A method for liquid so2 reduction of selenium

Abstract

The application discloses a liquid SO2 reduction selenium process method, and belongs to the field of smelting engineering by-product recovery. The method comprises the following steps: passing a deselenization solution into steam to heat the solution, adding sulfuric acid, and controlling the pH value at 6.2-6.5; when the solution is heated to 75-85 DEG C, the heating of the solution is stopped, and liquid SO2 is passed into the solution to perform deep reduction of selenium; a solution sample is taken out from a reaction tank, thiocyanate is added to the solution sample for colorimetry, whether the reduction process reaches an end point is judged through color change, the passing of the liquid SO2 is stopped after the selenium reduction reaction is completed; the solution is stirred, SO2 gas in the solution is completely removed, and then solid-liquid separation is performed; the filtered crude selenium is washed, and finally, a crude selenium product is output. The application adopts SO2 to reduce selenium in a selenium-containing solution, the utilization rate of SO2 is not less than 98%, the reduction rate of selenium is not less than 99%, and the selenium content in the solution is less than 100 mg / L.

Description

Technical Field

[0001] This invention belongs to the field of by-product recovery in metallurgical engineering, and specifically relates to a method for reducing selenium with liquid SO2. Background Technology

[0002] The treatment of copper electrolysis anode slime generally employs the Kaldor furnace pyrometallurgical process. In this process, the smelting flue gas in the Kaldor furnace is washed with a circulating washing solution to recover selenium. However, the current process and its set parameters are poorly adaptable to high-impurity anode slime. Furthermore, the current process conditions result in long processing times, high energy consumption, and high temperatures, affecting the Kaldor furnace's operating rate and selenium distillation indicators, thus impacting selenium recovery and compromising the selenium recovery rate. Secondly, the crude selenium is washed using natural filtration, which is slow, incomplete, and leads to low selenium recovery. Simultaneously, selenium is lost through external discharge, and absorption control is flawed; the loss is even more severe when the amount of floating selenium is large. Currently, domestic anode slime selenium production using traditional processes suffers from problems such as long processes, numerous steps, high pollution, high costs, and low metal recovery rates.

[0003] The Venturi scrubbing process for selenium recovery involves drawing flue gas from the Kaldo furnace into a Venturi tube via an induced draft fan and a booster fan. The flue gas flows upwards, interacting with the downward-spraying absorbent liquid in the spray layer. Through mass and heat transfer, and chemical reactions, components such as SO2, SO3, and SeO2 are washed away. During absorption, the washing liquid, flowing downwards, undergoes counter-current collisions with the high-temperature, high-speed flue gas, resulting in complex physical and chemical reactions on the surface. The washing liquid absorbs SO2, SO3, and SeO2 from the flue gas, creating a concentration gradient of SO2, SO3, and SeO2 within the particles, diffused from the outside in. Simultaneously, moisture on the surface of the washing liquid gradually evaporates, reducing surface moisture as it diffuses from the interior of the slurry to the surface. This absorption and evaporation process gradually decreases surface moisture, leading to a gradual increase in the concentration of SO2, SO3, and SeO2 on the surface, achieving highly efficient heat and mass transfer. The absorbed liquid phase flows into the storage tank and is recycled in the venturi via a circulation pump when the emission concentration control requirements are not met.

[0004] This invention improves the selenium recovery system process of copper smelting companies, optimizes the Kaldor furnace selenium distillation process, and increases the grade of crude selenium to over 95%, thereby improving economic efficiency and enhancing current production technology. Selenium exists primarily in solution as selenite. In addition to selenium, the washing liquid also contains other metals such as Te, Pb, As, and Cu. To ensure that the selenium reduction process produces high-quality crude selenium, an SO2 reduction process is adopted. Besides neutralization and impurity removal before reduction, and the removal of tellurium and lead, the sulfur dioxide reduction conditions must be controlled to minimize the reduction of other metal impurities in the washing liquid, achieving higher quality crude selenium and reducing selenium circulation in the Venturi. Summary of the Invention

[0005] The purpose of this invention is to provide a method for reducing selenium with liquid SO2 to improve the selenium recovery rate and reduce the selenium recycling in the venturi.

