Zinc removal from aluminate solutions

摘要

In a process of the preparation of alumina from an alumina value containing material wherein a caustic sodium aluminate process liquor is subjected to a treatment to reduce the level of zinc impurity by the addition of ZnS seed in the presence of sulfide ion, the improvement comprising: (I) forming the zinc sulfide seed a by process comprising the steps of: (A) dissolving ZnO in NaOH to produce a caustic Na2ZnO2 solution; and (B) reacting the solution of (A) with Na2S to form ZnS, the Na2S being present at a level sufficient to provide a concentration of Na2S of at least about 0.150 g/l of Na2S when the product of this step is added to the process liquor; (II) adding the product of step (B) to the process liquor to precipitate as ZnS, zinc contained as sodium zincate in the process liquor; and (III) filtering the process liquor to yield an NaAlO2 liquor containing less than 15 mg/l and preferably below about 10 mg/l zinc as ZnO.