Treatment of As-rich mine effluents and produced residues stability: Current knowledge and research priorities for gold mining

• Published in: Journal of hazardous materials 2020-03, Vol.386, p.121920-121920, Article 121920
• Main Authors: Coudert, L., Bondu, R., Rakotonimaro, T.V., Rosa, E., Guittonny, Marie, Neculita, C.M.
• Format: Article
• Language: English
• Subjects: As leaching; As-rich effluents treatment; As-rich sludge; Refractory gold leaching
• ISSN: 0304-3894; 1873-3336
• DOI: 10.1016/j.jhazmat.2019.121920

[Display omitted] •Refractory gold ore exploitation produces large volumes of As-rich mine water.•Efficient treatment of As-rich mine effluents is challenging due to their complex chemistry.•Fe-based processes are the best available technology economically achievable to treat As-rich water.•As immobilization as (nano-)scorodite seems to be the most appropriate option.•New research on the stability of As-rich residues from gold mining is mandatory. Refractory ores, in which gold is often embedded within As-bearing and acid-generating sulfide minerals, are becoming the main gold source worldwide. These ores require an oxidizing pre-treatment, prior to cyanidation, to efficiently breakdown the sulfides and enhance gold liberation. As a result, large volumes of As-rich effluents (> 500 mg/L) are produced through the pre-oxidation of refractory gold ores and/or the exposure of As-bearing tailings upon exposure to air and water. Limited information is available on performant treatment of these effluents, especially of pre-oxidation effluents characterized by a complex chemistry, extremely acidic or alkaline pH and high concentrations of arsenic. The treatment of As-rich effluents is mainly based on precipitation (using Al or Fe salts and/or Ca-based compounds) and (electro)-chemical or biological oxidation processes. A performant treatment process must maximize As removal from contaminated mine water and allow for the production of residues that are geochemically stable over the long term. An extensive literature review showed that Fe(III)-As(V) precipitates, especially bioscorodite and (nano)scorodite, appear to be the most appropriate forms to immobilize As due to their low solubility and high stability, especially when encapsulated within an inert material such as hydroxyl gels. Research is still required to assess the long-term stability of these As-bearing residues under mine-site conditions for the sustainable exploitation of refractory gold deposits.