26 августа, 2015 
Pokraskin An even rarer element, selenium is present at approximately 50 parts per billion of the earth’s crust. It is much rarer than its neighbor in the periodic table, sulfur. The ratio of selenium to sulfur has been calculated to be about 1:6000!
Like cadmium, selenium is mainly derived from the purification of other mineral ores, although the world’s first mine containing deposits of commercial grade selenium was opened in Wyoming in 1955. Most selenium is today obtained from anode slimes produced during the refining of nickel and copper sulfides.
The dark gray powder or pellets are sold as pigment grade selenium at typically 99.95% purity.
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