The application of modified hematite for removal of carmine red dye: performance and mechanism

Zero-valent iron (ZVI) was prepared by the hydrogen reduction of hematite and characterized by using techniques, such as XRD, XPS, and SEM. Using carmine as a representative dye, the factors, including pH, solid-liquid ratio, reaction time, and temperature, affecting the purification of dye wastewater by the ZVI were investigated. The removal mechanism was discussed based on the experimental data and characterization results. The results showed that under the conditions of pH 2.0 and a solid-liquid ratio of 1 g/L, the decolorizing efficiency by the ZVI reached 99% at a reaction time of 1 h due to the reduction mechanism of ZVI. Another index for the degradation of carmine is TOC, and its maximum removal efficiency is 57% at 24 h mainly due to complexation of Fe2+, adsorption of ZVI and precipitation by the corrosion products of iron. The removal of carmine chromaticity by ZVI exhibited first-order reaction kinetics. Meanwhile, the adsorption of isotherms and the kinetics of TOC on ZVI were fit well by the Freundlich and pseudo-second order kinetics, respectively. The results suggested the way for preparing ZVI is feasible and the prepared ZVI is proved to be a promising material for dealing with dyeing wastewater, which benefits the comprehensive application of natural mineral in environmental protection.