Method for preparing tellurium dioxide through oxidizing roasting-vacuum thermal decomposition of copper tellurium slag

Abstract

The invention belongs to the technical field of metallurgical waste recycling, and particularly relates to a method for preparing tellurium dioxide through oxidizing roasting-vacuum thermal decomposition of copper tellurium slag. The method comprises the following steps: oxidizing and roasting copper tellurium slag powder in an oxygen-containing mixed atmosphere at 400-600 DEG C to obtain a copper tellurium oxide; and performing vacuum thermal decomposition on the copper tellurium oxide, and condensing the obtained tellurium dioxide gas to obtain a tellurium dioxide product. The method can efficiently extract tellurium in the copper tellurium slag, and has the advantages of being short in technological process, low in energy consumption, environmentally friendly, high in tellurium recovery rate (larger than or equal to 95%) and high in tellurium dioxide product purity (larger than or equal to 99.5%).

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgical waste recycling, and particularly relates to a method for preparing tellurium dioxide by oxidative roasting-vacuum thermal decomposition of copper tellurium slag. Background Art

[0002] Tellurium is a rare metal with a very low content in the Earth's crust, but its unique physical and chemical properties make it one of the indispensable materials for modern industry and high-tech industries. Tellurium dioxide, as a representative compound of tellurium, has important economic value and social significance for its effective extraction from industrial waste such as copper tellurium slag. Copper tellurium slag mainly comes from the processing of copper anode mud and contains high-grade tellurium. However, the tellurium in copper tellurium slag often coexists with other metal elements such as copper, lead, and selenium, and has complex morphologies, making it difficult to extract directly. Traditional recovery processes include hydrometallurgy and pyrometallurgy. Hydrometallurgy involves sulfuric acid roasting, water leaching for copper removal, alkaline leaching for tellurium extraction, oxidation precipitation, and acid reduction, achieving a total tellurium recovery rate of up to 92% and a product purity of 94%. Pyrometallurgy involves mixing crushed copper-tellurium slag with a slagging agent, subjecting it to high-temperature smelting to separate tellurium from other metals, followed by acid leaching, precipitation, and purification to produce tellurium dioxide or elemental tellurium, with a product purity of up to 94%. However, both methods still offer relatively low recovery rates and product purities, and both suffer from lengthy processes, high energy consumption, and significant environmental pollution, making them insufficient to meet current societal needs. Summary of the Invention

[0003] In view of this, the object of the present invention is to provide a method for preparing tellurium dioxide by oxidative roasting and vacuum thermal decomposition of copper tellurium slag. This method can effectively separate and recover tellurium from copper tellurium slag with a high recovery rate (≥95%). The obtained tellurium dioxide product has high purity (≥99.5%), shortens the process flow, reduces energy consumption, and reduces the risk of environmental pollution.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] The present invention provides a method for preparing tellurium dioxide by oxidative roasting and vacuum thermal decomposition of copper tellurium slag, comprising the following steps:

[0006] The copper-tellurium slag powder is subjected to oxidation roasting in a mixed atmosphere containing oxygen to obtain copper-tellurium oxide; the oxidation roasting temperature is 400-600° C.;

[0007] The copper tellurium oxide is subjected to vacuum thermal decomposition, and the obtained tellurium dioxide gas is condensed to obtain a tellurium dioxide product.

[0008] Preferably, the particle size of the copper tellurium slag powder is 1 to 2 mm.

[0009] Preferably, the holding time of the oxidative roasting is 2 to 3 hours.

[0010] Preferably, the volume fraction of oxygen in the mixed atmosphere containing oxygen is 21 to 30%; and the flow rate of the mixed atmosphere containing oxygen is 0.5 to 3 m / s.

[0011] Preferably, the heating rate to the temperature of the oxidative roasting is 5 to 10° C. / min.

[0012] Preferably, the temperature of the vacuum thermal decomposition is 900-1200°C and the pressure is 4×10 -4 Pa~1Pa, the heat preservation and pressure holding time is 1~3h; the heating rate of heating to the temperature of vacuum thermal decomposition is 5~10℃ / min.

