Efficiency assessment of cascade aerator in a passive treatment system for Fe(II) oxidation in ferruginous mine drainage of net alkaline

Abstract

The primary purpose of this research was to assess the applicability of the cascade aerator in a passive treatment system for ferruginous mine drainages to increase efficiency and reduce the size of the passive treatment system. Two experiments of different aeration methods were executed: the air diffuser experiment and the cascade aerator experiment. Through the air diffuser experiment, it was verified that the main mechanisms that occur in the mine drainage were gas exchanges with the atmosphere, Fe(II) oxidation and subsequent precipitation. Aeration from the air diffuser accelerated the increase in DO and prompted the decrease in CO2, where the latter affected the eventual increase in pH level. Together with the increase in DO and pH, it can be concluded that the aeration has a clear effect on boosting the oxidation rate of Fe(II). The predictive model which was proposed in this research proved its applicability by reasonably estimating the changes in water qualities of the mine drainage. The aeration efficiency by the cascade aerator was chiefly influenced by drop height of the mine drainage, not by water qualities or depths of plunge pools. Various Fe(II) oxidation rates by the different heights of cascade aerator could be estimated by the predictive model using only initial water qualities and rate constants. Through series of experiments it is suggested that in a passive treatment system, a cascade aerator with even a relatively slight elevation of one step (70 cm) can effectively boost the Fe(II) oxidation rate of mine drainages of net alkaline.