Method for preparing 3N refined selenium from crude selenium
Through hydrogen peroxide digestion and liquid sulfur dioxide reduction methods, combined with microwave digestion and gas stirring devices, the existing crude selenium purification process is solved, and the efficient preparation of 3N refined selenium is achieved, simplifying the process and reducing costs.
Patent Information
- Application Number
- CN202510283675.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-11
- Publication Date
- 2025-06-20
AI Technical Summary
The existing crude selenium purification process has problems such as complex process, long cycle, high equipment and energy consumption costs, and poor operating environment, making it difficult to effectively improve the purity of selenium.
The digestion and reduction of liquid sulfur dioxide are adopted by hydrogen peroxide and the use of a gas stirring device to improve the digestion and reduction efficiency of crude selenium to achieve the preparation of 3N refined selenium.
The process flow is simplified, the equipment and energy consumption cost is reduced, the production cycle is shortened, the purity and purification efficiency of selenium are improved, and the working environment is improved.
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Figure CN120172358A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of wastewater treatment, and particularly relates to a method for preparing 3N refined selenium from crude selenium. Background Art
[0002] Due to its good physical and chemical properties, selenium plays an important role in many fields such as biomedicine, photocatalysis, thermoelectric converters, light-emitting diodes (LEDs), optical sensors, photodetectors, and field-effect transistors. The purity requirement for its use as an additive is above 99 wt%, the purity requirement for its use as a colorant is at least above 3N, and the purity requirement for its use as a semiconductor and sensor is even higher. Selenium rarely forms independent ore deposits in nature, and most of the selenium produced in industrial production is recovered as a by-product of the comprehensive utilization of copper anode slime. The selenium grade of the crude selenium initially produced in the process of comprehensive recovery of anode slime is generally 80 wt% - 95 wt%, which contains various impurities such as S, Pb, Te, Cu, and As. To meet the industrial application standards, further purification is required. Currently, the commonly used processes for purifying crude selenium include pyrometallurgical methods such as soda smelting, sulfation roasting, vacuum distillation, and low-temperature oxidation roasting, as well as hydrometallurgical methods such as alkali leaching and chlorination. In actual production, multiple methods are often required to jointly process to meet the corresponding refined selenium standards, which also results in disadvantages such as complex production process flows, long production cycles, high equipment and energy consumption costs, and poor working environments. Summary of the Invention
[0003] Aiming at the problems and deficiencies existing in the production of the above-mentioned crude selenium, the present invention aims to provide a method for preparing 3N refined selenium from crude selenium with a simple process, low equipment and energy consumption costs, a short production cycle, and can ensure the purification effect.
[0004] A method for preparing 3N refined selenium from crude selenium proposed by the present invention includes the following steps: 1) Slurry preparation of crude selenium: Using crude selenium as the raw material, add 8 - 10 times the mass of water to the preparation tank for slurry preparation, heat up to 50 - 60 °C, and start stirring; 2) Adding hydrogen peroxide for digestion: In the above-mentioned preparation tank, slowly add hydrogen peroxide, and the mass of hydrogen peroxide is 1.2 - 1.4 times the input amount of crude selenium. Keep the temperature at 50 - 60 °C unchanged and digest for 5 - 6 h. Under heating conditions, hydrogen peroxide first slowly decomposes by itself, and the reaction is as follows: 2H2O2 = 2H2O + O2↑. The O2 generated during the reaction oxidizes the selenium in the crude selenium, and the reaction is as follows: Se + O2 = SeO2. The generated SeO2 hydrolyzes in the hydrogen peroxide solution, and the reaction process is as follows: SeO2 + H2O = H2SeO3. Furthermore, the selenium in the crude selenium is digested in the digestion solution, and impurities such as lead and tellurium will remain in the residue because they cannot be digested by hydrogen peroxide. Filter the digestion solution to obtain a selenium-containing digestion solution; 3) Reduction: Pump the selenium-containing digestion solution obtained in step 2) into the reduction tank, adjust the temperature to 80 - 90 °C, set pulse gas stirring in the reduction tank, adjust the pH to 0.8 - 1 with sulfuric acid, and then introduce the SO2 reducing agent to reduce the crude selenium in the selenium-containing digestion solution. The reaction process is as follows: H2SeO3 + 2SO2 + H2O = 2H2SO4 + Se↓. Detect the pH value of the tail gas discharged from the tail gas pipe. When the pH of the discharged tail gas is neutral, continue stirring for 5 - 10 min, stop gas stirring, and filter to obtain selenium residue; 4) Water washing: Using the selenium residue obtained by filtration in step 3) as raw material, add pure water to make a slurry. The dosage of pure water is 3 - 5 times the mass of the selenium residue. Heat to 60 - 70 °C and wash while stirring for 1 - 2 h. Filter and dry to obtain 3N refined selenium.
