Method for preparing copper and tellurium by reducing copper tellurite slag through rice

Abstract

The invention discloses a method for preparing copper and tellurium by reducing copper tellurite slag through rice, and belongs to the field of metallurgical energy conservation and emission reduction and comprehensive utilization. The method provided by the invention comprises the following steps: washing, chopping and air-drying rice straws; fully mixing the treated crushed rice straw with the copper tellurite slag by using a ball mill; putting the mixed substances into a hydraulic tablet press, and pressing the mixed disintegrating slag into balls; carrying out two-stage vacuum pyrolysis reaction on the pretreated spherical mixture, wherein the first-stage reaction temperature is 350-500 DEG C; the reaction temperature of the second stage is 800-900 DEG C; and preparing to obtain metal copper and metal tellurium. The method overcomes the bottlenecks of pollution gas generation, pollution waste acid water generation, strong acid addition, long flow, complex process and the like in the traditional separation means of copper and tellurium in copper tellurite, realizes the separation of copper and tellurium in industrial grade copper tellurite compared with the traditional pyrolysis mode, and has the characteristics of environmental friendliness, low cost, stable product quality, easy realization of industrialization, and the like. And the like.

Description

Technical Field

[0001] The invention relates to a method for preparing copper and tellurium by reducing copper tellurite slag with rice, and belongs to the field of metallurgical energy conservation, emission reduction and comprehensive utilization. Background Art

[0002] Rice straw is the residue left after rice harvest, including the stems, leaves, and ears. Due to its high abundance and difficulty in processing, its development in the energy sector has attracted widespread attention. The Food and Agriculture Organization of the United Nations (FAO) considers rice straw a viable agricultural biomass resource and encourages its conversion into energy, feed, fertilizer, and other resources through appropriate technologies and management practices, thereby improving agricultural resource utilization efficiency, reducing waste, and promoting sustainable agricultural development.

[0003] Copper tellurite (CuTeO3) is one of the important forms of tellurium (Te) in copper anode mud. Its chemical composition is a composite oxide of copper, tellurium and oxygen. In its crystal structure, copper and tellurite (TeO3 2- ) are bound together through ionic bonds, exhibiting high chemical stability. As a rare and precious metal compound, copper tellurite is one of the key target phases for tellurium recovery during copper smelting. Its efficient extraction is crucial for achieving tellurium recycling. As a key carrier of tellurium in copper anode mud, its efficient recovery is crucial for alleviating tellurium resource shortages and promoting the development of green metallurgy.

[0004] At present, there are three methods for treating copper tellurite in copper anode mud: wet acid leaching technology, fire-wet combined process, and full wet cascade separation process. Wet acid leaching technology includes pressure acid leaching to remove copper tellurium, sodium sulfide tellurium separation method, nitric acid leaching-cyclone electrolysis and other methods. In these wet acid leaching processes, the basic principle is to use acidic solutions such as sulfuric acid or nitric acid, with the assistance of oxidants (such as H2O2, O2), to remove copper (Cu) in copper tellurite. 2+ ) and tellurium (TeO3 2- ) is dissolved into soluble ions to achieve metal separation. Although wet acid leaching technology can preferentially dissolve copper and tellurium and reduce the loss of precious metals (gold and silver), the process will produce waste gas (NO2, CI 2、SO2), consumes large amounts of reagents (highly costly) and produces significant amounts of wastewater, resulting in low metal recovery rates (tellurium leaching rates are typically only 60% to 80%). The combined pyrometallurgical-hydrometallurgical process includes reduction smelting-vacuum distillation and sulfate roasting-leaching. Its basic principle is to reduce copper tellurite to an alloy through pyrometallurgical smelting, then hydrometallurgically dissolve impurities such as lead and bismuth to further purify tellurium and precious metals. While this method offers high precious metal recovery rates, the pyrometallurgical smelting temperatures reach 1200-1400°C, resulting in high energy consumption and extremely demanding equipment. The fully hydrometallurgical cascade separation process, based on a multi-step hydrometallurgical separation process, achieves high overall metal recovery rates (copper, tellurium, and selenium recoveries all exceed 90%). However, the process is lengthy, involving multiple leaching, filtration, and purification steps. The complex operation also consumes large amounts of reagents, including sodium sulfide and sulfuric acid, increasing costs. Summary of the Invention

[0005] To solve the above technical problems, the present invention adopts a method for preparing copper and tellurium by reducing copper tellurite slag with rice, which realizes the efficient and green separation of copper and tellurium. This method has the advantages of low reaction cost, short process flow, green environmental protection, resource conservation, and high product quality.

