Recovery of magnetite from fluidized-bed homogeneous crystallization of iron-containing solution as photocatalyst for Fenton-like degradation of RB5 azo dye under UVA irradiation

Iron recovery from wastewater as magnetite (Fe₃O₄) pellets was performed in a fluidized-bed homogeneous crystallization (FBHC) process. The catalytic effectiveness of magnetite in the heterogeneous degradation of RB5 azo dye was evaluated. The key parameters of FBHC, including effluent pH, cross-section loading (L, kg/m².h), initial iron concentration ([Fe(II)], mg/L), and inlet supersaturation (S), were optimized to maximize the total iron removal (TR, %) and crystallization ratio (CR, %) from a fluidized-bed reactor. Under the conditions of pH = 8.5–9.5 and [Fe(II)]_in = 100 – 500 mg/L, the TR and CR values reached 99% and 77%, respectively. The magnetization and coercivity of the recovered Fe₃O₄ pellets were analyzed to confirm the magnetic characteristic. A Fenton-like degradation of RB5 azo dye was activated using the Fe₃O₄ pellets under UVA irradiation, pH = 2.75 – 3.0, initial peroxide concentration of 10 mM, and catalyst loading of 2 g/L. The efficiencies of decolorization and mineralization reached about 98 – 99% and 60 – 68%, respectively. FBHC method benefited the recovery of high-purity metal oxides and the production of a low quantity of sludge. Magnetic pellets transformed from the dissolved iron in wastewater were promising materials to reuse as a photochemical reactant for organic pollutant degradation.