Uptake of aqueous tungsten and molybdenum by a nitrate intercalated, pyroaurite-like anion exchangeable clay

Mg-Fe-NO3-LDH, a nitrate intercalated pyroaurite-like anion exchangeable clay, was synthesized for treating both tungsten- and molybdenum-bearing waters in this study. The maximum sorption capacities of Mg-Fe-NO3-LDH for aqueous tungsten and molybdenum were up to 69.9 mg/g and 21.3 mg/g, respectively. The mechanisms for the efficient removal of tungsten and molybdenum were investigated based on the XRD, SEM-EDX, and XPS analyses of the reacted solid samples. It was concluded that anion exchange between tungstate or molybdate in solution and nitrate in the interlayer regions of Mg-Fe-NO3-LDH was the primary mechanism, but the stronger inner-sphere complexation of tungstate or molybdate with iron in the layers made a non-negligible contribution as well. The high alkaline conditions, formed due to the pH buffering effect of Mg-Fe-NO3-LDH, were favorable for the removal of tungsten and molybdenum from the solutions. Moreover, the coexistence of competitive anions, such as SO42- and HCO3-, affected the tungsten and molybdenum sorption significantly. In general, the nitrate intercalated pyroaurite-like anion exchangeable clay used in this study exhibited high uptake capacities for aqueous tungsten and molybdenum, and it is promising for a practical application in removing tungsten and molybdenum from either contaminated natural waters or industrial wastewaters.