Article pubs.acs.org/est
Spontaneous Vegetation Encroachment upon Bauxite Residue (Red Mud) As an Indicator and Facilitator of In Situ Remediation Processes Talitha C. Santini*,‡,§,⊥ and Martin V. Fey ‡
School of Earth and Environment, University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia School of Geography, Planning, and Environmental Management, The University of Queensland, St Lucia, QLD 4072 ⊥ Centre for Mined Land Rehabilitation, Sustainable Minerals Institute, The University of Queensland, St Lucia, QLD 4072 §
S Supporting Information *
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.
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INTRODUCTION “Cap and store” approaches to tailings management involve establishment of vegetation in a capping layer over tailings, to minimize risks associated with water infiltration and leachate leakage from the tailings, and to provide a hospitable environment for vegetation growth.1 Cap and store approaches are slowly being replaced by in situ remediation and rehabilitation initiatives, which encourage soil formation and vegetation growth directly in tailings.2,3 Bauxite residue mud (alumina refining tailings; also known as “red mud”) is an alkaline, saline-sodic byproduct of the Bayer process, in which alumina is extracted from bauxite. Between 3 and 4 billion tonnes of bauxite residue are estimated to be currently stored in deposit areas worldwide, with an additional 120 million tonnes generated each year.4 Seeding or planting seedlings directly into fresh (
