Evaluation of sulfate rhizofiltration by Carpobrotus chilensis for treating mining waters

Chile, the world's leading copper producer, generates significant volumes of mining waters, some of which cannot be recirculated into the production process. These mining waters are characterized by elevated sulfate (${\text{SO}}_4^{2-}$) concentrations, requiring sustainable management strategies for potential reuse. This study aims to evaluate the rhizofiltration technique using Carpobrotus chilensis for treating mining waters with a high ${\text{SO}}_4^{2-}$ concentration. Initially, the mining waters exhibited a pH of 7.97 ± 0.16 and a ${\text{SO}}_4^{2-}$ concentration of 2,743 ± 137 mg L^-1, while the control water had a pH of 7.88 ± 0.08 and a ${\text{SO}}_4^{2-}$ concentration of 775 ± 19.0 mg L^-1. The plants were hydroponically cultivated in 40 L containers with mining waters and drinking water as a control. Over an 8-week period, the pH of the mining water decreased to 3.12 ± 0.01, and the ${\text{SO}}_4^{2-}$ concentration declined to 2,200 ± 110 mg L^-1. Notably, the fresh weight of roots was significantly higher in plants grown in mining water (22.2 ± 6.66 g) compared to those in the control treatment (14.3 ± 4.28 g). However, an undesirable increase in the acidity was observed in the mining waters after rhizofiltration, which was attributed to hydrogen sulfate (HSO₄^-) and/or root exudates. Despite the unexpected increase in acidity, C. chilensis effectively reduced the concentration of ${\text{SO}}_4^{2-}$ in mining waters by 20%. Additionally, the C. chilensis roots accumulated 4.84 ± 1.40% of sulfur (S), a level comparable to thiophore plants. This study provides evidence that this non-aquatic plant can be used in sulfate rhizofiltration.