Recovery of Phosphates from Elemental Phosphorus-Bearing Wastes

Abstract

A process for oxidizing aqueous elemental phosphorus containing residues (sludges) to produce orthophosphate containing slurries suitable for subsequent reaction with ammonia to produce nitrogen and phosphate containing fertilizer products. It comprises reacting aqueous elemental phosphorus containing residues with certain special mixtures of concentrated nitric acid and sulfuric acid to effect the conversion of the elemental phosphorus into mostly orthophosphoric acid and very little orthophosphorus acid with the relative ratios of the two acids being dependent upon the mole ratio of H2SO4:HNO3 employed in the processing. The resulting aqueous reaction intermediate is neutralized with ammonia during processing to a fluid or solid fertilizer product. Prior to the conversion to products, the aqueous reaction intermediate may be subjected to a solids separation step to remove insoluble salts of certain environmentally undesirable metals, such as Pb, Cd, Ba, and Cr.