Evaluation of Reactive Mixtures for Passive Treatment of Mine Drainage from a Waste Rock Storage Area

Abstract:

Laboratory column tests for a passive treatment system for mine drainage from a waste rock storage area was conducted to evaluate suitable reactive mixture, system configuration, flow rate, and residence time. Five columns containing straw, chicken manure, mushroom compost, and limestone, either in layered or mixed, were set up and operated for a total of 74 days to simulate the treatment system. The key variables determined from the tests include pH and redox adjustment of the treatment system, treatment efficiency for acidity and metals, sulfate removal rates, and precipitation of secondary minerals as sinks for metals. The results showed that all of the five columns removed metals of concern (i.e., Al, Cd, Co, Cu, Fe, Ni, Zn) with residence time of 15 hours and greater. The organic materials used in the test provided sufficient sulfate reduction that is available for metal removal in the mine drainage. The sulfate removal rates ranged between 200 and 600 mg/L/day. Reaction mechanisms responsible for the removal of metals may include sulfate reduction and subsequent sulfide precipitation, precipitation of secondary carbonates and hydroxides, co-precipitation, and sorption on organic materials and secondary precipitates. The results from the columns tests provide a basis for design of a pilot-scale field passive treatment system, such as permeable reactive barrier (PRB) or reducing and alkalinity producing system (RAPS).