The enhanced removal of highly toxic Cr(VI) by the synergy of uniform fiber ball loaded with Fe(OH)₃ and oxalate acid

In the view of green and efficient removal of chromium pollution, uniform fiber ball loaded with Fe(OH)₃ (UFB-Fe(OH)₃), was firstly synthesized and successfully used in the photoreduction of Cr(VI) by oxalate acid (Ox). The Cr(VI) removal in UFB-Fe(OH)₃+Ox + UV system was examined by the effect of concentration of Ox, initial Cr(VI) concentration, dosage of UFB-Fe(OH)₃ and the reusability of UFB-Fe(OH)₃. By studying the impact of the initial pH in the solution, the relationship between the change in pH during the reaction and the removal efficiency of Cr(VI), the effect of coexisting ion (NO₃^-), and the free radicals quenching tests, the Cr(VI) removal mechanism in UFB-Fe(OH)₃+Ox + UV system was further deduced. The results showed that UFB-Fe(OH)₃ could greatly enhance the photoreduction of Cr(VI) by Ox, 1.5 mM Cr(VI) was completely removed in 6 min by UFB-Fe(OH)₃+Ox + UV system. UFB-Fe(OH)₃ had the feasibility of multiple use, it still exhibited the excellent enhancement in Cr(VI) removal by Ox after six cycles of use. The Cr(VI) photoreduction mechanism was consist of three part: i) Ox generate a part of CO₂^·- under the ultraviolet (UV) to reduce Cr(VI); ii) the Fe(III) dissolved by UFB-Fe(OH)₃ formed FeOH²⁺ in the solution, and then generated very little Fe(II) under UV to remove Cr(VI); iii) the synergistic effect of UFB-Fe(OH)₃ and Ox rapidly generated a large number of CO₂^·- and Fe(II) under UV excitation to reduce Cr(VI).