Characterization of Untreated and Neutralized Bauxite Residue for Improved Waste Management

Abstract

Alumina refineries generate large volumes of bauxite residue daily, and as such, the storage, treatment, and reuse practices for residue are receiving increasing attention as refineries strive to reduce the potential environmental impact of their operations. To improve management decisions in the selection of appropriate storage, treatment, and reuse practices, the leaching behavior of bauxite residue was characterized using a standardized pH dependence leaching test. Leaching data was modeled using a geochemical speciation program to determine which chemical processes are controlling bauxite residue leaching behavior. This approach showed that the nine residue samples examined behaved very similarly for most elements, despite being generated by different refineries that utilize bauxite from different sources. Geochemical modeling of the leach data helped identify the solubility controlling minerals and other release controlling factors, which proved mostly the same for this wide range of samples. Residue treatments such as carbonation and seawater neutralization did affect the leaching of some elements, resulting in a change in the leaching behavior of the treated material compared with the untreated sample. Using geochemical speciation modeling, the changes were largely explained; hence, this approach, aimed at understanding the geochemical phases controlling release, provides a sound basis for waste management decisions in a wide range of storage and reuse scenarios.