Method for preparing sodium selenite from crude selenium recovered from copper anode slime

Abstract

The invention relates to a method for preparing sodium selenite from crude selenium recovered from copper anode slime. The method comprises the following steps: S1, oxidizing: oxidizing the crude selenium recovered from the copper anode slime under the conditions that the temperature is 500-550 DEG C and the oxygen flow is 0.9-1.0 L / min; after the selenium is completely burnt, stopping heating, continuing to introduce O2, and then cooling to room temperature in air to obtain an oxidation product SeO2; s2, separation and purification: fully dissolving the oxidation product SeO2 with deionized water, filtering, heating, evaporating and crystallizing, condensing, re-dissolving, boiling and cooling to obtain a seleninic acid solution; s3, neutralization and crystallization: adding a NaOH solution into the seleninic acid solution for reaction, and performing vacuum drying, standing, cooling and crystallization to obtain crystalline sodium selenite; and S4, heating and dehydrating: heating and dehydrating the crystallized sodium selenite to obtain an anhydrous sodium selenite product. The process is simple in production process, stable and reliable in quality, low in cost and high in economic benefit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of smelting engineering by-product recycling, and particularly relates to a method for preparing sodium selenite from crude selenium recovered from copper anode slime. BACKGROUND

[0002] In the feed industry, selenium is a trace element that has attracted much attention in recent years. It has certain nutritional functions and exists in all cells of the body to protect the cell membrane from oxidation in the form of glutathione oxidase. This enzyme can reduce peroxide esters to prevent the accumulation of such toxins in the body. Selenium has a similar effect to vitamin E in the body and can replace part of the function of vitamin E. It can also regulate the absorption and consumption of vitamins A, C, E and K in the body and can affect the speed of oxidation-reduction reactions, playing a certain catalytic role in biochemical processes. Sodium selenite is the best choice for adding selenium to feed.

[0003] Common methods for preparing sodium selenite include the sodium carbonate method, the nitric acid oxidation method, and the oxygen oxidation method. The sodium carbonate method involves adding sodium carbonate to a solution of sodium selenite, evaporating and crystallizing the solution, and drying to obtain the sodium selenite product. In the production process, a large amount of carbon dioxide gas is generated, which causes a room temperature effect. In addition, if the gas release is not properly controlled during the reaction process, safety accidents can easily occur. The nitric acid oxidation method involves reacting selenium with nitric acid to generate sodium selenite, which is then dried and ground to obtain the finished product. When selenium reacts with nitric acid, nitrogen oxides are generated, and the tail gas is difficult to handle, causing environmental pollution. Due to the strong acidity and oxidizing nature of nitric acid, the impurity content in the product is relatively high. The oxygen oxidation method involves first oxidizing elemental selenium with oxygen to generate selenium dioxide, which is then dissolved in water to form a sodium selenite solution. After neutralization with sodium hydroxide, the solution is concentrated, crystallized, centrifuged, dried, broken, and sieved to obtain the sodium selenite product. This process has serious equipment corrosion, a long production cycle, and high costs. In addition, the intermediate product, selenium dioxide, is a highly toxic substance.

[0004] CN102060274A discloses a method for producing sodium selenite. In this method, elemental selenium is used as the raw material, and high-pressure oxygen is introduced into an aqueous sodium hydroxide solution to produce oxidation. The entire process is carried out in an autoclave, and the elemental selenium has a purity of 99.999% (5N selenium).

[0005] The Kaldo furnace fire process is used to treat copper electrolytic anode slime in copper smelting plants. The Kaldo furnace smelting flue gas is washed with a circulating washing solution to recover selenium. When the selenium concentration in the washing solution reaches a certain level, neutralization and precipitation are performed to remove impurities. After removal of impurities, the solution is reduced by sulfur dioxide to recover crude selenium, and the filter residue is returned to the Kaldo furnace as a Venturi mud. However, there is currently no report on the use of crude selenium to prepare sodium selenite. SUMMARY

[0006] The technical problem solved by the present application is to provide a simple, low-cost, stable and reliable method for preparing sodium selenite from crude selenium recovered from copper anode slime.

