Formation, properties and revegetation prospects for bauxite processing residue and the effects of seawater neutralisation

Abstract

Partial neutralisation of bauxite residue (by treatment with seawater) prior to its deposition in land-based lagoons or impoundments minimises the need to treat the alkaline, sodic drainage both during operation of the alumina refinery and following its closure. Some of the Na present in the residue is replaced by Mg, Ca and K present in the seawater and reactive, soluble alkalinity is converted to poorly soluble alkaline solids (Mg and Ca hydroxides and hydroxycarbonates) with the result that the pH is reduced from 10-13 down to 8.5-9.0. However, the extent to which pH rises again during storage is unclear. There are, as yet, no reports of revegetation of seawater neutralised material. Growth limiting factors are likely to include alkalinity, sodicity, salinity, nutrient deficiencies and poor soil physical conditions but the severity of these constraints are as yet unknown. Research into the technology required for revegetation of this material is warranted.