[0006] In order to achieve the above object, the present invention comprises the following steps: (1) Wash the rice straw, dry it, and chop it to obtain rice straw residue.

[0007] (2) The rice straw residue and copper tellurite residue are mixed evenly and then pressed into a spherical mixture.

[0008] (3) The spherical mixture is subjected to a two-stage vacuum thermal reduction, and after cooling, elemental tellurium is obtained at the top of the furnace, and elemental copper is obtained in the reactants.

[0009] Preferably, in step (2), the mass ratio of rice straw residue to copper tellurite residue is 3:1 to 5:1.

[0010] Preferably, the conditions for the two-stage vacuum thermal reduction in step (3) are: first pyrolysis at 350-500°C and 10-50 Pa for 1-2 hours; then pyrolysis at 800-900°C and 1-10 Pa for 2-3 hours.

[0011] Preferably, the vacuum pyrolysis reduction in step (3) uses a tubular vacuum pyrolysis furnace.

[0012] Beneficial effects of the present invention: (1) Compared with the traditional method, the method of the present invention uses rice straw as a reducing agent to improve the recovery rate of copper and tellurium. Combined with the two-stage vacuum thermal reduction, copper and tellurium are efficiently separated, so that the recovery rates of copper and tellurium are as high as 98% and 99%, respectively. In addition, the reaction cost is lower, the process flow is shorter, it is green and environmentally friendly, saves resources, and has high product quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 The figure is a schematic diagram of the process flow of the method of the present invention. DETAILED DESCRIPTION

[0014] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0015] Example 1 A method for preparing copper and tellurium by reducing copper tellurite slag using rice. The contents of various substances in the copper tellurite slag sample used in this example are shown in the following table: Chemical composition of copper tellurite slag samples (wt%) The specific steps are as follows: (1) Wash the rice straw, dry it with hot air, and then chop it to obtain rice straw residue.

[0016] (2) The rice straw residue and the copper tellurite slag were mixed and fully mixed in a ball mill. The ball milling speed was set to 200 rpm and the ball milling time was set to 10 minutes. The mixture was placed in a hydraulic tablet press and pressed into a spherical mixture. The mass ratio of the rice straw residue to the copper tellurite slag was 5:1.

[0017] (3) The spherical mixture is placed in a special high-temperature-resistant and corrosion-resistant material tray, and then slowly placed in a vacuum pyrolysis reactor for two-stage vacuum thermal reduction. In the first stage, the pressure in the reactor is reduced to 10Pa to remove the air and other impurity gases in the reactor and reduce the oxidation reaction during the pyrolysis process. The heating system is started, the temperature in the reactor is raised to 500℃, and the pyrolysis is carried out for 1.5h. In the second stage, the pressure in the reactor is reduced to 3Pa, the temperature in the reactor is raised to 880℃, and copper tellurite is reduced by vacuum carbon thermal reduction for 2.5h. After cooling, elemental tellurium is obtained on the top of the furnace, and elemental copper is obtained in the reactants.

[0018] X-ray diffraction (XRD) analysis revealed that the recovery rates of copper and tellurium were 98% and 99%, respectively.

[0019] Example 2 A method for preparing copper and tellurium by reducing copper tellurite slag using rice. The contents of various substances in the copper tellurite slag sample used in this example are shown in the following table: Chemical composition of copper tellurite slag samples (wt%) The specific steps are as follows: (1) Wash the rice straw, dry it with hot air, and then chop it to obtain rice straw residue.

[0020] (2) The rice straw residue and the copper tellurite slag were mixed and fully mixed using a ball mill. The ball milling speed was set to 200 rpm and the ball milling time was set to 10 minutes. The mixture was pressed into a spherical mixture, wherein the mass ratio of the rice straw residue to the copper tellurite slag was 3:1.

[0021] (3) The spherical mixture is placed in a special high-temperature-resistant and corrosion-resistant material tray, and then slowly placed in a vacuum pyrolysis reactor for two-stage vacuum thermal reduction. In the first stage, the pressure in the reactor is reduced to 10Pa to remove the air and other impurity gases in the reactor and reduce the oxidation reaction during the pyrolysis process. The heating system is started, the temperature in the reactor is raised to 450℃, and pyrolysis is carried out for 1h. In the second stage, the pressure in the reactor is reduced to 1Pa, the temperature in the reactor is raised to 900℃, and copper tellurite is reduced by vacuum carbon thermal reduction for 3h. After cooling, elemental tellurium is obtained on the top of the furnace, and elemental copper is obtained in the reactants.