[0007] To solve the above problems, the method for preparing sodium selenite from crude selenium recovered from copper anode slime comprises the following steps: S1 oxidation: place the corundum boat containing crude selenium recovered from copper anode slime in a quartz tube, slowly pass O2, heat to 500-550 DEG C within 30 min, and control the oxygen flow rate to be between 0.9-1.0 L / min; stop heating when the selenium is completely burned, and continue to pass O2, then cool to room temperature in air, and obtain the oxidation product SeO2; S2 separation and purification: dissolve the oxidation product SeO2 in deionized water, filter to obtain a selenious acid solution A; heat and evaporate the selenious acid solution A to crystallize, then load into a container with a reflux condenser, dissolve in deionized water and boil, then cool to room temperature, precipitate and filter to obtain a selenious acid solution B; S3 neutralization and crystallization: in the selenious acid solution B, add a theoretical amount of NaOH solution with a mass concentration of 40%, and stop the reaction when the reaction end point is 11; vacuum dry the solution, cool to room temperature, and then perform standing cooling crystallization; after crystallization, suction filter, concentrate the obtained filtrate, and continue to crystallize; dry the filtered crystalline product at room temperature, and obtain crystalline sodium selenite (Na2SeO3·5H2O); S4 heating and dehydration: perform heating and dehydration treatment on the crystalline sodium selenite, and obtain anhydrous sodium selenite product.

[0008] In step S1, the mass percentage content of the main components in the crude selenium is: Se 75-95%, Te 1.0-2.0%, and S 1.0-3.0%.

[0009] In step S1, the heating temperature is controlled to be 500-550 DEG C during the oxidation of the crude selenium.

[0010] In step S3, the pH value of the reaction system in the neutralization and crystallization process is determined by the feeding amount of selenious acid and caustic soda, and the mass concentration of sodium selenite is 50-60% when the reaction is terminated.

[0011] In step S3, the temperature of vacuum drying is less than 50 DEG C, and the time is 4-5 hours.

[0012] Compared with the prior art, the present application has the following advantages: 1. In the present application, crude selenium recovered from copper anode slime produced by a copper smelting plant is used as raw material, and according to the physical and chemical characteristics of selenium, anhydrous sodium selenite is prepared through high-temperature oxidation combustion, neutralization and crystallization, and heating and dehydration processes.

[0013] 2. This invention utilizes the oxidation and combustion reaction between oxygen and molten selenium material to cause elements with similar properties, such as selenium and tellurium, to volatilize in the form of oxides. High-melting-point and high-boiling-point impurities (such as Fe, Cu, Ni, Pb, Sb, Bi, etc.) remain in the residue. The oxide gases of selenium and tellurium enter the condensation receiving section, where they are condensed. Low-boiling-point impurities (such as S, As, Cl and some of their compounds) still escape with the gas flow, thereby obtaining selenium dioxide containing a small amount of tellurium and other impurities separated from the main impurities.

[0014] 3. The method of this invention can effectively improve the system's operating efficiency, achieve stable and efficient selenium recovery, provide technical support for the development of the selenium industry chain, and increase the added value of selenium.

[0015] 4. The process of this invention is simple, the quality is stable and reliable, the cost is low, and the economic benefits are high. Detailed Implementation

[0016] A method for producing sodium selenite from crude selenium recovered from copper anode mud includes the following steps: S1 Oxidation: A corundum boat containing crude selenium recovered from copper anode mud is placed inside a quartz tube. O2 is slowly introduced while the temperature is raised to 500-550°C over 30 minutes. Selenium begins to melt at 220°C and starts to burn at 500°C. The oxygen flow rate is controlled between 0.9 and 1.0 L / min while increasing the oxygen flow rate. A small amount of air or oxygen is introduced to prevent backflow of the product, cooling the oxide generated during combustion to the rear end of the quartz tube. After complete combustion of the selenium, heating is stopped while continuing to introduce O2. The tube is then cooled to room temperature in air to obtain the oxidation product SeO2.

