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

• Coexisting Cr(VI) and 4-chlorophenol were removed with simple addition of nZVI and H2O2.
• Fe(II) produced from nZVI played a key role on the subsequent Fenton reaction.
• Most of reduced Cr(III) could be removed via co-precipitation with Fe(III).
• 4-CP could be was fast removed and not influenced by initial Cr(VI).

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 XPS analysis indicated that the prepared nZVI was composed of external FeO and FeOOH and internal Fe0. 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.