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Occurrence and Production of Arsenic
In 2005, China was the top producer of white arsenic with almost 50% world share followed by Chile and Peru, reports the British Geological Survey.
Arsenopyrite also unofficially called mispickel (FeAsS) is the most common arsenic-bearing mineral. On roasting in air, the arsenic sublimes as arsenic (III) oxide leaving iron oxides.
The most important compounds of arsenic are arsenic (III) oxide, As2O3, ('white arsenic'), the yellow sulfide orpiment (As2S3) and red realgar (As4S4), Paris Green, calcium arsenate, and lead hydrogen arsenate. The latter three have been used as agricultural insecticides and poisons. Orpiment and realgar were formerly used as painting pigments, though they have fallen out of use due to their toxicity and reactivity. Although arsenic is sometimes found native in nature, its main economic source is the mineral arsenopyrite mentioned above; it is also found in arsenides of metals such as silver, cobalt (cobaltite: CoAsS and skutterudite: CoAs3) and nickel, as sulfides, and when oxidised as arsenate minerals such as mimetite, Pb5(AsO4)3Cl and erythrite, Co3(AsO4)2 - 8H2O, and more rarely arsenites ('arsenite' = arsenate(III), AsO33- as opposed to arsenate (V), AsO43-). In addition to the inorganic forms mentioned above, arsenic also occurs in various organic forms in the environment. Inorganic arsenic and its compounds, upon entering the food chain, are progressively metabolised to a less toxic form of arsenic through a process of methylation.