Abstract: 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 Na.sub.2 ZnO.sub.2 solution; and(B) reacting the solution of (A) with Na.sub.2 S to form ZnS, the Na.sub.2 S being present at a level sufficient to provide a concentration of Na.sub.2 S of at least about 0.150 g/l of Na.sub.2 S 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 NaAlO.sub.2 liquor containing less than 15 mg/l and preferably below about 10 mg/l zinc as ZnO.