Method for efficiently removing arsenic from crude selenium produced by sulfating roasting of copper anode slime

Abstract

The invention discloses a method for efficiently removing arsenic from crude selenium produced by copper anode slime sulfating roasting, and belongs to the technical field of hydrometallurgy. According to the method, acid-alkali two-step wet pretreatment is combined with a vacuum distillation process. The method comprises the following steps: firstly, soaking crude selenium for the first time at a specific liquid-solid ratio by using a dilute sulfuric acid solution with the pH value of 1 to preliminarily remove most arsenic; then, an alkaline solution with the pH value being 9 is used, a composite vulcanizing agent is added, second-time soaking is carried out under the heating condition, impurities such as arsenic and tellurium are deeply removed, and washing is carried out through high-purity water; and finally, carrying out vacuum melting and distillation on the pretreated crude selenium to obtain a high-purity selenium product. The technical problem that arsenic and selenium are difficult to separate due to the fact that the boiling points are close is effectively solved, the technological process is short, operation is easy and convenient, the impurity removal efficiency is high, 3N or 4N high-purity selenium with the arsenic content lower than 0.0005% can be stably produced, and the industrial application value is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to an efficient method for removing arsenic from crude selenium produced by sulfation roasting of copper anode mud. It is particularly suitable for the pretreatment and removal of impurities such as arsenic and tellurium from crude selenium, providing technical support for the subsequent vacuum distillation preparation of high-purity selenium products. Background Technology

[0002] Traditional crude selenium refining processes primarily rely on pyrometallurgical vacuum distillation to produce 2N or 3N selenium products. Generally, because the boiling point of arsenic (approximately 615℃) is close to that of selenium (685℃), vacuum distillation struggles to achieve adequate arsenic separation from crude selenium. However, pre-treated crude selenium can yield compliant 3N or 4N selenium products using vacuum distillation. Furthermore, once arsenic enters the selenium product, it is difficult to remove even with secondary vacuum distillation, thus hindering product quality improvement. The efficient removal of arsenic and tellurium as impurities during crude selenium refining remains a significant challenge for the selenium purification and refining industry.

[0003] Crude selenium is produced during the sulfation roasting of copper anode mud, where flue gas in the form of selenium dioxide enters the selenium absorption tank and is reduced by sulfur dioxide in the flue gas. Crude selenium is generally used in oxidative refining to produce selenium dioxide. Selenium dioxide is highly hygroscopic, producing selenite, which is highly corrosive and requires a strict operating environment. When crude selenium is used to produce refined selenium, the main problem is excessive levels of arsenic and tellurium.

[0004] Patent application CN110745789A, entitled "A Method for Purifying Crude Selenium," describes a method that involves adding a regulator to crude selenium slag to induce oxidation of impurity elements, thereby altering their state. The method then utilizes the difference in properties between the impurity elements and selenium under vacuum conditions to separate selenium from the impurities through vacuum distillation. The selenium product obtained using this method meets the Se99 specification in the YS / T223-3007 standard.

[0005] The invention patent CN113548647A, entitled "A Method for Deep Removal of Arsenic and Mercury from Crude Selenium," describes a method that involves heating and melting crude selenium material in a reactor, then subjecting the resulting melt to negative pressure filtration. This initial separation of the main element selenium from arsenic and mercury yields an industrial-grade selenium melt. The negative pressure filtration process employs multi-stage filtration with a mesh size of 500-1500 mesh. The resulting industrial-grade selenium melt is then subjected to vacuum distillation in a vacuum furnace for a further separation of the main element selenium from arsenic and mercury, producing a selenium product that meets the Se999 specification of the YS / T223-3007 standard. While patents CN110745789A and CN113548647A propose some methods for purifying crude selenium, the similar boiling points of selenium and arsenic make it difficult to precisely control the distillation temperature during vacuum distillation to further separate arsenic and selenium. Furthermore, these methods suffer from problems such as long process flows, complex operations, and unstable arsenic removal efficiency. Therefore, developing an efficient, economical, and easy-to-operate method for removing arsenic from crude selenium has significant industrial application value. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for efficiently removing arsenic from crude selenium produced by sulfation roasting of copper anode mud. By combining acid-alkali two-step wet pretreatment with vacuum distillation, the method achieves efficient removal of impurities such as arsenic and tellurium from crude selenium, and finally produces a high-purity selenium product that meets the Se9999 grade in the YS / T223-2007 standard.