[0006] The technical solution of this invention is: a method for reducing selenium with liquid SO2, comprising the following steps: A. Initial Reduction of Selenium-Deselenate Solution by Heating: The selenium-deselenate solution is pumped into a reduction tank, heated by steam, and sulfuric acid is added, maintaining the pH at 6.2-6.5. This process reduces most of the selenium in the solution. Without heating the solution, SO2 reduction of selenium under cold conditions presents several disadvantages to production: firstly, the selenium reduction reaction is very slow, and some selenium is re-dissolved, resulting in incomplete reduction by SO2; secondly, the crude selenium product is prone to agglomeration and adhesion during reduction, clogging production pipelines. Furthermore, the agglomerates in the reaction tank are difficult to clean, causing significant inconvenience to production control and operation, and potentially damaging production equipment. Heating the solution before SO2 reduction results in a faster reduction rate, producing a powdery crude selenium product that is less prone to agglomeration and adhesion, making the production process easier to control. A certain concentration of sulfuric acid in the deselenic solution is conducive to the selenium reduction reaction, but if the sulfuric acid concentration is too high, it will also lead to the re-dissolution of some selenium. Based on the thermodynamic analysis of the existence form of SO2 in aqueous solutions at different pH values, the reducing power of SO2, and the calculation of the electrode potential of related elements, the pH is most suitable when controlled between 6.2 and 6.5.

[0007] B. Deep Reduction by Aeration: When the solution is heated to 75-85℃, heating is stopped, and liquid SO2 is introduced to perform deep reduction of selenium in the solution. Liquid SO2 has strong reducing properties and can reduce selenite and selenite in the solution.

[0008] C. Thiourea pulse colorimetry: Take the solution sample from the reaction tank, add thiourea pulse for colorimetric analysis, and judge whether the reduction process has reached the endpoint by the color change. If the thiourea pulse does not turn red, it means that the selenium reduction has reached the endpoint; if the thiourea pulse turns red, liquid SO2 needs to be continued until the endpoint. After the selenium reduction reaction is completed, stop the flow of liquid SO2.

[0009] D. Liquid-solid separation: If the solution is immediately separated into solid and liquid, it will pollute the production environment and harm the health of employees. Therefore, the solution is stirred to remove SO2 gas, and then the solution is filtered through a plate and frame filter to achieve solid-liquid separation.

[0010] E. Washing: After liquid-solid separation, the filtered crude selenium is washed to remove impurities such as sodium salts, metal ions, and free acids. The crude selenium content reaches over 94%, and the selenium recovery rate of the entire process can reach over 92%, ultimately producing crude selenium products.

[0011] As a further improvement of the present invention, in step B, during the initial stage of reduction, the rate of introduction of liquid SO2 is 40-50 m / s. 3 / h; As the selenium reduction reaction continues, the rate at which liquid SO2 is introduced is continuously reduced. This is because at the beginning of the selenium reduction reaction, the selenium concentration in the solution is high, requiring a large amount of SO2. As the selenium reduction reaction continues, the selenium concentration in the solution decreases. If a large amount of SO2 continues to be introduced, it will cause SO2 gas to escape, polluting the production site and surrounding environment and harming the physical and mental health of employees. Furthermore, the SO2 is discharged directly without participating in the reaction, increasing the production cost of selenium reduction.

[0012] As a further improvement of the present invention, in step B, the SO2 reduction reaction time is 4.0-5.0 h.

[0013] As a further improvement of the present invention, in step D, the stirring time is 30 to 40 minutes.

[0014] As a further improvement of the present invention, in step E, the washing is performed 3-4 times.

[0015] The beneficial effects of this invention are: 1. This invention heats the selenium-depleting solution and adjusts its pH value, then reduces it with liquid SO2, and after filtration, crude selenium is obtained. This can effectively improve the operating efficiency of the system, achieve stable and efficient selenium recovery, provide technical support for the extension of the selenium industry chain, and increase the added value of selenium.

[0016] 2. The present invention effectively removes impurity elements during the crude selenium production process, improving the quality of crude selenium and reducing the pressure of subsequent processing; at the same time, the pre-removal of selenium from the intermediate material Venturi mud reduces the system circulation of selenium, increases the direct recovery rate of selenium, and is effectively combined and matched with existing production processes.

