Hydrogeochemical arsenic simulation of V-Ti-Fe tailings pond ecosystem: A case study from Panxi region, China

The V-Ti-Fe mine tailings waste releases high concentrations of aquatic arsenic (As) ions to downstream ecosystems. The hydrogeochemical As simulation facilitates the prediction of toxicity (or redox state) and devising control strategies to mitigate the negative impacts. Therefore, this study utilizes the Wanniangou tailings pond (a V-Ti-Fe mine tailings reservoir) in the Panxi region, Sichuan province, China, as a case study to elucidate the As hydrogeochemical behaviour under varying pH and redox potential (Eh) conditions. Our study reveals that (1) the water-oxygen exchange and Mn are important to regulating the redox conditions in the filtrates. The Eh determines the valence states of As, which vary from reduced states to oxidized states during the runoff from the tailings pond to downstream (Rehe River). The flow of wastewater in Rehe River minimizes both the As toxicity and concentration, eventually improving water safety. (2) In a reducing environment, hematite exhibits a limited capacity for As(III) adsorption. In the case of oxidation conditions, goethite mainly adsorbed As(V), with an elevated adsorption capacity. Meanwhile, Fe-minerals remain relatively stable under varying redox and weakly acidic conditions. Consequently, targeted engineering interventions can achieve two crucial outcomes: (1) Minimize the acidity of the mine environment to retard the release of heavy metals from the tailings waste. (2) Prolonging the residence time of wastewater in Rehe River to promote the transition from a reducing state to an oxidizing state, thereby synergistically mitigating As toxicity.