Synthesis of zerovalent iron from water treatment residue as a conjugate with kaolin and its application for vanadium removal.

This study was aimed at examining the possible utilization of iron-rich groundwater treatment sludge in the synthesis of zerovalent iron (ZVI) as a conjugate with kaolin clay (Slu-KZVI), and its application for vanadium adsorption from aqueous solutions. Iron was extracted from the sludge using 1 M HCl and was used in ZVI synthesis by the sodium borohydride reduction method. The characteristics and performance of Slu-KZVI were compared to a kaolin modified with synthetic iron (FeCl3·6H2O) (Syn-KZVI). Adsorption results showed a competitive performance by both classes of KZVI, with Syn-KZVI slightly outperforming Slu-KZVI. X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy confirmed the formation of Fe0 on the core-shell structure of both modified adsorbents. In addition, the surface analysis of Slu-KZVI indicated the presence of P and Ca to a small extent, originating from the sludge. Both classes of sorbents performed better in solutions with acidic and neutral pH values (3-7). Surface complexation was thought to be the primary mechanism whereas simultaneous V(V) reduction and Fe oxidation (redox) reactions may also have taken place to some extent. A sorption test with groundwater confirmed that adsorbents were able to reduce vanadium to a very low concentration.