Removal of carmineusing red mud-supported ZVI materials

The industrial waste red mud was used as the iron source, and economical and environmentally friendly anthracite was used as the reducing agent to prepare red mud-supported zero-valent iron (RA@ZVI) composite materials by the carbothermal reduction method. The system evaluated the effects of the preparation conditions and removal conditions of RA@ZVI material on the degradation effect of carmine. The experimental results show that under the conditions of anthracite with a ratio of 35%, calcination at 1000 °C for 60 min, the prepared RA@ZVI material with a RA@ZVI dosage of 0.5 g/L, an initial carmine concentration of 50 mg/L, a solution pH value of 3, and a reaction temperature of 25 °C, the carmine removal rate is close to 100%. The material characterization results reveal that the high efficiency of RA@ZVI stems from its unique physicochemical properties. XRD analysis confirmed that a higher calcination temperature (1000 °C) effectively promoted the reduction of iron oxides in red mud to ZVI. SEM-EDS analysis indicated that micrometer-sized and well-dispersed zero-valent iron particles were formed in the prepared RA@ZVI material. Mechanism research has confirmed through free radical capture experiments that in the degradation process of carmine, hydroxyl radicals (·OH) and superoxide radicals (·O₂^-) play a key role. RA@ZVI undergoes a direct REDOX reaction with carmine through the strong reducing property of ZVI, and induces the generation of the above-mentioned highly active free radicals, which work in synergy to attack carmine molecules. Specifically, the azo bond (-N=N-) and anthraquinone ring structure of carmine are effectively disrupted, thereby achieving efficient mineralization and removal of the dye. This study not only provides an economically efficient and environmentally friendly high-value utilization approach for red mud waste, but also offers a new type of RA@ZVI material for the advanced treatment of complex azo dye wastewater. This material shows certain potential in the treatment of printing and dyeing wastewater.