Feasibility of reprocessing gold tailings: Integrated management approach for the control of contaminated neutral mine drainage

Abstract

Sulfide ore processing generates finely ground mine tailings that often contain sulfide minerals such as pyrite, pyrrhotite, arsenopyrite, and gersdorffite. These minerals can generate acid mine drainage or contaminated neutral drainage (CND) due to weathering (aqueous oxidation by oxygen, and bacterial activity). Contaminated neutral mine drainage affects the surrounding environment by contaminant release (e.g., As, Ni, Fe, Cu, and Zn), which is one of the most challenging environmental issues for the mining industry. This paper examines the feasibility of desulfurization by flotation at the laboratory scale as a sustainable tailings management approach to prevent CND generation from tailings produced by the Amaruq mine (Nunavut, Canada). The flotation tests were conducted using a five-level statistical experimental design (DOE) using five parameters that include: collector dosage (PAX), activator dosage (CuSO4), frother dosage (MIBC), pH, and solid content (Cs). The response surface methodology (RSM) was used to predict sulfur recovery and to choose the optimal conditions of flotation. The mineralogical properties of the samples before and after reprocessing were investigated by combining optical microscopy, X-ray diffraction spectroscopy (XRD), and the quantitative evaluation of materials by scanning electron microscopy (QEMSCAN®). The trace element (As, Co, Ni, etc.) microanalysis of the identified minerals was quantified using electron probe micro-analyser (EPMA), and the bulk chemical composition was analyzed using induction furnace, X-ray fluorescence, and ICP-AES/MS. Finally, the geochemical behavior of the initial (WTT) and desulfurized (DWT) tailings was evaluated using kinetic weathering cells. The main results demonstrated that sulfur recovery can reach up to 97 % using the following optimal conditions: pH of 11.5, PAX dosage of 158 g/t, CuSO4 dosage of 300 g/t, MIBC dosage of 55 g/t, and Cs of 29.3 %. Moreover, the residual sulfides within the desulfurized tailings were completely locked within the non-sulfide gangue minerals as analyzed by QEMSCAN® and optical microscopy. Kinetic testing was performed on WTT and DWT to assess their contaminant release rates (especially As, Ni, Cu, Fe, and Zn).The desulfurized material did not cause any significant risk of contaminated mine drainage generation. All released contaminants were below the limits of Quebec provincial legislation.