Selenium extraction process and technology

The selenium oxide in the raw selenium raw material is different from the volatile oxide in the selenium. Under the condition of aerobic presence and heating, selenium is easily oxidized to form volatile selenium dioxide, and most of the impurities in the crude selenium are difficult to generate. volatile oxides (e.g. copper oxide, iron oxide, tellurium oxide, etc.) remaining in the slag, the process after the crude selenium melted in an oxidizing furnace oxide, selenium dioxide volatilization of selenium was cooled settle in a settling tank to collect . Other gases such as nitrogen, carbon dioxide, a small amount of sulfur dioxide, etc., continue to purify and recover a small amount of selenium dioxide entrained therein through the collection tank into the exhaust gas absorption tank, purification bottle, and the like. The main reaction of the process is as follows:

Se+O2=SeO2↑

2Cu2S+3O2=2Cu2O+2SO2↑

C+O2=CO2↑

Most of the impurities remain in the oxidized slag after oxidation. Only a small part of the impurities become loose due to oxidation. The particles are fine and the specific gravity is small. In addition, the oxidation in the furnace is intense, sometimes the negative pressure fluctuates greatly, and the gas is brought into the selenium dioxide. The collecting box or the exhaust gas absorption tank, the selenium dioxide is taken out from the collecting box, and after being cooled, weighed and packaged, the product selenium selenide anode selenium is obtained. The selenium in the industry is generally extracted from the anode slime of copper electrolytic refining. The main form of selenium in the anode mud is Cu2Se, Ag2Se, etc., and the content is 3-14%. Currently, the sulphation roasting method is widely used. The main advantage of this method is that the recovery rate of selenium is high (>93%); it is suitable for processing a variety of raw materials.

The production process of recovering selenium by sulphating roasting method is as follows: firstly, the anode slime is dehydrated at 140 ° C, then mixed with concentrated sulfuric acid, and added to the rotary kiln for sulfation roasting, and the following reaction occurs at 250 ° C: Cu2Se+6H2SO4-→2CuSO4+ SeO2+4SO2+6H2O, when the temperature is increased to 700-750 °C, selenium dioxide (SeO2) volatilizes (SeO2315 °C sublimation), cerium oxide is poor in volatility, and remains in the calcined slag together with the sulfate. The selenium dioxide-containing flue gas from the roaster enters the absorption tower, and SeO2 is absorbed by water to form selenite (H2SeO3), which is reduced to elemental selenium by sulfur dioxide (SO2) in the flue gas: H2SeO3+2SO2+H2O-→ Se+2H2SO4, the precipitate was filtered, washed and dried to obtain 98 to 99% of coarse ash selenium. The absorption liquid still contains selenium which accounts for 3 to 10% of the selenium content of the raw material, and Cu2Se precipitation can be obtained from the copper displacement method, and then returned to the sulphation roasting process, or the crude selenium can be directly precipitated by the SO2 reduction method.

In addition, soda roasting method is used to recover selenium. The purification method for preparing selenium from high-purity selenium is distillation method and oxidation-reduction precipitation method, and the latter is widely used for preparing pure selenium with purity greater than 99.992%. The method firstly oxidizes the molten coarse selenium through oxygen, causes the selenium to be dissolved into SeO2 and enters the absorption tank, and forms ion selenous acid solution with the ion exchange water therein, and then introduces SO2 to precipitate pure selenium from the solution.

In order to obtain high-purity selenium with a purity exceeding 99.999%, vacuum distillation, ion exchange, selenide thermal decomposition, and selenium dioxide gas phase ammonia reduction may be employed.

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