Physical, chemical, and surface charge properties of bauxite residue derived from a combined process

Abstract

A detailed understanding of the composition, buffering capacity, surface charge property, and metals leaching behavior of bauxite residue is the key to improved management, both in reducing the environmental impact and using the material as an industrial by-product for other applications. In this study, physical, chemical, and surface charge properties of bauxite residue derived from a combined process were investigated. Results indicated that the main alkaline solids in bauxite residue were katoite, sodalite, and calcite. These minerals also lead to a higher acid neutralizing capacity of bauxite residue. Acid neutralizing capacity (ANC) to pH 7.0 of this residue is about 0.9 mol H+/kg solid. Meanwhile, the Fe-, Al-, and Si-containing minerals in bauxite residue resulted in an active surface; The isoelectric point (IEP) and point of zero charge (PZC) were 7.88 and 7.65, respectively. This also leads to a fact that most of the metals in bauxite residue were adsorbed by these surface charged solids, which makes the metals not readily move under natural or even moderately acidic conditions. The leaching behavior of metals as a function of pH indicated that the metals in bauxite residue present low release concentrations (pH > 3).