Method for recovering materials from waste or scrap via improved carbothermal reduction process

Abstract

The method according to the invention comprises: - mixing the reactants of a carbothermal reduction reaction to form a mixture to be subjected to a thermal treatment, the reactants comprising a component (MO) containing the element (M) to be recovered and a carbon-containing component (C), the component (MO) being contained in a waste material; - placing the mixture in a crucible and placing the crucible in a heat-resistant chamber (2) having a side wall (23), the surface of which is coated with a layer (5) of microwave-sensitive material; - placing the heat-resistant chamber (2) in a microwave oven operated at power W for a time T. The innovations of the method include achieving the carbothermal reduction reaction in a shorter time than those presented in the literature (15 minutes versus 60 minutes as tested using a rotary pilot oven) and lower power consumption.

Description

[Technical field]

[0001] The present invention relates to a method for recovering materials from waste or scrap via an improved carbothermal process.

[0002] Carbothermal reduction reactions involve the reduction (change of oxidation state) of elements (often metals) using carbon-containing materials (e.g., coal, coke, charcoal, vegetable charcoal, etc.) as reducing agents, and these processes are applied to obtain elementary forms of many compounds.

[0003] Carbothermal reduction reactions are generally carried out at very high temperatures, up to several hundred degrees Celsius, and require high energy consumption. At the industrial level, non-renewable energy sources are generally used to carry out these reactions.

[0004] The object of the present invention is to provide a method for recovering important materials (e.g. some oxides) and / or elements (Al, Fe, Cu, Co, Ni, Zn, Pb, etc.) from any kind of production waste or scrap, including phosphorus in the ash of, for example, biomass. Furthermore, the object of the present invention is to recover the components effectively without resorting to high energy usage.

[0005] This object is achieved by a method for recovering elements from waste materials via an improved microwave carbothermal process using inserts that increase thermal efficiency. This object is achieved by a method according to claim 1 and a heat-resistant chamber according to claim 9. The dependent claims disclose further advantageous embodiments of the invention. [Brief description of the drawings]

[0006] The features and advantages of the method according to the invention will become apparent from the following detailed description, given by way of non-limiting example in accordance with the figures of the attached drawings, in which: [Figure 1A] FIG. 1A shows an axonometric view of a heat-resistant chamber according to the present invention. [Figure 1B] FIG. 1B shows a cross-sectional view of a heat-resistant chamber according to the present invention. [Diagram 2] FIG. 2 refers to embodiment A and shows the XRD spectrum (X-ray diffractometry or X-ray diffraction) of sample PP8, showing the KPO3 peaks after microwave treatment with the insert. [Diagram 3] FIG. 3 refers to Example Embodiment B and shows the diffraction spectra of Sample A by itself (TQ; top) and after treatment (PT; bottom). [Figure 4] FIG. 4, referring to Example Embodiment B, shows the diffraction spectra of Sample C by itself (TQ; top) and after treatment (PT; bottom). [Diagram 5] FIG. 5, referring to Example Embodiment B, shows the diffraction spectra of Sample E by itself (TQ; top) and after treatment (PT; bottom). [Figure 6A] FIG. 6A, referring to Example Embodiment C, shows the diffraction spectra of Sample F after 5 minutes treatment with a heat-resistant chamber (PT; top) and after 5 minutes treatment without a heat-resistant chamber (PT; SR; bottom). [Figure 6B] FIG. 6B, referring to Example Embodiment C, shows the diffraction spectra of Sample F after 10 minutes treatment with a heat-resistant chamber (PT; top) and after 10 minutes treatment without a heat-resistant chamber (PT; SR; bottom). [Figure 6C] FIG. 6C, referring to Example Embodiment C, shows the diffraction spectra of Sample F after 15 minutes treatment with a heat-resistant chamber (PT; top) and after 15 minutes treatment without a heat-resistant chamber (PT; SR; bottom). [Figure 7] FIG. 7 shows a crucible containing material to be subjected to a carbothermal reduction treatment placed in the refractory chamber of FIG. 1b, which is then placed in a microwave oven. [Figure 8]FIG. 8 shows a controlled atmosphere bell (or hollow vessel, bell) in the heat-resistant chamber of FIG. 1b, in which the crucible is placed.

