As part of a U.S. Bureau of Mines research program to study processes for extraction of alumina from domestic resources, a bench- scale evaporate crystallizer was operated with solutions of impure aluminum chloride hexahydrate (ach). The purpose of the research was to determine the distribution of impurities in the bleedstream section of a proposed clay-hcl process. Impurities including mg, p, na, k, cr, and s were determined in ach crystals produced from feed solutions with a threefold range of impurities and at varied crystallizer slurry percent solids. Phosphorus was the limiting contaminant; 0.83 pct of the process alumina would have to be discarded for control. Crystallizer slurry in the range of 10 to 25 pct solids had little effect on crystal purity.