The weathering signature of mine waste facilities is intrinsically linked to the availability, depletion, and transport of oxygen. Key to these processes is the oxygen consumption rate of the mining waste, often termed Oxygen Consumption Rate (OCR). This is a material specific parameter with the rate being influenced by many factors such as sulfide mineral liberation (ultimately determining sulfide mineral exposed surface area), temperature, pore water pH, microbial population, water content and various galvanic interactions. There are several methods available for the determination of OCR either directly through measurement of oxygen depletion or indirectly through measurement of sulfur release and assuming stoichiometry with sulfide oxidation. However, most current techniques rely on highly bespoke measurement apparatus and or undertaking long-term kinetic tests. The high cost and complexity of the existing methods means that in depth studies trialling of multiple variables and waste rock materials is often not feasible.
We demonstrate the application of commercially available apparatus designed for determination of soil respirometry (Xylem Oxitop®) for determination of oxygen consumption rates in mining wastes. The OxiTops® utilise Warburg constant volume respirometry method where the oxygen consumption rate is determined through monometric determination of the pressure drop within a sealed container of fixed volume. A 30-day measurement period is usually adequate for most samples to determine the oxygen consumption rate at a given temperature and moisture content. The relatively low cost, short measurement time, and simplicity of the test makes the method particularly attractive. Coupled with standard geochemical test (e.g. NAG, ABA, HCT) use of Oxitops is a highly promising geochemical measurement tool for future waste studies.
The paper demonstrates the use of the measuring method for the prediction of OCR with example from a Scandinavian mining waste facility.
