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

• Published in: The Science of the total environment Vol. 576; pp. 572 - 585
• Main Authors: Plaza, Fernando, Wen, Yipei, Perone, Hanna, Xu, Yi, Liang, Xu
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.01.2017
• Subjects: Acidic neutralization; Coal refuse; Dissolved metal removal; Mine waste; Pyrite oxidation; Mine waste; Coal refuse; Dissolved metal removal; Pyrite oxidation; Acidic neutralization
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2016.10.076

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. [Display omitted] •Alkaline clay, industrial waste, is mixed with coal refuse to neutralize acidity.•Static and kinetic (e.g. column leaching) experiments are performed.•Field measurements from a mine waste site are made.•Amended and non-amended scenarios were modeled using PHREEQC.•Alkaline clay is an effective and long-term reliable material for Acid Rock Drainage treatment.