Predicting arsenic behavior in the wastewater of Mouteh Gold Plant: geochemical modeling

Arsenic is one of the heavy metals and nearly all its compounds, especially organic compounds, are toxic. The wide spectrum of diseases caused by this element has led to the evaluation of toxicity of different arsenic species and identification of the major natural and anthropogenic pollution sources of it in nature. Mining activities are among the main sources of anthropogenic pollution of soil and water by arsenic. Using geochemical modeling of different arsenic species in the wastewater of the tailings dam of Mouteh Gold processing plant in Iran, this paper aims to evaluate the effect of pH and temperature on the stability of these components. Modeling was done using MINTEQ software. The results showed that arsenic species at different pH values under study were H3AsO3, H2AsO3- and HAsO32-, and their actual concentration in the plant wastewater were negligible. MINTEQ software introduced H3AsO4, H2AsO4-, HAsO42- and AsO43- as arsenic V species at different pH values, of which HAsO42- and AsO43- were the main components of arsenic in plant wastewater. Given the low toxicity of arsenic V species and their easier elimination relative to arsenic III species, in the current conditions, the plant wastewater is in a good status in terms of arsenic pollution. Moreover, temperature changes have little effect on the concentration of various arsenic species in the wastewater; therefore, it is predicted that climatic changes in different seasons have no pollution effect on the wastewater. The results also showed that ytterbium and barium have higher affinity to form precipitates with arsenic and prevent saturation of other species in the solution by removing arsenic.