Oxidative decolorization of direct light red F3B dye at natural manganese mineral surface

Abstract

In this paper, the characteristics of natural manganese mineral collected from Guangxi Province, China, including crystalline properties, elemental composition, organic substrates content (0.17%) and BET surface area (29.8 m 2/g), were determined. By X-ray powder diffraction and fluorescence spectrograph analysis, it is shown that manganese oxide in the natural mineral exists in the crystal structure of α-Mn 2O 3 and the contents of manganese (II) and manganese (IV) oxides are 4.6 and 42.6%, respectively. The solubility experiments show that manganese dissolved in solution can be ignored at a higher pH value, but its significant solubility is observed with the decrease of pH value. Moreover, the decolorization properties of direct light red F3B dye on natural manganese mineral surface were studied by batch technique. The effects of pH value, temperature, inert electrolyte, light, particles concentration and size, the presence of calcium and phosphate as well as oxygen on the decolorization efficiency of the dye were investigated in detail. The results show that the decolorization of the dye is strongly dependent on pH value, with lower decolorization percentage at higher pH values, and the higher concentration of inert electrolyte and temperature favor the decolorization reaction of the dye on the particle surface. By Arrhenius Equation, the apparent activation energy is found to be at 71.7 kJ/mol, indicating the surface chemical reaction as a rate-limiting step in the overall interface process. The illumination enhances the surface chemical reaction of the dye on manganese mineral particles. The decolorization rate of the dye compound is increased with the increase of particle concentration and the decrease of size since the available surface sites grow in number. The presence of phosphate greatly inhibits the decolorization reaction by competitive adsorption on the mineral surface with the dye anion, while the addition of calcium promotes the decolorization rate of direct light red F3B dye.