Method for incinerating waste containing fluorine and precious metals

Abstract

The present invention relates to a method for incinerating waste containing fluorine and precious metals in a chamber furnace, wherein the fluorine content of the waste is in the range of >5-70 wt. % and the precious metal content of the waste is in the range of 0.1-30 wt. %, and the furnace chamber of the chamber furnace is lined with a chromium corundum material containing ≥80 wt. % alpha-Al2O3, 1-20 wt. % Cr2O3, and 0-5 wt. % SiO2.

Description

[Technical Field]

[0001] The present invention relates to a method for incinerating waste containing fluorine and precious metals. The precious metal-enriched ash residue obtained after carrying out the method can be treated to recover the precious metals contained therein.

[0002] As used herein, the term "noble metal" is used. Noble metals within the meaning of the present invention are silver, ruthenium, rhodium, palladium, iridium and platinum, each alone or in any combination of two, more or all of these metals.

[0003] EP 2 700 726 A1 discloses a method for incinerating waste containing fluorine and precious metals for the purpose of concentrating the precious metals. Incineration of such waste produces, among other things, hydrogen fluoride or hydrofluoric acid. As a thermal treatment plant in which incineration takes place, EP 2 700 726 A1 discloses a chamber furnace having a refractory insulating lining in the form of a ramming mass inside the furnace chamber, the refractory insulating lining having a high proportion of aluminum oxide, greater than 85 wt.%, particularly greater than 88 wt.%. In addition to aluminum oxide, the refractory insulating lining may also contain calcium oxide and silicon dioxide in various proportions. According to EP 2 700 726 A1, the refractory insulating lining is not corroded by hydrofluoric acid, even when the proportion of calcium oxide and / or silicon dioxide in the ramming mass is up to 15% by weight, particularly up to 12% by weight. EP 2 700 726 A1 states that the disclosed method is preferably suitable for treating materials with a fluorine content of up to 5% by weight. The waste materials preferably used in this method and subjected to thermal treatment are fluoroorganic materials, PTFE films, fuel cells, catalysts, and / or pastes. In principle, this method is suitable for all materials with a fluorine content of up to 5% by weight that decompose at temperatures of about 800°C, particularly about 600°C, i.e., at the latest when the temperature reaches about 800°C, particularly about 600°C.

[0004] The object of the present invention was to find a method for concentrating precious metals for the incineration of waste containing fluorine and precious metals, in particular waste with a high fluorine content. It has been found that the method known from EP 2 700 726 A1 reaches its limits as soon as the fluorine content in the fluorine- and precious metal-containing material to be incinerated exceeds 5% by weight, especially if this is the case, for example, regularly for each batch or substantially each batch.

[0005] This object can be achieved by a method for incinerating waste containing fluorine and precious metals in a chamber furnace, wherein the fluorine content of the waste is in the range of >5-70 wt. % and the precious metal content of the waste is in the range of 0.1-30 wt. %, and the furnace chamber (furnace space, furnace interior) of the chamber furnace is lined with a chromium corundum material containing ≥80 wt. % alpha-Al2O3, 1-20 wt. % Cr2O3, and 0-5 wt. % SiO2.

[0006] The method according to the present invention comprises the successive steps of: (1) introducing fluorine- and precious metal-containing waste to be incinerated into a furnace chamber of a chamber furnace, the waste having a fluorine content in the range of >5-70 wt.% and a precious metal content in the range of 0.1-30 wt.%, (2) incinerating the waste, and (3) removing the ash formed after completion of step (2), wherein the furnace chamber of the chamber furnace is lined with a chromium corundum material containing ≥80 wt.% alpha-Al2O3, 1-20 wt.% Cr2O3, and 0-5 wt.% SiO2.

[0007] If the fluorine content and / or precious metal content of the fluorine- and precious metal-containing waste to be incinerated by the method according to the invention are not directly known, they can be measured using conventional analytical methods known to those skilled in the art. The skilled artisan will select the analytical method depending on the type of waste. If necessary, the waste can first be homogenized at least macroscopically. The fluorine content of a waste sample can be measured, for example, by combustion digestion (pyrohydrolysis) followed by ion chromatography (combustion IC). To measure the precious metal content, the waste sample can be examined directly using X-ray fluorescence analysis or after incineration in a laboratory furnace. Alternatively, the precious metal content of the ash can be transferred to an aqueous solution using wet chemicals, for example, aqua regia, and measured, for example, using ICP-OES analysis.

