A conceptual model for the description of oxidation and transport processes in sulphidic waste rock dumps

Basic mathematical equations which describe the processes of sulphide oxidation and gas, heat and water transport in waste rock dumps are presented and discussed. The governing equations account for gas and water flow, vapourisation and condensation with latent heat effects, heat transport and mass balance. Gas, water and solid phases are assumed to be in local thermal equilibrium at all times. Air is approximated as an ideal three-component gas. Different semi-empirical relationships between physical values are used: Darcy's law for fluid flow, ideal gas law, the Van Genuchten formula for the relationship between degree of water saturation and pressure head, Mualem's formula for the relative hydraulic conductivity as a function of pressure head, etc. Some important global quantities, such as the fraction of sulphide sulphur oxidised and the global oxidation rate, are defined and considered as functions of time.