AMENDING BAUXITE RESIDUE SANDS WITH RESIDUE FINES TO ENHANCE GROWTH POTENTIAL

Long term success of rehabilitation on bauxite-processed residue storage areas is dependant on establishing a capping stratum which will satisfy water use and nutrient cycling requirements of the intended plant community. Bauxite residue sand is the primary growth media for rehabilitating residue disposal areas (RDAs) in Western Australia however; the sustainability of the vegetation cover can be compromised by the poor water-retention and nutrient cycling properties of the residue sand. This glasshouse study was conducted to determine if adding untreated or altered residue fines (< 150 m) to residue sand (> 150 m) would improve the characteristics of the final storage capping layer for sustained plant growth. Residue sand was amended by adding increments (1, 2, 3, 5, 10, 20 % w/w) of untreated or treated (carbonated or seawater washed) residue fines to determine whether these materials affected the chemical and physical properties of the growth media, and their ability to support vegetative growth (Acacia saligna), compared with the current practice of using only residue sand. Addition of residue fines increased water retention and extractable nutrient concentrations relative to untreated residue sand. However, the addition of residue fines increased both the electrical conductivity and exchangeable sodium percentage. Vegetative growth over a 3-month growing period varied with rate of residue fines addition, and residue fines pre-treatment (seawater > carbonated = unaltered). However, the addition of residue fines did not yield greater growth when compared with unamended residue sand. The importance of differences found in water retention and nutrient concentrations among residue treatments for plant growth need to be investigated in a water-limited field environment.