Chemical and Biological Oxidation of Iron in Acid Mine Water

Abstract.   Prior to limestone neutralization of acid water, ferrous iron needs to be oxidized to prevent downstream oxidation and the formation of acid. This study assessed the effect of various parameters on the biological and chemical rate of iron oxidation, both chemically and biologically. In batch experiments, it was found that although the use of support media had no effect on the chemical iron oxidation rate, it was important when iron was oxidised biologically. Under continuous flow conditions, the highest oxidation rate occurred when the initial Fe (II) concentration was between 4.5 to 4.8 g/L, geotextile was used as the support medium, and when nutrients were added to the reactor. The optimal iron oxidation rate was achieved at a hydraulic retention time of 8 h. The chemical iron oxidation rate depends on the concentration of suspended Fe(OH)₃ and CaSO₄, which act as catalysts. The biological iron oxidation rate was dependent on the bacterial growth, which was influenced by several parameters (support media, nutrients, CO₂, and oxygen).