Removal of Mn(II) from Acidic Wastewater on the Red Mud– Loess Mixture: Fixed–Bed Column Tests

Abstract

In this study, the purification effect of red mud–loess mixture (RM–L) as a reactive medium in a permeable reactive barrier (PRB) for groundwater contaminated by acidic wastewater (AW) containing Mn(II) was explored considering removal capacity and pH value, and the safety of Mn(II) on RM–L after purification was evaluated. The breakthrough parameters of the Mn(II) were determined and the purifying performances of RM–L toward AW were evaluated by fixed-bed column tests at various initial concentrations of Mn(II), flow rates, and packing heights. The speciation of Mn(II) loaded on the RM–L was evaluated by the Tessier method. Results show the RM–L with a removal capacity of 17.30 mg·g−1 at 100 mg·L−1 initial concentration, 1 mL·min−1 flow rate and 7 cm packing height. The reduction in initial concentration and flow rate and the increase in packing height improve the total removal percentage of Mn(II) and the removal capacity of the RM–L. Moreover, the RM–L has a long-term effective acid buffer capacity for AW containing Mn(II), ensuring the pH values of effluent could be maintained at a neutral value. Furthermore, the Mn(II) could be loaded on the RM–L after the purification in stable forms that are dominated by the iron-manganese oxidate form.