Selenium purification method

The present invention provides a selenium purification method, which comprises: (1) oxidizing crude selenium to obtain an oxidation product, dissolving the oxidation product in water, and carrying out solid-liquid separation to obtain a seleninic acid solution; (2) heating, evaporating and crystallizing the obtained seleninic acid solution to obtain selenium dioxide, mixing the selenium dioxide with water and formic acid to form a solution, carrying out reflux condensation, cooling after the reaction is finished, and carrying out solid-liquid separation on a product to obtain elemental selenium; (3) mixing elemental selenium with sodium nitrate, heating, stirring, slagging off, and cooling to obtain a purified selenium block; and (4) carrying out vacuum distillation on the selenium block to obtain high-purity selenium. According to the purification method, the technical problems that new impurities are easily brought by pure chemical purification, the deep purity requirement cannot be met by adopting a distil