Chapter 7 - Management and disposal of alumina production wastes

Abstract

Approximately 60Tg/year of red mud, which is a highly alkaline residue from refining the bauxite ore to produce aluminum, is generated as a by-product of alumina refining annually. Most red mud (85%) is stored in impoundments on-site or adjacent to alumina refineries. In this chapter, the chemical and mineralogical compositions of red mud are investigated, and major, minor, and trace elements in the leachates are analyzed. The mineral and chemical compositions of red mud vary as per the refining processes (i.e., Bayer, sintering, and combined methods) and parental bauxites. Bauxite liquors, the leachate from the red mud, are hyperalkaline (pH>12), with ionic strength up to 1.5M. The chemistry of the red mud could potentially affect the surrounding environment and decrease the functionality of the liners of the red mud reservoir. The lining material for the containment of the red mud is evaluated to aid the design of the impoundment and reservoir of the red mud. The hydraulic conductivity of the liner is critical to contain the bauxite liquor. Sodium bentonite and bentonite–polymer composite geosynthetic clay liners were explored as the alternative liner material for traditional compacted soil liner using bauxite liquors obtained from alumina refineries worldwide. Additional studies are needed to beneficially reuse the red mud, further reducing the waste generation and quantity for disposal.