Acid Mine Drainage Dynamics from a Paste Tailing Deposit: Effect of Sulfate Content on the Consistency and Chemical Stability after Storage

Abstract

Surface paste tailings’ disposal has emerged recently as an optimal and efficient method to favor tailings’ self-containment after being deposited into dams. This disposal method can improve the reuse of water and reduce the generation of acid mine drainage (AMD) and the release of leachates (e.g., acid and heavy metals). However, the implications of chemical factors or mixed-water chemistry in the stability of paste tailings over time are not clear. In this work, we evaluated the release of sulfate from tailing samples and the role of sulfate as a critical factor in the tailings’ strength, consistency, and stability. Our results showed that the release of acid runoff with high sulfate load from the tailings is negligible. Leaching tests were performed for 180 days and did not show a significant release of sulfate, heavy metals, or acid waters. However, the presence of sulfate salts derived from the binders used in the pretreatment of the paste tailings shows an impact on the tailings’ consistency. Undrained triaxial monotonic compression tests revealed low effective cohesion forces in the tailings samples. In addition, it was observed that, in tailings slurries prepared with varying concentrations of sulfate (0, 500, and 1000 mg/L), the slump test value dropped Δ−55% when the sulfate concentration increased from 0 to 1000 mg/L. These results support the idea that the presence of sulfate within the tailings could be relevant for the paste consistency after storage. This knowledge will contribute to a better understanding of the critical chemical factors that affect the stability of paste tailings over time.

Real-Time Electrical Conductivity Monitoring and Correlation with Sulfate Release and Acid Mine Drainage Potential from a Gold/Silver Paste Tailing Storage

“…For the analysis, different surface tailings samples (30 cm deep) at different points of the TSF were sampled according to their greater contact with water and their greater oxygenation, which affects its potential for AMD generation. The sampling was carried out in a zone of 1 m 2 for each point, specifically in a straight line with three equidistant sampling points (T1, T2 and T3), crossed by a perpendicular line with three other sampling points (T4, T5, T6) (Figure 1) [36]. For the selection of sampling points, a visual analysis of the surface of the tailings was carried out, determining different zones on the surface of the deposit.…”

“…The analyses were carried out on previously digested tailings samples according to the EPA 3050B digestion method [37]. The procedure was performed as described in Leiva et al [36].…”

“…Humidity cells involve repetitive cycles with the supply of dry air and humid air on a sample, which simulates the oxidation processes of a real sample and thus estimates the release of metals, pH, and sulfate from the weathering of sufides. The kinetic tests were carried out according to protocol first developed by Sobek et al [39] However, the final procedure used was the same as that described by Leiva et al [36], which includes adaptations to the protocol of Sobek et al [39].…”

“…The chemical analyses of the tailing samples are presented in Table 1 (complemented from Leiva et al, [36]). It is observed that the sulfur content is less than 2 wt% in all the samples except for the sample T4 0-10 cm (2.25 wt%).…”

“…To complement the mineralogical and compositional information of the tailing samples, the elemental composition of the surface of tailing samples was determined by using Scanning Electron Microscopy (SEM-EDS). EDS microanalysis showed dominant atomic percentages of Si (27.5%), Fe (5.6%), and Alumnium (5%) (Figure A2, [36]). Similar to those observed for the chemical analysis of the tailing samples, the atomic percentages of Zn and S were low and less than 1% (Figure A2).…”