Method for incinerating waste containing fluorine and precious metals

Abstract

The invention relates to a method for incinerating waste containing fluorine and precious metals in a box furnace, the waste having a fluorine content gt; the waste has a noble metal content in the range of from 5 wt.% to 70 wt.%, and the noble metal content of the waste is in the range of from 0.1 wt.% to 30 wt.%, and the furnace chamber of the box furnace is lined with a chrome corundum material comprising > = 80 wt.% alpha-Al2O3, 1 wt.% to 20 wt.% Cr2O3 and 0 wt.% to 5 wt.% SiO2.

Description

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

[0002] The term "noble metals" is used herein. 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 enriching precious metals. When such waste is incinerated, hydrogen fluoride or hydrofluoric acid is produced, among other things. As a thermal treatment facility in which incineration is carried out, EP 2 700 726 A1 discloses a box furnace with a refractory heat-insulating lining in the form of a ramming mass inside the furnace chamber, wherein the refractory heat-insulating lining has a high proportion of aluminum oxide of 85wt.% (weight %) or higher, particularly 88wt.% or higher. In addition to aluminum oxide, the refractory heat-insulating lining may also include calcium oxide and silicon dioxide in different proportions. Although the proportion of calcium oxide and / or silicon dioxide in the ramming mass is up to 15wt.%, particularly up to 12wt.%, according to EP 2 700 726 A1, it is not corroded by hydrofluoric acid. EP 2 700 726 A1 points out that the disclosed method is preferably suitable for treating materials with a fluorine content of up to 5wt.%. Preferably, the waste materials to be subjected to the thermal treatment used in the method are organic fluorine materials, PTFE membranes, fuel cells, catalysts and / or pastes. In principle, the method is suitable for all materials with a fluorine content of up to 5 wt.%, which decompose at a temperature below about 800° C., in particular about 600° C., but decompose at the latest when the temperature of about 800° C., in particular about 600° C., is reached.

[0004] The object of the present invention is to find a method for enriching precious metals for the incineration of fluorine- and precious metal-containing wastes having a particularly 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 wt.%, in particular if this is the case regularly, for example for every batch or substantially every batch.

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

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

[0007] If the fluorine content and / or the precious metal content of the fluorine- and precious metal-containing waste to be incinerated by means of the method according to the invention is not directly known, it can be determined using conventional analytical methods known to the person skilled in the art. The person skilled in the art will select the analytical method according to the type of waste. If necessary, the waste can first be homogenized at least macroscopically. The fluorine content of the waste sample can be determined, for example, by combustion digestion (pyrohydrolysis) and then by ion chromatography (combustion IC). In order to determine the precious metal content, the waste sample can be examined using X-ray fluorescence analysis directly or after incineration in a laboratory furnace; alternatively, the precious metal content of the ash can be transferred to an aqueous solution using wet chemistry (for example using aqua regia) and determined, for example, using ICP-OES analysis.

[0008] The process according to the invention is a discontinuous process; the process can be carried out batchwise, wherein identical, similar or different batches of fluorine- and precious metal-containing waste to be incinerated can be incinerated one after another according to the process according to the invention, i.e. according to the sequence of steps (1)-(2)-(3). This refers to identical, similar or different batches of fluorine- and precious metal-containing waste to be incinerated; the individual batches can therefore differ in their qualitative and / or quantitative composition, but they are always batches of fluorine- and precious metal-containing waste to be incinerated having a fluorine content in the range of >5 wt.% to 70 wt.% and a precious metal content in the range of 0.1 wt.% to 30 wt.%. In batchwise operation, the furnace chamber is charged with a batch of waste to be incinerated (a batch of waste to be incinerated is introduced into the furnace chamber), the batch of waste is incinerated and removed from the furnace chamber after incineration; then, the process characterized by the sequence of steps (1)-(2)-(3) starts again with the next batch of waste. It is self-evident to the person skilled in the art that the temperature of the furnace chamber of the box furnace drops between the removal of a batch of waste to be incinerated and the reloading of the furnace chamber with a subsequent batch of waste to be incinerated. However, in particular for reasons of energy efficiency, this cooling of the furnace chamber is preferably kept as small as possible and the subsequent batches are fed as quickly as possible. For example, cooling the interior of the furnace chamber to a temperature below the range of 400° C. to 600° C. is avoided as much as possible. In other words, the method according to the invention can preferably be implemented in a continuous operation mode, not only from the perspective of energy saving, but also from the perspective of a high level of facility utilization. The term "continuous operation" as used herein means that the method according to the invention is repeated continuously in batches in the same box furnace, preferably with as few interruptions as possible due to loading and unloading between specific incineration cycles.

