High Purity Selenium Purification Process

In order to improve the purification ability of the high-purity selenium and to prepare the high-purity selenium material, to break down the monopolize the market in the high-purity rare metal materials by foreign companies in China, and to reduce markedly the import cost of the high-purity selenium, to further improve the market share of domestically produced high-purity selenium and the lay the foundation for technological development, the purification technology of the high purity selenium ia selected as the research topic for the thesis. By combining the chemical purification and vacuum distillation process, high-purity selenium with 6 N (99.9999%) was obtained from the crude selenium with purity of 99.9%. The results resolved the technical problems that new impurity formation, distillation or crystallization met in simple chemical easily. The main results are showed as follows.The combustion and oxidation of selenium, and the separation and purification process of SeO2 were studied. The results show that the heating temperatures of 500-550℃and oxygen flow rate of 0.9-1.0 L·min-1 are the suitable technique for the stable accessing of SeO2. Then the preliminary purification can be achieved by filtration and evaporation of the crystallization process.By using the hydrazine hydrate as reducing agent selenite solution, the experiments showed that the H2SeO3 concentration of 20% and hydrazine hydrate concentration of 12% and the dropping rate of 90 ml/min are the appropriate reaction condition for the selenium reduction.For the difficult problem that the impurity of tellurium exists in the selenium during purification process, sodium nitrate was selected as the oxidant in this work. Experiments show that the addition of oxidant capacity and the quality of selenium ratio of 1:1, the heating temperature of 350℃was the best condition for of tellurium purification. The content of impurity tellurium content can be reduced to 0.1ppm after the purification process repeated for 3 times.A vacuum distillation device was designed and produced. By studying the relationship among the heating temperature, evaporation rate and degree of variation of the vacuum, the stable distillation condition of selenium was found to be the heating temperature of 350℃and vacuum less than 20Pa.