Investigation of Sludge Volume from Abandoned Mine Wastewater Treatment by Layered Double Hydroxides: A Case Study Targeting As and Fe

We treated three samples of wastewater from an abandoned mine using NO 3 -type Mg–Al layered double hydroxides with different Mg/Al ratios (denoted LDH-2 and LDH-4) and the conventional neutralizer Ca(OH) 2 . We determined the optimal condition for each treatment before confirming the residual As and Fe concentrations, pH, and the amount of suspended solids (SS) in the supernatant after treatment under optimal conditions. We then estimated and compared the volume of sludge generated over 8 h in each treatment. We found that when treated under optimal conditions, both As and Fe were removed in compliance with Japan’s Uniform National Effluent Standards and that pH and SS met the standard in all cases. The final sludge volume at 8 h was 70 mL when Ca(OH) 2 was used; this was twice as much when LDH-2 was used (30 mL) and four times that when LDH-4 was used (15 mL). These results strongly suggest that LDH has a high potential for treating wastewater from mines.