XANES evidence of molybdenum adsorption onto novel fabricated nano-magnetic CuFe₂O₄

An efficient Molybdenum (Mo) removal technology in aqueous solutions was developed for the first time using nano-magnetic CuFe₂O₄ manufactured from printed circuit board (PCB) industrial sludge. This nano-magnetic CuFe₂O₄ adsorbent displayed a nonlinear L-type isotherm that fitted well with the Langmuir isotherm, suggested limited adsorption sites and monolayer sorption on surface. The K-edge X-ray absorption near-edge structure (XANES) spectra demonstrated that Mo(VI) was the predominant oxidation species on nano-magnetic CuFe₂O₄ and the maximum adsorption capacity was found to be 30.58mgg^-1 at pH 2.75. When pH became higher, more negative charges would occur at the surface of adsorbent and lead to more electric repulsion. Consequently, Mo adsorption was sharply reduced in alkaline condition. Importantly, these adsorbed Mo anions were replaced easily by OH^- ions in NaOH solution and showed huge potential for removal/concentration of Mo in industrial wastewater, groundwater, and tap water. This unique Mo separation technique can also be potentially applied for geochemical investigation in various natural aqueous solutions.