Purification and recovery of crystals of metal salts

Claim 1

THE PROCESS OF RECOVERING ZINC VALUES FROM A SOLID METALLURGICAL FUME COMPRISING CHIEFLY ZINC AND SUBSTANTIALLY QUANTITIES OF WATER INSOLUBLE COMPOUNDS OF OTHER METALS, SAID PROCESS COMPRISING ADDING SAID FUME TO A SATURATED SOLUTION OF ZINC SULFATE, TREATING THE RESULTING MIXTURE, WHILE MAINTAINING THE TEMPERATURE BETWEEN 38* C. AND 60* C., WITH SUFFICIENT CONCENTRATED SULFURIC ACID TO CONVERT THE ZINC VALUES IN SAID FUME TO ZINC SULFATE HEXAHYDRATE CRYSTALS WITHOUT ANY SUBSTANTIAL SOLUBILIZING OF THE ZINC SULPHATE FORMED, COOLING THE MIXTURE TO THE TRANSITION TEMPERATURE AT WHICH ZINC SULFATE HEXAHYDRATE IS CONVERTED TO ZINC SULFATE HEPTAHYDRATE, FURTHER COOLING THE RESULTING MIXTURE THROUGH THE TRANSITION TEMPERATURE AT A RATE TO CONVERT SUBSTANTIALLY COMPLETELY SAID ZINC SULFATE HEXAHYDRATE TO SAID ZINC SULFATE HEPTAHYDRATE, SEPARATING THE RESULTING ZINC SULFATE HEPTHYDRATE FROM THE MOTHER LIQUOR CONTAINING SAID WATER INSOLUBLE COMPOUNDS AND RECYCLING A PORTION OF THE MOTHER LIQUOR CONTAINING SAID WATER INSOLUBLE COMPOUNDS FOR THE TREATMENT OF A FRESH BATCH OF SAID METALLURGICAL FUME.