[0013] Preferably, the condensation is to pass the tellurium dioxide gas into a condensation device filled with a coolant for condensation; the coolant is water; the condensation device is a spiral inner tube water-cooled condenser; the inlet temperature of the condensation device filled with coolant is 20-30°C, and the outlet temperature is 40-50°C; the flow rate of the coolant in the condensation device filled with coolant is 1.5-2.5m / s; the introduction flow rate of the tellurium dioxide gas is 1-3m / s.

[0014] Preferably, after the oxidative roasting, the process further comprises: cooling, crushing and screening the product of the oxidative roasting in a protective gas in sequence to obtain a powder of copper tellurium oxide; the protective gas comprises nitrogen or an inert gas; the mesh size of the sieve used for the screening is 50 to 100 meshes, and the particle size of the copper tellurium oxide powder obtained after crushing and screening is ≤300 μm.

[0015] Preferably, the copper-tellurium slag powder comprises, by mass percentage, 30-50% copper, 30-50% tellurium, and the remainder being impurity elements, which include one or more of silver, iron, and sulfur.

[0016] Preferably, the recovery rate of the tellurium dioxide product is ≥95%, and the purity is ≥99.5%.

[0017] The present invention provides a method for preparing tellurium dioxide by oxidative roasting and vacuum thermal decomposition of copper tellurium slag, comprising the following steps: oxidative roasting copper tellurium slag powder in an oxygen-containing mixed atmosphere to obtain copper tellurium oxide; the oxidative roasting temperature is 400-600°C; and vacuum thermal decomposition of the copper tellurium oxide to condense the resulting tellurium dioxide gas to obtain a tellurium dioxide product. In the oxygen-containing mixed atmosphere, tellurium and copper in the copper tellurium slag are oxidized to copper tellurium oxide at high temperature. This process is then subjected to vacuum thermal decomposition. This process utilizes the difference in sublimation points between TeO2 and copper oxide (for example, CuO) (TeO2 sublimates at approximately 733°C, while CuO decomposes at temperatures above approximately 1000°C and is not easily sublimated under normal conditions). This allows tellurium to escape as tellurium dioxide gas, while copper remains as solid copper oxide, effectively separating the tellurium from the copper. Moreover, the vacuum environment condition can reduce the volatilization temperature of tellurium dioxide, promoting the generation and efficient separation of tellurium dioxide gas. Oxidative roasting and vacuum thermal decomposition work synergistically to improve the volatilization efficiency and recovery rate of tellurium. The present invention realizes the separation of copper tellurium and the extraction of tellurium through oxidative roasting and vacuum thermal decomposition, omitting multiple steps such as leaching, purification, and precipitation in traditional hydrometallurgy, significantly shortening the process flow. Vacuum thermal decomposition can lower the reaction temperature, reduce energy consumption, and improve energy utilization efficiency. Oxidative roasting and vacuum thermal decomposition are carried out in a closed system, which reduces the emission of harmful gases, and compared with traditional hydrometallurgy, this method does not require the use of a large amount of chemical reagents, reducing the risk of environmental pollution. Therefore, the method provided by the present invention can efficiently extract tellurium from copper tellurium slag, and has the advantages of short process flow, low energy consumption, environmental friendliness, high tellurium recovery rate (≥95%) and high purity of tellurium dioxide product (≥99.5%). BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the process for preparing tellurium dioxide by oxidation roasting and vacuum thermal decomposition of copper tellurium slag in an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention provides a method for preparing tellurium dioxide by oxidative roasting and vacuum thermal decomposition of copper tellurium slag, comprising the following steps:

[0020] The copper-tellurium slag powder is subjected to oxidation roasting in a mixed atmosphere containing oxygen to obtain copper-tellurium oxide; the oxidation roasting temperature is 400-600° C.;

[0021] The copper tellurium oxide is subjected to vacuum thermal decomposition, and the obtained tellurium dioxide gas is condensed to obtain a tellurium dioxide product.

[0022] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products known to those skilled in the art can be used.

[0023] The invention oxidizes and roasts copper-tellurium slag powder in a mixed atmosphere containing oxygen to obtain copper-tellurium oxide.

