Bauxite residue fines as an amendment to residue sands to enhance plant growth potential—a glasshouse study
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- Anderson, J.D., Bell, R.W. & Phillips, I.R. J Soils Sediments (2011) 11: 889. doi:10.1007/s11368-011-0379-7
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This glasshouse study was conducted to determine if amending bauxite residue sand with residue fines would improve its suitability as a growth medium. Alcoa’s West Australian operations mechanically separate residue into two size fractions: residue fines (which are dominated by particles <150 μm) and residue sands (>150 μm). Residue sand represents the primary material used as a growth medium for rehabilitation, and prior to amendments, it exhibits many characteristics unfavourable for plant growth.
Materials and methods
Residue sand was amended by adding increments (1%, 2%, 3%, 5%, 10%, 20% w/w) of unaltered or pre-treated (carbonated or seawater-washed) residue fines making 18 fines treatments compared to the residue sand alone. Growth medium characteristics assessed were water retention measured as volumetric and plant available water; nutrient concentrations in the growth medium at the initiation and completion of the growth period (13 weeks); plant nutrient concentrations at the termination of the study; and the shoot and root biomass of Acacia saligna.
Results and discussion
Addition of residue fines more than doubled plant available water and increased extractable nutrient concentrations relative to unaltered residue sand. Additions of seawater-washed fines increased extractable Mg, K and B concentrations in the growth medium, while carbonated and unaltered fines increased extractable S and P concentrations relative to the residue sand. However, all residue fines treatments increased both the electrical conductivity and exchangeable sodium percentage. Vegetative growth over a 13-week period varied with rate of addition and pre-treatment (seawater > carbonated = unaltered) of residue fines. Carbonated and unaltered fines treatments resulted in shoot biomass with elevated Na concentrations and reduced growth, but the seawater fines treatments increased plant Mg and B without increasing Na concentrations relative to the residue sand.
Although improvements in water retention and nutrient concentrations were found in some treatments with residue fines additions, the effect of residue treatments on plant growth was confounded by the short-term increase in Na concentrations.
KeywordsAcacia salignaExchangeable cationsPlant available waterRed mudResidue rehabilitation
Residue disposal area