Spontaneous Vegetation Encroachment upon Bauxite Residue (Red Mud) As an Indicator and Facilitator of In Situ Remediation Processes

Abstract

The spontaneous colonization of a bauxite residue (alumina refining tailings) deposit by local vegetation in Linden, Guyana, over 30 years, indicates that natural weathering processes can ameliorate tailings to the extent that it can support vegetation. Samples were collected from vegetated and unvegetated areas to investigate the relationships between bauxite residue properties and vegetation cover. Compared to unvegetated areas, bauxite residue in vegetated areas had lower pH (mean pH 7.9 vs 10.9), lower alkalinity (mean titratable alkalinity 0.4 vs 1.4 mol H(+) kg(-1)), lower electrical conductivity (mean EC 0.3 vs 2.1 mS cm(-1)), lower total Al (mean Al2O3 19.8 vs 25.8% wt) and Na (mean Na2O 0.9 vs 3.7% wt), and less sodalite and calcite. Accumulation of N, NH4(+), and organic C occurred under vegetation, demonstrating the capacity for plants to modify residue to suit their requirements as a soil-like growth medium. Aeolian redistribution of coarse grained tailings appeared to support vegetation establishment by providing a thin zone of enhanced drainage at the surface. Natural pedogenic processes may be supplemented by irrigation, enhanced drainage, and incorporation of sand and organic matter at other tailings deposits to accelerate the remediation process and achieve similar results in a shorter time frame.

A review of the characterization and revegetation of bauxite residues (Red mud)

“…Both the structure and physico-chemical properties of bauxite residues, which can limit plant growth, require further improvement, although little attention has focused on natural processes of soil formation and development (Courtney et al 2009a, b). Recently, Santini and Fey (2013) highlighted that more attention should be given to pedogenic processes within bauxite residue, thereby enhancing substrate amelioration. Numerous measures have been taken to improve the physical, chemical, and microbial properties of bauxite residues, and this paper will review the characterization and revegetation strategies currently available for its management in the environment.…”

Experimental Simulation of Long Term Weathering in Alkaline Bauxite Residue Tailings

“…Under hydrothermal conditions, we expected to observe some conversion of mineral phases that are commonly associated with Bayer process conditions, such as conversion of gibbsite to boehmite [21], goethite to hematite [22], tricalcium aluminate to calcite [23], and quartz to desilication products [24]. Dissolution of sodalite and calcite has been observed during weathering under leaching conditions [3,25,26]. However, dissolution of these minerals was not expected within this experiment because no leaching was possible.…”

“…Tailings have typically been treated solely as waste materials; however, tailings are increasingly being recognized as substrates for soil development [2][3][4]. The annual mass of tailings produced globally is approximately one-third of the mass of soil lost through erosion globally [1,5].…”

“…Refinery scale Bayer processing commenced in 1894, which gives 120 years exposure to weathering in the very oldest residue deposits [7]. The longest weathering timeframe for bauxite residue reported in studies to date was 40 years under a tropical climate in Guyana, in which dissolution of sodalite and calcite were observed [3]. This reflects the fact that weathering of primary minerals, an essential part of soil formation, can be a slow process in the field which is partially constrained by reaction kinetics.…”

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

“…Wehr et al, 2005). Nonetheless, there are several examples of successful revegetation Santini and Fey, 2013; Aluminium for Future Generations, 2016). Visual observations at sites where successful revegetation has been achieved suggest that upon drying the mud solidifies and loses a substantial volume.…”