thereof.

3. Method according to one of claims 1 or 2, wherein the powdery material comprises at least 40% by weight of sodium chloride relative to the total dry weight of the powdery material.

4. Method according to one of claims 1 to 3, wherein the powdery material is air pollution control residue.

5. Method according to one of claims 1 to 4, wherein the thermoplastic polymer is selected among polyolefins, polyvinyls, polystyrenes, poly(meth)acrylics, polyamides, polycarbonates, linear polyesters, fluoropolymers, polyacetals, polysulfones, cellulose-based polymers, and mixtures thereof.

6. Method according to one of claims 1 to 5, wherein the shaping b) is selected among extrusion, injection molding, molding, thermoforming, rotational molding, compression, calendering, metal fabrication, pultrusion, and combinations thereof.

7. A method for purifying flue gases resulting from waste incineration, making use of the treatment method as defined in any one of claims 1 to 6 and further comprising the following step:- bringing the incineration flue gases into contact with a flue gas treatment material to form an air pollution control residue, the air pollution control residue subsequently being utilized in step a) of the treatment method.

8. Method according to claim 7, wherein the flue gas treatment material is sodium bicarbonate, lime, or mixtures thereof.

9. A solid composite product comprising particles of a powdery material dispersed within a thermoplastic polymer, the solid composite product comprising a leachable soluble fraction.

10. Solid composite product according to claim 9, wherein the content of 5 leachable soluble fraction in the solid composite product is less than 10% by weight relative to the total dry weight of the solid composite product.

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