[0017] 3. The production process of this invention is simple, the quality is stable and reliable, the cost is low, and it has good economic benefits.

[0018] 4. This invention solves the problems of long process flow, high pollution, high cost and low metal recovery rate in crude selenium processing, and realizes the efficient operation of crude selenium recovery system.

[0019] 5. This invention uses SO2 to reduce selenium in a selenium-containing solution, with SO2 utilization rate not less than 98%, selenium reduction rate not less than 99%, and selenium content in the solution <100mg / L. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments.

[0022] After copper and tellurium are removed by sulfuric acid leaching of copper anode mud, it is smelted in a Kaldo furnace. During the chlorine smelting process, selenium metal is oxidized to selenium dioxide and volatilizes into the flue gas. The flue gas is then washed by a Venturi scrubber, and selenium enters the washing solution in the form of selenic acid. The deselenized solution is then treated using the method of this invention.

[0023] The content of the main components in the deselenate solution, expressed as a percentage by weight, is shown in Table 1.

[0024] The composition analysis of crude selenium products is shown in Table 2.

[0025] Example 1 The main components of the selenium-depleted solution, by weight percentage, are: Se: 59.6%, Te: 3.23%, As: 1.9%.

[0026] A method for reducing selenium with liquid SO2 includes the following steps: A. Initial reduction of the deselenization solution by heating: 20m 3 The selenium-depleted solution is pumped into the reduction tank, steam is introduced to heat the solution, sulfuric acid is slowly added, and the pH is controlled between 6.2 and 6.5 for 30 minutes. B. Deep reduction via aeration: When the solution is heated to 80℃, the steam valve is closed to stop heating the solution, and the steam is allowed to continue at a 40m ventilator. 3 Liquid SO2 is introduced at a rate of / h to carry out deep reduction of selenium in the solution. As the selenium reduction reaction continues, the amount of SO2 introduced is continuously reduced. C. Thiourea Pulp Colorimetry: After the reduction reaction in step B has been carried out for 4.0 hours, a solution sample is taken out from the reaction tank, and thiourea pulp is added for colorimetry. The color change is used to determine whether the reduction process has reached the endpoint. If the thiourea pulp does not turn red, it means that the selenium reduction has reached the endpoint. The flow of liquid SO2 is stopped, and the content of Se in the solution is <50mg / L. D. Liquid-solid separation: Stir the solution for 30 minutes to remove SO2 gas from the solution, and then separate the solid and liquid by plate and frame filtration. E. Washing: After liquid-solid separation, the filtered crude selenium is washed three times to remove impurities such as sodium salts, metal ions, and free acids. The final crude selenium product is then air-dried and becomes a qualified product.

[0027] The crude selenium obtained in this embodiment has the following main components: Se: 94.87%, Mg: 1.020%, Al: 0.232%, Fe: 0.012%.

[0028] Example 2 The main components of the selenium-depleted solution, by weight percentage, are: Se: 61.3%, Te: 2.37%, As: 2.2%.

[0029] A method for reducing selenium with liquid SO2 includes the following steps: A. Initial reduction of the deselenization solution by heating: 30m 3 The selenium-depleted solution is pumped into the reduction tank, steam is introduced to heat the solution, sulfuric acid is slowly added, and the pH is controlled between 6.2 and 6.5 for 40 minutes. B. Deep reduction via aeration: When the solution is heated to 75℃, the steam valve is closed to stop heating the solution, and the steam is allowed to continue for 50 minutes. 3 Liquid SO2 is introduced at a rate of / h to carry out deep reduction of selenium in the solution. As the selenium reduction reaction continues, the amount of SO2 introduced is continuously reduced. C. Thiourea Pulp Colorimetry: After the reduction reaction in step B has been carried out for 5.0 hours, a solution sample is taken out from the reaction tank and thiourea pulse is added for colorimetry. The color change is used to determine whether the reduction process has reached the endpoint. If the thiourea pulse does not turn red, it means that the selenium reduction has reached the endpoint. The flow of liquid SO2 is stopped and the content of Se in the solution is <60mg / L. D. Liquid-solid separation: Stir the solution for 40 minutes to remove SO2 gas from the solution, and then separate the solid and liquid by plate and frame filtration. E. Washing: After liquid-solid separation, the filtered crude selenium is washed four times to remove impurities such as sodium salts, metal ions, and free acids. The final crude selenium product is then air-dried and becomes a qualified product.

