THE REMOVAL OF ZINC FROM SOLUTIONS BY FOAM SEPARATION .2. PRECIPITATE FLOTATION OF ZINC HYDROXIDE

Zinc removal vs. pH by anionic collectors has three characteristic stages: removal increase (which starts at the lower pH with the higher zinc concentration in the feed solution), maximum removal in the pH range 7.5-10, and removal decrease. Increased concentration of inorganic electrolytes and the valency of their anions cause a decrease in hydroxide removal by means of lauryl sulfate, whereas removal of the collector is improved. Moreover, increased concentration of electrolytes has a positive effect on the hydroxide removal with cetyltrimethylammonium bromide. Both the adsorption of lauryl sulfate on the hydroxide and the supernatant surface tension decrease with increasing electrolyte concentration and anion valency while the adsorption of the cetyltrimethylammonium collector increases with increasing electrolyte concentration, but the surface tension decreases. The isoelectric point of zinc hydroxide in water is about pH 9. In the presence of lauryl sulfate and electrolyte, the zeta potential and the IEP pH of the hydroxide decrease. However, in the presence of the cetyltrimethylammonium collector, the zeta potential and the IEP pH of the hydroxide increase. The interpretation of the hydroxide removal as well as the changes in interfacial phenomena is based on the analysis of interactions between the surface sites of hydroxide and the collector (or electrolyte) anions. © 1990.