[0005] Further, in step 2), the addition time of hydrogen peroxide is controlled within 1 - 2 h.
[0006] Further, in step 2), after the complete addition of hydrogen peroxide, turn on the microwave, and stir and digest the crude selenium under microwave conditions. Under microwave conditions, the crude selenium generates thermal vibration. Hydrogen peroxide takes the core of the crude selenium particles and decomposes to produce oxygen on the surface of the crude selenium. The oxygen generated during the decomposition process can better contact the interface of the crude selenium, improving the oxidation effect of oxygen on the crude selenium, thereby accelerating the digestion process of the crude selenium.
[0007] Further, the microwave time is controlled within 2 - 4 h.
[0008] Further, the sulfuric acid in step 3) is concentrated sulfuric acid with a concentration of 95 - 98%.
[0009] Further, in step 3), the purity of SO2 in the introduced SO2 reducing agent is 99.0 - 99.9%.
[0010] Further, the SO2 reducing agent is liquid sulfur dioxide, and the introduced mass of the liquid sulfur dioxide is 1.1 - 1.2 times the input amount of the crude selenium.
[0011] Further, in step 3), the reduction tank includes a gas stirring device and an SO2 ventilation pipe. The outlet end of the SO2 ventilation pipe is provided with a spherical rotating jet head. The SO2 ventilation pipe is connected to an SO2 liquid supply high-pressure pipe with heat preservation outside through a pressure reducing valve. The pressure of the SO2 ventilation pipe is controlled by the pressure reducing valve to be 0.1 - 0.5 Mpa. The gas stirring device is provided with a coil around the SO2 ventilation pipe. The gas outlet end of the coil is provided with a plurality of one-way valves. The plurality of one-way valves are evenly arranged along the outer wall of the coiled pipe. The opening of the one-way valve faces downward. During the introduction of the SO2 reducing agent, when the low-temperature SO2 reducing agent enters the SO2 ventilation pipe from the SO2 liquid supply high-pressure pipe through the pressure reducing valve, it instantaneously vaporizes. The SO2 gas is sprayed and rotated through the spherical rotating jet head and mixed in the selenium-containing digestion solution in the reduction tank in the form of bubbles. After synchronously starting the gas stirring device to stir, the stirring gas is ejected through the one-way valve of the coil and agitates the selenium-containing digestion solution, thereby realizing the rapid mixing of SO2 and the selenium-containing digestion solution and the occurrence of a reduction reaction. The heat generated during the reduction reaction and the heat absorbed during the vaporization of SO2 cancel each other out, and the stirring by the gas stirring device ensures uniform reaction temperature, making the reduction reaction stable and not overheating locally.
[0012] Further, the gas stirring device further includes an air inlet pipe and a hose connected between the air inlet pipe and the coil. A spring is connected to the upper part of the coil. The gas stirring is pulsed gas stirring. Since the opening of the one-way valve faces downward, when ventilating, the stirring gas impacts the bottom of the reduction tank, and the bottom of the reduction tank generates an upward reaction force on the coil, causing the coil to move upward with the hose as a fulcrum. When the gas stops, the coil falls under the action of gravity or spring stretching, causing the coil to move downward with the hose as a fulcrum. Through pulsed gas stirring, the coil of the gas stirring device forms regular up-and-down shaking, greatly improving the deep stirring of the selenium-containing digestion solution. After the reaction, due to the downward opening of the one-way valve for stirring and inflation, the stirring gas can stir the selenium settled at the bottom of the reduction tank and also prevent the blockage of the discharge port at the bottom of the reduction tank.
[0013] Further, the stirring gas of the gas stirring device is nitrogen.
