Recovery of useful products from by-products of phosphate conversion coating process

摘要

The process is described for treating the sludge formed in a phosphate conversion bath, and in particular, in zinc phosphate conversion baths to convert the sludge into useful chemical materials thereby eliminating the need for disposal to landfill. The process comprises the steps of (A) recovering the solid by-products from the used phosphating solution; (B) treating the solid by-products with an aqueous base at a pH of greater than 10 to form a first aqueous phase and a metal-containing precipitate; (C) recovering the metal-containing precipitate from the first aqueous phase as a first product of the process; (D) acidifying the first aqueous phase obtained in (C) to a from about 7 to about 10 to form a second aqueous phase and an insoluble metal-containing precipitate; (E) recovering the solid metal-containing precipitate from the second aqueous phase as a second product of the process; and (F) recovering the second aqueous phase as a third product of the invention.