Use of O_2 consumption and CO_2 production in kinetic cells to delineate pyrite oxidation-carbonate buffering and microbial respiration in unsaturated media

摘要

Identifying zones of sulphide oxidation and carbonate buffering is important in the development of a management plan for mine waste-rock piles. In this study, we used a kinetic cell technique to measure rates of O_2 consumption and CO_2 production in low sulphide (<0.12 wt.% S), low inorganic carbon (<0.20 wt.% C_(inorganic)), gneissic waste rock and associated organic-rich lake sediment (0.7 wt.% C_(organic)), and forest soil (1.4 wt.% C_(organic)) collected from the Key Lake uranium mine in Saskatchewan, Canada. Solid chemistry, stable carbon isotope, pore water sulphate concentration data, and stoichiometric considerations indicated that O_2 consumption and CO_2 production were constrained by microbial respiration in the lake sediment and forest soil and by pyrite oxidation-carbonate buffering in the gneissic waste rock. Mean ratios of molar CO_2 production to O_2 consumption rates were 0.5 for lake sediment, 0.7 for forest soil, and 0.2 for gneissic waste rock. The different O_2/CO_2 ratios suggested that O_2-CO_2 monitoring may provide a practical tool for identifying the zones of microbial respiration and pyrite oxidation-carbonate buffering in mine waste-rock piles. Rates of O_2 consumption and CO_2 production were about one order of magnitude greater in lake sediment than in gneissic waste rock, indicating that microbial respiration would exert a control on the distribution of O_2 and CO_2 gas in waste-rock piles constructed upon the dewatered lake sediments.