Predominant chemical kinetics in laboratory prediction of ARD

Laboratory-based leaching tests are used to predict the potential of mine wastes to generate acid rock drainage (ARD). This paper presents data on the influence of experimental procedure on generation of ARD in the laboratory. The leaching cells and operational procedures used were based on the design and operation of ‘humidity cells’, commonly used throughout the mining industry to define the characteristic leaching behaviour of mine wastes. The results of speciation modelling (using PHREEQC) of the generated leachates reveal that iron (III) is the dominant cation in solution during periods of maximum leaching. Data are presented that indicate that the characteristic leaching behaviour of the mine waste is ultimately controlled by the various geochemical sinks and sources of ferric iron within the leaching system. In particular, the data emphasises the critical importance of microbial oxidation of iron (II). The implications of these findings are that the leaching rates observed in the laboratory are a result of microbial dynamics occurring within the artificial laboratory environment, whether or not these rates are applicable to material leaching in real mine environments is an important question that has been raised by this research