[0014] In step 3), after the SO2 reducing agent completely reduces the selenium in the selenium-containing digestion solution, a small amount of excess SO2 gas can be further purged by nitrogen, and the excess SO2 gas is discharged through the tail pipe for pollution-free treatment with alkali solution.
[0015] The main innovative points and beneficial effects of the present invention are as follows: Hydrogen peroxide is used to digest crude selenium, enabling the selenium element in the crude selenium to enter the solution, while impurities such as lead and tellurium, which cannot be digested by hydrogen peroxide, will remain in the residue, thus achieving the purpose of impurity removal; then, sulfur dioxide is used to reduce the selenium in the selenium-containing digestion solution to elemental selenium, and selenium residue is obtained through filtration; the selenium residue only needs to be simply washed with water to remove the sulfur and a small amount of soluble salts therein to obtain 3N refined selenium.
[0016] In the present invention, by further adopting the microwave digestion method, the digestion of crude selenium is greatly improved, and the digestion efficiency of crude selenium is enhanced. At the same time, in the reduction step, highly reactive liquid sulfur dioxide is utilized, and it is combined with an efficient gas stirring device for stirring, so that the reduction efficiency and selectivity of selenium in the selenium-containing digestion solution are increased, preventing other impurities in the selenium-containing digestion solution from being mixed into the product during the purification method of crude selenium.
[0017] In the present invention, by arranging a gas stirring device in the reduction tank and adopting pulsed gas stirring, the coil tube forms regular up-and-down shaking, greatly strengthening the reaction effect between the SO2 reducing agent and the selenium-containing digestion solution. Moreover, through the stirring action of the gas, it can also prevent the reduced selenium from depositing on the surface of the coil tube.
[0018] Compared with the commonly used crude selenium purification methods in current production, the present invention has the advantages of simple process and equipment, low energy consumption, high efficiency, and a relatively good production operation environment. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 It is a process schematic diagram for preparing 3N refined selenium from crude selenium of the present invention.
[0020] Figure 2 It is a structural schematic diagram of the reduction tank.
[0021] Figure 2 In it, 1 - reduction tank, 2 - SO2 gas pipe, 3 - SO2 liquid injection high-pressure pipe, 4 - pressure reducing valve, 5 - spherical rotating jet head, 6 - gas stirring device, 61 - inlet pipe, 62 - hose, 63 - coil tube, 64 - check valve, 65 - spring, 7 - sulfuric acid dropping pipe, 8 - tail gas pipe. DETAILED DESCRIPTION OF THE INVENTION
[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the following further describes the present invention in detail with reference to the drawings and embodiments.
[0023] In an embodiment of the present invention, the crude selenium used is the crude selenium produced during the comprehensive utilization of anode slime. The crude selenium is used as the source for the implementation of the present invention after being crushed and ground. Among them, the crude selenium is sampled, and the contents of various components in the crude selenium are measured. By weight, the selenium grade is 90 wt%, containing 0.75 wt% of tellurium, 1.59 wt% of sulfur, 0.37 wt% of lead, and there are also some other impurities such as arsenic and copper.
[0024] The technological process of the method for preparing 3N refined selenium from crude selenium is implemented with reference to Figure 1 the process schematic diagram.
[0025] Example 1: Take 10.20 kg of crude selenium (selenium grade is 90%), add 81.60 kg of water with 8 times the mass to the crude selenium to make a slurry, and heat it to 60°C. Start stirring. In the preparation tank, slowly add 12.2 kg of hydrogen peroxide. The addition time of hydrogen peroxide is controlled within 1 - 2 h. After the hydrogen peroxide is completely added, turn on the microwave. The crude selenium is stirred and digested under the microwave condition, keeping the temperature at 60°C unchanged for 5 h, and the microwave time is controlled within 2 - 4 h. Then filter to obtain the selenium-containing digestion solution.
[0026] The digestion reaction process is as follows: 2H2O2 = 2H2O + O2↑; Se + O2 = SeO2; SeO2 + H2O = H2SeO3.