[0024] As an embodiment, the copper-tellurium slag powder comprises, by weight percentage, 30-50% copper and 30-50% tellurium, with the remainder being impurity elements, including one or more of silver, iron, and sulfur. In a specific embodiment of the present invention, the copper-tellurium slag powder comprises, by weight percentage, 38.7% copper and 32.6% tellurium, with the remainder being impurity elements including silver, iron, and sulfur; or the copper-tellurium slag powder comprises, by weight percentage, 39.74% copper and 34.3% tellurium, with the remainder being impurity elements including silver, iron, and sulfur.

[0025] In one embodiment, the copper-tellurium slag powder has a particle size of 1-2 mm, specifically 1 mm or 1.5 mm. The copper-tellurium slag powder is prepared by sequentially crushing, screening, and magnetically separating the copper-tellurium slag to obtain the copper-tellurium slag powder. The present invention achieves small-particle copper-tellurium slag powder through crushing to increase its surface area, allowing for more complete contact with oxygen, thereby improving the efficiency of oxidative roasting and the yield of tellurium oxide. Magnetic separation is also used to remove ferromagnetic impurities from the copper-tellurium slag to prevent them from interfering with subsequent processes.

[0026] As an embodiment, the temperature of the oxidation roasting is 400-600°C, specifically 550°C or 600°C, and the holding time is 2-3h, specifically 2.5h or 3h; the equipment used for the oxidation roasting is a roasting furnace; the heating rate to the temperature of the oxidation roasting is 5-10°C / min, specifically 5-8°C / min. The present invention sets the temperature of the oxidation roasting within the above range to help promote the formation of tellurium oxide and avoid tellurium volatilization or equipment damage due to excessive temperature. The present invention sets the heating rate to the temperature of the oxidation roasting within the above range. Slow heating helps uniform oxidation, avoids thermal stress, and ensures the formation of tellurium oxide. The present invention sets the time of the oxidation roasting within the above range to ensure sufficient time for the oxidation reaction to be complete while avoiding excessive energy consumption.

[0027] In one embodiment, the oxygen-containing mixed atmosphere is a mixture of oxygen and a protective gas, or air, specifically a mixture of oxygen and a protective gas in a specific embodiment. The protective gas is nitrogen or an inert gas, specifically nitrogen in a specific embodiment. The inert gas is argon. The volume fraction of oxygen in the oxygen-containing mixed atmosphere is 21-30%, specifically 25-30% in a specific embodiment. The flow rate of the oxygen-containing mixed atmosphere is 0.5-3 m / s, specifically 0.5-0.8 m / s or 1-3 m / s in a specific embodiment. A volume fraction of 30% oxygen in the oxygen-containing mixed atmosphere facilitates full oxidation of tellurium compounds, improving recovery rates while balancing the oxidation effect with impurity introduction, ensuring sufficient tellurium oxidation while avoiding the introduction of impurities due to excessive oxidation. Setting the flow rate of the oxygen-containing mixed atmosphere within the above range ensures sufficient contact between oxygen and copper-tellurium slag powder, promoting the oxidation reaction.

[0028] As an embodiment, after the oxidation roasting, the process further includes: cooling, crushing and screening the product of the oxidation roasting in a protective gas in sequence to obtain a powder of copper tellurium oxide; the protective gas includes nitrogen or an inert gas, specifically nitrogen; the cooling is natural cooling to room temperature; the crushing is grinding; the mesh size of the sieve used for the screening is 50-100 mesh, specifically 80-100 mesh in the specific embodiment, and the particle size of the copper tellurium oxide powder obtained after crushing and screening is ≤300μm, specifically ≤178μm or ≤150μm in the specific embodiment. The present invention crushes and screens the product of the oxidation roasting by oxygen isolation with a protective gas to ensure better vacuum thermal decomposition and improve the efficiency of subsequent vacuum thermal decomposition. The present invention crushes and screens the product of the oxidation roasting to obtain a powder with a particle size of 50-100 mesh, thereby increasing the surface area of the product of the oxidation roasting, promoting the oxidation reaction, and improving the recovery rate. When the copper tellurium oxide powder has an appropriate particle size, it exhibits high reactivity in the vacuum thermal decomposition furnace, facilitating uniform gas release. However, powder that is too small may agglomerate due to electrostatic effects during the subsequent vacuum thermal decomposition process, resulting in uneven release of tellurium dioxide gas from the powder particles and affecting decomposition efficiency. Furthermore, the resulting powder clumps can block the gas escape path of the thermal decomposition furnace, not only affecting the amount of tellurium dioxide gas released but also potentially causing an increase in internal pressure and accidents due to gas blockage, posing a safety hazard. Furthermore, as the powder size decreases, the frequency of collisions between small particles and the inner walls of the equipment increases significantly during transportation, which can significantly increase wear on the equipment and shorten its service life. Therefore, in a specific embodiment of the present invention, 80 mesh is selected as the particle size of the copper tellurium oxide powder after screening. This ensures that the copper tellurium oxide powder particle size is sufficiently fine to improve vacuum thermal decomposition efficiency while minimizing the aforementioned problems caused by excessively fine particles.