[0007] Carbothermal reduction reactions involve the reduction of compounds, often oxides, using carbon as a reducing agent. The method according to the invention uses microwaves to induce heating in a carbothermal reduction reaction, using for example carbon (generally in the form of graphite or anthracite) as the reducing agent. Furthermore, the method according to the invention provides for the use of at least one special insert, in particular a heat-resistant chamber, which allows optimizing the heating of the material obtained by the use of microwaves.

[0008] The object of the present invention is therefore a method for recovering element M (or its oxides resulting from the carbothermal reduction reaction) from waste materials via an improved microwave carbothermal reduction process using at least one insert that increases the thermal efficiency.

[0009] A typical carbothermal reduction reaction can be written (simplified) as follows: MO + C → M + CO MO: starting material (e.g. contained in various types of matrix or scrap), M is the element to be recovered M: The element to be recovered, referred to as the reduced element M C: Carbon O: oxygen

[0010] For example, to recover iron (M=Fe), the reaction is: Fe2O3+ 3CO → 2Fe + 3CO2

[0011] For example, to recover silicon (M=Si), the reaction is: 3SiO2+ 9C → 3SiC + 6CO

[0012] The method of the present invention also provides for the recovery of elements contained in a phase (e.g., an oxide) from an oxidation state to a lower oxidation state. For example: 4LiNiO2(s)+ C(s) → 2Li2O(s) + 4NiO(s) + CO2(g).

[0013] In this case, lithium oxide and nickel oxide are recovered.

[0014] The starting waste material (containing MO and therefore the element M to be reduced) may be a powder, ash (e.g. resulting from incineration, waste-to-energy processes, pyrolysis processes, etc.), slag (obtained as an industrial by-product), sludge, or any material containing oxidized elements that can be converted to a reduced form.

[0015] The starting waste material may already have been chemically or thermally pretreated. In the case of sludge, it may be, for example, dewatered sludge or sludge stabilized with additives.

[0016] The starting waste material MO may be in a matrix phase, such as metal oxides in sand.

[0017] If necessary, other substances or additives Y may be added to facilitate certain reactions.

[0018] As an example, consider the following phosphorus recovery reaction (M=P), where silicon oxide (Y=SiO2) was added as an additive to accelerate the reaction: 2Ca3(PO4)2+ 10C + 3SiO2-> 3Ca2SiO4+ 10CO + 2P2

[0019] For example, in the phosphorus recovery reaction shown above, the starting waste material [Ca3(PO4)2] is derived from biomass ash, and the additive to promote the reaction (3SiO2) is a by-product (silica fume) of the iron and silicon alloy industry.

[0020] Below is a further example of phosphorus recovery shown above in Figures 6B and 6C, where calcium phosphate (Ca3(PO4)2, e.g. amorphous or whitlockite form) is converted to sodium phosphate (Na3PO4) or calcium phosphate (CaNaPO4) by microwave carbothermal reduction according to the present invention. According to this example, the following is mixed by weight: 60% sludge ash, 25% sodium bicarbonate (NaHCO3) and 15% graphite. The microwave oven treatment was set at MW power of 1000W for 15 minutes. As can be seen in Figures 6B and 6C, a bioavailable CaNaPO4 (buchwaldite) phase was produced from the carbothermal reduction. It should be noted that any other carbon-rich reduced material, such as dewatered sludge, can be used instead of graphite. Instead of sodium bicarbonate, other salts can be used, for example chlorides or carbonates, or bromides or iodides of sodium or potassium. It is also possible to add silica fume. The reaction can be represented as follows: Ca3(PO4)2+ 6NaHCO3→ 2Na3PO4+ 3Ca(OH)2+ 6CO2

[0021] Advantageously, the method according to the invention requires that at least some of the reactants, preferably all of the reactants, originate from and / or are contained in waste or by-products.

