Effect of major anions on arsenate desor

The influence of background electrolytes (Na2HPO4/C12H2O, NaHCO3, Na2SO4, NaNO3 and NaCl) on arsenate (As(V)) desorption from three environmental samples (a tailings sample, a stream-bed sediment and a top soil) containing ferrihydrite as the main As-bearing phase has been studied through kinetic batch experiments and geochemical simulations. The experimental results indicate a significant increase in As(V) release in the presence of dissolved phosphate and carbonate species. Similar to phosphate, a strong surface interaction of inner-sphere type between ferrihydrite and aqueous carbonate species is suggested. Nitrate and chloride have negligible effects on the As(V) desorption reaction, while sulfate exhibits intermediate behavior depending on its dissolved concentration, influencing the type of surface complex formed. The process of As(V) release follows a modified Lagergren first-order rate equation for desorption, with most desorption rate constant values ranging from 0.0012–0.0030 min−1. Modeling of the desorption experiments using PHREEQC highlights that the influence of pH is significantly less important than the displacement action of carbonate species in determining the amount of As(V) released to solution. This study's findings are consistent with recent literature yet cannot be generalized to all natural systems, although they bear environmental implications for arsenic mobility and potential applications in various fields.