[0029] After obtaining the copper tellurium oxide, the present invention performs vacuum thermal decomposition on the copper tellurium oxide to obtain tellurium dioxide gas and copper oxide.

[0030] As an embodiment, the temperature of the vacuum thermal decomposition is 900-1200°C, specifically 950-1100°C, and the pressure is 4×10 -4 Pa~1Pa, in the specific embodiment, 5×10 -4 Pa~8×10 -4 Pa, the holding time is 1-3 hours, specifically 2-3 hours in a specific embodiment; the heating rate to the vacuum thermal decomposition temperature is 5-10°C / min, specifically 5-8°C / min in a specific embodiment; the container used for the vacuum thermal decomposition is made of quartz or stainless steel, specifically quartz in a specific embodiment; and the equipment used for the vacuum thermal decomposition is a vacuum thermal decomposition furnace. The present invention sets the vacuum thermal decomposition temperature within the above range to efficiently separate tellurium as tellurium dioxide gas, ensuring complete decomposition of tellurium oxide into tellurium dioxide gas and improving recovery rates. High temperatures can significantly accelerate the decomposition rate of copper tellurium oxide, shorten reaction time, and increase production efficiency. However, high temperatures should be avoided, such as tellurium volatilization caused by high temperatures, incomplete condensation caused by excessive gas flow rates, or equipment damage. The present invention sets the heating rate to the vacuum thermal decomposition temperature within the above range, slowly increasing the temperature to ensure uniform decomposition of copper tellurium oxide, improve the purity of the tellurium dioxide product, and avoid equipment damage. The present invention sets the vacuum thermal decomposition pressure within the aforementioned range. Low pressure lowers the boiling point of tellurium, promotes the separation of tellurium dioxide gas, inhibits the volatilization of potentially harmful substances, reduces energy consumption, and avoids excessive equipment costs. The present invention sets the vacuum thermal decomposition time within the aforementioned range to ensure sufficient time for complete decomposition of copper tellurium oxide while avoiding excessive energy consumption. The present invention places copper tellurium oxide in a quartz or stainless steel container for vacuum thermal decomposition to avoid contamination of the tellurium dioxide product and ensure the container's high-temperature and corrosion resistance.

[0031] As an embodiment, the copper oxide is used as a by-product as a catalyst, a battery additive or as a raw material for reducing metallic copper; the catalyst is an oxidation reaction catalyst; the battery additive is an additive for lithium-ion battery positive electrode materials; the raw material used for reducing metallic copper is specifically reduced and extracted by hydrogen reduction or carbon thermal reduction.

[0032] After obtaining the tellurium dioxide gas, the present invention condenses the tellurium dioxide gas to obtain a tellurium dioxide product.

[0033] In one embodiment, the condensation is performed by passing the tellurium dioxide gas into a condensation device containing a coolant for condensation; the coolant is water; the condensation device is a water-cooled condenser with a spiral inner tube; the inlet temperature of the condensation device containing the coolant is 20-30°C, specifically 25°C or 20°C in specific embodiments, and the outlet temperature is 40-50°C, specifically 45°C or 50°C in specific embodiments; the flow rate of the coolant in the condensation device containing the coolant is 1.5-2.5 m / s, specifically 2 m / s or 1.8 m / s in specific embodiments; and the flow rate of the tellurium dioxide gas is 1-3 m / s, specifically 1.5-2 m / s in specific embodiments. The present invention utilizes a spiral inner tube to increase the internal area, which helps accelerate the condensation of the tellurium dioxide gas. The present invention sets the inlet and outlet temperatures within the aforementioned ranges. The low inlet temperature creates a large temperature difference with the tellurium dioxide gas, leading to faster heat transfer, accelerated condensation of the tellurium dioxide gas, and improved recovery rates. The outlet temperature also slows the rate at which heat absorption capacity decreases, ensuring a sufficient temperature difference to drive heat exchange and fully condense the tellurium dioxide gas. This prevents excessively high coolant temperatures after heat absorption, which could reduce cooling efficiency, and excessively low coolant temperatures, which could increase energy consumption or damage equipment. The present invention sets the coolant flow rate within the aforementioned range to balance heat exchange efficiency and energy consumption, improving heat exchange efficiency, accelerating cooling, and promoting rapid condensation of tellurium dioxide gas, thereby increasing tellurium recovery rates.

