Removal of organics from Bayer liquors via foam flotation

Rich foam is often formed in Bayer liquors, providing a promising short green process for the removal of organics by foam flotation. In this study, foam flotation of sodium oxalate (SO), sodium benzoate (SB), sodium citrate (SC), and sodium stearate (SS) was investigated using sodium dodecyl sulfate (SDS) as a frother and collector in a synthetic sodium aluminate solution. The feasibility of foam flotation in industrial production was then verified using Bayer liquor from alumina refineries. Low molecular weight organics achieved high maximum surface excesses, and elevated temperatures reduced them in the synthetic solution. Foams containing bubbles of different sizes were generated in the synthetic solution, and the stability of the foam increased with decreasing temperature. Medium molecular weight organics readily adhered to the bubble surface owing to their good surface activities, and the removal rate followed the order SO < SB < SS < SC. Increasing the temperature increased the removal rate of organics in both the synthetic solution and the Bayer liquor. Additionally, two types of Bayer liquor with a high total organic carbon (TOC) concentration produced a rich foam consisting of small, uniform bubbles. Over 31% of the removed organics were enriched in the foam for the Bayer liquor with TOC above 9 g L−1. A concentration coefficient of 3.46 could be achieved, resulting in a TOC greater than 51.9 g L−1 in the foam. These foam enrichment results were mainly attributed to small bubbles, high TOC concentrations, and multilayer adsorption.