Rapid and efficient removal/recovery of molybdenum onto ZnFe₂O₄ nanoparticles

An efficient method for removing and recovering molybdenum (Mo) from water was developed by using ZnFe₂O₄ nanoparticles. The Mo adsorption displayed a nonlinear isotherm that fitted well with the Langmuir isotherm, showing limited adsorption sites on the surface of ZnFe₂O₄. The adsorption of Mo(VI) was dependent on solution pH. With increasing pH, the build-up of negative charges of both adsorbent and adsorbate led to enhanced electric repulsion between them. The K-edge XANES spectra for the adsorbents collected after Mo adsorption revealed that Mo(VI) was the predominant oxidation state sorbed on ZnFe₂O₄, indicating that the reduction of Mo(VI) did not occur on ZnFe₂O₄. The different peak positions of k-space and R-space shown in K-edge EXAFS spectra demonstrated that the adsorbed Mo could be bound on the surface or be slipped in the vacancy position of the ZnFe₂O₄ crystal. Importantly, Mo could be efficiently adsorbed from photoelectric industrial wastewater and these adsorbed Mo anions were rapidly replaced by OH^- ions, implying the potential for Mo removing and recovering in industrial wastewater.