[0027] The selenium-containing digestion solution is pumped into Reduction Tank 1, and the temperature is adjusted to 80°C. Pulse gas stirring is set inside Reduction Tank 1. Use 95 - 98% concentrated sulfuric acid to adjust the pH to 1. Reduction Tank 1 can be referred to Figure 2 the shown structure. Reduction Tank 1 includes a gas stirring device 6 and a SO2 ventilation pipe 2. The outlet end of the SO2 ventilation pipe 2 is provided with a spherical rotating jet head 5. The SO2 ventilation pipe 2 is connected to a liquid SO2 storage tank with low-temperature high-pressure storage through a pressure reducing valve 4 and a SO2 liquid delivery high-pressure pipe 3 with heat preservation outside it. The pressure of the SO2 gas introduced into the SO2 ventilation pipe 2 is controlled at 0.1 - 0.5 Mpa through the pressure reducing valve 4. After the liquid SO2 is decompressed by the pressure reducing valve 4, it instantly vaporizes and is sprayed into the selenium-containing digestion solution in Reduction Tank 1 through the rotation of the spherical rotating jet head 5. The spherical rotating jet head 5 rotates and sprays, so that the SO2 gas is dispersed in the form of bubbles and enters the interior of the selenium-containing digestion solution in Reduction Tank 1.
[0028] The gas stirring device 6 includes an air inlet pipe 61, a coil pipe 63 surrounding the SO2 vent pipe 2, and a flexible hose 62 connecting the air inlet pipe 61 and the coil pipe 63. A plurality of one-way valves 64 are provided at the air outlet end of the coil pipe 63. The plurality of one-way valves 64 are uniformly arranged along the outer wall of the coiled coil pipe 63. The opening of the one-way valve 64 faces downward. A spring 65 is connected to the upper part of the coil pipe 63. The gas stirring is pulsed gas stirring. Since the opening of the one-way valve 64 faces downward, when ventilating, the stirring gas impacts the bottom of the reduction tank 1, and the bottom of the reduction tank 1 generates an upward reaction force on the coil pipe 63, causing the coil pipe 63 to move upward with the flexible hose 62 as a fulcrum. When the gas supply stops, the coil pipe 63 falls under the action of gravity or the stretching of the spring 65, causing the coil pipe 63 to move downward with the flexible hose 62 as a fulcrum. Through pulsed gas stirring, the coil pipe 63 of the gas stirring device 6 forms regular up and down shaking. When adjusting the pH value of sulfuric acid, it is dropped through the sulfuric acid dropping pipe 7, and stirring is realized by using the gas stirring device 6; during the process of introducing the SO2 reducing agent, the local stirring effect of the gas itself in the gas stirring device 6 on the selenium-containing digestion solution and the overall stirring effect of the coil pipe 63 due to up and down shaking on the selenium-containing digestion solution greatly improve the deep stirring of the selenium-containing digestion solution, realizing the rapid mixing of SO2 and the selenium-containing digestion solution and the occurrence of a reduction reaction. Moreover, the heat generated during the reduction reaction and the heat absorbed when SO2 gasifies offset each other, and the stirring by the gas stirring device 6 ensures uniform reaction temperature, making the reduction reaction stable and not overheating locally. After the reaction, due to the downward opening of the one-way valve 64 for stirring and inflation, the stirring gas can stir the selenium settled at the bottom of the reduction tank 1 and also prevent the blockage of the discharge port at the bottom of the reduction tank 1.
[0029] The stirring gas of the gas stirring device 6 is nitrogen, the SO2 reducing agent is liquid sulfur dioxide, the purity of SO2 is 99.0 - 99.9%, the mass of the introduced liquid sulfur dioxide is 12.24 kg, the crude selenium in the selenium-containing digestion solution is reduced, and the pH value of the tail gas discharged from the tail gas pipe 8 is detected. When the pH of the discharged tail gas is neutral, continue stirring for 5 - 10 min, and then stop the gas stirring.
[0030] The reaction process is as follows: H2SeO3 + 2SO2 + H2O = 2H2SO4 + Se↓, and 9.12 kg of selenium residue is obtained by filtration.
[0031] Taking 9.12 kg of the selenium residue obtained by filtration as raw material, adding pure water to make a slurry, the amount of pure water used is 5 times the mass of the selenium residue, heating to 60 °C, washing while stirring for 2 h, and filtering and drying to obtain 9.05 kg of 3N refined selenium.