[0009] The term "incineration" is used herein; it refers to the formation of ash by pyrolysis (thermal decomposition, carbonization) and / or oxidation, wherein this process occurs in particular as combustion. In general, the incineration in the method according to the invention comprises both pyrolysis and oxidation or combustion, wherein the pyrolysis and oxidation processes can be carried out one after the other or in parallel, and if necessary also alternately. This can depend, among other things, on the type of fluorine- and precious metal-containing waste to be incinerated and on its presentation in the furnace chamber, the temperature control in the furnace chamber and the air or oxygen supply therein.

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

[0011] The fluorine- and precious metal-containing waste to be incinerated in the method according to the invention is not conventional household or commercial waste, which may contain low proportions of fluorine and precious metals, for example less than 3 wt.% of fluorine and less than 0.05 wt.% of precious metals. More precisely, the fluorine- and precious metal-containing waste to be incinerated is a waste having a relatively high fluorine content in the range of >5 wt.% to 70 wt.% and a relatively high precious metal content in the range of 0.1 wt.% to 30 wt.%, the relatively high proportion of valuable precious metals not only justifying the recovery of precious metals, but also being practically necessary from the point of view of resource protection. Thus, the fluorine- and precious metal-containing waste to be incinerated in the method according to the invention may be, for example, chemical waste, such as residues from chemical production, such as spent catalysts, synthesis residues, defective batches, distillation residues, etc.; fuel cell waste, in particular membrane materials from fuel cells; and / or electrolytic cell waste (electrolyzer waste), in particular membrane materials from electrolytic cells (electrolyzers). It is clear to the skilled person that the fluorine- and precious metal-containing waste to be incinerated in the method according to the invention always contains organic chemicals or organic chemical components. The term "organic chemical" explicitly includes "organometallic"; organic chemical materials or organic chemical material components include not only perfluorinated chemicals and polyfluorinated chemicals, but also organic polymer materials, such as fluoropolymer materials as typical representatives of membrane materials from fuels and electrolyzers. Organic chemical materials may also include volatile organic compounds, in particular organic solvents. In addition to the precious metal content and the organic chemical material part, it may particularly contain carbon, such as a catalyst support material in the form of activated carbon, and / or inorganic materials, such as inorganic catalyst support materials (e.g. refractory oxidizing materials, such as alumina, silica and zeolites). Water may also be contained.

[0012] In the case of chemical waste in the form of residues from chemical production, the precious metal content usually comes from the precious metal catalysts or degradation products contained therein. In membrane materials from fuels and electrolyzers, the precious metal content usually comes from catalyst layers containing precious metals and located on the front and / or back of the membrane. As already mentioned, in membrane materials from fuels and electrolyzers, the fluorine content usually comes from the membrane itself, so that the actual membrane material is usually a polymer, such as polytetrafluoroethylene or so-called ionomers such as, in particular, copolymers of tetrafluoroethylene and (per)fluorovinyl ethers containing sulfonic acid groups, such as PTFE from Chemours.

