Multilayer adsorption improving the organic removal by foam flotation from sodium aluminate solutions

Abstract

Effective enrichment of organics by foam flotation will notably contribute to the removal of organics from the Bayer liquor. The present study shows that the removal efficiency increased with increasing concentration of sodium laurate (SL) and sodium stearate (SS). Over 29% SS removal with a concentration ratio of 2.92 was obtained from the Bayer liquor. The surface pressure increased with increasing spreading concentration, while the mean molecular area decreased. From the remarkable difference in the π-A isotherms of SS on the surface of sodium aluminate solution and water, a minimum molecular area of 2.39 Å2 occurred in the sodium aluminate solution, which was notably lower than 24.6 Å2 in water. Adding sodium palmitate (SP) into SS increased the minimum molecular area, while the addition of sodium oleate (SO) raised the maximum surface pressure. From Langmuir-Blodgett films, the micellar size of SS and SL increased with increasing spreading concentration. Adding SP and SO into SS enlarged the micellar size owing to the synergistic interaction between organics. As a result, the complicated interfacial structure, multilayer adsorption of micelles at the air/solution interface, and precipitation of aluminum hydroxide synergistically promoted the removal efficiency of organics from the sodium aluminate soluion.