[0034] As an embodiment, the recovery rate of the tellurium dioxide product is ≥95%, specifically 95%, and the purity is ≥99.5%, specifically 99.7% or 99.8%.

[0035] Figure 1 Schematic diagram of the process for preparing tellurium dioxide by oxidation roasting and vacuum thermal decomposition of copper tellurium slag in an embodiment of the present invention. Figure 1 As shown, the present invention oxidizes and roasts the crushed copper tellurium slag obtained by crushing and grinding the copper tellurium slag at high temperature with oxygen, and vacuum thermally decomposes the copper tellurium oxide obtained after the oxidative roasting to obtain tellurium dioxide gas and copper oxide, respectively. The tellurium dioxide gas is spirally water-cooled using water as a coolant to obtain high-purity tellurium dioxide; the obtained copper oxide can be used as an oxidation reaction catalyst or an additive for lithium-ion battery positive electrode materials, or the copper oxide can be reduced to copper by hydrogen reduction or carbon thermal reduction. The method of preparing tellurium dioxide by oxidative roasting-vacuum thermal decomposition of copper tellurium slag of the present invention can efficiently separate and extract tellurium from the copper tellurium slag and prepare a high-purity tellurium dioxide product. The method of preparing tellurium dioxide by oxidative roasting-vacuum thermal decomposition of copper tellurium slag provided by the present invention has the advantages of a short process flow, low energy consumption, environmental friendliness, high tellurium recovery rate, and high purity of the obtained tellurium dioxide product.

[0036] The technical solutions of the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention, but they should not be understood as limiting the scope of protection of the present invention.

[0037] Example 1

[0038] Copper tellurium slag (containing 38.7% copper, 32.6% tellurium, and the remainder being impurity elements, including silver, iron, and sulfur) was crushed, screened, and magnetically separated in sequence to remove ferromagnetic impurities to obtain pretreated copper tellurium slag with a particle size of 1.5 mm. 1000 g of the pretreated copper tellurium slag was weighed and placed in a roasting furnace. A mixed gas of oxygen and nitrogen was introduced into the furnace at a flow rate of 0.5 m / s, and the volume fraction of oxygen in the mixed gas was 25%. The temperature was raised to 600° C. at a rate of 5° C. / min for oxidative roasting for 2.5 h. After the roasting was completed, the material was taken out, naturally cooled to room temperature in nitrogen, ground, and sieved with an 80-mesh sieve. The resulting powder with a particle size of ≤178 μm was placed in a quartz container and then placed in a vacuum thermal decomposition furnace. The vacuum system pressure was controlled to 5×10 -4 Pa, heated to 1100°C at a rate of 5°C / min for 2 hours in vacuum thermal decomposition to produce tellurium dioxide gas and copper oxide. The generated tellurium dioxide gas was passed through a spiral inner tube water-cooled condenser at an inlet flow rate of 1.5 m / s, using water as the coolant. The inlet temperature was controlled at 25°C and the outlet temperature was maintained at 45°C. The cooling water flow rate was 2 m / s to solidify the tellurium dioxide gas and collect it, yielding tellurium dioxide with a purity of 99.7% and a recovery rate of 95%. The copper oxide obtained during the vacuum thermal decomposition process can be used as a by-product in catalysts, battery additives, or as a raw material for reducing metallic copper.