[0032] Example 2: Take 10.15 kg of crude selenium (selenium grade is 90 wt %), add 101.51 kg of water with a mass 10 times that of the crude selenium to make a slurry, heat it to 50 °C, start stirring. In the preparation tank, slowly add 14.2 kg of hydrogen peroxide, and control the addition time of hydrogen peroxide within 1 - 2 h. After the hydrogen peroxide is completely added, turn on the microwave, and stir and digest the crude selenium under microwave conditions, keeping the temperature at 50 °C unchanged for 5 h, with the microwave time controlled within 2 - 4 h. Filter to obtain a selenium-containing digestion solution.
[0033] Pump the selenium-containing digestion solution into Reduction Tank 1, adjust the temperature to 90 °C, set pulsed gas stirring in Reduction Tank 1, adjust the pH to 0.8 with 95 - 98% concentrated sulfuric acid. During the introduction of the SO2 reducing agent, simultaneously turn on the gas stirring device 6 to stir, and the stirring gas of the gas stirring device 6 is nitrogen. The SO2 reducing agent is liquid sulfur dioxide, the purity of SO2 is 99.0 - 99.9%, the SO2 reducing agent controls the inlet pressure of the SO2 gas pipe 2 to be 0.1 - 0.5 Mpa through the pressure reducing valve 4, the mass of the introduced liquid sulfur dioxide is 12.18 kg, and the crude selenium in the selenium-containing digestion solution is reduced. Detect the pH value of the tail gas discharged from the tail gas pipe 8. When the pH of the discharged tail gas is neutral, continue stirring for 5 - 10 min, stop the gas stirring, and filter to obtain 9.08 kg of selenium residue.
[0034] Take the filtered selenium residue as raw material, add pure water to make a slurry, the dosage of pure water is 3 times the mass of the selenium residue, heat it to 70 °C, wash it while stirring for 1 h, filter and dry to obtain 9.04 kg of 3N refined selenium.
[0035] Example 3: Take 10.34 kg of crude selenium (selenium grade is 90 wt %), add 103.32 kg of water with a mass 10 times that of the crude selenium to make a slurry, heat it to 50 °C, start stirring. In the preparation tank, slowly add 14.3 kg of hydrogen peroxide, and control the addition time of hydrogen peroxide within 1 - 2 h, keep the temperature at 50 °C unchanged, and digest for 5 h without turning on the microwave. Filter to obtain a selenium-containing digestion solution.
[0036] Pump the selenium-containing digestion solution into Reduction Tank 1, adjust the temperature to 90 °C, set pulsed gas stirring in Reduction Tank 1, adjust the pH to 0.8 with 95 - 98% concentrated sulfuric acid. During the introduction of the SO2 reducing agent, simultaneously turn on the gas stirring device 6 to stir, and the stirring gas of the gas stirring device 6 is nitrogen. The SO2 reducing agent is liquid sulfur dioxide, the purity of SO2 is 99.0 - 99.9%, the inlet pressure of the SO2 reducing agent is 0.1 - 0.5 Mpa, the mass dosage of the introduced liquid sulfur dioxide is 12.41 kg, and the crude selenium in the selenium-containing digestion solution is reduced. Detect the pH value of the tail gas discharged from the tail gas pipe 8. When the pH of the discharged tail gas is neutral, continue stirring for 5 - 10 min, stop the gas stirring, and filter to obtain 9.22 kg of selenium residue.
[0037] The selenium residue obtained by filtration is used as the raw material, and pure water is added to make a slurry. The amount of pure water used is 3 times the mass of the selenium residue. It is heated to 70 °C and washed with stirring for 1 h, then filtered and dried to obtain 9.13 kg of 3N refined selenium.
[0038] Example 4: Take 10.25 kg of crude selenium (selenium grade is 90 wt %), add 91.37 kg of water, which is 9 times the mass of the crude selenium, to make a slurry, and heat it to 60 °C. Start stirring. In the preparation tank, slowly add 13.28 kg of hydrogen peroxide. The addition time of hydrogen peroxide is controlled within 1 - 2 h. After the hydrogen peroxide is completely added, turn on the microwave. The crude selenium is stirred and digested under microwave conditions, keeping the temperature at 60 °C unchanged for 5 h, and the microwave time is controlled within 2 - 4 h. Then filter to obtain a selenium-containing digestion solution.
