Valorisation of Partially Oxidized Tailings in a Cover System to Reclaim an Old Acid Generating Mine Site

Abstract

The reclamation of acid-generating mine tailings typically involves building cover systems to limit interactions with water or oxygen. The choice of cover materials is critical to ensure long-term performance, and partly determines the environmental footprint of the reclamation strategy. The objective of this research was to evaluate if tailings pre-oxidized on-site could be used in cover systems. Column experiments were performed to assess the effectiveness of a cover with capillary barrier effects (CCBE), where the moisture retention layer (MRL) was made of pre-oxidized tailings with little to no remaining sulfides (LS tailings). The columns were submitted to regular wetting and drying cycles, and their hydrological and geochemical behaviour was monitored for 510 days. The LS tailings showed satisfying hydrological properties as an MRL and remained saturated throughout the test. The concentrations of Cu in the drainage decreased by more than two orders of magnitude compared to non-covered tailings. In addition, the pH increased by nearly one unit compared to the control column, and Fe and S concentrations decreased by around 50%. Despite these improvements, the leachate water remained acidic and contaminated, indicating that acid drainage continued to be generated despite a hydrologically efficient CCBE.

Limited Access to Oxygen Reduces the Release of Harmful Trace Elements from Submerged Alum Shale Debris

“…These results indicate that weathering of the alum shale occurred on site in a similar manner to that observed in the laboratory leaching experiments. In both scenarios, laboratory and disposal site, non-weathered black shale was used (i.e., blasted rock was transported directly from the tunnel to disposal in the bog); yet, if weathered acid-producing rock were to be stored, oxidation processes could have continued even without oxygen due to Fe(III) acting as oxidant and, in turn, avoiding future acid rock drainage can become difficult (Dublet-Adli et al, 2021).…”

A review of major applied research on restoration of ecological balance on mining lands in global subsoil use

“…For the mines situated in the Iberian Pyrite Belt on the Iberian Peninsula, it is recommended to introduce the soil layer with fly ash after biomass combustion and with paper-and-pulp industry sludge, as well as with processing tailings with low concentration of sulfides, and with waste rock [3,11]. In Brazil, it is proposed to perform reclamation of land disturbed during iron ore and gold mining with adding the soil mixture with biocoal and organic compost in the former case, and with coffee grouts, tegument of Brazil nuts and biocoal in the latter case [5,6]. In Inner Mongolia in China, the recommended soil admixtures are cornstalks, sheep and black cattle manure and microbial agents [29].…”