Selenium Refining by Nitrate Fluxing

AbstractThe refining of mist precipitated selenium, assaying approximately 98% selenium, by the addition of a nitrate flux was studied in the temperature range 250–350°C. Optimum operating conditions were identified which yielded a uniform selenium product averaging 99.79% purity. The maximum purity of the selenium product was limited by the inability of the nitrate flux to react with mercury and silver from the feed material. The removal of Cu, Pb, S, Si, Fe, Zn, Bi, Sn, As and Te was greater than 90%, and in some cases approached 100% removal. The major impurities in the selenium product were copper (1000 ppm), mercury (850 ppm), lead and silver (100 ppm).The application of the nitrate flux proved to be an effective method for the purification of selenium already close to meeting requirements. The purification was accomplished at a fast rate, with low reagent consumption and at low reaction temperatures.