[0007] The technical solution of this invention is achieved as follows: A method for efficiently removing arsenic from crude selenium by sulfation roasting of copper anode mud includes the following steps: a. Acid leaching pretreatment: The crude selenium produced by sulfation roasting of copper anode mud is mixed with a dilute sulfuric acid solution with a pH of 0.5-1.5 and soaked for 0.5-1.0 hours under the condition of liquid-solid ratio of 3-5:1 to carry out the first stage of arsenic removal; b. Alkali leaching and sulfidation pretreatment: The crude selenium treated in step a is mixed with an alkaline solution with a pH of 8-10 and a composite sulfiding agent. The mixture is then soaked for 0.5-1.0 hours at a liquid-to-solid ratio of 2-3:1 and a temperature of 50-75℃ to remove arsenic and tellurium in the second stage. The mixture is then washed with high-purity water until neutral. c. Vacuum distillation refining: The crude selenium processed in step b is vacuum melted, and then vacuum distilled under conditions of vacuum degree not exceeding 50 Pa and distillation temperature of 600-700℃ to obtain high-purity selenium product. Preferably, the dilute sulfuric acid solution in step a is industrial-grade dilute sulfuric acid, and the pH value of the dilute sulfuric acid solution is 1. Preferably, the pH value of the alkaline solution in step b is 9, and the alkaline solution is a sodium hydroxide or potassium hydroxide solution; Preferably, the composite sulfiding agent in step b is one or more of sodium sulfide, ammonium sulfide, or ammonium polysulfide, and its addition amount, calculated as sulfur (S), accounts for 0.5%-5% of the mass of crude selenium; Preferably, the mass percentage of sulfur in the composite vulcanizing agent is 40%. Preferably, the conductivity of the high-purity water in step b is not greater than 5 μS / cm; Preferably, in step c, the temperature of vacuum distillation is controlled at 600-700℃, and the vacuum degree is not higher than 10 Pa; Preferably, the arsenic content in the selenium product obtained by the method is less than 0.0005%, which meets the requirements of the Se9999 grade in the YS / T223-2007 standard.

[0008] The core principle of this invention is based on the chemical phases and amphoteric properties of impurity elements such as arsenic and tellurium. Through stepwise directional chemical reactions, these elements are selectively separated preferentially from crude selenium, thereby solving a problem that is difficult to solve by physical methods (vacuum distillation).

[0009] Selenium (Se) and arsenic (As) have very similar physical properties, especially their boiling points: Arsenic (As) has a boiling point of ~615℃, while selenium (Se) has a boiling point of ~685℃, a difference of only about 70℃. In vacuum distillation, the limited precision in temperature and pressure control leads to the simultaneous evaporation and co-condensation of large amounts of arsenic and selenium, making efficient separation impossible. Similar to the fractional distillation of alcohol and water, if the boiling points of the two liquids are very close, the separation purity will be poor. This is an inherent bottleneck in traditional pyrometallurgical refining processes.

[0010] This invention cleverly bypasses the limitations of physical properties and instead utilizes the differences in chemical properties between selenium and impurities such as arsenic and tellurium to remove them through a wet process before distillation.

[0011] Principle 1: First step: acid leaching – utilizing the acidic oxide properties of arsenic to remove soluble arsenic compounds.

[0012] Chemical principle: Arsenic in crude selenium usually exists in the form of arsenic trioxide (As2O3) or other soluble arsenates formed during the roasting of selenite. As2O3 is an acidic oxide that is soluble in acids or alkalis.

[0013] As₂O₃ + 3H₂O → 2H₃AsO₃ (arsenous acid, soluble in water) As2O3+ 6H + → 2As 3+ + 3H₂O (dissolves in strong acid) Function: Soaking in dilute sulfuric acid (pH=1) creates a highly acidic environment. Under this environment, a large number of soluble arsenic compounds (such as As₂O₃ and H₃AsO₃) in the crude selenium dissolve into the solution, thus achieving preliminary and large-scale arsenic removal (removal rate >75%). Simultaneously, this step may also dissolve some other metallic impurities (such as Cu and Sb).