[0039] The selenium-containing digestion solution is pumped into Reduction Tank 1, and the temperature is adjusted to 90 °C. Pulse gas stirring is set in Reduction Tank 1. Use 95 - 98% concentrated sulfuric acid to adjust the pH to 1.0. During the introduction of the SO2 reducing agent, start the gas stirring device 6 to stir simultaneously. The stirring gas of the gas stirring device 6 is nitrogen. The SO2 reducing agent is ordinary sulfur dioxide gas, and the purity of SO2 is 99.0 - 99.9%. The mass of the introduced sulfur dioxide gas is 12.30 kg. The crude selenium in the selenium-containing digestion solution is reduced. Detect the pH value of the tail gas discharged from the tail gas pipe 8. When the pH of the discharged tail gas is neutral, continue stirring for 5 - 10 min, stop the gas stirring, and filter to obtain 9.28 kg of selenium residue.
[0040] The selenium residue obtained by filtration is used as the raw material, and pure water is added to make a slurry. The amount of pure water used is 3 times the mass of the selenium residue. It is heated to 70 °C and washed with stirring for 1 h, then filtered and dried to obtain 9.16 kg of 3N refined selenium.
[0041] Example 5: Take 10.16 kg of crude selenium (selenium grade is 90%), add 92.02 kg of water, which is 9 times the mass of the crude selenium, to make a slurry, and heat it to 60 °C. Start stirring. In the preparation tank, slowly add 13.21 kg of hydrogen peroxide. The addition time of hydrogen peroxide is controlled within 1 - 2 h, and keep the temperature at 6 °C unchanged. Digest for 6 h without turning on the microwave, and then filter to obtain a selenium-containing digestion solution.
[0042] The selenium-containing digestion solution is pumped into the reduction tank 1, and the temperature is adjusted to 90 °C. Pulse gas stirring is set in the reduction tank 1, and the pH is adjusted to 1.0 with 95-98% concentrated sulfuric acid. During the introduction of the SO2 reducing agent, the gas stirring device 6 is simultaneously started for stirring. The stirring gas of the gas stirring device 6 is nitrogen. The SO2 reducing agent is ordinary sulfur dioxide gas, and the purity of SO2 is 99.0-99.9%. The mass of the introduced sulfur dioxide gas is 11.18 kg, and the crude selenium in the selenium-containing digestion solution is reduced. The pH value of the tail gas discharged from the tail gas pipe 8 is detected. When the pH of the discharged tail gas is neutral, stirring is continued for 5-10 min, the gas stirring is stopped, and 9.14 kg of selenium residue is obtained by filtration.
[0043] Taking the selenium residue obtained by filtration as the raw material, pure water is added for pulping. The dosage of pure water is 3 times the mass of the selenium residue, heated to 70 °C, washed while stirring for 1 h, and 9.03 kg of 3N refined selenium is obtained by filtration and drying.
[0044] Comparative Example 1: Take 10.22 kg of crude selenium (selenium grade is 90%), add 92.00 kg of water with 9 times the mass to the crude selenium for pulping, and heat up to 60 °C. Start stirring. In the preparation tank, slowly add 13.28 kg of hydrogen peroxide. The addition time of hydrogen peroxide is controlled within 1-2 h. Start the microwave, and the crude selenium is stirred and digested under the microwave condition, keeping the temperature at 60 °C unchanged for 5 h, and the microwave time is controlled within 2-4 h. The selenium-containing digestion solution is obtained by filtration.
[0045] The selenium-containing digestion solution is pumped into the reduction tank 1, and the temperature is adjusted to 90 °C. The pH is adjusted to 1.0 with 95-98% concentrated sulfuric acid. Ordinary sulfur dioxide gas is directly introduced into the selenium-containing digestion solution. The purity of SO2 is 99.0-99.9%. The mass of the introduced sulfur dioxide gas is 11.24 kg. The selenium-containing digestion solution is mechanically stirred by a motor with a stirring paddle, and the crude selenium in the selenium-containing digestion solution is reduced. The pH value of the tail gas discharged from the tail gas pipe 8 is detected. When the pH of the discharged tail gas is neutral, stirring is continued for 5-10 min, the mechanical stirring is stopped, and 9.11 kg of selenium residue is obtained by filtration.
