The Effects of Galvanic Interactions with Pyrite on the Generation of Acid and Metalliferous Drainage

Abstract

Although the acid generating properties of pyrite (FeS) have been studied extensively, the impact of galvanic interaction on pyrite oxidation, and the implications for acid and metalliferous drainage, remain largely unexplored. The relative galvanic effects on pyrite dissolution were found to be consistent with relative sulfide mineral surface area ratios with sphalerite (ZnS) having greater negative impact in batch leach tests (sulfide minerals only, controlled pH) and galena (PbS) having greater negative impact in kinetic leach column tests (KLCs, uncontrolled pH, >85 wt% silicate minerals). In contrast the presence of pyrite resulted consistently in greater increase in galena than sphalerite leaching suggesting that increased anodic leaching is dependent on the difference in anodic and cathodic sulfide mineral rest potentials. Acidity increases occurred after 44, 20, and 12 weeks in the pyrite-galena, pyrite-sphalerite, and the pyrite containing KLCs. Thereafter acid generation rates were similar with the Eh consistently above the rest potential of pyrite (660 mV, SHE). This suggests that treatment of waste rocks or tailings, to establish and maintain low Eh conditions, may help to sustain protective galvanic interactions and that monitoring of Eh of leachates is potentially a useful indicator for predicting changes in acid generation behavior.

Novel and Emerging Strategies for Sustainable Mine Tailings and Acid Mine Drainage Management

“…For instance, the leaching of chalcopyrite can be enhanced through association with pyrite [182]. Galvanic interactions can substantially increase the leaching of one or both of the minerals that constitute the galvanic cell: galvanically promoted dissolution has been reported in laboratory and field studies with mine waste rock [163, [183][184][185]. Even though mineral occlusion, passivation, and association are known to critically determine waste-rock reactivity [115,186], and techniques such as electron microscopy and automated mineralogy (e.g., MLA, QEMSCAN) now allow for such parameters to be quantified with increasing ease, few waste-rock studies and drainage prediction models have given consideration to mineralogical and petrographic aspects (e.g., through refinement of kinetic rates) [187][188][189][190], given the cost of a representative assessment at full scale (Sections 2.6 and 3.4).…”

Mine Waste Rock: Insights for Sustainable Hydrogeochemical Management

“…For instance, the leaching of chalcopyrite can be enhanced through association with pyrite [182]. Galvanic interactions can substantially increase the leaching of one or both of the minerals that constitute the galvanic cell: galvanically promoted dissolution has been reported in laboratory and field studies with mine waste rock [163,[183][184][185]. Even though mineral occlusion, passivation, and association are known to critically determine waste-rock reactivity [115,186], and techniques such as electron microscopy and automated mineralogy (e.g., MLA, QEMSCAN) now allow for such parameters to be quantified with increasing ease, few waste-rock studies and drainage prediction models have given consideration to mineralogical and petrographic aspects (e.g., through refinement of kinetic rates) [187][188][189][190], given the cost of a representative assessment at full scale (Sections 2.6 and 3.4).…”

Oxidative Dissolution of Sulfide Minerals in Single and Mixed Sulfide Systems under Simulated Acid and Metalliferous Drainage Conditions

“…To address this issue, we have recently examined the dissolution and acid generation behaviors of pyrite, sphalerite, and galena under AMD-relevant kinetic leach column (KLC) conditions of 2 wt % total sulfide S, with 0.2 wt % S contributed from sphalerite or galena. 27 The extent of reduction of pyrite dissolution was proposed to be proportional to the surface area of the anodic sulfide mineral. In contrast, the presence of pyrite resulted in more galena dissolution than sphalerite dissolution, consistent with the greater difference in anodic and cathodic rest potentials.…”

“…However, the conditions examined were limited with a fixed mass ratio of pyrite to sphalerite or galena. 27 Under real AMD environments (e.g., waste rocks), the sulfide mineral ratios will vary from one site to another and the role of possible galvanic interactions under such conditions remains unclear.…”