[0039] Example 2

[0040] Copper tellurium slag (containing 39.74% copper, 34.3% tellurium, and the remainder being impurity elements, including silver, iron, and sulfur) was crushed, screened, and magnetically separated in sequence to remove ferromagnetic impurities to obtain pretreated copper tellurium slag with a particle size of 1 mm. 1000 g of the pretreated copper tellurium slag was weighed and placed in a roasting furnace. A mixed gas of oxygen and nitrogen was introduced into the furnace at a flow rate of 0.8 m / s, and the volume fraction of oxygen in the mixed gas was 30%. The temperature was raised to 550° C. at a rate of 5° C. / min for oxidative roasting for 3 h. After the roasting was completed, the material was taken out, naturally cooled to room temperature in nitrogen, ground, and sieved with an 80-mesh sieve. The resulting powder with a particle size of ≤178 μm was placed in a quartz container and then placed in a vacuum thermal decomposition furnace. The vacuum system pressure was controlled to 8×10 -4Pa, heated to 1000°C at a rate of 5°C / min for 3 hours in vacuum thermal decomposition to produce tellurium dioxide gas and copper oxide. The generated tellurium dioxide gas was passed through a spiral inner tube water-cooled condenser at an inlet flow rate of 1.5 m / s, using water as the coolant. The inlet temperature was controlled at 20°C and the outlet temperature was maintained at 50°C. The cooling water flow rate was 1.8 m / s to solidify the tellurium dioxide gas and collect it, yielding tellurium dioxide with a purity of 99.8% and a recovery rate of 95%. The copper oxide obtained during the vacuum thermal decomposition process can be used as a by-product in catalysts, battery additives, or as a raw material for reducing metallic copper.

[0041] Comparative Example 1

[0042] Copper-tellurium slag with the same copper-tellurium content, impurity element content, and content as in Example 1 (38.7% copper, 32.6% tellurium, with the remainder being impurity elements, including silver, iron, and sulfur) was sequentially crushed, screened, and magnetically separated to remove ferromagnetic impurities, yielding a pretreated copper-tellurium slag with a particle size of 1 mm. The pretreated copper-tellurium slag was weighed and placed in a roasting furnace. It was then subjected to atmospheric oxidative roasting at 500°C in an air atmosphere for 3 hours. The resulting atmospheric oxidative roasting product was leached with a 4 mol / L NaOH solution at 90°C for 4 hours to produce a Na2TeO3 solution. This solution was acidified by slowly adding a 1 mol / L H2SO4 solution until the pH dropped to 3.0, causing tellurium to precipitate as TeO2. The tellurium dioxide product was then filtered and dried to yield a tellurium dioxide product. Testing revealed a tellurium recovery rate of 82.3%, and the purity of the resulting tellurium dioxide product was 92.5%.

[0043] Compared with Example 1, the technical solution in Comparative Example 1 consumes large amounts of acid and alkali reagents and produces saline wastewater, resulting in high chemical reagent costs and environmental impacts. This technical solution also suffers from a lengthy and time-consuming process, resulting in tellurium loss during the process. The final tellurium recovery rate is 12.7% lower than that in Example 1, and the purity of the tellurium dioxide product is 7.2% lower. These data highlight the advantages of the oxidative roasting-vacuum thermal decomposition method employed in the present invention in terms of resource utilization and environmental performance.

[0044] Comparative Example 2

[0045] The copper tellurium slag (containing 39.74% copper, 34.3% tellurium, and the remainder being impurity elements, including silver, iron, and sulfur) having the same copper tellurium content, impurity elements, and content as in Example 2 was crushed, sieved, and magnetically separated in sequence to remove ferromagnetic impurities to obtain a pretreated copper tellurium slag with a particle size of 1.5 mm. 1000 g of the pretreated copper tellurium slag was weighed and placed in a roasting furnace. A mixed gas containing oxygen and nitrogen at a flow rate of 1 m / s was introduced into the furnace, wherein the volume fraction of oxygen in the mixed gas was 25%. The temperature was raised to 350° C. at a rate of 5° C. / min and the oxidative roasting was performed for 2.5 h. After the roasting was completed, the oxidative roasting product was taken out, naturally cooled to room temperature in nitrogen, ground, and sieved with an 80-mesh sieve. The powder having a particle size of ≤178 μm was placed in a quartz container and then placed in a vacuum thermal decomposition furnace. The vacuum system pressure was controlled to be 5×10 -4 Pa, vacuum pyrolysis was performed at 1000°C for 3 hours to produce tellurium dioxide gas and copper oxide. The generated tellurium dioxide gas was passed through a spiral inner tube water-cooled condenser at an inlet flow rate of 1.5 m / s, using water as the coolant. The inlet temperature was controlled at 35°C and the outlet temperature was maintained at 50°C. The cooling water flow rate was 1.8 m / s, causing the tellurium dioxide gas to solidify and be collected to obtain the tellurium dioxide product. Testing showed that the tellurium recovery rate was only 78.1%, and the purity of the obtained tellurium dioxide product was 89.4%. The copper oxide obtained during the vacuum pyrolysis process can be used as a by-product in catalysts, battery additives, or as a raw material for reducing metallic copper.

