SULFIDE MINERAL OXIDATION AND SUBSEQUENT REACTIVE TRANSPORT OF OXIDATION-PRODUCTS IN MINE TAILINGS IMPOUNDMENTS - A NUMERICAL-MODEL

A versatile numerical model that couples oxygen diffusion and sulfide- mineral oxidation (PYROX) has been developed to simulate the oxidation of pyrite in the vadose zone of mine tailings. A shrinking-core oxida tion model and a finite element numerical scheme are used to simulate the transport of oxygen and oxidation of pyrite grains. The rate of py rite oxidation is assumed to be limited by the transport of oxygen to the reaction site, The model determines the spatially variable bulk di ffusion coefficient for oxygen on the basis of moisture content, poros ity, and temperature, all of which are variable input parameters. The model PYROX has been coupled to an existing reactive transport model ( MINTRAN), which uses a finite element scheme for transport of contamin ants and MINTEQA2 to solve for the equilibrium geochemistry, The react ions described by MINTRAN are subject to the local equilibrium assumpt ion. The resulting model, MINTOX, is capable of simulating tailings im poundments where the oxidation of pyrite or pyrrhotite is causing acid ic drainage and where acid neutralization and attenuation of dissolved metals can be attributed to equilibrium reactions, Because MINTOX use s realistic boundary conditions and hydrogeological properties, the po tential benefits of various remediation schemes, such as moisture-reta ining covers, can be quantitatively evaluated.