RECYCLING OF SOLID ZINC PHOSPHATING PROCESS WASTE

A METHOD FOR RECYCLING ZINC PHOSPHATING PROCESS WASTE IS PROPOSED. ABOUT THREE MILLION POUNDS OF SOLID CHEMICAL WASTE IS GENERATED ANNUALLY FROM ZINC PHOSPHATING IN NORTH AMERICA. THE WASTE IS AN INORGANIC MIXED ZINC/IRON TERTIARY SALT OF PHOSPHORIC ACID. TOXICITY LEVELS VARY BUT MOST WASTES CONTAIN NICKEL, CHROME, LEAD, AND OTHER TOXINS IN SMALL QUANTITIES. THE METHOD DEPENDS UPON CONTINUOUS REMOVAL OF IRON AS THE CENTRAL MECHANISM OF THE RECOVERY PROCESS. THE WASTE IS CONVERTED TO AN AQUEOUS SOLUTION OF PRIMARY ZINC PHOSPHATE. BY ADJUSTING THE CONCENTRATION OF VARIOUS ADDITIVES, A PRODUCT EQUIVALENT TO THE ORIGINAL ZINCPHOSPHATING FEED STOCK MAY BE CREATED. A METHOD OF CONVERSION OF THE SEPARATED IRON TO FERROUS OXIDE IS ALSO PROPOSED. BOTH END PRODUCTS HAVE A PROVEN MARKET. THE PROPOSED PROCESS DOES NOT GENERATE WASTE PRODUCTS OF ITS OWN.