The Application of MnO2 in the Removal of Manganese from Acid Mine Water

Abstract

In recent years, much attention has been devoted in developing inexpensive or alternative systems for treating acid mine drainage (AMD). Manganese is a common component of AMD, and it is traditionally removed by precipitation. However, in order to meet the standard limits for discharging, usually <1 mg L−1, it is necessary to raise the pH above 10 which implies in high consumption of reagents and a final pH that does not meet the required value for discharging. This study investigated the removal of manganese from an acid mine effluent and laboratory solutions by using an industrial residue consisted of manganese dioxide (MnO2). The pH of the acid effluent is around 2.7, and the manganese concentration is approximately 140 mg L−1. Batch experiments assessed the influence of pH and the efficiency of manganese dioxide (MnO2) in the Mn+2 removal. In the presence of MnO2, the metal concentration meets the discharging limit at pH range of 6.8 to 7.2. Experiments carried out with columns packed with MnO2 assessed the influence of the flow rate on the process. Best results were obtained for columns fed with mine water neutralized with limestone at pH 7.0 and a residence time of 3.3 h. The maximum manganese loading capacity for MnO2 was around 14 mg g−1. RAMAN spectroscopy showed that the MnO2 is essentially constituted of pyrolusite. In addition, the solid hausmannite (Mn3O4) was observed on the surface of the MnO2 residue after its contact with the Mn+2 solution.