[0046] Taking the selenium residue obtained by filtration as the raw material, pure water is added for pulping. The dosage of pure water is 3 times the mass of the selenium residue, heated to 70 °C, washed while stirring for 1 h, and 8.65 kg of 3N refined selenium is obtained by filtration and drying.
[0047] For the 3N refined selenium prepared in Examples 1-5 and Comparative Example 1, referring to the non-ferrous metal industry standards YS / T223-2007 and YS / T226.13-2009 of the People's Republic of China, the purity of the 3N refined selenium is detected by an inductively coupled plasma mass spectrometer (ICP-MS); the detection results of the contents of various main elements of the 3N refined selenium are shown in Table 1.
[0048] As can be seen from Table 1, in Examples 1 to 5, the products prepared by the method for preparing 3N refined selenium from crude selenium of the present invention have a content greater than 99 wt%, meeting the national standard requirements.
[0049] Among them, compared with Example 3 in Examples 1 to 2, in Examples 1 to 2, a microwave digestion-assisted method was adopted during the hydrogen peroxide digestion reaction, resulting in a higher selenium content in the prepared product. Even the content reached 99.9 wt%. Correspondingly, the content of impurities in the product was significantly lower, indicating that under the condition of hydrogen peroxide digestion reaction, microwave action can well promote the digestion of crude selenium and improve the purity of the product.
[0050] In Examples 1 to 2 compared with Example 4, the SO2 reducing agent added in Example 4 is ordinary sulfur dioxide gas. Compared with the liquid sulfur dioxide used in Examples 1 to 2, due to the low activity of ordinary sulfur dioxide gas, the selenium content in the prepared product is low, indicating that under the condition of using liquid sulfur dioxide reaction, liquid sulfur dioxide has a higher reaction activity when gasifying from a liquid state and adding it to the selenium-containing acidolysis solution at the moment in the SO2 gas pipe 2. The high reaction activity is more conducive to improving the purity of selenium in the product. When the activity of liquid sulfur dioxide is increased, the selenium-containing digestion solution is rapidly reduced. When the concentration of other impurities in the selenium-containing digestion solution is low after the reaction of liquid sulfur dioxide, they are not easily generated, and the selectivity rate of liquid sulfur dioxide for reducing selenium in the selenium-containing digestion solution is greatly improved.
[0051] Table 1
[0052] In Examples 1 to 2 compared with Example 5, in Example 5, an ordinary digestion method was adopted during the hydrogen peroxide digestion reaction and the added SO2 reducing agent was ordinary sulfur dioxide gas, indicating that the microwave digestion method and the activity of the SO2 reducing agent have a great influence on the selenium content of the prepared product. Adopting the microwave digestion method of hydrogen peroxide and a highly active SO2 reducing agent is more conducive to improving the purity of selenium in the crude selenium purification method.
[0053] In Example 1 to Example 5, compared with Comparative Example 1, Comparative Example 1 does not use the pulse gas stirring device 6, but uses the continuous stirring method of the motor to reduce the selenium-containing digestion solution. It is found that by using the pulse gas stirring device 6, the effect of crude selenium purification can be significantly improved. The purity of the product obtained in Comparative Example 1 is much lower than the content of the products obtained in Example 1 to Example 5, among which the content of sulfur impurities is significantly increased. This is because the concentration of sulfur dioxide gas in the local part of the selenium-containing digestion solution is uneven by mechanical stirring, the reduction reaction is intense, and there are many side reactions, so impurities are easily entrained in the obtained product. Moreover, the mechanical stirring is too intense on the whole, and the sulfur dioxide gas stops during the mechanical stirring process. The time that sulfur dioxide gas stays in the selenium-containing digestion solution is too short, and sulfur dioxide gas is easily taken out of the reduction kettle by the stirring paddle, resulting in incomplete reduction. As a result, a part of selenium-containing substances cannot be completely reduced and remain in the selenium-containing digestion solution, resulting in selenium loss. Therefore, rapid mechanical stirring cannot improve the effect of crude selenium purification. Instead, it is necessary to adopt a local bubbling oscillation stirring and an overall slow vibration stirring method. This can ensure the full mixing of sulfur dioxide gas and selenium-containing digestion solution, and prevent sulfur dioxide gas from being taken out of the selenium-containing digestion solution due to intense stirring, thereby increasing the residence time of sulfur dioxide gas in the selenium-containing digestion solution. A pulsed gas stirring device 6 is used to meet the local bubbling oscillation stirring and an overall slow vibration stirring method, which has a significant improvement in the purification of crude selenium.
