Vacuum Distillation Process Of The Metal Selenium Research

Selenium, which is molten at temperature 221 C and boiling at temperature 685 C, is a good volatile element. Based on easy volatility of selenium, extraction of metal selenium by vacuum distillation can avoid some defections in the old course of producing selenium. These defections are low recovery rate, badly environmental contamination, relative high cost of production and so on. Besides, extraction of metal selenium by vacuum distillation has short technological process, little erosion on equipment and so on. It is important part to enhance production efficiency of selenium and promote its application in the factory.Based on vacuum distillation theory, a new process that is mainly vacuum distillation technology comes into being on the paper. The raw materials comes from industrial materials containing 50% Se in the process, which includes selenium extraction and selenium purification and melting selenium material. The research result is followed:(1) Extracting selenium by vacuum distillation.Under the given conditions, enhancing temperature and prolonging time can decrease selenium residual quantity in the residue. Prolonging time will decrease its production efficiency, and enhancing temperature will increase its loss in the process of extracting selenium. Considering these factors, the optimal conditions are 350 C, 90min and 30Pa in the furnace. Residual selenium amount decreases the minimum 0.28g after 20g selenium material is distillated under the above conditions, and the remainder contains 8.42% Se.(2) Purifying selenium by vacuum distillation.Metal selenium purification is on the base of different elemental volatility. After distillated for 2min at temperature 300 C, the residual amount is 20 percent of 20g law material. Selenium purity is higher than the raw materials. Every elemental content change in selenium materials. The result shows in the table 1:From the tabl, vacuum distillation is suitable to separate element copper, iron and lead from selenium material, but not element arsenic or tellurium.(3) Tellurium separation from selenium material by vacuum distillation.Under the given conditions, the content ratio between selenium and tellurium is little by little increasing in the condensate when residual amount increases and vaporizing temperature falls. So decreasing temperature and increasing residual amount is favorable to separate tellurium from selenium materials. After 20g selenium material containing 1.28% Te is distillated at temperature 250~350"C, the maximum content ratio between selenium and tellurium is 117 in the condensate, and the minimum of tellurium content is 0.843%, and tellurium coefficient is at range from 1.86 to 3.09.(4) Tellurium removal by smelting selenium materials.Under some conditions, nitrate mixture can oxidize tellurium, but cannot oxidize selenium[37, 42]. Smelting test is carried out at temperature 310~380 C while material ratio is Se: NaNO3 : KNO3 = 200g: 45.7g : 54.3g, and tellurium removal efficiency is very high in selenium material. The result shows in the tab2.