Cost-efficient removal of organics from Bayer liquor by tricalcium aluminate hexahydrate: Insights into the organic micelle and multilayer adsorption

Abstract

The existence state and effective removal of organics from Bayer liquor have troubled the alumina industry for six decades. This study delved into the aggregation behavior and micellization of organics in Bayer liquor. Tricalcium aluminate hexahydrate (3CaO·Al2O3·6H2O, TCA) was then employed as a cost-effective adsorbent to remove organics by regulating the aggregation behavior of organics. Sodium dodecylsulfate (SDS), acting as a research object of organics, aggregated into inhomogeneous and large micelles (>3080.00 nm) with an extremely low critical micelle concentration (CMC) of 0.14 mmol·L−1 in the sodium aluminate solution (CNa2O = 2.42 mol·L−1, αK = 3.0, I ≥ 4.84 mol·L−1) at 298 K. Decreasing temperature facilitated the formation of these large micelles and the micellar size reached 2.20 μm in length. The solvated Ca2+ (Ca(OH)+) of TCA, acting as counterions with a content exceeding 11.97 wt%, initially induced the formation of micelles and then enlarged their size. Furthermore, these large micelles exhibited a preferential aggregation at the active concave of TCA. As a result, the interaction among inhomogeneous micelles, solvated Ca2+ (Ca(OH)+), and special active concave collectively contributed to the maximum organic carbon adsorption capacity of 32.46 mg·g−1 (equivalent to 64.92 mg·g−1 of SDS) at 298 K. These results open up new perspectives for understanding the existence state of the anionic organics in sodium aluminate solutions, as well as a cost-effective and eco-friendly approach to removing organics from Bayer liquor.