[0022] The method that is the object of the present invention is a method for recovering materials from waste or scrap via a microwave carbothermal reduction process improved by the use of a heat-resistant chamber. The method comprises: mixing the reactants of the carbothermal reduction reaction, i.e. the component MO containing the element (M) to be recovered, the carbon-containing component C and any additives Y, forming a mixture 80 to be subjected to a thermal treatment, the component (MO) and preferably also the components C and / or Y being waste materials; - placing the mixture 80 in a crucible 90, preferably having a cover, the crucible preferably being made of a microwave sensitive material, i.e. a material capable of absorbing electromagnetic energy and converting it into heat, such as carbon, graphite, or silicon carbide; placing the crucible 90 in a heat-resistant chamber 2 having a side wall 23 surrounding an inner chamber 4 in which the crucible is placed, the side wall 23 being made of a heat-resistant material and having a surface facing the inner chamber 4, the surface of the side wall 23 being covered by a layer 5 made of a microwave-sensitive material; - placing the heat-resistant chamber in a microwave oven 80 operated at a given power W for a given time T; Includes.

[0023] Preferably, the crucible in which the mixture to be subjected to the heat treatment is placed is cylindrical and has a cover, and is preferably made of graphite.

[0024] Preferably, a heat-resistant chamber 2 is shown in FIG. 9 which houses a crucible containing the mixture to be subjected to heat treatment.

[0025] The heat-resistant chamber 2, which is preferably cylindrical but may be of another shape and size, comprises a sidewall 23 that surrounds an inner chamber 4 in which the crucible is disposed.

[0026] Preferably, the heat-resistant chamber 2 comprises an upper wall 24, either integral with or separate from the side wall 23, which closes the inner chamber 4 at the top. If an upper wall 24 is present, the upper wall 24 comprises a vent channel 7, which connects the inner chamber 4 with the external environment. The vent channel 7 terminates in an upper opening 6.

[0027] Preferably, the refractory chamber 2 comprises a bottom wall 22, integral with or separate from the side walls 23, which closes the inner chamber 4 at the bottom. If the bottom wall 22 is present, the crucible is supported on the bottom wall 23.

[0028] The heat-resistant chamber 2, and in particular at least the side walls 23, are made of a heat-resistant material (e.g., ceramic) to retain heat inside the inner chamber 4. Preferably, the top wall and / or the bottom wall 22 of the heat-resistant chamber 24 are also made of a heat-resistant material (e.g., ceramic).

[0029] The surface of the side wall 23 facing the inner chamber 4 is covered by a layer 5 of microwave sensitive material, i.e. such material is capable of absorbing electromagnetic energy and converting it into heat. The layer 5 is made, for example, of graphite, carbon or silicon carbide.

[0030] The heat-resistant chamber 2 is formed of a heat-resistant material (e.g., ceramic) and at least the sides of the inner chamber are coated with a layer of graphite 5. By using a circular wall formed of a heat-resistant material coated with graphite, microwave radiation is reflected towards the centre of the inner chamber 4. Thus, since the heat-resistant chamber 2 is essentially centrally located within the microwave oven, the concentration of microwave radiation is much higher inside the inner chamber 4 than in the outer regions of the heat-resistant chamber 2.

[0031] Advantageously, the heat-resistant chamber 2 according to the invention is lined internally with a layer 5 of a sensitive material that can enhance the effectiveness of microwaves. Comparative tests were carried out with a heat-resistant chamber without an internal lining of a sensitive material, the results of which are summarized in the table below. [Table 1]

[0032] As can be seen from the higher percentage of weight loss measured, the method carried out in a heat resistant chamber according to the invention is much more effective, up to three times, compared to tests carried out in a heat resistant chamber without an internal lining of sensitive material.

[0033] Furthermore, processes carried out in a heat-resistant chamber according to the present invention require much shorter heating times than conventional heating methods.

[0034] In one embodiment, a bell 70 is disposed within the heat-resistant chamber 2, where the bell defines a controlled atmosphere compartment 71 within which is placed a crucible 90 containing the mixture to be subjected to a carbothermal reduction process. The bell 70 is formed of a material transparent to microwaves and has an inlet channel 72 and an outlet channel 73 for gas. For example, the bell 70 is formed of ceramic or glass.

[0035] The method that is the object of the present invention is applied, for example but not limited to: the recovery of phosphorus (P) in biomass ash (Examples A and B); the recovery of important elements such as metals in batteries (Li, Co, Mn, Cu, Zn, etc., Example C); the recovery of other elements (Al, Fe, Cu, Co, Ni, Zn, Pb, etc.) from any kind of industrial waste or scrap; the production of graphene from waste containing silica.

