Removal of copper and cadmium in acid mine drainage using Ca-alginate beads as biosorbent

Biosorption experiments were performed to investigate the ability of Ca-alginate beads as biosorbent for the removal of Cu and Cd in acid mine drainage (AMD). From the results of batch experiments, the removal efficiencies of both Cu and Cd for Ca-alginate beads were found to increase to 95% within 3 hours in the temperature range of 15–40 °C, indicating that it is possible to treat AMD using Ca-alginate beads within a short time period under various field conditions. For the column experiments, 381.8 g of Ca-alginate beads was packed in a Pyrex column (2.5 cm in diameter and 100 cm in height) and 119.7 liters (900 pore volumes) of AMD from the Ilgwang mine in Korea was successfully treated. The Cu and Cd removal efficiencies were maintained at levels higher than the Korean remediation goal (86% for Cu and 58% for Cd) and it was possible to treat more than 300 mL of AMD using only 1 g of Ca-alginate beads. Although AMD with a pH below 3 was injected into the column, the pH of the effluents was maintained above 3 for 1,140 pore volumes of flushing due to the buffer action of the beads. In SEM/EDS analysis of the Ca-alginate beads after the experiment, void spaces of the beads were found to be filled with precipitates of heavy metals, showing that Ca-alginate beads can be successfully used as a biosorbent for the removal of Cu and Cd in AMD.