Increasing precipitation rate from sodium aluminate solution by adding active seed and ammonia

Abstract

Remarkably increasing precipitation rate of sodium aluminate solution was studied by adding active seed and ammonia. The fine active gibbsite seed with irregular edge, large specific area and high oil adsorption capacity was prepared by sodium bicarbonate solution and sodium aluminate. The seeded precipitation rate reached up to 65% by adding <20 g L−1 active seeds into the sodium aluminate solution. Moreover, 75% precipitation rate was obtained due to the coupling contribution from the active seed and ammonia. Ammonia added in the initial precipitation stage improved precipitation rate, whereas minimal change in precipitation rate occurred by adding ammonia in latter period of precipitation. High precipitation rate also led to precipitation of fine gibbsite. In addition, increasing ammonia amount benefitted the formation of Al(OH)4− and slightly reduced the amount of Al2O(OH)62−. Electrical conductivity in solution was decreased by adding ammonia. This is quite probably attributed to the increase in ionic pairs of Na+Al(OH)4− and subsequently precipitation of gibbsite from Al(OH)4−.