[0036] Furthermore, the method of the present invention can be applied to the production of hydrogen from methane and alkali metal hydroxides, preferably obtained as industrial by-products, the hydroxides reacting with carbon monoxide to form carbonates. In this case, the reaction is, for example: 2NaOH + CH4 → Na2CO3 + 2H2

[0037] The method object of the present invention may be followed by a recovery step (in this case, for example selective) of the material of interest by wet processing (for example using solutions of different pH values).

[0038] The table below shows the carbothermal reduction conditions in a muffle (standard process used as a reference in the prior art) and in a microwave oven with the addition of at least one insert according to the invention. The conditions were chosen so that, through the present invention, i.e. with a microwave oven and an insert, the same temperatures, i.e. the same results by carbothermal reduction, are obtained and achievable in a standard system using a muffle.

[0039] [Table 2]

[0040] Example A: Recovery of KPO3 from chicken manure ash by microwave carbothermal reduction using an insert (to recover P=phosphorus)

[0041] The goal of this series of experiments is to recover KPO3 as a phosphorus-based compound to support the agricultural fertilizer industry. Taking the stoichiometric equation of the carbothermal reduction process as a reference, 12 different experiments with various compositions were designed: TIFF2025505110000004.tif34139

[0042] A compound MO containing orthophosphate is mixed with a silica-based material Y and carbon as an oxidizer.

[0043] Two different types of phosphorus-containing waste materials were used in compound MO: chicken manure ash, specifically economizer fly ash, and sewage sludge ash.

[0044] For material Y, silica, two different sources were used: silica fume, an industrial by-product of processing Fe-Si alloys, and colloidal silica as a gel.

[0045] Finally, three different materials were selected as the carbon component (activated carbon, anthracite and graphite), which differ in their morphological characteristics and fixed carbon content in the solid matrix. [Table 3]

[0046] The sample components are mixed and prior to heat treatment, the sample is compressed in a hydraulic press to form a compact disc.

[0047] The sample is subjected to microwave heat treatment: the sample is placed in a graphite crucible according to the invention, the closing cap of the crucible is placed on it and the latter (graphite crucible) is placed in a heat-resistant chamber 2 according to the invention for microwave thermochemical treatment.

[0048] Microwave experiments were carried out using an oven (230V, 50Hz) with a fixed power setting of 1000W.

[0049] Figure 1 shows the XRD spectrum of sample PP8 as an example, where the KPO3 peak can be seen after microwave treatment, indicating that a high temperature was reached.

[0050] Example embodiment B: Recovery of phosphorus (P) from sewage sludge ash by microwave carbothermal reduction using inserts

[0051] The ash samples (component MO of the reaction) come from incineration plants located in Italy (A, B, F, G), Germany (C), Switzerland (D) and Portugal (E). Except for sample E which contains poultry waste (or litter), all the others contain sewage sludge as their original source.

[0052] Other components of the reaction include sodium bicarbonate (NaHCO3) as an additive Y for ash stabilization and anthracite (80% fixed carbon) as a reducing agent (C) with a high calorific value due to the temperature increase during the process.

[0053] The sample percentages are shown in Table 3 below. [Table 4]

[0054] The composition is mixed and milled to a uniform particle size.

[0055] The powder sample after grinding is placed in a graphite crucible according to the invention, a crucible closure cap is placed thereon and the latter (graphite crucible) is placed inside a heat-resistant chamber 2 according to the invention for a microwave carbothermal reduction treatment of sample stabilization and conversion of phosphorus to compounds bioavailable for plants.

[0056] Microwave experiments were carried out using an oven (230V, 50Hz) with a fixed power setting of 1000W.

[0057] When the thermal treatment is carried out, the diffraction spectrum undergoes a significant phase change: for example in the case of samples A (Figure 3), B and C (Figure 4), the phosphate is present in the form of NaCaPO4 compound, a water-soluble phase, whose uptake by plants is proven in the literature. The technological innovation of the present process is that it allows to obtain the compound in a shorter time than indicated in the literature (15 min vs. 60 min in tests using a rotary pilot oven) and with a smaller power consumption for the same amount of test material.

[0058] In the case of samples D and E (Figure 5), this phase forms in a mixed complex with silicate (Na2Ca4(PO4)2SiO4) and in the particular case of E, some of the Na+ cations combine directly with phosphate to obtain Na3PO4, another water-soluble phase and a compound known commercially in detergent applications.

