Process for preparing iron free zinc oxide

Abstract

The present invention provides a process for the separation and removal of iron ions from a basic zinc solution. The process involves: treating an aqueous basic zinc solution with a solid ion exchange resin containing an insoluble cross-linked polymer which contains at least one pendant phosphonate group, at a pH of from about 8 to about 12, and a temperature of from about 10° C. to about 90° C., for a time period sufficient to form solid phase-bound iron ions and a liquid phase containing the aqueous basic zinc solution having an iron ion concentration that is substantially reduced; separating the solid phase-bound iron ions and the liquid phase; and treating the solid phase-bound iron ions with an aqueous acidic solution under conditions sufficient to regenerate the solid ion exchange resin. The present invention also provides a process for preparing zinc oxide that is substantially free of iron ions. This process involves: (a) treating ammonium carbonate and zinc oxide to form a mixture containing a zinc ammonia carbonate complex and metal impurities such as iron, lead, and cadmium, and optionally sulfur; (b) optionally filtering the mixture from (a) to produce a residue containing mostly sulfur and a filtrate containing mostly the zinc ammonium carbonate complex and metal impurities containing iron, lead and cadmium; (c) treating the filtrate from (b), or the mixture from (a) with zinc(0) to remove the lead and cadmium and to form a cementation product, and filtering the cementation product to form a cementation residue containing mostly lead and cadmium and a cementation filtrate containing mostly zinc and iron ions; (d) treating the cementation filtrate from (c) with the above mentioned ion exchange resin, for a time period sufficient to form solid phase-bound iron ions and a liquid phase containing the cementation filtrate having an iron ion concentration that is substantially reduced; (e) heating the liquid phase from (d) to remove ammonia and to precipitate zinc ions in solution as mostly zinc carbonate; and (f) calcining the zinc carbonate precipitate of step (e) at a temperature of from about 200° C. to about 1100° C. to convert the zinc carbonate to zinc oxide.

Dependencies are inferred from the claim text.