Acid rock drainage passive remediation: Potential use of alkaline clay, optimal mixing ratio and long-term impacts

Abstract

Acid rock drainage (ARD) is one of the most adverse environmental problems of the mining industry. Surface and ground water affected by this pollution are characterized by their acidity and the high content of sulfates and metals/metalloids. In this study, alkaline clay (AC), an industrial waste with a high alkalinity, which is utilized in the alumina refining process, was used as the remediation material to inhibit pyrite oxidation in waste coal piles. Through a series of laboratory experiments (static and kinetic), complemented with field measurements and geochemical modeling, three important issues associated with this passive and sustainable ARD remediation method were investigated: 1) the potential use of alkaline clay as an ARD remediation material, 2) the adequate alkaline clay/coal refuse mixing ratio (AC/CR) to ensure pH values close to neutral conditions, and, 3) the implications for long-term performance, in terms of the trends of the main parameters involved in this process such as pH, concentrations of sulfate, iron and other dissolved contaminants. Both field measurements and the samples used for the experiments came from a local waste coal site. Through the analysis of the field measurements and the outcome of the laboratory experiments, AC proved to be an effective remediation material for ARD. Compared to those found in mine tailings, the concentrations of contaminants such as iron, manganese or sulfate were significantly reduced with this remediation approach. Moreover, results suggest a reliable long-term stability of the remediation (i.e. neutral pH conditions are maintained), thus enhancing the generation of iron precipitates that could produce pyrite grain coating. These processes also made the amended layer less porous, thus increased water retention and hindered oxygen diffusion.

Parametric assessment of hydrochemical changes associated to underground pumped hydropower storage

“…Reactions R1, R2 and R3 reduce the pH and are characteristic of acid mine drainage processes (Banks et al, 1997;Robb, 1994) that produce well known adverse impacts on water resources (Plaza et al, 2017).…”

Environmental Sustainability of Open-Pit Coal Mining Practices at Baganuur, Mongolia

“…These acids act as solutes, causing leaching of metals from the waste and increasing the potential for subsequent water and soil contamination through dissolution and precipitation processes of secondary minerals [12][13][14][15][16]. Therefore, environmental management systems must be implemented to prevent and mitigate various environmental issues and improve the sustainability of both the mining industry and the communities living in mining areas.…”

A hydro-thermal-geochemical modeling framework to simulate reactive transport in a waste coal area under amended and non-amended conditions

“…In plot 2, the simulated SO 4 and Fe (total) captured the patterns of field observations as well, although the relative errors are 11% and over 100% for SO 4 and Fe (total), respectively. The much higher relative errors in plot 2 are due to the much lower concentrations in plot 2 than those in plot 1 except for the total calcium which might be caused by the dissolution of Ca carbonates, such as calcite (CaCO3), due to the alkaline additive, thus releasing Ca (Plaza et al, 2017). Usually, calcite is identified with acidic neutralization, enabling various metal removal mechanisms (Sun et al, 2013).…”

“…The compositions of 90% CR þ 10% BR, i.e., the amended zone in plot 2, mainly include Quartz, K-mica, Jarosite-K, Kaolinite, Dicalcium silicate, Sodalite, Calcite, Gehlenite, Gypsum, Hematite, Pyrite, Calcium aluminum sulfate, Calcium titanium oxide, Titanium dioxide and Gibbsite, which were detected in the mixing material sample and shown in Table 2c. Previous research has shown, based on the analyses of potential acidity production and acid neutralization, along with kinetic experiments, that a 10% BR/90%CR ratio will not potentially generate acid mine drainage and that this ratio is appropriate for long-term remediation (Plaza et al, 2017(Plaza et al, , 2018.…”