Circular 58Economic recovery of selenium by flotation from sandstone ores of New Mexico
By R. B. Bhappu, 1961, 42 pp., 10 tables, 2 sheets.
Investigation has shown
that the selenium-bearing sandstone ores from the Morrison and Galisteo
formations of New Mexico are amenable to simple froth-flotation procedures.
The common flotation reagents used are soda ash, sodium silicate, a neutral
oil (kerosene), a xanthate, and a frother. Conditioning of the pulp prior
to flotation plays an important role in the process, especially if the sandstone
contains excessive amounts of slimy clays and shales. Under optimum conditions,
the selenium flotation is rapid and selective; selenium recovery above 85%
is possible; and an acceptable grade of concentrates above 4% is obtainable.
From the economic viewpoint, flotation recovery of selenium appears attractive. The cutoff grades for the profitable recovery of selenium as the major ore constituent are 0.12 and 0.04% for the underground and open-pit mining operations respectively. One the other hand, when selenium is recovered as a byproduct of some other mining operation, such as mining for uranium, the cutoff grade is only 0.01%.
If an element could be said to have "magical properties," it is probably
that high-purity selenium would come closest to fitting this description.
Despite this tribute, selenium remains a metal with an unimpressive background
and an unknown and unpredictable future.
Although selenium is widely distributed in the Earth's crust, the known deposits are either so small or of such low grade that they cannot be processed economically for selenium alone. Many years ago the sole source of selenium was thought to be the flue dusts from metallurgical processes utilizing sulfur ores; today, however, recovery from this source is virtually nonexistent. The anode slimes from electrolytic copper refineries are now providing the source of most of the world's selenium, and its production is centered at such refineries in the industrialized nations of the world.
The most serious problem confronting the selenium industry is its dependence on the refining of electrolytic copper, for this byproduct source is not sufficiently flexible to permit a normal supply-demand balance. The remedy, it is apparent, lies in the development of alternate sources of selenium on an economic and commercial scale. Efforts, however, to find such sources, even under a price inducement nearly double that in effect today, have not been successful.