[0013] The fluorine content of the fluorine- and precious metal-containing waste to be incinerated in the method according to the invention is in the range of >5 wt.% to 70 wt.%, in particular 15 wt.% to 60 wt.%, and its precious metal content is in the range of 0.1 wt.% to 30 wt.%, in particular 0.5 wt.% to 8 wt.%. The fluorine content and precious metal content mentioned here are the fluorine content and precious metal content of a specific batch of fluorine- and precious metal-containing waste to be incinerated. In other words, a batch of waste can be an inherently homogeneous or at least macroscopically homogeneous waste, or it can be a combination of different wastes or different types of waste; however, despite this, the individual fluorine content and precious metal content of each batch of fluorine- and precious metal-containing waste to be incinerated in the method according to the invention always have an average value for the fluorine content in the range of >5 wt.% to 70 wt.%, in particular 15 wt.% to 60 wt.%, and always have an average value for the precious metal content in the range of 0.1 wt.% to 30 wt.%, in particular 0.5 wt.% to 8 wt.%.

[0014] According to the invention, the incineration is carried out in a box furnace, more precisely in the furnace chamber of the box furnace, which is the central element of the incineration facility. In addition to the box furnace, the incineration facility may also include facilities for thermal afterburning. Incineration facilities usually include an exhaust gas cleaning system with a scrubber to remove hydrogen fluoride or hydrofluoric acid and 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 with a supporting metal or steel construction or a metal or steel shell of the chamber; however, it is important for the invention that the chamber of the chamber furnace is lined with a chrome corundum material, which contains ≥80 wt.% of α-Al2O3, 1 wt.% to 20 wt.% of Cr2O3 and 0 wt.% to 5 wt.% of SiO2. For example, the chrome corundum material contains or consists of 80 wt.% to 95 wt.% of α-Al2O3, 1 wt.% to 20 wt.% of Cr2O3 and 0 wt.% to 5 wt.% of SiO2. Preferably, the chrome corundum material contains or consists of 85 wt.% to 95 wt.% of α-Al2O3, 2 wt.% to 15 wt.% (in particular 5 wt.% to 15 wt.%) of Cr2O3 and 0 wt.% to 2 wt.% (in particular 0 wt.%) of SiO2.

[0016] The chrome corundum lining is a refractory insulating lining and can be in the form of a ramming mass, as pre-compacted fibers and / or as chrome corundum bricks. The chrome corundum lining can have a typical thickness of a refractory insulating lining in the range of, for example, 10 cm to 100 cm. This internal insulating lining is used to protect the supporting metal structure or metal shell of the furnace chamber in two ways, namely, thermally and chemically, on the one hand as a durable refractory or insulating material, and on the other hand as a durable barrier against the entry of hydrogen fluoride or hydrofluoric acid into the metal. It is particularly noteworthy that the protective effect lasts for a relatively long time, as a result of which the method according to the present invention can be operated in a continuous operation mode even if the fluorine content of the fluorine-containing and precious metal waste to be incinerated is extremely high. In this context, continuous operation means that no renovation or repair or replacement of the insulating lining is required for two or more years (e.g., 2000 or more incineration cycles).

[0017] As described, in step (1) of the method according to the invention, the fluorine- and precious metal-containing waste to be incinerated is introduced into the furnace chamber, i.e., it is loaded into the furnace chamber, the waste having a fluorine content in the range of >5wt.% to 70wt.% and a precious metal content in the range of 0.1wt.% to 30wt.%. For this purpose, the furnace chamber comprises an opening for introducing suitable materials. The furnace chamber can be operated in the absence of air or in excess of air. As for the presentation of the fluorine- and precious metal-containing waste to be incinerated in the furnace chamber, the furnace chamber may have equipment for incinerating the fluorine- and precious metal-containing waste to be incinerated inside it. These include, for example, grids for holding trays for burning solid materials. Thin or viscous materials can be introduced into the furnace chamber in cans or via suitable dosing equipment and incinerated in the chamber.

[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 to a temperature suitable for incineration, i.e., it is heated. The furnace temperature during incineration is in the range of 650°C to 950°C, as a continuous temperature (short-term temperature peaks of up to 1200°C are possible). The continuous temperature can be a temperature that is essentially constant once reached, or it can be a temperature program that operates within the continuous temperature range. For the purpose of heating to the continuous temperature, all commonly used energy supply methods can be used after the furnace chamber is loaded and closed, i.e., direct and indirect heating of the furnace chamber, such as gas combustion, oil combustion and / or electrical heating. Preferably, indirect heating is performed with hot gases, in particular hot air. The heating rate can even reach up to 200°C per hour, which is relatively high. Advantageously, the chrome corundum lining has been shown to be extremely resistant to temperature changes in terms of both the speed of temperature changes and the frequency of temperature changes.

