| abstract |
In the manufacture of phosphoric acid by treatment of phosphate ores with excess phosphoric acid and precipitation of calcium ions as calcium sulfate, the purity and quality of the byproduct calcium sulfate is substantially improved by subjecting the monocalcium phosphate extract of the ore before precipitation of calcium sulfate to one or more preliminary treatments, whereby contaminent ions are substantially and preferentially removed from the extract while the calcium remains substantially in solution. These preliminary treatments may include separation of fluoride by reaction with silicon compounds, separation of radium by reaction with barium compounds in the presence of sulfate ions, and separation of strontium as strontium sulfate. |