Abstract
Arsenic-rich contaminated neutral mine drainage (CND-As) is a rising environmental concern because of a worldwide increasing trend of extracting gold and silver from refractory and As bearing ores. Passive biofilters have shown promising results in the treatment of CND-As, but they also generate significant quantities of residues when exhausted/dismantled. This research evaluated the environmental behaviour of the residues generated from a field-scale passive system for CND-As treatment. Thirty (30) residue samples were collected from a 20-year-old biofilter on the rehabilitated Wood-Cadillac mine site, in northwest Quebec, Canada. Depth profile samples were collected from five locations covering the two inlets and the outlet of the field system. A physicochemical characterization was performed on these samples, and the potential mobility of the contaminants was assessed via the Toxicity Characteristic Leaching Procedure (TCLP) and the Synthetic Precipitation Leaching Procedure (SPLP) tests. Residues contained high contents of metals (up to 2.3 g/kg of As, 41.1 g/kg of Fe, 19.5 g/kg of Al). Metal concentrations in the upper layer were nearly two times greater than in the bottom layer. The results of TCLP classified the residues as nonhazardous according to USEPA criteria. Furthermore, none of the SPLP results exceeded USEPA guidelines, reducing the potential of groundwater contamination from residue leachates. However, the residues were considered leachable for As according to Quebec regulations (D019). Further environmental and mineralogical characterizations are necessary. Future work should focus on As speciation of the residues and its removal mechanisms, to understand the As-phase stability and suggest novel concept-design of other efficient passive biofilters.