[0008] The method according to the invention is a discontinuous method and can be carried out in batches, whereby identical, similar, or different batches of waste containing fluorine and precious metals to be incinerated can be incinerated one after the other according to the method according to the invention, i.e., according to the sequence of steps (1)-(2)-(3). This refers to identical, similar, or different batches of waste containing fluorine and precious metals to be incinerated; therefore, although individual batches may differ in their qualitative and / or quantitative composition, they are always batches of waste containing fluorine and precious metals to be incinerated having a fluorine content in the range of >5-70% by weight and a precious metal content in the range of 0.1-30% by weight. In batch operation, the furnace chamber is filled with a batch of waste to be incinerated (the batch of waste to be incinerated is introduced into the furnace chamber), the batch of waste is incinerated, and after incineration, the batch of waste is removed from the furnace chamber, and then the process characterized by the sequence of steps (1)-(2)-(3) begins again with the next batch of waste. Those skilled in the art will understand that the temperature of the furnace chamber of a chamber furnace drops between the removal of an incinerated batch of waste and the refilling of the furnace chamber with the subsequent batch to be incinerated. However, at least for reasons of energy efficiency, this cooling of the furnace chamber is preferably kept as minimal as possible, and subsequent batches are fed as quickly as possible. For example, cooling the interior of the furnace chamber to temperatures below the range of 400-600°C is avoided as much as possible. In other words, the method according to the present invention can be preferably carried out in continuous operation, not only from the viewpoint of energy conservation but also from the viewpoint of high plant utilization. As used herein, the term "continuous operation" refers to the repetition of the method according to the present invention in successive batches in the same chamber furnace, preferably with as few interruptions as possible between specific incineration cycles due to loading and unloading.

[0009] The term "incineration" is used herein to refer to the formation of ash by pyrolysis (thermal decomposition, carbonization) and / or oxidation, this process being carried out in particular as combustion. Generally, incineration in the method according to the invention comprises both pyrolysis and oxidation or combustion, the pyrolysis and oxidation processes being carried out in sequence or in parallel, and if necessary, can also be carried out alternately. This may depend, inter alia, on the type of fluorine- and precious metal-containing waste to be incinerated and its presence in the furnace chamber, the temperature control in the furnace chamber and the supply of air or oxygen therein.

[0010] A distinction is made herein between the waste containing fluorine and precious metals to be incinerated in the process according to the invention and the waste containing fluorine and precious metals incinerated in the process according to the invention. The waste containing fluorine and precious metals incinerated in the process according to the invention is the product of the process according to the invention, i.e., ash. The process according to the invention leads to a concentration of precious metals, and the ash is therefore characterized by a higher precious metal content than the precious metal content of the original waste containing fluorine and precious metals to be incinerated.

[0011] The fluorine- and precious metal-containing waste incinerated in the process according to the invention is not conventional household or commercial waste, which may contain low proportions of fluorine and precious metals, e.g., less than 3% by weight fluorine and less than 0.05% by weight precious metals. Rather, the fluorine- and precious metal-containing waste incinerated is waste with a relatively high fluorine content in the range of >5-70% by weight and a relatively high precious metal content in the range of 0.1-30% by weight, where the relatively high proportion of valuable precious metals not only justifies but actually requires precious metal recovery from a resource conservation perspective. Thus, the fluorine- and precious metal-containing waste incinerated in the process according to the invention may be, for example, chemical waste, e.g., residues from chemical manufacturing, such as spent catalysts, synthesis residues, rejected batches, distillation residues, etc.; fuel cell waste, particularly membrane materials from fuel cells; and / or electrolysis cell waste, particularly membrane materials from electrolysis cells. It is clear to those skilled in the art that the fluorine- and precious metal-containing waste incinerated in the method according to the present invention always contains organic chemical materials or organic chemical material components. The term "organic chemical" explicitly includes "organometallics," and organic chemical materials or organic chemical material components include not only perfluorinated and polyfluorinated chemicals but also organic polymeric materials, such as fluoropolymer materials, which are typical representatives of fuels and membrane materials from electrolysis cells. Organic chemical materials may also contain volatile organic compounds, especially organic solvents. In addition to the precious metal content and the organic chemical material portion, the waste may contain inorganic materials, such as carbon, especially catalyst support materials in the form of activated carbon, and / or inorganic catalyst support materials (e.g., refractory oxide materials such as aluminum oxide, silicon dioxide, and zeolites). Water may also be present.

[0012] In the case of chemical waste in the form of residues from chemical production, the precious metal content generally comes from the precious metal catalysts contained therein or from decomposition products. In membrane materials from fuel cells and electrolysis cells, the precious metal content usually comes from the catalyst layers containing precious metals and located on the front and / or back side of the membrane. As already mentioned, in membrane materials from fuel cells and electrolysis cells, the fluorine content usually comes from the membrane itself, so the actual membrane material is generally a polymer such as polytetrafluoroethylene or a so-called ionomer, for example, in particular a copolymer of tetrafluoroethylene and a sulfonic acid group-containing (per)fluorovinyl ether, such as Nafion® from Chemours.

