Tristage crystallization and hydrolysis process for recovering vanadium phosphorus and chromium from ferrophosphorus and like materials

Claim 1

IN A PROCESS FOR THE PRODUCTION OF VANADIUM RED-CAKE, CHROME YELLOW, AND TRISODIUM PHOSPHATE FROM FERROPHOSPHORUS CONTAINING ALSO VANADIUM AND CHROMIUM, INVOLVING ROASTING SUCH FERROPHOSPHORUS WITH SALT AND SODA ASH, THE IMPROVEMENT WHICH COMPRISES LEACHING THE ROASTED PRODUCT WITH WATER, SEPARATING A LEACH SOLUTION CONTAINING TRISODIUM-PHOSPHATE, -VANADATE AND -CHROMATE, THEN COOLING SAID SOLUTION AND SEPARATING IN A PRIMARY CRYSTALLIZATION STEP, A CROP OF TRISODIUM PHOSPHATE CRYSTALS CONTAINING ALSO VANDIUN AND CHROMIUM, REDISSOLVING SAID PRIMARY CRYSTAL CROP IN WATER AND RECOVERING BY RECRYSTALLIZATION A SECONDARY CROP OF TRISODIUM PHOSPHATE CRYSTALS AS A PRODUCT, RETURNING THE MOTHER LIQUOR FROM RECRYSTALLIZATION TO THE LEACH SOLUTION, THEN ADDING PHOSPHORIC ACID TO THE MOTHER LIQUOR FROM SAID PRIMARY CRYSTALLIZATION TO CONVERT RESIDUAL DISSOLVED PHOSPHATE VALUES INTO DISODIUM HYDROGEN PHOSPHATE, SUBJECTING THE THUS TREATED SOLUTION TO A TERTIARY CRYSTALLIZATION STEP TO RECOVER A CROP OF DISODIUM HYDROGEN PHOSPHATE CRYSTALS AND A PREGNANT SOLUTION LOW IN PHOSPHORUS BUT CONTAINING CHROMIUM AND VANADIUM, RETURNING SAID DISODIUM HYDROGEN PHOSPHATE CRYSTALS TO THE SAID LEACH SOLUTION, THEN ADDING CALCIUM CHLORIDE TO THE PREGNANT SOLUTION TO PRECIPITATE RESIDUAL PHOSPHATE AS TRICALCIUM PHOSPHATE, SEPARATING SAID PRECIPITATED TRICALCIUM PHOSPHATE, ACIDIFYING THE SOLUTION WITH SULPHURIC ACID AND HEATING AND AGITATING THE REMAINING SOLUTION CONTAINING CHROMIUM AND VANADIUM, AT AN ACIDIC PH, TO PRECIPITATE VANADIUM RED-CAKE, SEPARATING THE RED-CAKE AND TREATING THE MOTHER LIQUOR WITH ENOUGH LIME TO PRECIPITATE RESIDUAL VANADIUM AND PART OF THE CALCIUM SULFATE, REMOVING THE PRECIPITATE, PRECIPITATING CHROME YELLOW FROM THE REMAINING SOLUTION BY ADDITION OF LEAD NITRATE, AND THEN SEPAARATING AND RECOVERING THE CHROME YELLOW.