Ameliorating caustic properties of aluminum extraction residue to establish a vegetative cover

Abstract

High pH, electrical conductivity (E.C.), and extractable Na levels in the residue remaining after aluminum was extracted from bauxite were greater than can support vigorous plant growth. These caustic properties must be ameliorated so that vegetation could be established on the surface of large disposal ponds. Fresh residue was added to 14 field lysimeters of dimensions 3 m long x 3 m wide x 1 m deep. Internal drainage was enhanced in some lysimeters and restricted in others. Gypsum applied at the rate of 7.5% of the weight of the top 15 cm of residue in selected lysimeters. These management issues were studied to determine how their influence would lower chemical properties to support vegetation. Residue samples were removed annually for 5 years after the lysimeters were established to determine changes in pH, E.C., and extractable Na and Al over time. Plant species C. dactylon (bermudagrass), Atriplex nummalari (oldman saltbush), and Atriplex canescens (fourwing saltbush) were planted either as seeds or transplants beginning the third year after lysimeter establishment. Residue pH, E.C. Na, and Al decreased annually, but more gradually in restricted drainage. Species survival in the enhanced drainage treatments was more vigorous with gypsum amendments beginning in the third year after lysimeter establishment. This coincided with a decrease in the mean pH below 9.5 and decrease in mean E.C. below 10 dS/m. Extractable Na and Al did not seem to influence survivability. Survival of seeded and transplanted C. dactylon was greater than the two Atriplex spp. each year. This study proved that the caustic properties of this residue could be lowered enough to support vegetation, but not without appropriate drainage. The addition of gypsum amendments and appropriate amounts of supplemental water would accelerate the timeframe for vegetation establishment probably at a level commensurate with the application rate of both inputs in a well-drained system.

Spatial analysis of fine root distribution on a recently constructed ecosystem in a water-limited environment

“…The RDA is an artificially constructed landform designed to store residues from a bauxite refinery. The residue, a waste product from the extraction of alumina from bauxite is mechanically separated into highly caustic (pH: 12.5) red mud (<150 μm in diameter) with high electrical conductivity (60,800 μS cm −1 ) and extractable sodium (28 g kg −1 ), and process residue sand (>150 μm in diameter) (Courtney and Timpson 2005;Wong and Ho 1993;Woodard et al 2008). The caustic nature, and high salinity and sodicity of the red mud make it nonconducive for root growth.…”

“…Consequently, the extent to which fine root distribution on such ecosystems conform to the global model of Jackson et al (1996) remains unknown, and for comparative purposes, the type of natural vegetation ecosystem that most closely matches the rooting distribution of engineered cover systems also remains unknown. The few studies conducted on rehabilitated mined sites focussed on coarse root architecture, qualitative root distribution and plant establishment (Enright and Lamont 1992;Rokich et al 2001;Szota et al 2007;Woodard et al 2008) but did not reveal spatial patterns of fine roots and their relationship with soil properties. These earlier studies suggest that high penetration resistance and dry soil bulk densities (Enright and Lamont 1992;Rokich et al 2001;Szota et al 2007) and adverse chemical conditions particularly high soil pH and electrical conductivity (Woodard et al 2008) influence root growth on reconstructed or artificial ecosystems diameter (ϕ, mm) ≤5 mm, which combines both fine such as engineered covers.…”

“…The few studies conducted on rehabilitated mined sites focussed on coarse root architecture, qualitative root distribution and plant establishment (Enright and Lamont 1992;Rokich et al 2001;Szota et al 2007;Woodard et al 2008) but did not reveal spatial patterns of fine roots and their relationship with soil properties. These earlier studies suggest that high penetration resistance and dry soil bulk densities (Enright and Lamont 1992;Rokich et al 2001;Szota et al 2007) and adverse chemical conditions particularly high soil pH and electrical conductivity (Woodard et al 2008) influence root growth on reconstructed or artificial ecosystems diameter (ϕ, mm) ≤5 mm, which combines both fine such as engineered covers. Elsewhere in Estonia, Ostonen et al (2006) observed that tree species, stage age and microbial community also influenced root parameters on revegetated oil shale mining sites.…”

Spatial analysis of fine root distribution on a recently constructed ecosystem in a water-limited environment

“…Consequently, the extent to which fine root distribution on such ecosystems conform to the global model of Jackson et al (1996) remains unknown, and for comparative purposes, the type of natural vegetation ecosystem that most closely matches the rooting distribution of engineered cover systems also remains unknown. The few studies conducted on rehabilitated mined sites focussed on coarse root architecture, qualitative root distribution and plant establishment (Enright and Lamont 1992;Rokich et al 2001;Szota et al 2007;Woodard et al 2008) but did not reveal spatial patterns of fine roots and their relationship with soil properties. These earlier studies suggest that high penetration resistance and dry soil bulk densities (Enright and Lamont 1992;Rokich et al 2001;Szota et al 2007) and adverse chemical conditions particularly high soil pH and electrical conductivity (Woodard et al 2008) influence root growth on reconstructed or artificial ecosystems such as engineered covers.…”

Revegetation strategies for seawater neutralized bauxite residue at Rio Tinto Alcan using various amendments

“…In a soil, values are typically less than 400 mS m -1 (Meecham and Bell, 1977a;Woodard et al, 2008) so that bauxite residues are considered as highly saline. Inhibition of plant growth (Maas, 1990) is usually slight at EC values between 200-400 mS m -1 , severe between 400-600 mS m -1 and death typically occurs at > 600 mS m -1 (Maas, 1990).…”