Removal of coexisting Cr(VI) and 4-chlorophenol through reduction and Fenton reaction in a single system

Removal of coexisting Cr(VI) and 4-chlorophenol (4-CP) from aqueous solutions was achieved in a single system, which was capable of reduction of Cr(VI) with synthesized nano-scale zero-valent iron (nZVI) and oxidation of 4-CP with simple addition of H2O2. XRD and)(PS analysis indicated that the prepared nZVI was composed of external FeO and FeOOH and internal Fe-0. Cr(VI) could be completely reduced by nZVI within 20 min, and most of produced Cr(III) was removed mainly via co-precipitation in the form of FeCr2O4 and CrxFe1-x(OH)(3) complex. More importantly, Fe(II) produced from nZVI during reduction played a key role to promote a subsequent Fenton reaction by its coupling with H2O2, and thus significantly enhanced degradation of 4-CP within only 10 min. Solution pH was a primary controlling factor on oxidation of 4-CP, and the optimum pH was about 3. In addition, optimal initial concentration of nZVI and H2O2 were found to be 0.4 g/L and 9.79 mM. Removal efficiency of 4-CP seemed not influenced by initial Cr(VI) of 0-5 mg/L since enough surplus Fe(II) had been maintained for the Fenton reaction at later stage. This study is of particular use for treatment of wastewater containing both heavy metals and bio-refractory organic pollutants in many industrial sectors. (c) 2014 Elsevier B.V. All rights reserved.