[0013] The fluorine content of the fluorine- and precious metal-containing waste to be incinerated in the process according to the invention is in the range of >5 to 70% by weight, in particular 15 to 60% by weight, and the precious metal content of the waste is in the range of 0.1 to 30% by weight, in particular 0.5 to 8% by weight. The fluorine and precious metal contents referred to here are the fluorine and precious metal contents of the particular batch of fluorine- and precious metal-containing waste to be incinerated. In other words, the batch of waste may be essentially homogeneous or at least macroscopically homogeneous waste, or may be a combination of different wastes or different types of waste, but regardless of this, the individual fluorine and precious metal contents of each batch of fluorine- and precious metal-containing waste to be incinerated in the process according to the invention always have an average value in the range of >5 to 70% by weight, in particular 15 to 60% by weight, for the fluorine content, and an average value in the range of 0.1 to 30% by weight, in particular 0.5 to 8% by weight, for the precious metal content.

[0014] According to the invention, incineration is carried out in a chamber furnace, more precisely in the furnace chamber of the chamber furnace, which is the central element of the incineration plant. In addition to the chamber furnace, the incineration plant may be equipped with a facility for thermal post-combustion. The incineration plant is usually equipped with an exhaust gas cleaning system with a scrubber for removing hydrogen fluoride or hydrofluoric acid as well as other pollutants that should not be released into the environment.

[0015] The chamber furnace used in the method according to the invention is a conventional chamber furnace, usually having a supporting metal or steel structure or a metal or steel shell for the furnace chamber. However, what is essential for the invention is that the furnace chamber of the chamber furnace is lined with a chrome-corundum material containing ≥80 wt.% alpha-Al2O3, 1-20 wt.% Cr2O3, and 0-5 wt.% SiO2. For example, the chrome-corundum material contains or consists of 80-95 wt.% alpha-Al2O3, 1-20 wt.% Cr2O3, and 0-5 wt.% SiO2. Preferably, the chrome-corundum material contains or consists of 85-95 wt.% alpha-Al2O3, 2-15 wt.%, particularly 5-15 wt.% Cr2O3, and 0-2 wt.%, particularly 0 wt.% SiO2.

[0016] The chrome corundum lining is a refractory insulating lining, which may be in the form of a ramming mass, as pre-compressed fibers, and / or as chrome corundum bricks. The chrome corundum lining may have a thickness typical of refractory insulating linings, for example, in the range of 10-100 cm. This inner insulating lining protects the supporting metal structure or metal shell of the furnace chamber in two ways: thermally and chemically, on the one hand, as a long-lasting fireproof or thermal insulation, and on the other hand, as a long-lasting barrier against the penetration of hydrogen fluoride or hydrofluoric acid into the metal. Particularly noteworthy is the relatively long life of the protective effect, which allows the method of the present invention to be operated continuously, even when the fluorine content of the fluorine- and precious metal-containing waste to be incinerated is exceptionally high. In this context, continuous operation means more than two years (e.g., more than 2,000 incineration cycles) without requiring modification, repair, or replacement of the insulating lining.

[0017] As described above, in step (1) of the method according to the present invention, the waste material containing fluorine and precious metals to be incinerated, having a fluorine content in the range of >5-70% by weight and a precious metal content in the range of 0.1-30% by weight, is introduced into the furnace chamber, i.e., the furnace chamber is filled with it. For this purpose, the furnace chamber includes an opening for introducing the appropriate material. The furnace chamber can be operated with either a lack of air or an excess of air. Regarding the provision of the waste material containing fluorine and precious metals to be incinerated in the furnace chamber, the furnace chamber may have an internal device for incinerating the waste material containing fluorine and precious metals to be incinerated. These may include, for example, a grate for holding trays for burning solid materials. Thin or viscous materials can be introduced into the furnace chamber in a tank or via a suitable input device and incinerated therein.

[0018] The actual incineration of the waste takes place in step (2) of the method according to the invention. For this purpose, the furnace temperature (the temperature inside the furnace chamber) is set, i.e., heated, to a temperature suitable for incineration. The furnace temperature during incineration ranges from 650 to 950°C as a continuous temperature (short-term temperature peaks up to 1200°C are possible). The continuous temperature may be a temperature that remains substantially constant once reached, or it may be a temperature ramp-up program carried out within the continuous temperature range. To heat to the continuous temperature, all conventional methods of energy supply can be used, i.e., both direct and indirect heating of the furnace chamber, e.g., gas-fired, oil-fired, and / or electrical heating, after the furnace chamber is filled and closed. Indirect heating by hot gas, especially hot air, is preferred. The heating rate can also reach up to 200°C per hour, which is relatively high. Advantageously, chrome corundum linings have been found to be highly resistant to temperature changes, both in terms of the rate and frequency of temperature changes.

