The zero-valent iron (ZVI) immobilized in an alginate microsphere was prepared by using sodium alginate as a support material. The characteristics of the Fe0/alginate microsphere was characterized by FT-IR, SEM, BET, and XPS. The SEM and BET analyses showed that the Fe0/alginate microsphere had a multilevel porous structure and could adsorb ARB. Combined with Fe0 reduction and Fe3+/Fe2+ catalytic oxidation, the mineralization of ARB could be effectively realized. The ARB in the solution was discolored rapidly by the reduction of Fe0/alginate microsphere and then oxidized efficiently by the subsequent Fenton reaction. The discoloration rate of ARB in the reduction stage was 96.8%, with an Fe0/alginate microsphere dosage of 0.24g·L-1 and pH of 2.96 after reaction time of 180 min. ARB was reduced to organics of lower molecular weight due to the degradation of azo groups by Fe0. In the subsequent Fenton oxidation stage, the mineralization degree of ARB increased to 64.7% after the addition of 10.75 mmol·L-1 H2O2. The influence of the Fe0/alginate microsphere dosage, pH, reusability of the Fe0/alginate microsphere, and the stability of iron ions in the alginate microsphere were investigated. Due to the coordination of Fe3+/Fe2+ ions with -COO--in the alginate, the iron ion in the solution was 3.9% of the total iron content in the microsphere. Iron ions could be well immobilized in calcium alginate microspheres, so the iron hydroxides were generated in lower amounts. The Fenton reaction can be conducted in a wide range of pH. The Fe2+/Fe3+immobilized in the alginate microsphere demonstrated good catalytic performance after it was reused four times. Therefore, the synergy of reduction and Fenton oxidation by the Fe0/alginate microsphere was a better strategy for dye degradation.
Keywords: Fenton oxidation; acid red B (ARB); calcium alginate; reduction; zero-valent iron.