Environmental behavior of metal-rich residues from the passive treatment of acid mine drainage

Marouen Jouini; Carmen Mihaela Neculita; Thomas Genty; Mostafa Benzaazoua

doi:10.1016/j.scitotenv.2020.136541

Environmental behavior of metal-rich residues from the passive treatment of acid mine drainage

Sci Total Environ. 2020 Apr 10:712:136541. doi: 10.1016/j.scitotenv.2020.136541. Epub 2020 Jan 7.

Authors

Marouen Jouini¹, Carmen Mihaela Neculita², Thomas Genty¹, Mostafa Benzaazoua¹

Affiliations

¹ Research Institute on Mines and Environment (RIME), University of Québec in Abitibi-Témiscamingue (UQAT), Canada.
² Research Institute on Mines and Environment (RIME), University of Québec in Abitibi-Témiscamingue (UQAT), Canada. Electronic address: Carmen-Mihaela.Neculita@uqat.ca.

PMID: 32050384
DOI: 10.1016/j.scitotenv.2020.136541

Abstract

In closed or abandoned mine sites, passive systems are often used for acid mine drainage (AMD) treatment. They generate metal-rich residues with variable chemical stability, which is rarely reported. The objective of the present study was to evaluate the potential mobility of contaminants (metals and sulfates) from AMD post-treatment residues to better anticipate their fate and enable their proper management. Sampling of a field tri-step passive system, consisting of two passive biochemical reactors (PBR1 and PBR2), separated by a wood ash reactor (WA), implemented in the reclaimed Lorraine mine site, QC, Canada, was carried out. Samples were collected from the inlet (In) and the outlet (Out) of each treatment unit. Physicochemical and mineralogical characterization was performed. The potential mobility of the metals was then assessed via static and kinetic leaching tests. Results showed that all residues had high metal contents (e.g. Fe content >29 g/kg in PBR1-In, > 76 g/kg in WA-In and > 80 g/kg in PBR2-Out). A high residual neutralizing potential was also found in the WA residues (inorganic carbon 6.5%). Native and organic sulfur were found in the PBR2 residues, while Fe-oxyhydroxide (hematite, goethite and magnetite), carbonate and sulfate minerals were present in all residues. According to USEPA regulations, all residues were considered non-hazardous, but Quebec's provincial regulation relative on mining effluents classifies these residues as leachable for some metals, such as Fe, Al, Ni, Zn and Mn. A potential generation of contaminated neutral mine drainage (Al, Ni, Mn and Zn concentrations exceeding criteria) could occur from PBR1 (In & Out) and WA (In & Out) residues. Moreover, the PBR2 residues (In & Out) regenerated AMD rich in Fe and sulfates, especially for PBR2-Out (1 g/L Fe and 6 g/L sulfates). Therefore, all residues were proven to require stabilization prior to their landfill (co-)disposal with municipal waste.

Keywords: Contaminants' leaching potential; Kinetic test; Mine waste; Sludge management; Toxicity characteristic leaching procedure.