The early diagenesis of submerged sulphide-rich mine tailings in Anderson Lake, Manitoba

Abstract

The oxidation of sulphide-rich mine tailings stored on land by acidophilic bacteria is frequently associated with severe environmental degradation, as metal-rich acid drainage from the tailings contaminates groundwater and surface runoff. Permanent storage of tailings underwater may prove to be more chemically benign if oxidation is inhibited sufficiently. To assess this possibility, the chemistry of interstitial waters and the associated solid phases in tailings and organic-rich (20–30 wt.% C) natural sediments in Anderson Lake, Manitoba, is examined. The lake has been used as a receiving basin for sulphide-rich tailings since 1979, and is contaminated with metals as a result of the input of acid mine drainage along the north shore and the discharge of mill process water with the tailings. Three cores were collected and processed under nitrogen to extract interstitial waters. At all sites, the occurrence of high concentrations of dissolved iron in shallow pore waters indicates that the deposits are anoxic within several millimetres of the sediment–water interface. Despite high dissolved metal inventories in the lake, the concentrations of Zn, Cu, Pb, and Cd decrease abruptly with depth in the pore waters. This cannot be due to non-steady-state effects and indicates unequivocally that both the tailings and natural sediments are acting as sinks for metals, rather than as sources. Dissolved sulphate data and the widespread occurrence of framboidal pyrite in surface sediments suggest that the metals are being precipitated as sulphide phases at shallow depths.

The biogeochemical cycling of Zn, Cu, Fe, Mn, and dissolved organic C in a seasonally anoxic lake

“…Concentration maxima of dissolved Zn and Cu at the sediment-water interface, which reflect rapid recycling from newly deposited particles, and decreased solubility under anoxic conditions are key characteristics of the two metals. Although en hanced removal of Zn and Cu, attributed to sulfide precipitation, has frequently been reported in anoxic lake sediments (Carignan and Nriagu 1985;Carignan and Tessier 1985;Pedersen et al 1993;Tessier et al 1989), there is little previous evidence that watercolumn concentrations can also be affected (HamiltonTaylor and Davison 1995) as observed for Zn in Esthwaite Water. The speciation and solubility calculations highlight deficiencies in the available models of trace metal behavior in anoxic systems, especially in regard to the nature of metal-sulfide complexes and the oxidation state of cu.…”

Modeling diagenesis of lead in sediments of a Canadian Shield lake

“…Postdepositional mobilization of lead and its redistribution within the sediment column, or its loss to the water column, is also suggested from the Pb or 210 Pb porewater profiles reported for various aquatic environments, including a freshwater reservoir (Benoit and Hemond, 1991), a crater lake (Viollier et al, 1995), lakes impacted by mine effluents (Pedersen et al, 1993;Widerlund et al, 2002), Lake Superior (McKee et al, 1989), Lake Erie (Matisoff et al, 1980), the Laurentian Trough (Gobeil and Silverberg, 1989), the San Francisco Bay (Rivera-Duarte and Flegal, 1994), and a river wetland (Van den Berg et al, 1998). Lead concentration profiles obtained in the water column of lakes (Balistrieri et al, 1994;Taillefert et al, 2000;Taillefert and Gaillard, 2002) and marine systems (Wei and Murray, 1994) indicate also that dissolved Pb concentrations can vary across redox boundaries.…”

Long-term mineralogical and geochemical evolution of sulfide mine tailings under a shallow water cover

“…Furthermore, despite the textural difference between the host pyrite and the fine-grained marcasite rim, the two were difficult to distinguish in backscattered-electron images because both minerals had the same composition. Other studies (e.g., Pedersen et al, 1993;Paktunc and Davé, 2002;Lindsay et al, 2011) have also reported the presence of secondary sulfide minerals, which control metal and sulfate concentrations in sulfate-reducing zones at mining-impacted sites.…”

“…In addition to limiting O 2 diffusion, covers also contain the tailings and protect them from wind and water erosion (Kossoff et al, 2014 Water covers offer an alternative approach to dry covers for managing sulfide-mineral oxidation. Sub-aqueous tailings deposition has potential to limit sulfide-mineral oxidation and associated environmental impacts (e.g., Hamilton and Fraser, 1978;Pedersen et al, 1993;Yanful and Simms, 1997;Jacob and Otte, 2004;Vigneault, 2007). The O 2 ingress into tailings is limited by the low diffusion coefficient of the water cover.…”

“…For example, the diffusive flux of O 2 to water covered tailings may decrease by up to 10,000 times relative to sub-aerial tailings (Robertson et al, 1997;Awoh et al, 2013). Suppression of sulfide-mineral oxidation therefore may be accomplished by disposal of tailings into lakes or deep marine environments (Pedersen, 1985;Pedersen et al, 1993;Poling et al, 2002), or by the construction of wet covers on existing tailings impoundments (Robertson, 1992). A number of laboratory and field studies have investigated the short-term storage of tailings under shallow water covers (Davé et al, 1997;Li et al, 1997;Vigneault et al, 2001;Elberling and Damgaard, 2001;Samad and Yanful, 2005), but only a few studies have considered the reactivity of tailings that have been submerged over long time periods (e.g., Jacob and Otte, 2004;Vigneault et al, 2007).…”