Nitric acid acidulation of phosphate rock

Claim 1

A PROCESS FOR PRODUCING PHOSPHORIC ACID BY THE ACIDULATION OF PHOSPHATE ROCK WITH NITRIC ACID WHICH COMPRISES DISSOLVING THE PHOSPHATE ROCK IN AN EXCESS OF NITRIC ACID HAVING A CONCENTRATION OF 40-70 PERCENT UNDER BOILING CONDITIONS AT A TEMPERATURE RANGE OF 100-130*C., AND AT A PRESSURE OF FROM ABOUT 200 MM. OF HG TO ABOUT ATMOSPHERIC PRESSURE, AND IN THE PRESENCE OF AT LEAST ABOUT ONE-HALF PART FINELY DIVIDED SILICON FOR EACH PART FLUORINE PRESENT IN THE ROCK, VOLATILIZING FROM THE REACTION MIXTURE AN EFFLUENT COMPRISING UNREACTED NITRIC ACID, SILICON TETRAFLUORIDE AND HF, THEREAFTER REMOVING THE FLUORINE AS AN ALKALI METAL SILICON HEXAFLUORIDE AND RETURNING THE NITRIC ACID OF THE EFFLUENT TO THE ACIDULATION REACTION REMOVING SUBSTANTIALLY ALL OF THE CALCIUM CONSTITUENTS FROM THE REMAINING REACTION MIXTURE, AND THEREAFTER SUBJECTING THE RESULTANT PHOSPHORIC ACID-NITRIC ACID CONTAINING LIQUOR TO VACUUM STRIPPING AND VOLATILIZING THE REMAINING NITRIC ACID BY CONTACT WITH COOLER LIQUID NITRIC ACID, AND THEN RECOVERING THE REMAINING PHOSPHORIC ACID.