[0019] Incineration of a batch of waste at continuous temperatures typically takes 4 to 15 hours. It will be appreciated by those skilled in the art that if volatile components such as organic solvents and / or water are present in the fluorine- and precious metal-containing waste to be incinerated, such volatile components will initially evaporate prior to the actual incineration or during the filling of the furnace chamber and / or during the heating process in step (2).

[0020] During incineration, the furnace atmosphere is formed from exhaust gases containing significant amounts of hydrogen fluoride, either formed by the exhaust gases or as a result of the high fluorine content of the fluorine- and precious metal-containing waste being incinerated, which hydrogen fluoride forms hydrofluoric acid together with water.

[0021] In step (3) of the method according to the present invention, the ash formed after completion of step (2) is removed from the furnace chamber. The ash is characterized by being enriched in precious metals compared to the fluorine- and precious-metal-containing waste to be incinerated, i.e., its precious metal content is, for example, in the range of 0.5 to 60% by weight. The precious metals can be present in elemental metal form, as oxides, oxyfluorides, and / or fluorides. Furthermore, mineral materials, such as mineral materials derived from activated carbon materials such as potassium carbonate or inorganic catalyst support materials, such as the aforementioned refractory oxide materials, can be contained in the ash. Depending on the completeness of the incineration process in step (2), the ash can also contain portions of coked materials, coke, and / or coal.

[0022] The precious metal-containing ash can be treated using conventional methods, especially wet chemical methods, for the purpose of precious metal recovery.

[0023] In summary, the method according to the invention offers, inter alia, the following advantages over the prior art, as shown, for example, in EP 2700726 A1:

[0024] 1. The process according to the invention can be carried out with fluorine- and precious metal-containing waste, even in continuous operation, despite high fluorine contents of >5-70% by weight.

[0025] 2. The process according to the invention can be carried out at high heating rates. Such rapid temperature changes in the furnace chamber result in relatively short processing times for individual batches, which in turn allows for quick batch exchange and high processing capacities in continuous operation (high space / time yield).

[0026] 3. The method according to the invention can be carried out in continuous operation for many cycles or for long periods of time until interruptions are required due to necessary modifications, repairs or necessary replacement of the chrome corundum insulating lining.

Claims

1. 1. A method for incinerating waste containing fluorine and precious metals in a chamber furnace, wherein the fluorine content of the waste is in the range of >5-70 wt. %, the precious metal content of the waste is in the range of 0.1-30 wt. %, and the furnace chamber of the chamber furnace is ≥80 wt. % alpha-Al ２ O ３ , 1 to 20 wt. % Cr ２ O ３ and 0 to 5 wt. % SiO ２ The method of claim 1, wherein the surface is lined with a chrome corundum material comprising:

2. The method includes the following successive steps: (1) introducing fluorine- and precious metal-containing waste to be incinerated into the furnace chamber of the chamber furnace, the waste having a fluorine content in the range of >5-70 wt.% and a precious metal content in the range of 0.1-30 wt.%, (2) incinerating the waste, and (3) removing the ash formed after completion of step (2), wherein the furnace chamber of the chamber furnace contains ≥80 wt.% alpha-Al. ２ O ３ , 1 to 20 wt. % Cr ２ O ３ and 0 to 5 wt. % SiO ２ The method of claim 1 , wherein the surface is lined with a chrome corundum material comprising:

3. 3. The method according to claim 1 or 2, wherein the waste material containing fluorine and precious metals is chemical waste, fuel cell waste and / or electrolytic cell waste.

4. 4. The method according to claim 1, wherein the fluorine content of the waste containing fluorine and precious metals is in the range of 15 to 60% by weight.

5. 5. The method according to claim 1, wherein the precious metal content of the waste containing fluorine and precious metals is in the range of 0.5 to 8% by weight.

6. The chromium corundum material is 80 to 95 wt. % alpha-Al ２ O ３ , 1 to 20 wt. % Cr ２ O ３ and 0 to 5 wt. % SiO ２ 6. The method according to any one of claims 1 to 5, comprising or consisting of:

7. The chromium corundum material is 85 to 95 wt. % alpha-Al ２ O ３ , 2 to 15 wt. % Cr ２ O ３ and 0 to 2 wt. % SiO ２ 6. The method according to any one of claims 1 to 5, comprising or consisting of:

8. 8. The method according to claim 1, wherein the chrome corundum lining is designed in the form of a ramming mass, as pre-compressed fibers and / or as chrome corundum bricks.

9. 9. A method according to any one of claims 1 to 8, wherein the furnace temperature during incineration is in the range of 650 to 950°C as a continuous temperature.

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