[0022] X-ray diffraction (XRD) analysis revealed that the recovery rates of copper and tellurium were 97% and 97%, respectively.

[0023] Example 3 A method for preparing copper and tellurium by reducing copper tellurite slag using rice. The contents of various substances in the copper tellurite slag sample used in this example are shown in the following table: Chemical composition of copper tellurite slag samples (wt%) The specific steps are as follows: (1) Wash the rice straw, dry it with hot air, and then chop it to obtain rice straw residue.

[0024] (2) The rice straw residue and the copper tellurite slag were mixed and fully mixed in a ball mill. The ball milling speed was set to 200 rpm and the ball milling time was set to 10 minutes. The mixture was placed in a hydraulic tablet press and pressed into a spherical mixture. The mass ratio of the rice straw residue to the copper tellurite slag was 4:1.

[0025] (3) The spherical mixture is placed in a special high-temperature-resistant and corrosion-resistant tray, and then slowly placed in a vacuum pyrolysis reactor for two-stage vacuum thermal reduction. In the first stage, the pressure in the reactor is reduced to 50Pa to remove the air and other impurity gases in the reactor and reduce the oxidation reaction during the pyrolysis process. The heating system is started, the temperature in the reactor is raised to 350℃, and pyrolysis is carried out for 2h. In the second stage, the pressure in the reactor is reduced to 10Pa, the temperature in the reactor is raised to 800℃, and copper tellurite is reduced by vacuum carbon thermal reduction for 2h. After cooling, elemental tellurium is obtained on the top of the furnace, and elemental copper is obtained in the reactants.

[0026] X-ray diffraction (XRD) analysis revealed that the recovery rates of copper and tellurium were 97% and 96%, respectively.

[0027] Comparative Example 1 For comparison, the difference between this comparative example and Example 1 is that rice straw is not used. The other steps are the same as those in Example 1. The specific steps are as follows: (1) The copper tellurite slag was fully ball-milled in a ball mill at a speed of 200 rpm for 10 minutes. After 10 minutes, the copper tellurite slag was placed in a hydraulic tablet press and pressed into balls.

[0028] (3) The spherical objects are placed in a special high-temperature resistant and corrosion-resistant material tray, and then slowly placed in a vacuum pyrolysis reactor for two-stage vacuum thermal reduction. In the first stage, the pressure in the reactor is reduced to 10Pa to remove the air and other impurity gases in the reactor and reduce the oxidation reaction during the pyrolysis process. The heating system is started, the temperature in the reactor is raised to 500℃, and the pyrolysis is carried out for 1.5h. In the second stage, the pressure in the reactor is reduced to 3Pa, the temperature in the reactor is raised to 880℃, and copper tellurite is reduced by vacuum carbon thermal reduction for 2.5h. After cooling, elemental tellurium is obtained on the top of the furnace, and elemental copper is obtained in the reactants.

[0029] X-ray diffraction (XRD) analysis revealed that the recovery rate of copper was 75% and the recovery rate of tellurium was 67%.

[0030] The recovery rates of copper and tellurium in this comparative example are lower than those in Example 1 because rice straw is not used, resulting in a lack of the high surface functional groups, microporous structure, and alkali metal flux unique to rice straw biochar in the reaction. This results in insufficient reducing agent activity, making it difficult to efficiently reduce copper and tellurium oxides. Furthermore, the lack of a low-melting-point eutectic aggravates tellurium volatilization losses. Without straw, the aforementioned multiple factors act together, resulting in inadequate reduction and uncontrolled tellurium volatilization, ultimately reducing recovery efficiency. Comparative studies have shown that the use of rice straw can increase copper recovery rates from 75% to over 98%, and tellurium recovery rates from 67% to over 99%. Comparative Example 2 For comparison, the difference between this comparative example and Example 1 is that only one-stage vacuum thermal reduction is performed, and the specific steps are as follows: (1) Wash the rice straw, dry it with hot air, and then chop it to obtain rice straw residue.

[0031] (2) The rice straw residue and the copper tellurite slag were mixed and fully mixed in a ball mill. The ball milling speed was set to 200 rpm and the ball milling time was set to 10 minutes. The mixture was placed in a hydraulic tablet press and pressed into a spherical mixture. The mass ratio of the rice straw residue to the copper tellurite slag was 5:1.

