GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 251-9
Presentation Time: 10:20 AM


ANGAI, Joanne U.1, PTACEK, Carol J.1, VERBUYST, Brent R.1, BAIN, Jeff G.1, HOLLAND, Steven P.1, PAKOSTOVA, Eva1, WHITE, Heather2 and BLOWES, David W.1, (1)Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada, (2)Ministry of Energy, Northern Development and Mines, Sudbury, ON P3E 6B5, Canada

The Long Lake Mine near Sudbury, Ontario, was the site of intermittent Au production from 1909-1939, during which tailings containing on average 5 wt. % As were deposited without containment on the mine site. Dissolved As concentrations up to 600 mg L-1 are present in the tailings pore water, and acidic conditions prevail. A series of laboratory column experiments was conducted to evaluate the effectiveness of a mixture containing natural organic material and granular zero-valent iron for As removal. The reactive mixtures varied from between 20-40 wt. % organic carbon and 10-30 wt. % zero-valent iron. Arsenic-rich groundwater collected from the tailings area was used as influent for these experiments. Groundwater was pumped through the columns at a velocity three times greater than the site groundwater velocity; the extent of As removal at the accelerated velocity can be used to predict long-term treatment capacity. In addition, a reaction cell, consisting of a 30 cm ID by 98 cm long PVC cylinder was installed on site, and As-bearing groundwater from a piezometer downgradient from the tailings area was pumped through the cell. The reaction cell was operated for several months during the fall of 2018 to evaluate temperature-dependence and seasonal performance of the reactive media. The experimental results indicate extensive removal of As in both the laboratory and field experiments, with removal of As observed up-gradient from the first sampling port along the flow path. Average influent concentrations of As were between 5-10 mg L-1 while the concentrations of As in all column and reaction cell effluent water were below 10 ug L-1. Arsenic removal was accompanied by an increase in pH from acidic to circumneutral values and a decline in the concentrations of dissolved metals, including Al, Cu, and Zn. Removal of As and dissolved metals is attributed to precipitation of low-solubility sulfide phases due to microbially-mediated sulfate reduction; these observations are consistent with the presence of aqueous sulfide in the effluent water and the results of microbiological analyses.