Mouna Cherif, PhD
M. Cherif1, B. Plante1, J-É. Guérin2
1Research Institute on Mines and the Environment (RIME), Université du Québec en Abitibi-Témiscamingue (UQAT), Rouyn-Noranda, Quebec, Canada
2Arvida Research and Development Centre, Rio Tinto, Saguenay, Quebec, Canada
Acid mine drainage (AMD) from open-pit mines contaminates surface and groundwater, causing significant damage. Therefore, alternative solutions are needed to address this significant environmental issue. Bauxsol™ is an amendment derived from pre-neutralised Australian bauxite residue produced during the alumina refining process. It has been studied in several countries, where its effectiveness in stabilising water and soil has been demonstrated. This study evaluates the effectiveness of Bauxsol™ produced at the Vaudreuil alumina refinery in Quebec using Virotec technology for neutralising acidic mine drainage and immobilising dissolved metals.
Granulometric and mineralogical analyses reveal its fine texture (d₅₀ = 2.6 µm) and high specific surface area (22 m².g⁻¹), which promote chemical reactivity. The material is dominated by ferric and aluminous phases (gibbsite 28.4%, hematite 25.3%, goethite 13.2%), providing a strong buffering capacity and adsorption sites.
Batch tests carried out on waste rocks generating AMD show a gradual increase in leachate pH, rising from 2.9 (control) to 6.75 after 24 hours with 15% Bauxsol™ amendment, indicating controlled neutralisation. At the same time, the redox potential (Eh) decreases from 823 mV to 431 mV, limiting sulfide oxidation and metal release. Unlike lime, which induces extreme alkalinity (pH > 12) and very low Eh even at the initial ratios, Bauxsol™ provides gradual chemical stabilization, reducing ecotoxicological risks associated with overly basic conditions.
The effectiveness of Bauxsol™ in immobilizing metals is notable. Aluminium (Al) and iron (Fe) are removed from aqueous phase by more than 99% with just 8% amendment, mainly through hydroxide precipitation and adsorption on ferric oxides. Trace metals such arsenic (As), chromium (Cr), lead (Pb), Zinc (Zn), Cobalt (Co) and nickel (Ni) are captured. However, the chemical composition of Bauxsol™ leads to a significant release of sodium (Na) (up to 2895 mg.L⁻¹ for Na) increasing the electrical conductivity (12.5 mS.cm⁻¹) and posing a risk of salinisation. This phenomenon, although secondary to neutralisation, requires careful dose management to avoid impacts on water quality.
In conclusion, Bauxsol™ could serve as an effective alternative for stabilising AMD, thanks to its buffering capacity and its combined mechanisms of sorption and coprecipitation.