Developments in phosphate-rock beneficiation and the problems with Indian phosphorites

Phosphate-rock or more precisely the phosphorites form the repository of phosphate supply for the fertilizer industry for manufacture of elemental phosphorus, phosphoric acid and innumerable alkali phosphates. It has now been universally agreed that phosphorites have some kind of sedimentary marine origin, the source of phosphorous being of organic and/or inorganic origin (1). The principal phosphate mineral occuring in these deposits is referred by its generic designation as collophane (2), a carbonate bearing variety apatite, whose formula is approximately Cato ( PO4 CO3.H20 with a little of F. It is porous and crypto-crystalline, occuring as compact nodules or pellets as disseminations in calcitic or qurtzitic sedimentary rocks along with clay, sericite, silt, chert, free carbon and invariably associated with a little uranium (0.002 to 0.008% U308 e). The typical apatite [Ca 6(PO4)3 F] is crystalline and occurs usually in igneous and metamorphic rocks, pegmatites, granites, and schists. Its chemical composition is more defined and constant compared to the collophane of sedimentary origin. Fertilizer industry, though uses phosphate from both sources; the super phosphate manufacturers prefer phosphate-concentrates from phosphorite because of the ease with which collophane goes into solution with sulphuric acid. The physical characteristics of collophane also have bearing on its flotability.