Observation of surface precipitation of ferric molybdate on ferrihydrite: Implication for the mobility and fate of molybdate in natural and hydrometallurgical environments.

Abstract Adsorption of molybdate (Mo(VI)) on the surfaces of ferrihydrite is one of the most critical processes that control its mobility and fate in the environment. However, the sorption mechanism and the effect of pH on the speciation of Mo(VI) on ferrihydrite surfaces are not well understood. In this study, X-ray diffraction (XRD), Raman, Fourier transform infrared (FTIR), and Mo K-edge and L3-edge X-ray absorption spectroscopy (XAS) have been utilized to characterize the Mo(VI) species sorbed on ferrihydrite under various pH conditions. XRD, Raman, and FTIR results show that at acidic pH, surface precipitation of poorly crystalline ferric molybdate (PCFM) occurs under apparently undersaturated conditions (theoretical log IAP