Selenium secondary sources

The primary sources of selenium are volcanic emanations and metallic sulfides associated with igneous activity. Secondary sources are biological sinks in which it has accumulated. The selenium content of black shales, coal, and petroleum is 10-20 times the crustal abundance (0.05 ppm). Seleniferous black shales are the parent materials of the widespread seleniferous soils of the western plains of the United States. When burned, coal and petroleum containing selenium give rise to a redistribution of particulate Se and SeOg. The average selenium content of U. S. coal is about 3 ppm and of petroleum about 0.2 ppm. Selenium is an essential nutrient for animals and is required at a concentration of about 40 ppb in their diet at concentrations of 4000 ppb and above, however, it becomes toxic to animals. 

Worn-out and damaged photocopier drums, other industrial scrap and residues from chemical processes are of increasing importance as raw material. About 15% of selenium production come from these secondary sources. 

Under the assumption that the gaseous sulfur, fine particle selenium and secondary fine particle sulfur measured at an ambient site originates from a single point source the tracer hybrid receptor model can be expressed in terms of the two equations... 

They also studied the reaction between Pb (II) oleate and diphenylphos-phine selenide and found that the secondary phosphine was responsible for the dissociation or activation of the Pb-oleate to form a reactive Pb-phosphine complex intermediate which reacts with TOPSe to produce PbSe QDs. Thus, TOPSe acts only as a source of selenium whereas the growth of the PbSe QDs was accelerated by the secondary phosphine. Similar observation was noted for the formation of CdSe QDs, hence this mechanism could possibly be applicable to all phosphine-based syntheses of II-VI and IV-VI QDs. 

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