[0014] Principle 2: The second step is alkaline leaching and sulfidation—utilizing the amphoteric nature of arsenic and tellurium and the precipitation characteristics of sulfidation for deep removal.

[0015] This is the most crucial and ingenious step in this invention.

[0016] The role of alkaline environment: After acid leaching, the remaining arsenic exists in a more stable form or in combination with selenium. Arsenic and tellurium are both amphoteric elements, and their oxides are soluble in both acids and alkalis. In an alkaline environment with pH=9, they can form soluble oxyacid anions, which are then desorbed from the surface of selenium particles.

[0017] As2O3 + 6OH - → 2AsO3 3- + 3H₂O (arsenite ion) TeO2+ 2OH - → TeO3 2- + H2O (tellurite ion) The core function of the composite vulcanizing agent is not merely to dissolve arsenic and tellurium; they must be completely "fixed" and removed from the system. This invention achieves this by adding a composite vulcanizing agent (such as Na2S). Under alkaline conditions, the vulcanizing agent provides sulfur. 2- Ions, arsenic and tellurium ions with S 2- It has an extremely strong affinity and will form extremely insoluble sulfide precipitates: 2AsO3 3- + 3S 2- + 9H + -> As2S3↓ + 3H2O (arsenic sulfide, yellow precipitate) TeO3 2- + 2S 2- + 3H₂O -> TeS₂↓ + 6OH⁻ - (Tellium sulfide, precipitate) The "killing two birds with one stone" effect: the alkaline environment "activates" arsenic and tellurium impurities into reactive ionic states, while sulfide ions immediately "capture" them to form stable precipitates. These precipitates can be easily separated from the crude selenium solids through subsequent filtration and washing steps.

[0018] The principle of process collaboration in this invention is the division of labor and cooperation between "wet pretreatment and pyrometallurgical refining".

[0019] This invention does not completely replace vacuum distillation, but rather complements it perfectly: Wet pretreatment: This addresses a problem that vacuum distillation struggles with—removing impurities (As, Te) with similar physical properties to selenium. It achieves targeted and deep removal through chemical reactions.

[0020] Pyrometallurgical refining: This process addresses problems that hydrometallurgical methods struggle with—efficiently and on a large scale purifying the main element, selenium, and removing volatile impurities with significantly different boiling points from selenium. After pretreatment, the material entering the distillation furnace is already very "clean," allowing vacuum distillation to focus solely on purifying selenium itself, easily producing high-purity selenium products of 3N or 4N.

[0021] The principle of this invention avoids the shortcomings of physical properties: it avoids the physical separation problem caused by the close boiling points of arsenic and selenium, and makes full use of the advantages of chemical properties: it utilizes the acidity of arsenic oxides to initially remove them by acid leaching.

[0022] By utilizing the amphoteric nature of arsenic and tellurium, they are activated by alkaline leaching. Then, taking advantage of the extremely low solubility of arsenic and tellurium sulfides, they are deeply precipitated and removed using a sulfiding agent. Ultimately, this chemically based targeted impurity removal pretreatment creates excellent conditions for subsequent physical separation methods (vacuum distillation), thus achieving the overall goal of efficient, low-cost, and high-quality production of high-purity selenium.

[0023] The beneficial effects of this invention are as follows: This invention effectively solves the technical problem of arsenic and selenium being difficult to separate due to their similar boiling points by using a two-step acid-base pretreatment method, and significantly reduces the content of impurities such as arsenic and tellurium in crude selenium; the process is short, easy to operate, low in cost, and highly adaptable; it can provide high-quality raw materials for vacuum distillation and ensure the stable production of high-purity selenium products; it also has a certain removal effect on impurity elements such as antimony, lead, and copper. Attached Figure Description

[0024] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0025] The present invention will be further illustrated by the following embodiments, but the present invention is not limited to the following embodiments. Example