[0030] The crude selenium obtained in this embodiment has the following main components: Se: 96.43%, Mg: 1.160%, Al: 0.164%, Fe: 0.023%.

[0031] Example 3 The main components of the selenium-depleted solution, by weight percentage, are: Se: 56.26%, Te: 4.17%, As: 2.6%.

[0032] A method for reducing selenium with liquid SO2 includes the following steps: A. Initial reduction of the deselenization solution by heating: 25m 3 The selenium-depleted solution is pumped into the reduction tank, steam is introduced to heat the solution, sulfuric acid is slowly added, and the pH is controlled between 6.2 and 6.5 for 35 minutes. B. Deep reduction via aeration: When the solution is heated to 85℃, the steam valve is closed to stop heating the solution, and the solution is then subjected to a 45m... 3 Liquid SO2 is introduced at a rate of / h to carry out deep reduction of selenium in the solution. As the selenium reduction reaction continues, the amount of SO2 introduced is continuously reduced. C. Thiourea Pulp Colorimetry: After the reduction reaction in step B has been carried out for 4.5 hours, a solution sample is taken out from the reaction tank and thiourea pulp is added for colorimetry. The color change is used to determine whether the reduction process has reached the endpoint. If the thiourea pulp does not turn red, it means that the selenium reduction has reached the endpoint. The flow of liquid SO2 is stopped and the content of Se in the solution is <100mg / L. D. Liquid-solid separation: Stir the solution for 35 minutes to remove SO2 gas from the solution, and then separate the solid and liquid by plate and frame filtration. E. Washing: After liquid-solid separation, the filtered crude selenium is washed four times to remove impurities such as sodium salts, metal ions, and free acids. The final crude selenium product is then air-dried and becomes a qualified product.

[0033] The crude selenium obtained in this embodiment has the following main components: Se: 96.37%, Mg: 1.280%, Al: 0.225%, Fe: 0.019%.

Claims

1. A method for reducing selenium with liquid SO2, characterized in that, Includes the following steps: A. Initial reduction of deselenoside solution by heating: The deselenoside solution is pumped into a reduction tank, steam is introduced to heat the solution, sulfuric acid is added, and the pH is controlled at 6.2-6.5; B. Deep reduction by aeration: When the solution is heated to 75-85℃, the heating of the solution is stopped, and liquid SO2 is introduced to carry out deep reduction of selenium in the solution. C. Thiourea pulse colorimetry: Take out the solution sample from the reaction tank, add thiourea pulse and compare its color. The color change indicates whether the reduction process has reached the endpoint. If the thiourea pulse does not turn red, it means that the selenium reduction has reached the endpoint. If the thiourea pulse turns red, liquid SO2 needs to be continued until the endpoint. After the selenium reduction reaction is completed, stop the flow of liquid SO2. D. Liquid-solid separation: Stir the solution to remove SO2 gas, and then filter the solution through a plate and frame filter to achieve solid-liquid separation. E. Washing: After the liquid-solid separation is completed, the filtered crude selenium is washed to finally produce crude selenium product.

2. The method for reducing selenium with liquid SO2 according to claim 1, characterized in that: In step B, during the initial stage of reduction, the rate of liquid SO2 introduction is 40-50 m / s. 3 / h; As the selenium reduction reaction continues, the rate at which liquid SO2 is introduced is continuously reduced.

3. The method for reducing selenium with liquid SO2 according to claim 2, characterized in that: In step B, the SO2 reduction reaction time is 4.0-5.0 h.

4. The method for reducing selenium with liquid SO2 according to claim 1, characterized in that: In step D, the stirring time is 30 to 40 minutes.

5. The method for reducing selenium with liquid SO2 according to claim 1, characterized in that: In step E, wash 3-4 times.

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