Geochemical processes in mill tailings deposits: modelling of groundwater composition

A general model is presented for geochemical processes occurring in the unsaturated zone of a carbonate-depleted, pyritic tailings deposit. Quantification of slow geochemical reactions, using published, empirical rate laws from small-scale experiments on monomineralic samples, and geochemical equilibrium reactions successfully reproduced the relative rates of field processes in the case study, Impoundment 1 in Kristineberg. Reproduction of absolute rates was achieved by scaling down all laboratory-derived mineral weathering rates by two orders of magnitude. The sensitivity of the modelled groundwater composition and pH to rates of pH-buffering processes and redox reactions indicated that inclusion and accurate quantification of all dominant geochemical processes on the field scale is necessary for reliable prediction of groundwater composition and pH. (C) 2003 Elsevier Ltd. All rights reserved.