2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 7
Presentation Time: 9:35 AM


LINDSAY, Matthew B.J.1, BLOWES, David W.2, CONDON, Peter D.3 and PTACEK, Carol J.2, (1)Earth and Environmental Sciences, University of Waterloo, 200 University Ave. W, Waterloo, ON N2L 3G1, Canada, (2)Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada, (3)Environmental Department, Hecla Greens Creek Mining Company, P.O. Box 32199, Juneau, AK 99803, mbjlinds@uwaterloo.ca

Organic carbon amendment of mine tailings was evaluated as a passive in situ technique for inducing sulfate reduction to minimize the transport of sulfide-mineral oxidation products. Seven experimental cells, including five amendments and two controls, were constructed in the vadose zone of sulfide- and carbonate-rich polymetallic tailings deposit. Unoxidized tailings were amended with mixtures of peat, spent brewing grain (SBG), and municipal biosolids (MB) at rates of 5 and 10 vol. %. Pore-water chemistry, microbiology, mineralogy and hydrology were monitored over a four-year period. Near-neutral pH conditions and elevated concentrations of SO4, S2O3, Zn, Fe, Mn, Sb, As and Tl were observed at the onset of the experiment. Conditions favorable to sulfate reduction developed in all amended cells; however, large decreases in SO4 concentrations were limited to SBG amended cells. Removal of SO4 was generally associated with increased populations of sulfate-reducing bacteria (SRB), H2S production, 34S-SO4 enrichment, and alkalinity production. Sulfate removal was also associated with undersaturation of pore-water with respect to gypsum [CaSO4·2H2O] and removal of Zn, Mn, Sb, and Tl. Organic carbon amendments supported Fe and As mobilization within the first two years of the experiment. However, subsequent decreases in aqueous Fe and As concentrations were observed. Mineralogical examination of core samples revealed the common presence of secondary Fe-S and Zn-S phases within cells which supported sulfate reduction. General decreases in the mobility of sulfide-oxidation products suggest that this technique has potential as a method of tailings pore-water quality management.