Simulating and predicting drainage quality of mine tailings impoundments

A dynamic model for tailings-water interaction is presented considering the coupling and feedback among many factors and processes such as sulfide oxidation, gangue dissolution, oxygen diffusion, water flow and mass transport, evolution of porosity and permeability of tailings induced by dissolution and precipitation of minerals. The finite element and updated Lagrangian approach was used to solve the dynamic equation sets and compile the modeling code. The Xiangxi Gold Mine was taken as an example to illustrate the application of this model in the simulation and prediction of the quality of tailings effluents. The numerical modeling results suggest that tailings-water interaction at the early stage leads to the acidification and release of heavy metals which are responsible for the persistent pollution to the environment for 30 years. Tailings pore water can be gradually neutralized and the content of polluted species tends to decline markedly with time. It is also shown that the gangue dissolution and organic matter reaction can stimulate the acid neutralization and decrease the diffusion rate of oxygen in tailings impoundments. The content of pore-water species in upper tailings is significantly higher than in lower part and changes severely at 6 m depth. Hence the hydrological zoning phenomenon in tailings impoundments accounts for geochemical zonation. Our modeling results agree with field data very well, suggesting that this model has the potential to predict drainage quality of sulfide mine tailing impoundments.