[0026] The composition of crude selenium produced by sulfation roasting of copper anode slime is shown in the table below: Table 1. Content of each element in crude selenium (%) element As Te Sb Pb Cu content(%) 0.0048 0.0022 0.0066 0.0152 0.0026 Step a: Use a dilute sulfuric acid solution with pH=1, a liquid-to-solid ratio of 4:1, and soak for 0.8 hours. After treatment, the arsenic content decreased to 0.0012%, with a removal rate of 75%. The content of each element in the crude selenium after the first step of arsenic removal is shown in Table 2. Table 2. First step of crude selenium arsenic removal: content of each element in crude selenium (%) auxiliary materials element As Te Sb Pb Cu Dilute sulfuric acid solution (pH 1) content(%) 0.0012 0.0016 0.0052 0.0082 0.0012 Step b: Using a NaOH solution with pH=9 and sodium sulfide (sulfur content 40%) at a liquid-to-solid ratio of 2.5:1, soak at 65℃ for 0.8 hours, then wash with high-purity water until pH=7. After treatment, the arsenic content is <0.0005%, and the tellurium content is reduced to 0.0012%. The elemental contents in the crude selenium after the second arsenic removal step are shown in Table 3. Table 3. Arsenic Removal in Crude Selenium (Step 2): Element Content (%) auxiliary materials element As Te Sb Pb Cu Alkaline solution (pH 9) content(%) ＜0.0005 0.0012 0.0021 0.0026 0.0005 Step c: The pretreated crude selenium is melted in a vacuum furnace and vacuum distilled at 650℃ and 5 Pa to finally obtain a 4N selenium product with an arsenic content of <0.0005%.

[0027] The method described in this invention is not only applicable to crude selenium from copper anode mud, but can also be used for the pretreatment of other arsenic-containing selenium materials, and has broad industrial application prospects.

Claims

1. A method for efficient removal of arsenic from crude selenium produced by sulfuric acid roasting of copper anode slime, characterized in that The method comprises the following steps: a. acid leaching pretreatment: the crude selenium produced by sulfuric acid roasting of copper anode slime is mixed with a dilute sulfuric acid solution with a pH value of 0.5-1.5, and is soaked for 0.5-1.0 hours under the condition of a liquid-solid ratio of (3-5):1 to remove arsenic in the first stage; b. alkali leaching and sulfidation pretreatment: the crude selenium treated in step a is mixed with an alkaline solution with a pH value of 8-10 and a composite sulfidation agent, and is soaked for 0.5-1.0 hours under the condition of a liquid-solid ratio of (2-3):1 and a temperature of 50-75℃ to remove tellurium and arsenic in the second stage, and then is washed with high-purity water until neutral; c. vacuum distillation refining: the crude selenium treated in step b is subjected to vacuum melting, and then is subjected to vacuum distillation under the condition of a vacuum degree of not higher than 50 Pa and a distillation temperature of 600-700℃ to obtain a high-purity selenium product.

2. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 1, wherein the process is characterized by The dilute sulfuric acid solution in step a is an industrial-grade dilute sulfuric acid, and the pH value of the dilute sulfuric acid solution is 1.

3. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 1, wherein the process is characterized by The pH value of the alkaline solution in step b is 9, and the alkaline solution is a sodium hydroxide or potassium hydroxide solution.

4. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 1, wherein the process is characterized by The composite sulfidation agent in step b is one or more of sodium sulfide, ammonium sulfide or polyammonium sulfide, and the addition amount of the composite sulfidation agent, calculated in terms of sulfur (S), accounts for 0.5%-5% of the mass of the crude selenium.

5. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 4, wherein the process is characterized by The mass fraction of sulfur in the composite sulfidation agent is 40%.

6. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 1, wherein the process is characterized by The conductivity of the high-purity water in step b is not higher than 5 μS / cm.

7. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 1, wherein the process is characterized by The temperature of the vacuum distillation in step c is controlled at 600-700℃, and the vacuum degree is not higher than 10 Pa.

8. A process for efficient removal of arsenic from crude selenium produced by sulphatizing roasting of copper anode slime as claimed in claim 1, wherein the process is characterized by The selenium product obtained by the method has an arsenic content of less than 0.0005%, which meets the requirements of the Se9999 grade in YS / T223-2007.

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