Equilibrium and Kinetic Simulation of Groundwater Deironing and Demanganation

Abstract

Chemical equilibria of iron and manganese aqueous species were analyzed at various Eh–pH and aqueous CO₂ concentration. Thermodynamic and equilibrium-kinetic simulations were conducted for the oxidations of iron and manganese aqueous species with reference to groundwater demanganation and deironing, using the most probable rate constants of congruent dissolution reactions of iron and manganese carbonates, rate constants of homogeneous iron oxidation, and surface catalytic oxidation of manganese on suspension of iron hydroxide in aqueous solution. A kinetic–thermodynamic model is suggested for iron and manganese oxidation in groundwater under the effect of dissolved oxygen. The numerical simulations show that deironing is relatively effective, whereas the dissolved manganese(II) concentration increases because of slower manganese oxidation and the dissolution of manganese-bearing siderite. Hence, effective groundwater demanganation is possible if the host rocks contain no manganese-bearing siderite.