Abstract
Selenium was discovered in 1818 by the great Swedish chemist, Berzelius, who was investigating the nature of reddish substances depoited on the walls of lead chambres in a sulphuric acid plant in Gripsholm. No mineral ores contain economicaly - significant concentrations of selenium. The largest source of selenium is the anode slime formed during the electrolytic refining of copper. Selenium recovered as a byproduct during the copper smelting generally contains less than 90% Se. A variety of the processes exist for refining crude selenium to the commercial grade 99,5% or to a high grade purity selenium 99,99%. Chemical and physical methods are used. Chemical methods of impurity removal generally cannot produce a product greater than 99,95% Se, and may require several process stages and long residence times. The volatile impurities can be separated by distillation, or by rectification. The different methodes of crude selenium refinning are discussed in this paper.
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