Fe0-H2O2 for advanced treatment of citric acid wastewater: Detailed study of catalyst after several times use

Abstract

Fe0-H2O2 Fenton-like process was effectively applied in the advanced treatment of citric acid wastewater. The important reaction conditions were optimized. When the initial pH was 3.0, H2O2/COD = 0.7∗ Fe0/H2O2 = 3.29 (weight ratio), coagulation pH = 9.0, the COD removal reached to over 35% in 2 h. Especially, the reuse of Fe0 was studied in details. The 2nd use of Fe0 performed better than the pristine Fe0 in COD reduction with a promotion of 28.78%, and the promotion maintained till the 5th reuse. During the recycling and reusing process, Fe0 kept good stability in reaction activity though gradually covered by a filmy oxidation layer on its surface. In order to examine the changes of Fe0 after several uses, samples were characterized by TEM, HRTEM, SEM, EDS, XPS, and XRD. It was found that the surface of Fe0 particles was smooth before use while rough after reactions. Though it generated a filmy oxidation layer covering on the Fe0 surface, the intensity of peak at 110 crystal planes kept strong and distinct, detecting by XRD. After 5 times of use, the EDS spectrum showed only about 7.35% more of oxygen content was increased on Fe0 surface. XPS spectra demonstrated that Fe(OH)3 and FeOOH were the main oxidation production generated on surface of Fe0 particles during the Fenton-like reaction. The existence of this oxidation layer did not weaken the effect of Fe0-Fenton process, but strengthened it. The presumed reaction mechanism of Fe0-Fenton was proposed, including the reaction process and the materials conversion.