[0059] Another common phase obtained in cases A, B, C and D is sodium aluminum silicate (NaAlSiO4), a low flux form of a specific subfamily of nepheline crystals (formed at 900°C and identified as "low carnegieite"), which is responsible for the compaction of the powder.

[0060] In case E, the silicate produced contains Ca instead of Al, which results in a compound of the NaCaSiO4 series.

[0061] Finally, another phase indicated is iron phosphate (FeP), an important indication that the temperature reached in the last 5 minutes of the experiment was higher than 1200°C, the minimum temperature required for the reduction of orthophosphate and the minimum temperature at which this phase forms in the presence of Fe.

[0062] Further experiments were carried out to demonstrate that the use of an insert (ie, a heat-resistant chamber) was necessary to be able to reach temperatures in excess of 1000° C. in a short period of time.

[0063] In tests without the refractory cylinder, all samples showed only a 5% weight loss, mostly related to the conversion of sodium bicarbonate to sodium carbonate around 200°C and the formation of low melting tectosilicates (as lisetite CaNa2Al4SiO16). Regarding the remaining phases, all samples had phases that were not pretreated (e.g. whitlockite and quartz), indicating that treatment without the refractory cell was not effective to reach the temperatures reached by the laboratory muffle oven or the pilot rotary oven.

[0064] If inserts are used instead:

[0065] - After 5 minutes, both sample F (Figure 6A) and sample G only show a change of sodium bicarbonate to sodium carbonate, except for sample F, which has Fe compounds in the form of magnetite (Fe3O4) instead of hematite. The weight loss is 15%.

[0066] After -10 min (Figure 6B), a weight loss of about 28% is recorded, along with the formation of NaCaPO4, NaAlSiO4 in both samples, and also Na3PO4 in sample G. These three phases indicate that the phosphates are water soluble and can be utilized by plants for fertilizer applications. This also indicates that the temperature reached in the chamber ranges between 800 and 900 °C.

[0067] After -15 min (Figure 6C), there is a weight loss equivalent to 35% and the formation of iron phosphate (Fe2P), indicating that the temperature exceeded 1100 °C.

[0068] Therefore, considering the economics and environmental impact of a unique and alternatively innovative process compared to those found in the prior art, it is apparent that the refractory material insert provides thermal (1200°C) and time conditions (10 minutes) to stabilize and process the ash samples for secondary use.

[0069] Example embodiment C: Extraction of metals from LIB batteries (lithium ion batteries)

[0070] The "black mass" (BM) samples were obtained from the dismantling, crushing and shredding of lithium (Li) batteries (precisely low-grade cobalt (Co) NMC category), which are collected during the recycling of batteries (NMC, Ni-MH and alkaline types). After mechanical "pretreatment", parts of the material belonging to the battery anode (graphite) are mixed with the material of the cathode (based on metal oxides), so it is defined as "black mass", and its dark color is due to the presence of graphite. In order to remove the material, which also contains aluminum (Al) and copper (Cu) residues, a first oven drying was performed at 105 °C for 1 h, which removed the moisture from the material and thus made it more efficient for the subsequent sieving. The sieving was performed on ASTM Giuliani sieves with a particle size of 17 mesh (1 mm) and then 35 mesh (0.5 mm). The fine material passing both sieves was selected to carry out the experiments.

[0071] The method according to the invention (an improved carbothermal reduction process using a heat-resistant chamber) was combined with an organic acid (L-malic acid) leaching process to extract metals (nickel, (Ni), manganese (Mn) and (Co)) from "black mass".

[0072] For the carbothermal reduction recovery method, the battery cathode material can be represented by the general formula LiNixCoyMnzO2. These metals need to be reduced from their valence state to a lower valence state, which increases their solubility in acidic or aqueous solutions, and therefore allows for more efficient extraction of the metals via the subsequent leaching process.

[0073] In the case of cathode materials available as "black mass", carbon is already present in the material being processed (typically in the form of graphite), and therefore does not necessarily need to be added to achieve the carbothermal reduction reaction.

