Occurrence and Release of Trace Elements in Pyrite-Rich Waste Rock

Abstract

Waste rock can contain high concentrations of deleterious trace elements, which upon oxidation can be released, having a significant impact on water quality. Therefore, knowledge about their occurrence and overall mobility is crucial to ensure suitable environmental protection measures. Sulfide-rich waste rock was characterized and quantified using automated mineralogy (QEMSCAN). Selected pyrite grains were analyzed for trace element occurrence using LA-ICP-MS before, during, and after leaching the waste rock in 10 L small-scale test cells for two years to assess trace element occurrence and mobility. Sequential extraction was used to estimate elemental sequestration during the experiment. The high abundance of pyrite (66%) and scarcity of buffering minerals resulted in low pH (<1.3) leachate with high concentrations of trace elements such as As (21 mg/L), Cu (20 mg/L), Hg (13 µg/L, Pb (856 µg/L), Sb (967 µg/L), Tl (317 µg/L ), and Zn (23 mg/L) in solution with limited retention in secondary minerals, primarily due to these elements’ association with pyrite either as inclusions or impurities showing an average abundance of 193 ppm As, 15 ppm Cu, 13 ppm Hg, 20 ppm Pb, 24 ppm Sb, 26 ppm Tl, and 74 ppm Zn in the waste rock. The occurrence of Cu and Zn as inclusions associated with the pyrite led to their extensive mobilization of 79% and 72%, respectively, despite their low abundance in the waste rock. Provided the overall leachability of S (11%) and limited formation of secondary minerals, the average oxidation rate suggests depletion of the pyrite within approximately 18 years. In conclusion, this study shows the importance of detailed mineralogical investigations and early preventive measures of waste rock to ensure sustainable mine waste and water management.

Assessment of ecotoxicological effects of Fojo coal mine waste elutriate in aquatic species (Douro Coalfield, North Portugal)

“…Mining activities promote a large environmental modification in the landscape's outline, chemistry, and biology (Sonter et al, 2018). The acidic nature of water circulating in coal mine waste usually results from the oxidation of pyrite, and the low pH increases the dissolution of PTE, favoring their transport in the leachates (Costa and Duarte, 2005;Nyström et al, 2021). The chemical mobility of pollutants is fundamental to understand toxicity, bioavailability, and geochemical behavior (Dang et al, 2002;Ribeiro et al, 2010a).…”

Revisiting Selenium Interactions with Pyrite: From Adsorption to Coprecipitation

“…A major environmental issue associated with the oxidation of pyrite is coal acid mine drainage. That process can release toxic trace elements in aquatic systems . In natural pyrite, different reduced Se species are present within or at the surface, like ferroselite (FeSe 2 ) and dzharkenite (FeSe) .…”

“…Pyrite is the most abundant sulfide mineral and can be found in igneous, metamorphic, and marine sedimentary rocks as well as in submarine hydrothermal vents . The wide range of crystal chemical and surface properties displayed by pyritesurface complexation, electron transfer, secondary mineral phases, short-range order, and structure sensitivitymakes this mineral an important redox catalyst for a multitude of reactions involving trace elements, such as uranium, molybdenum, arsenic, Se, and Tc . A major environmental issue associated with the oxidation of pyrite is coal acid mine drainage.…”