Effects of pH Manipulation, Biological Reduction, and Plant Growth on Cu2+ and Zn2+ Removal from Mine Drainage Using Iron‐Oxide‐Enriched Red Earth Soils

Constructed wetland is an efficient method used to control heavy metal pollution from acidic wastewater, especially when local soils could be used as filling material to reduce construction cost. This study investigated the effects of pH manipulation, biological reduction, and plant growth on the removal of heavy metals (Cu2+ and Zn2+) using iron-oxide-enriched red earth soils. Results indicated that red earth soils had limited metal retention capacity (MRC), whereas CaCO3 alteration significantly improved MRC. In the batch experiment, MRCs of Cu2+ and Zn2+ in 3% CaCO3 alteration were 420 and 291mg/kg, respectively, compared with values of 246 and 117mg/kg without alteration. In column studies, the effluent concentrations of Cu2+ and Zn2+ remained <0.03 and 0.13mg/L, respectively, compared with over 0.96 and 10.81mg/L without alteration. Biological reduction caused iron-oxide mineral dissolution, but heavy metals remained within the soils. The growth of Canna (Canna indica) prompted Cu2+ transport deep into soil layers. However, the metal transport was retarded by CaCO3 alteration. In, conclusion, red earth soils with CaCO3 alteration could be cost-effective filling materials to attenuate heavy metal pollution from mining drainage using constructed wetland even under biological reduction and plant growth conditions.