[0054] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.
Claims
1. A method for preparing 3N refined selenium from crude selenium, characterized in that: The steps include: 1) Crude selenium slurry preparation: Take crude selenium as raw material, add 8-10 times the mass of water into the preparation tank to prepare the slurry, raise the temperature to 50-60℃, and start stirring; 2) Add hydrogen peroxide for digestion: slowly add hydrogen peroxide in the above-mentioned preparation tank. The mass of hydrogen peroxide is 1.2-1.4 times of the amount of crude selenium input. Keep the temperature at 50-60°C and digest for 5-6 hours. The selenium in the crude selenium is digested in the digestion solution. Impurities such as lead and tellurium cannot be digested by hydrogen peroxide and will remain in the slag. Filter the digestion solution to obtain a digestion solution containing selenium. 3) Reduction: pump the selenium-containing digestion solution obtained in step 2) into a reduction tank, adjust the temperature to 80-90°C, set pulse gas stirring in the reduction tank, adjust the pH to 0.8-1 with sulfuric acid, then introduce SO2 reducing agent to reduce the crude selenium in the selenium-containing digestion solution, detect the pH value of the tail gas discharged from the tail gas pipe, and when the pH of the tail gas discharged is neutral, continue stirring for 5-10 minutes, stop gas stirring, and filter to obtain selenium residue; 4) Water washing: Use the selenium slag obtained by filtration in step 3) as raw material, add pure water to prepare the slurry, the amount of pure water used is 3 to 5 times the mass of the selenium slag, heat to 60 to 70°C, wash for 1 to 2 hours while stirring, filter and dry to obtain 3N refined selenium.
2. The method for preparing 3N refined selenium from crude selenium according to claim 1, characterized in that: In step 2), the addition time of hydrogen peroxide is controlled within 1 to 2 hours.
3. The method for preparing 3N refined selenium from crude selenium according to claim 1, characterized in that: In step 2), after the hydrogen peroxide is completely added, the microwave is turned on, and the crude selenium is stirred and digested under the microwave condition.
4. The method for preparing 3N refined selenium from crude selenium according to claim 3, characterized in that: The microwave time is controlled at 2-4 hours.
5. The method for preparing 3N refined selenium from crude selenium according to claim 1, characterized in that: The sulfuric acid in step 3) is 95-98% concentrated sulfuric acid.
6. The method for preparing 3N refined selenium from crude selenium according to claim 1, characterized in that: In step 3), the purity of SO2 in the SO2 reducing agent introduced is 99.0-99.9%.
7. The method for preparing 3N refined selenium from crude selenium according to claim 1, characterized in that: The SO2 reducing agent is liquid sulfur dioxide, and the mass of the liquid sulfur dioxide introduced is 1.1 to 1.2 times the amount of crude selenium input.
8. The method for preparing 3N refined selenium from crude selenium according to claim 1, characterized in that: In step 3), the reduction tank includes a gas stirring device and a SO2 vent pipe, the outlet end of the SO2 vent pipe is provided with a spherical rotating jet head, the SO2 vent pipe is connected to a SO2 liquid high-pressure pipe with a heat-insulating device through a pressure reducing valve on its outside, the pressure of the SO2 vent pipe is controlled by the pressure reducing valve to be 0.1~0.5Mpa, the gas stirring device is provided with a coil surrounding the SO2 vent pipe, the outlet end of the coil is provided with a plurality of one-way valves, the plurality of one-way valves are evenly arranged along the outer wall of the spiral coil, and the openings of the one-way valves face downward.
9. The method for preparing 3N refined selenium from crude selenium according to claim 8, characterized in that: The gas stirring device also includes an air inlet pipe and a hose connected between the air inlet pipe and the coil, and the upper part of the coil is connected with a spring.
10. The method for preparing 3N refined selenium from crude selenium according to claim 8, characterized in that: The stirring gas of the gas stirring device is nitrogen.