The adsorption behavior of thioarsenite on magnetite and ferrous sulfide

Thioarsenite (TAsIII) is an important arsenic (As) species under sulfidic environments. Adsorption behavior of TAsIII on iron (Fe)-bearing minerals affects the transformation and the distribution of As at solid-liquid interface. In this study, we investigated the formation of TAsIII species in the mixed arsenite and sulfide (AsIII-S-II) solutions with different S/As ratios and adsorption behavior of TAsIII on the surface of magnetite (Fe3O4) and ferrous sulfide (FeS). It was found that the extent of S-substitution of TAsIII was enhanced with the increasing S/As molar ratio in the AsIII-S-II solutions. The adsorption experiments showed that As in the AsIII-S-II solutions was adsorbed to a less extent on two Fe minerals than that of AsIII in circumneutral to alkaline solutions, indicating that TAsIII has lower affinity to Fe3O4 and FeS. The adsorption of TAsIII on the surface of Fe3O4 led to hydrolyzation and AsIII is the main sorbed species. On the surface of FeS, the extent of S-substitution of TAsIII was promoted and As sulfide surface precipitate may form. Overall, the formation of TAsIII species is the vital factor affecting the redistribution of As between solid and aqueous phase in sulfidic environment.