[0017] The main components of crude selenium are as follows: Se 75-95%, Te 1.0-2.0%, and S 1.0-3.0% by mass percentage. Crude selenium is obtained as follows: First, copper anode mud is leached with sulfuric acid to remove copper and tellurium. The copper-removed anode mud is then smelted in a Kaldo furnace. During the smelting process, selenium metal is oxidized to selenium dioxide and volatilizes into the flue gas. The flue gas is then scrubbed with a Venturi scrubber, and selenium enters the scrubbing solution in the form of selenic acid. Some tellurium, lead, arsenic, copper, gold, and silver metals also enter the scrubbing solution along with the selenium. The scrubbing solution is then reduced with liquid sulfur dioxide. While the selenium is being reduced, small amounts of tellurium, lead, copper, gold, and silver metals are also reduced. After filtration, crude selenium is obtained.

[0018] The heating temperature is controlled to be 500-550°C during the oxidation of the crude selenium. In the present application, the oxidation degree of the selenium is more sufficient with the increase of the heating temperature under a certain oxygen flow. When the heating temperature is less than 500°C, the oxidation of the selenium is incomplete, and part of the evaporated selenium is not oxidized but condensed, so that the content of the elemental selenium in the oxidation product is high. When the heating temperature is more than 500°C, the oxidation combustion reaction is generated, the oxidation is complete, and the content of the elemental selenium in the product is greatly reduced. The change is small when the heating temperature is more than 550°C, so the heating temperature is controlled to be 500-550°C.

[0019] S2 separation and purification: the oxidation product SeO2 is dissolved in deionized water, filtered, and SeO2 solution A is obtained; SeO2 solution A is evaporated and crystallized, and then loaded into a container with a reflux condenser, dissolved in deionized water and boiled, then cooled to room temperature, precipitated and filtered to obtain SeO3 solution B.

[0020] The solubility of SeO2 in water is large, and SeO2 forms selenious acid after being dissolved in water: SeO2+H2O=H2SeO3 After SeO2 is dissolved in water and filtered and evaporated and crystallized, a small amount of Se that is not fully oxidized can be separated first; at the same time, the difference in solubility of oxidized selenium and oxidized tellurium in water can be used to preliminarily purify and separate the oxidized selenium and the oxidized tellurium.

[0021] By comparing the impurity contents before and after the purification of SeO2, it can be seen that most of the main impurity elements are reduced, especially the content of Te is greatly reduced. The main reason for the analysis is that TeO2 is an amphoteric compound, although it is an acid anhydride like SeO2, but it is greatly different from SeO2 in that the solubility of TeO2 in water is extremely small, less than 1 / 15000, which provides the condition for the separation of SeO2 and TeO2. After the purification by the oxidation combustion method and the purification process of SeO2, the contents of the main impurities are significantly reduced, which plays a role in purification and lays a foundation for the next stage of deep purification and final purification.

[0022] S3 neutralization and crystallization: in SeO3 solution B, a theoretical amount of NaOH solution with a mass concentration of 40% is added, and an intense exothermic reaction occurs: H2SeO3+2NaOH=Na2SeO3+2H2O When neutralizing, the alkali solution is slowly added to the H2SeO3 solution under stirring. The solution gradually becomes viscous as the alkali solution is added. When the reaction endpoint is reached, the reaction is stopped, at which time the mass concentration of sodium selenite is 50-60%, preferably 50%. The solution at this time is vacuum dried at a temperature of less than 50°C for 4-5 hours. Then, the solution is cooled to room temperature and allowed to stand to crystallize. The crystallization is completed by suction filtration using a porcelain funnel (without washing). The obtained filtrate is concentrated and further crystallized. The crystallized product is dried at room temperature to obtain crystalline sodium selenite (Na2SeO3·5H2O).

