Effect of Water Addition Frequency on Oxygen Consumption in Acid Generating Waste Rock

Abstract

The oxygen decay coefficient is a key parameter used to predict the distribution of oxygen concentrations spatially and temporally in a waste rock pile. The present study proposes a new equation to calculate the oxygen decay coefficient based on the oxidation rate ͑sulfate release rate͒ of the waste rock, dry density, and equivalent porosity for oxygen transport. The equation gave oxygen decay coefficients that were of the same order of magnitude as those obtained from a semianalytic solution to the modified Fick's law with an oxygen consumption term. Values were in the range of 3.74ϫ 10 −8 s −1 for air dry waste rock and 3.99ϫ 10 −7 s −1 for moist waste rock. The effect of water addition frequency on the oxidation rate and the oxygen decay coefficient was investigated through four column experiments with various flushing rates and a laboratory case simulating actual precipitation at a specific site. The results indicated that the oxygen decay coefficient was dependent on not only the oxidation rate but also on the physical characteristics of the waste rock, such as porosity and dry density. The flushing rate had a significant influence on the oxidation rate of the waste rock and the calculated oxygen decay coefficient. The oxidation rate of the waste rock decreased from 1.19ϫ 10 −6 to 5.32ϫ 10 −7 s −1 with an increase in flushing intervals from 1 week to 4 weeks. When the drying period was longer than 3 weeks, the oxidation rate decreased very slowly with an increase in drying period for the tested waste rock.

Laboratory and numerical modeling of water balance in a layered sloped soil cover with channel flow pathway over mine waste rock

“…TDR measured volumetric water contents of the waste rock likely did not reflect actual values because they were significantly different from water contents (0.1-0.19) obtained from oven drying at the end of the test. Previous study by Song and Yanful (2009b) using column tests with similar precipitation events gave volumetric water content of similar order (0.16, on average). Visual inspection after the test indicated that the waste rock close to the bottom of the box was nearly saturated.…”