Chemical beneficiation of phosphatic limestone and phosphate rock with alpha -hydroxysulfonic acids

A method of selectively extracting calcite and dolomite away from apatite in phosphate rock or phosphatic limestone wherein the phosphate rock or phosphatic limestone is treated with a mixture of sulfur dioxide, water, and a carbonyl compound. Solids are separated from the liquid phase. The solids consist principally of apatite admixed with clay, quartz, and other accessory minerals originally in the rock. The solids are heated to drive off adhering sulfur dioxide, water, and carbonyl. The liquid phase consists of carbonyl, water, sulfur dioxide, and magnesium and calcium ions. Heating this liquid preferentially precipitates CaSO3.1/2H2O. This solid is filtered off and the filtrate further heated to precipitate MgSO3.3H2O largely free of CaSO3.1/2H2O. All off gas and filtrate is returned to the process.