[0046] Compared with Example 2, the technical solution in Comparative Example 2 failed to completely decompose the copper tellurium oxide due to insufficient oxidation roasting temperature, resulting in a high tellurium content in the residual solids, which in turn affected the tellurium recovery rate. Furthermore, the cooling water inlet temperature of 35°C was too high compared to Example 2, exceeding the set range of 20-30°C. This resulted in a small temperature difference and low condensation efficiency, causing some TeO2 gas to escape. The final recovery rate was 16.9% lower than that of Example 2, and the purity was 10.4% lower. These data confirm that the roasting temperature and condensation temperature difference affect the recovery rate, highlighting the advantages of the oxidation roasting-vacuum thermal decomposition process adopted in the present invention in terms of resource utilization and environmental performance.

[0047] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing tellurium dioxide by oxidative roasting and vacuum thermal decomposition of copper tellurium slag, comprising the following steps: The copper-tellurium slag powder is subjected to oxidation roasting in a mixed atmosphere containing oxygen to obtain copper-tellurium oxide; the oxidation roasting temperature is 400-600° C.; The copper tellurium oxide is subjected to vacuum thermal decomposition, and the obtained tellurium dioxide gas is condensed to obtain a tellurium dioxide product.

2. The method according to claim 1, characterized in that The particle size of the copper-tellurium slag powder is 1-2 mm.

3. The method according to claim 1, characterized in that The heat preservation time of the oxidation roasting is 2 to 3 hours.

4. The method according to claim 1, wherein The volume fraction of oxygen in the mixed atmosphere containing oxygen is 21-30%; the flow rate of the mixed atmosphere containing oxygen is 0.5-3 m / s.

5. The method according to claim 1, characterized in that The heating rate for heating to the temperature of the oxidation roasting is 5 to 10° C. / min.

6. The method according to claim 1, characterized in that The temperature of the vacuum thermal decomposition is 900-1200°C and the pressure is 4×10 -4 Pa~1Pa, the heat preservation and pressure holding time is 1~3h; the heating rate of heating to the temperature of vacuum thermal decomposition is 5~10℃ / min.

7. The method according to claim 1, characterized in that The condensation is carried out by passing the tellurium dioxide gas into a condensation device filled with a coolant for condensation; the coolant is water; the condensation device is a spiral inner tube water-cooled condenser; the inlet temperature of the condensation device filled with coolant is 20-30°C, and the outlet temperature is 40-50°C; the flow rate of the coolant in the condensation device filled with coolant is 1.5-2.5m / s; the introduction flow rate of the tellurium dioxide gas is 1-3m / s.

8. The method according to claim 1, characterized in that After the oxidative roasting, the process also includes: cooling, crushing and screening the product of the oxidative roasting in a protective gas in sequence to obtain a powder of copper tellurium oxide; the protective gas includes nitrogen or an inert gas; the mesh size of the sieve used for the screening is 50 to 100 meshes, and the particle size of the copper tellurium oxide powder obtained after crushing and screening is ≤300 μm.

9. The method according to claim 1, characterized in that Calculated by mass percentage, the copper-tellurium slag powder comprises 30-50% copper, 30-50% tellurium, and the remainder is impurity elements, which include one or more of silver, iron and sulfur.

10. The method according to claim 1, characterized in that The recovery rate of the tellurium dioxide product is ≥95%, and the purity is ≥99.5%.

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