[0019] Incineration of a batch of waste at continuous temperature usually requires 4 to 15 hours. It is self-evident to the person 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 are first evaporated before the actual incineration or during the charging of the furnace chamber and / or during the heating process in step (2).

[0020] During incineration, the furnace atmosphere is formed with or from waste gases which, owing to the high fluorine content of the fluorine- and precious metal-containing waste to be incinerated, contain large amounts of hydrogen fluoride which forms hydrofluoric acid with water.

[0021] In step (3) of the method according to the 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 in the range of, for example, 0.5 wt.% to 60 wt.%. The precious metals may be present in elemental metal form, such as oxides, oxyfluorides and / or fluorides. In addition, the ash may contain mineral materials, such as mineral materials derived from activated carbon materials, such as potassium carbonate, or mineral materials derived from inorganic catalyst support materials, such as the above-mentioned refractory oxidic materials. Depending on the integrity of the incineration process in step (2), the ash may also contain part of the coking material, coke and / or coal.

[0022] For the purpose of recovering precious metals, the precious metal-containing ash can be treated by conventional methods, in particular wet-chemical methods.

[0023] In summary, the method according to the invention offers, among others, the following advantages compared to the prior art, represented for example by EP 2 700 726 A1:

[0024] 1. The process according to the invention can be carried out even in a continuous operation with wastes containing fluorine and precious metals, despite high fluorine contents of >5 to 70 wt.%.

[0025] 2. The method according to the invention can be implemented at high heating rates. Thus, the rapid temperature change in the furnace chamber makes it possible to allow relatively short processing times for individual batches, leading to rapid batch changes and thus to high capacities (high space / time yields) in continuous operation.

[0026] 3. The method according to the invention can be carried out in a continuous operation for a number of cycles or for a longer period of time before it needs to be interrupted due to necessary renovation, repair or necessary replacement of the chrome corundum thermal insulation lining.

Claims

1. A method for incinerating waste containing fluorine and precious metals in a box furnace, wherein the fluorine content of the waste is in the range of >5wt.% to 70wt.%, and the precious metal content of the waste is in the range of 0.1wt.% to 30wt.%, and wherein the furnace chamber of the box furnace is lined with a chrome corundum material, the chrome corundum material comprising ≥80wt.% α-Al2O3, 1wt.% to 20wt.% Cr2O3 and 0wt.% to 5wt.% SiO2.

2. The method according to claim 1, comprising the following consecutive steps: (1) introducing fluorine- and precious metal-containing waste to be incinerated into the furnace chamber of a box furnace, the waste having a fluorine content in the range of >5wt.% to 70wt.% and a precious metal content in the range of 0.1wt.% to 30wt.%, (2) incinerating the waste, and (3) removing ash formed after completion of step (2), wherein the furnace chamber of the box furnace is lined with a chrome corundum material, the chrome corundum material comprising ≥80wt.% of α-Al2O3, 1wt.% to 20wt.% of Cr2O3 and 0wt.% to 5wt.% of SiO2.

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

4. The method according to any one of the preceding claims, wherein the fluorine content of the fluorine- and precious metal-containing waste is in the range of 15 wt.% to 60 wt.%.

5. The method according to any one of the preceding claims, wherein the precious metal content of the fluorine- and precious metal-containing waste is in the range of 0.5 wt.% to 8 wt.%.

6. The method according to any one of the preceding claims, wherein the chrome corundum material comprises or consists of 80 wt.% to 95 wt.% of α-Al2O3, 1 wt.% to 20 wt.% of Cr2O3 and 0 wt.% to 5 wt.% of SiO2.

7. The method according to any one of claims 1 to 5, wherein the chrome corundum material comprises or consists of 85 wt.% to 95 wt.% of α-Al2O3, 2 wt.% to 15 wt.% of Cr2O3 and 0 wt.% to 2 wt.% of SiO2.

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

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