[0074] For metal recovery, the reaction may be, for example: 4LiNiO2(s)+C(s)→2Li2O(s)+4NiO(s)+CO2(g) 4LiCoO2(s)+3C(s)→2Li2O(s)+4Co(s)+3CO2(g) 6LiCoO2(s)+5C(s)→3Li2O3(s)+6Co(s)+CO2(g) +CO(g) 2LiMn2O4(s)+2C(s)→Li2CO3(s)+4MnO(s)+CO(g)

[0075] Thus, in some cases, the metal is obtained, and in other cases, the oxide is obtained in which the metal is in a lower oxidation state and therefore more soluble and more easily recoverable than before.

[0076] Carbon molecules (eg, in the form of graphite) act as active absorbers of microwaves, and the resulting thermal effect can provide the heat required for the reduction reaction.

[0077] The first step of the carbothermal reduction process using microwaves and a heat-resistant chamber allows the separation of plastic residues present as components in the battery from the solid matrix formed by metal oxides and graphite. Microwave heating can also increase the surface area of ​​the material, making it more efficient for leaching (or release) into the leachate.

[0078] For the first step of the carbothermal reduction process, the sieved sample is placed in a graphite crucible, a cover is placed on the crucible and the crucible is placed in a heat-resistant chamber 2 which is then placed in a microwave oven. The weight is recorded using an electronic balance before and after the process (after the crucible has cooled down).

[0079] The microwave oven experiments were carried out at power settings of 1000W, 600W, and 440W.

[0080] Taking into account the energy consumption, the times were set to optimize the weight loss (changing the power to achieve the same % weight loss) as follows: thus, 4 min at 1000W, 8 min at 600W and 12 min at 440W. [Table 5]

[0081] From Table 4, it is clear that without the use of Heat Resistant Chamber 2, it is difficult to change the weight of the material by varying both power and time. This means that without the use of Heat Resistant Chamber 2, the material does not reach a temperature that would volatilize at least one component of the polymer residue. The weight loss is on average 1% and is related to the humidity accumulated by the material on the surface of the particles. When Heat Resistant Chamber 2 is used instead, a significant change in weight is evident as the time is changed at the same power. [Table 6]

[0082] The next leaching step uses L-malic acid because it is a cost-effective reactant to produce, has no emissions unlike inorganic acids, and less is consumed to leach the same material. Therefore, overall this reactant is more sustainable. Therefore, the reactant for the leaching trials is L-malic acid (99%) with hydrogen peroxide (30% w / w) used as a reducing agent, making the release of the metals into the acidic solution more efficient. [Table 7]

[0083] The analysis of acid leaching after heat treatment shows that in the case of treatment with the heat-resistant chamber 2, the extraction rate (dissolution of metals) is more than 90% for Co, Fe and Mn respectively, whereas Ni is approximately 70%. Instead, in the case of the sample heat-treated without the use of the heat-resistant chamber (P1), the experiment shows that the elemental concentration values ​​of all metals are at least halved. This result shows that the use of the heat-resistant chamber 2 leads to a more efficient dissolution of the metals into the acid solution, making the process more efficient, with the added advantage of an effective removal of plastic residues in terms of more sustainable time and energy consumption compared to conventional methods of pyrolysis of materials.

[0084] Innovatively, the heating properties of microwaves are particularly suitable for the thermal treatment of dielectric materials capable of absorbing microwaves (such as carbon), and also for a uniform thermal treatment. The process carried out with this technology turns out to be more efficient, faster and more sustainable than standard processes operated in ovens using non-renewable energy sources (such as coal) or other electric ovens that do not use microwaves. With the proposed technology, temperatures of over 1000°C can be reached even in a few minutes, allowing the (carbothermal) reduction reaction to be carried out in an efficient and rapid manner. Advantageously, moreover, the use of a graphite crucible placed in a heat-resistant chamber 2 with a graphite coating inside makes it possible to reach higher temperatures (over 500°C) than can be obtained with a simple microwave oven.

[0085] The innovations of the present method include achieving the carbothermal reduction reaction in a shorter time than those presented in the literature (15 min versus 60 min as tested using a rotary pilot oven) and lower power consumption.

[0086] It is obvious that a person skilled in the art can modify the above method to meet additional requirements, all of which fall within the scope of protection defined in the following claims.