[0023] The product Na2SeO3·5H2O is white needle-shaped or prismatic crystals, easily soluble in water, with a solubility of 68 g at 20°C, insoluble in alcohol, and weathered to white powder in dry air by losing water. Therefore, further heating and dehydration are required.

[0024] During the neutralization and crystallization process, the pH value of the reaction system is determined by the amounts of selenite and caustic soda added. When the reaction endpoint is reached, the product mass meets the requirements.

[0025] S4 Heating and dehydration: The melting point of crystalline sodium selenite is low. Therefore, the crystalline sodium selenite is subjected to heating and dehydration treatment to obtain anhydrous sodium selenite product. The specific process is as follows: 1) Dehydration using a general constant temperature drying oven: Na2SeO3·5H2O is placed in a porcelain dish, and the temperature is controlled to be less than 60°C. After continuous drying for several days, white anhydrous sodium selenite can be obtained. The crystallization is stirred from time to time to prevent the crystallization from adhering firmly to the container.

[0026] 2) Dehydration using a vacuum drying oven: The temperature is less than 60°C, and the vacuum degree is 66.6 kPa. Under the same weight and layer thickness as the general drying, the dehydration time can be shortened by 3-5 times.

[0027] The solubility of sodium selenite in water is very large, and the supersaturation is also very large. To reduce costs, the concentration is heated to 40°C to start dehydration and convert into anhydrous salt. The solution of sodium selenite can also be directly concentrated to obtain anhydrous sodium selenite. The concentration should be as large as possible to not bring significant difficulties to the production process.

[0028] Example 1 A method for preparing sodium selenite from crude selenium recovered from copper anode slime, comprising the following steps: S1 Oxidation: A corundum boat containing 79 g of crude selenium is placed in a quartz tube, and O2 is slowly introduced while heating to 500°C within 30 min to start combustion. The flow rate of O2 is between 0.9 L / min. The oxide generated by combustion is cooled at the back end of the quartz tube. After 0.5 h of selenium combustion reaction, heating is stopped and O2 continues to be introduced. Then, the system is cooled to room temperature in air to obtain the oxidation product SeO2.

[0029] The composition of the crude selenium is Se: 86.8%, Te: 1.5%, and S: 1.3% by weight percentage.

[0030] S2 Separation and purification: The oxidation product in step S1 is dissolved in 40 ml of deionized water and filtered to obtain a selenite solution A. The solution is heated and evaporated to crystallize, and then loaded into a round-bottom flask with a reflux condenser device. 500 ml of deionized water is added to dissolve the solution. The solution is boiled and cooled to room temperature, and the precipitate is filtered to obtain a selenite solution B.

[0031] S3 Neutralization and crystallization: The selenite solution B obtained in S2 is slowly added to the H2SeO3 solution with alkali. There is an exothermic reaction, and the solution becomes sticky. During the addition of NaOH, the pH value is tested at any time. When the reaction endpoint is 11, the reaction is stopped, and the mass concentration of sodium selenite is 55%. The liquid is placed in a vacuum drying box at 45°C, and vacuum dried for 4.0 hours. It is cooled to room temperature and allowed to stand for cooling crystallization.

[0032] S4 Heating and dehydration: The crystallized sodium selenite in step S3 is dehydrated in a normal constant temperature drying box. Na2SeO3·5H2O is placed in a porcelain dish, and the temperature is controlled at 50°C. After continuous drying for 2 days, white anhydrous sodium selenite is obtained. The product contains 98.6% of sodium selenite by weight percentage.

[0033] Example 2 A method for preparing sodium selenite from crude selenium recovered from copper anode slime, comprising the following steps: S1 Oxidation: A corundum boat containing 100 grams of crude selenium is placed in a quartz tube, and O2 is slowly introduced while heating to 520°C to start combustion within 30 min. The flow rate of O2 is between 0.95 L / min. The oxide generated by combustion is cooled at the back end of the quartz tube. After 40 min of selenium combustion reaction, heating is stopped and O2 continues to flow. Then it is cooled to room temperature in air to obtain the oxidation product SeO2.

