Ferrous ortho-arsenate, Fe3(AsO4)2.6H2O, occurs in nature as the mineral simplesite.
It may be prepared by the action of disodium hydrogen arsenate upon ferrous sulphate solution: -
4FeSO4 + 4Na2HAsO4 = Fe3( AsO4)2 + Fe(H2AsO4)2 + 4Na2SO4,
and gradually undergoes oxidation upon exposure to moist air, yielding ferric arsenate and ferric oxide. |