Multicomponent reactive transport modeling of effluent chemistry using locally obtained mineral dissolution rates of forsterite and pyrrhotite from a mine tailings deposit

Abstract

Multicomponent reactive transport modeling using PHREEQC of a Ni-sulfide tailings deposit was undertaken to assess how effective locally-obtained mineral dissolution rates in simulating long-term kinetic testing results of the tailings material. Forsterite and pyrrhotite were used as proxies for the chemical reactions occuring within the tailings. The dissolution rates of forsterite and pyrrhotite were obtained based on the actual kinetic testing data and PHREEQC inverse modeling. BET (Brunauer Emmet Teller) and geometric surface area-derived rates were used in the kinetic test data simulation and long-term prediction for 100 years. Results indicate that the geochemical models for both the BET and geometric surface area-derived rates are generally consistent with the actual pH, Mg, SO4 and Ni of the kinetic testing data. Long term prediction of effluent chemistry suggests that pH will continue to increase until a stable pH of 8 is achieved while the predicted Mg, SO4 and Ni concentrations will be stable and will be close to the concentrations observed towards the end of the kinetic test. This method of using locally-obtained mineral dissolution rates in multicomponent reactive transport modeling of a kinetic test data has proven to be reliable as compared to using literature dissolution rate values. This method can then be used for a quick and cost-effective way for future effluent chemistry prediction rather than conducting long and expensive kinetic tests.