[0034] The composition of the crude selenium is Se: 86.8%, Te: 1.5%, and S: 1.3% by weight percentage.

[0035] S2 Separation and purification: The oxidation product in step S1 is dissolved in 40 ml of deionized water and filtered to obtain a selenite solution A. The solution is heated and evaporated to crystallize, and then loaded into a round-bottom flask with a reflux condenser device. 500 ml of deionized water is added to dissolve the solution. The solution is boiled and cooled to room temperature, and the precipitate is filtered to obtain a selenite solution B.

[0036] S3 Neutralization and crystallization: slowly add alkali to the H2SeO3 solution obtained in S2, and a violent exothermic reaction occurs. Stir constantly, and test the pH of the solution at any time during the addition of NaOH. As the alkali is added, the solution gradually becomes viscous. When the reaction endpoint is 11, the reaction is stopped, and the mass concentration of sodium selenite is 58%. Place the solution in a vacuum drying oven at 38°C, and dry for 4.5 hours under vacuum. Cool to room temperature, and allow to stand and cool to crystallize.

[0037] S4 Dehydration by heating: take the crystallized sodium selenite in step S3, and dehydrate it in a normal constant-temperature drying oven. Place the Na2SeO3-5H2O in a porcelain dish, and control the temperature at 40°C. After continuous drying for 3 days, white anhydrous sodium selenite is obtained. The product is detected to contain 99.2% sodium selenite by weight.

[0038] Example 3 A method for preparing sodium selenite from crude selenium recovered from copper anode slime, comprising the following steps: S1 Oxidation: place a corundum boat containing 100 g of crude selenium in a quartz tube, slowly pass in O2, and at the same time heat to 550°C to start combustion within 30 min. The flow rate of the oxygen is between 1.0 L / min. Cool the oxide generated by combustion at the back end of the quartz tube. Stop heating after 40 min of selenium combustion reaction, and continue to pass in O2. Then cool to room temperature in air to obtain the oxidation product SeO2.

[0039] The composition of the crude selenium is Se: 83.6%, Te: 1.7%, and S: 2.0% by weight.

[0040] S2 Separation and purification: dissolve the oxidation product in step S1 in 50 ml of deionized water, filter to obtain a selenious acid solution A, heat and evaporate to crystallize, and then load into a round-bottom flask with a reflux condenser. Add 500 ml of deionized water to dissolve, boil the solution, and then cool to room temperature. Filter the precipitate to obtain a selenious acid solution B.

[0041] S3 Neutralization and crystallization: slowly add alkali to the H2SeO3 solution obtained in S2, and a violent exothermic reaction occurs. Stir constantly, and test the pH of the solution at any time during the addition of NaOH. As the alkali is added, the solution gradually becomes viscous. When the reaction endpoint is 11, the reaction is stopped, and the mass concentration of sodium selenite is 58%. Place the solution in a vacuum drying oven at 38°C, and dry for 4.5 hours under vacuum. Cool to room temperature, and allow to stand and cool to crystallize.

[0042] S4 Dehydration by Heating: Take the crystalline sodium selenite from step S3 and dehydrate it using a standard constant temperature drying oven. Place Na2SeO3·5H2O in a porcelain dish, control the temperature at 43℃, and dry continuously for 3 days to obtain white anhydrous sodium selenite. The product contains 98.4% sodium selenite by weight.

[0043] Example 4 A method for producing sodium selenite from crude selenium recovered from copper anode mud includes the following steps: S1 Oxidation: A corundum boat containing 158 g of crude selenium was placed in a quartz tube, and O2 was slowly introduced while heating to 550 °C within 30 min to start combustion. The oxygen flow rate was between 1.0 L / min. The oxide generated by combustion was cooled at the rear end of the quartz tube. After the selenium combustion reaction was completed for 60 min, heating was stopped and O2 was continued to be introduced. Subsequently, it was cooled to room temperature in air to obtain the oxidation product SeO2.