Claims

1. 1. A method for recovering materials from waste or scrap via an improved carbothermal reduction process, comprising: - mixing the reactants of the carbothermal reduction reaction to form a mixture to be subjected to a thermal treatment, the reactants comprising a component (MO) containing the element (M) to be recovered and a carbon-containing component (C); - placing the mixture in a crucible; - placing the crucible in a heat-resistant chamber (2) comprising a side wall (23) surrounding an inner chamber (4) in which the crucible is placed; - placing the heat-resistant chamber (2) in a microwave oven operated at power W for a time T; and The component (MO) is contained in the waste material, The sidewall (23) is made of a heat-resistant material and has a surface facing the inner chamber (4); and The surface of the sidewall (23) is covered with a layer (5) made of a microwave sensitive material.

2. 2. A method according to claim 1, wherein the side walls (23) are made of ceramic and the layer (5) is made of carbon, graphite or silicon carbide.

3. 10. The method of claim 1, wherein the crucible is also formed from a microwave sensitive material.

4. 4. The method of claim 3, wherein the crucible is made of carbon, graphite, or silicon carbide.

5. 2. The recovery method of claim 1, wherein the carbon-containing component (C) is also a waste material.

6. 2. The method of claim 1, wherein the component (MO) containing the element (M) to be recovered is a powder, ash, slag, sludge or other material containing the element in an oxidized state that can be converted to a reduced form.

7. The element (M) to be recovered is phosphorus (P), and the carbothermal reduction reaction is: 2Ca ３ (PO ４ ) ２ +10C+3SiO ２ →3Ca ２ SiO ４ +10CO+2P ２ It can be expressed as 2. The method for recovering an element (M) according to claim 1, wherein the component (MO) containing the element (M) to be recovered is derived from biomass ash, chicken manure ash, or sewage sludge ash, the additive (Y) is silica fume or colloidal silica, and the carbon-containing component (C) is activated carbon, anthracite, or graphite.

8. -Component (MO) is LiNi ｘ Co ｙ Mn ｚ O ２ It is a "black mass" powder from recycled lithium batteries called; the element (M) to be recovered is lithium oxide and / or nickel oxide and / or manganese oxide and / or cobalt oxide, or other metals / oxides; - carbon is already present in the form of graphite in the "black mass" powder component (MO); -Carbothermal reduction reactions can be carried out depending on the starting materials: 4LiNiO2(s)+C(s)→2Li ２ O(s)+4NiO(s)+CO ２ (g) or 4LiCoO ２ (s)+3C(s)→2Li ２ O(s)+4Co(s)+3CO ２ (g) or 6LiCoO ２ (s)+5C(s)→3Li ２ O ３ (s)+6Co(s)+CO ２ (g) + CO(g) or 2LiMn ２ O ４ (s)+2C(s)→Li ２ CO ３ 2. The recovery method of claim 1, wherein the reaction product can be (s) + 4MnO(s) + CO(g).

9. The element (M) to be recovered is phosphorus (P), and the carbothermal reduction reaction is: Ca ３ (PO ４ ) ２ +6NaHCO ３ →2Na ３ PO ４ +3Ca(OH) ２ +6Cyd ２ It can be expressed as 2. The method of claim 1, wherein the component (MO) containing the element (M) to be recovered originates from sewage sludge ash, the additive (Y) is sodium bicarbonate or another sodium or potassium salt, or a bromide or iodide, and the carbon-containing component (C) is graphite or dewatered sludge.

10. 2. The method of claim 1, wherein a bell (70) is disposed within the heat-resistant chamber (2), wherein the bell defines a controlled atmosphere compartment (71) in which the crucible is disposed.

11. 2. A method according to claim 1, wherein the bell (70) is made of a material transparent to microwaves and has an inlet channel (72) and an outlet channel (73) for the gas.

12. A heat-resistant chamber (2) for recovering elements from waste materials via microwave carbothermal reduction, comprising: an inner chamber (4) capable of containing the material to be subjected to microwave carbothermal reduction; - a side wall (23) having a surface facing the inner chamber (4); and The sidewall (23) is made of a heat-resistant material; and a heat-resistant chamber (2) characterized in that the surface of the side wall (23) facing the inner chamber (4) is covered with a layer (5) of microwave-sensitive material.

13. 13. A heat-resistant chamber (2) according to claim 12, wherein the side walls (23) are made of ceramic and the layer (5) is made of carbon, or graphite or silicon carbide.

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