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

In this paper, the characteristics of natural manganese mineral collected f rom Guangxi Province. China, including crystalline properties, elemental co mposition, organic substrates content (0.17%) and BET surface area (29.8 m( 2)/g), were determined. By X-ray powder diffraction and fluorescence spectr ograph analysis, it is shown that manganese oxide in the natural mineral ex ists in the crystal structure of alpha-Mn2O3 and the contents of manganese (II) and manganese (IV) oxides are 4.6 and 42.6%, respectively. The solubil ity experiments show that manganese dissolved in solution can be ignored at a higher pH value, but its significant solubility is observed with the dec rease of pH value. Moreover. the decolorization properties of direct light red F3B dye on natural manganese mineral surface were studied by batch tech nique. The effects of pH value, temperature, inert electrolyte, light, part icles 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 de pendent on pH value, with lower decolorization percentage at higher pH valu es, and the higher concentration of inert electrolyte and temperature favor the decolorization reaction of the dye on the particle surface. By Arrheni us 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 ove rall interface process. The illumination enhances the surface chemical reac tion of the dye on manganese mineral particles. The decolorization rate of the dye compound is increased with the increase of particle concentration a nd the decrease of size since the available surface sires grow in number. T he presence of phosphate greatly inhibits the decolorization reaction by co mpetitive adsorption on the mineral surface with the dye anion, while the a ddition of calcium promotes the decolorization rate of direct light red F3B dye. (C) 2000 Elsevier Science Ltd. All rights reserved.