Effects of Phosphate, Silicate, and Bicarbonate on Arsenopyrite Dissolution and Secondary Mineral Precipitation

Managed aquifer recharge (MAR) has been applied to meet quickly growing water demands. However, during MAR operations, the injected water can induce dissolution of local minerals and result in the release of toxic metalloids, such as arsenic. To alleviate this concern, it is pivotal to understand the effects of injected water chemistry on the arsenic mobilization during MAR. In this bench-scale study with geochemical conditions relevant to MAR operations, we investigated the impacts of three environmentally abundant oxyanions (i.e., phosphate, silicate, and bicarbonate) on arsenic mobilization from arsenopyrite (FeAsS) and secondary mineral precipitation. Phosphate showed time-dependent reversed effect on arsenic mobility. In short term (6 hours), phosphate promoted the dissolution of FeAsS through monodentate mononuclear surface complexation, while over a longer experimental time (7 days), the enhanced formation of secondary minerals, such as iron(III) (hydr)oxide (maghemite, γ-Fe2O3) and iron(III) phosp...