Chemical purifn of wet process phosphoric acid - by treatment with phosphate rock, calcium sulphate and sodium ions

摘要

Wet process phosphoric acid, after filtering and cooling, is treated with finely powdered phosphate rock (phosphorite), CaSO4.2H2 to give an H2SO4 content of 1.4 plus-or-minus 0.2%, and with the precise quantity of Na ions, obtd. from a soluble salt, required to eliminate F- and SiO2 as Na2SiF6; the supersatd. suspension of the solids formed by the CaSO4.2H2O, Na2SiF6 and a small quantity of monocalcium phosphate dihydrate is maintained by vigorous agitation for =8 hrs., and the purified phosphoric acid is sepd. from the sludge with opt. recovery of the phosphoric acid contained in the sludge. Very pure phosphoric acid is obtd. with a low content of organic material, SO4=, F-, SiO2, and Ca++.