[0044] The crude selenium composition, by weight percentage, is Se: 80.6%, Te: 1.8%, and S: 2.5%.

[0045] S2 Separation and Purification: The oxidation product in step S1 was fully dissolved in 100ml of deionized water and filtered to obtain selenite solution A. The solution was heated and evaporated to crystallize, and then placed in a round-bottom flask equipped with a reflux condenser. 600ml of deionized water was added to dissolve the crystals. The solution was boiled and cooled to room temperature. The precipitate was filtered to obtain selenite solution B.

[0046] S3 Neutralization and Crystallization: The selenite solution B obtained in S2 was slowly added to the H2SeO3 solution with alkali solution. A vigorous exothermic reaction occurred, and the solution was stirred continuously. pH values ​​were measured periodically during the addition of NaOH. As alkali solution was added, the solution gradually became viscous. When the reaction reached its endpoint (11), the reaction stopped, and the sodium selenite mass concentration was 58%. This solution was placed in a vacuum drying oven at 35°C and vacuum dried for 5.0 hours. After cooling to room temperature, it was allowed to stand and crystallize.

[0047] S4 Dehydration by Heating: Take the crystalline sodium selenite from step S3 and dehydrate it using a vacuum drying oven. Place Na2SeO3·5H2O in a porcelain dish, dry at 50℃ and a vacuum of 66.6 kPa for 2 consecutive days to obtain white anhydrous sodium selenite. The product contains 98.7% sodium selenite by weight.

Claims

1. A method for producing sodium selenite from crude selenium recovered from copper anode mud, comprising the following steps: S1 oxidation: A corundum boat containing crude selenium recovered from copper anode mud is placed in a quartz tube, and O2 is slowly introduced while heating to 500~550℃ within 30 min, and the oxygen flow rate is controlled between 0.9~1.0 L / min; when the selenium is completely burned, heating is stopped and O2 is continued to be introduced, and then cooled to room temperature in air to obtain the oxidation product SeO2; S2 separation and purification: The oxidation product SeO2 is fully dissolved in deionized water and filtered to obtain selenite solution A; after heating and evaporating the selenite solution A to crystallize it, it is placed in a container with a reflux condenser, deionized water is added to dissolve and boiled, and then cooled to room temperature. After precipitation and filtration, selenite solution B is obtained. S3 Neutralization Crystallization: Add 40% NaOH solution to selenite solution B according to the theoretical amount. When the reaction endpoint is 11, the reaction is stopped. The solution at this point is then vacuum dried, cooled to room temperature, and allowed to stand and cool for crystallization. After crystallization is complete, filter the solution. Concentrate the filtrate and continue crystallizing. Air-dry the filtered crystallized product at room temperature to obtain crystalline sodium selenite. S4 Heating Dehydration: The crystalline sodium selenite is heated and dehydrated to obtain anhydrous sodium selenite product.

2. A process for the production of sodium selenite from crude selenium recovered from copper anode slime as claimed in claim 1, wherein: The mass percentage content of the main components in the crude selenium in step S1 is: Se 75~95%, Te 1.0~2.0%, S 1.0~3.0%.

3. A process for the production of sodium selenite from crude selenium recovered from copper anode slime as claimed in claim 1, wherein: In step S1, the heating temperature is controlled to be maintained at 500~550℃ during the oxidation of crude selenium.

4. A process for the production of sodium selenite from crude selenium recovered from copper anode slime as claimed in claim 1, wherein: In step S3, during the neutralization and crystallization process, the pH value of the reaction system is determined by the amount of selenite and caustic soda fed, and the mass concentration of sodium selenite is 50-60% when the reaction is terminated.

5. A process for the production of sodium selenite from crude selenium recovered from copper anode slime as claimed in claim 1, wherein: In step S3, the vacuum drying temperature is below 50°C, and the time is 4-5 hours.