Simulating reactive transport in time dependent multiphase flow problems

This paper discusses issues on time stepping and time weighing when simulating reactive transport in time dependent multiphase flow problems. It proposes to solve the flow and transport equation with different time increments. We analyze how the time varying flow properties should be evaluated in order to obtain correct solute mass balances. The proposed algorithm is illustrated by an example that models pyrite oxidation in an unsaturated soil. The example shows that flow and transport may require completely different time steps for numerical reasons and illustrates well the utility of using different time steps. (orig.)