Abstract
Flooding of cemented paste backfill (CPB) filled mine workings is, commonly, a slow process and could lead to the formation of unsaturated zones within the CPB fillings. This facilitates the oxidation of sulfide minerals and thereby increases the risk of trace metal leaching. Pyrrhotitic tailings from a gold mine (cyanidation tailing (CT)), containing elevated concentrations of nickel (Ni), copper (Cu), and zinc (Zn), were mixed with cement and/or fly ash (1–3 wt%) to form CT-CPB mixtures. Pyrrhotite oxidation progressed more extensively during unsaturated conditions, where acidity resulted in dissolution of the Ni, Cu, and Zn associated with amorphous Fe precipitates and/or cementitious phases. The establishment of acidic, unsaturated conditions in CT-CBP:s with low fractions (1 wt%) of binders increased the Cu release (to be higher than that from CT), owing to the dissolution of Cu-associated amorphous Fe precipitates. In CT-CPB:s with relatively high proportions of binder, acidity from pyrrhotite oxidation was buffered to a greater extent. At this stage, Zn leaching increased due the occurrence of fly ash-specific Zn species soluble in alkaline conditions. Irrespective of binder proportion and water saturation level, the Ni and Zn release were lower, compared to that in CT. Fractions of Ni, Zn, and Cu associated with acid-soluble phases or amorphous Fe precipitates, susceptible to remobilization under acidic conditions, increased in tandem with binder fractions. Pyrrhotite oxidation occurred irrespective of the water saturation level in the CPB mixtures. That, in turn, poses an environmental risk, whereas a substantial proportion of Ni, Cu, and Zn was associated with acid-soluble phases.
Highlights
Cyanide is typically used to extract gold occurring as inclusions in sulfide minerals, such as pyrrhotite and pyrite
Flooding of cemented paste backfill (CPB)-filled mine facilities is, commonly, a slow process where unsaturated zones may form within the CPB mass
Cyanidation tailings (CT) with elevated concentrations of Cu, Ni, and Zn and a pyrrhotite content of 1 wt% were managed by using CPB (CT-CPB)
Summary
Cyanide is typically used to extract gold occurring as inclusions in sulfide minerals, such as pyrrhotite and pyrite. The goal of this step is to increase the availability of cyanide for dissolving the gold This process is seldom 100% effective, and remnants of sulfide minerals often occur in tailings obtained through a cyanide leaching process (cyanidation tailing (CT)). These sulfides often contain trace metals such as copper (Cu), arsenic (As), and zinc (Zn). Sulfide minerals exposed to atmospheric oxygen and water may become oxidized. These reactions (reaction 1) yield sulfate and an acid leachate, referred to as acid mine drainage (AMD), with a high content of metals (Blowes et al 2003). Owing to the co-occurrence of these trace metals and the sulfide minerals, CT must be carefully handled to avoid pollution of the surrounding environment
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