Amending Bauxite Residue Sands With Residue Fines to Enhance Growth Potential

Abstract

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 µm) to residue sand (> 150 µm) 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.

Zinc forms in compost and red mud-amended bauxite residue sand

“…Although the extraction of Zn increased with leaching events, all levels recorded remained well below the deficient range of Zn for plant growth (e.g., Brennan et al 1993) suggesting the importance of appropriate Zn fertiliser input on residue sand. These findings are in agreement with past studies conducted in residue sand (Bell 1981;Gherardi and Rengel 2003a, b;Eastham and Morald 2006;Anderson et al 2007). Zinc content of plants grown with poultry manure and Zn fertiliser additions in the bauxite residue sand areas showed a significant drop in the Zn levels in 4-year-old residue rehabilitation sites relative to those in 1-year-old residue and may indicate a future risk of its deficiency (Thiyagarajan et al 2009).…”

“…Despite low inherent Zn status, seawater-washed red mud had significantly lower pH which increased the DTPA Zn while carbonated red mud had higher pH and exchangeable sodium percentage which decreased the Zn extractability. Similar increases in concentration of other plant nutrients due to seawater-washed red mud additions were reported by Menzies and Fulton (2004) and Anderson et al (2007) in residue sand column studies. Low DTPA Zn was in agreement with the past studies conducted in residue sand (Bell 1981;Gherardi and Rengel 2003a, b;Doye and Duchesne 2003;Courtney et al 2003;Eastham and Morald 2006;Anderson et al 2007).…”

“…However, the long-term success of rehabilitation depends particularly on a capping stratum that ensures good water and nutrient retention. A possible practice in rehabilitation of bauxite residue is to incorporate the finer red mud fraction in the capping stratum to improve the physical fertility of residue sand (Anderson 2009). However, the greater substitution of sands with red mud may lead to increased alkalinity which would impair Zn availability to plant growth.…”

“…Recently, co-disposal of fine-textured red mud with residue sand at 3-20% (w/w) was reported to improve water and nutrient retention characteristics (Anderson et al 2007;Courtney and Timpson 2004). Addition of 25% (w/ w) red mud to sandy soils also seems to increase growth and nutrient uptake by plants owing to considerable improvement in physicochemical properties (Snars et al 2003;Menzies and Fulton 2004;Courtney and Timpson 2005).…”

“…Addition of 25% (w/ w) red mud to sandy soils also seems to increase growth and nutrient uptake by plants owing to considerable improvement in physicochemical properties (Snars et al 2003;Menzies and Fulton 2004;Courtney and Timpson 2005). Though high rates of red mud addition increased water retention and extractable nutrient content appreciably in bauxite residue sand, it also increased exchangeable Na and electrical conductivity due to the extremely high pH (≈12) and salinity of red mud (Courtney et al 2003;Anderson et al 2007). Although amending residue sand with red mud is predicted to increase vegetation success to varying degrees, the impact on micronutrient availability and mobility remains a major research gap in sustaining vegetation on bauxite residue sand.…”