Evaluation of Laboratory Kinetic Test Methods for Measuring Rates of Weathering

A study was conducted to compare laboratory kinetic test methods for predicting acid rock drainage rates of weathering. Five laboratory kinetic test protocols (standard humidity cells, non-aerated cells, tall cells, shaken cells and NP depletion columns) were evaluated by comparing sulfate release and NP depletion rates, and predicted time to acidity (defined as pH 6). Our tests indicate that the standard humidity cell creates an unnatural oxidizing environment due to its extreme wetting and drying cycles, and therefore produces erratic results. The non-aerated test cells likely create an oxidizing environment that more closely represents the natural conditions, producing more consistent results and therefore a better estimate of the sulfide oxidation rate. The practice of shaking cells to promote efficient rinsing of weathering products disturbs the oxidizing environment and may retard the oxidation rate. Accelerating NP depletion by the high addition of acidic water creates an unnatural leaching environment, producing results that are not consistent with those obtained from other testing protocols having more natural leaching environments.