[0032] (3) The spherical mixture is placed in a special high-temperature-resistant and corrosion-resistant material tray, and then slowly placed in a vacuum pyrolysis reactor for one-stage vacuum thermal reduction, so that the pressure in the reactor drops to 3Pa, the temperature in the reactor is raised to 880℃, and the copper tellurite is vacuum carbon-thermally reduced for 2.5h; after cooling, elemental tellurium is obtained at the top of the furnace, and elemental copper is obtained in the reactants.

[0033] X-ray diffraction (XRD) analysis revealed that the recovery rate of copper was 78% and the recovery rate of tellurium was 81%.

[0034] The copper and tellurium recovery rates in this comparative example were lower than those in Example 1. This is because the single-stage vacuum thermal reduction process lacks the directional biochar preparation process and its synergistic effects. The straw undergoes high-temperature carbonization without undergoing low-temperature carbonization, leading to collapse of the porous skeleton and decomposition of surface functional groups. Furthermore, 70–80% of the alkali metals (K and Na) are lost due to high-temperature volatilization. This prevents the formation of a low-melting-point eutectic to immobilize tellurium (TeO2 is lost due to sublimation), and also increases the activation energy for copper oxide reduction, making it difficult to reduce. The single-stage process lacks the synergistic effect of "biochar structure optimization and vacuum carbon thermal reduction," ultimately reducing recovery efficiency. Comparative studies have shown that the two-stage process can increase copper recovery from 78% to 98% and tellurium from 81% to 99%.

[0035] Comparative Example 3 For comparison, in this comparative example, rice straw and copper tellurite slag were simply mixed without tableting. The specific steps were as follows: (1) Wash the rice straw, dry it with hot air, and then chop it to obtain rice straw residue; (2) The rice straw residue and the copper tellurite slag are uniformly mixed to obtain a mixture, wherein the mass ratio of the rice straw residue to the copper tellurite slag is 5:1.

[0036] (3) The mixture is placed in a special high-temperature-resistant and corrosion-resistant tray, and then slowly placed in a vacuum pyrolysis reactor for two-stage vacuum thermal reduction. In the first stage, the pressure in the reactor is reduced to 10Pa to remove the air and other impurity gases in the reactor and reduce the oxidation reaction during the pyrolysis process. The heating system is started, the temperature in the reactor is raised to 500℃, and the pyrolysis is carried out for 1.5h. In the second stage, the pressure in the reactor is reduced to 3Pa, the temperature in the reactor is raised to 880℃, and copper tellurite is reduced by vacuum carbon thermal reduction for 2.5h. After cooling, elemental tellurium is obtained on the top of the furnace, and elemental copper is obtained in the reactants.

[0037] X-ray diffraction (XRD) analysis revealed that the recovery rate of copper was 86% and the recovery rate of tellurium was 88%.

[0038] The copper and tellurium recovery rates in this comparative example were lower than those in Example 1. This is because simple mixing, due to the lack of mechanical force, results in insufficient physical contact, mass transfer efficiency, and chemical reaction activity between rice straw and copper tellurite slag. In particular, the coarse straw structure and copper tellurite slag agglomerates hinder the effective release of copper and tellurium. Through treatment methods such as ball milling and tableting, the microscopic dispersion and reaction interface of the materials can be significantly improved, thereby improving the metal recovery rate. Comparative studies have shown that the use of ball milling and tableting processes can increase the copper recovery rate from 86% to 98% and the tellurium recovery rate from 88% to 99%.

[0039] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to existing technologies, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing copper and tellurium by reducing copper tellurite slag with rice, characterized in that: The following steps are involved: (1) Washing the rice straw, drying it, and chopping it to obtain rice straw residue; (2) Mixing rice straw residue and copper tellurite residue evenly and pressing the mixture into a ball-shaped mixture; (3) The spherical mixture is subjected to a two-stage vacuum thermal reduction, and after cooling, elemental tellurium is obtained at the top of the furnace, and elemental copper is obtained in the reactants.

2. The method for preparing copper and tellurium by reducing copper tellurite slag with rice according to claim 1, characterized in that: In step (2), the mass ratio of rice straw residue to copper tellurite residue is 3:1 to 5:

1.

3. The method for preparing copper and tellurium by reducing copper tellurite slag with rice according to claim 1, characterized in that: The conditions for the two-stage vacuum thermal reduction in step (3) are: first, pyrolysis at 350-500°C and 10-50 Pa for 1-2 hours; then, pyrolysis at 800-900°C and 1-10 Pa for 2-3 hours.

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