Kinetic, isotherm and pH dependency investigation and environmental application of cationic dye adsorption on montmorillonite

Abstract

In this study, individual and competitive adsorption of three cationic dye onto montmorillonite were investigated. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models were used to analyze experimental data for individual and competitive adsorption of dyes. Surface precipitation occured in the presence of inert electrolyte because of decreasing solubility of dye. The organic dye adsorption was pH-independent in a pH scale between 2 and 6. It is, thus, assumed that the adsorption took place between cationic organic dye and permanently negatively charged surface, which is a pH-independent surface site of adsorbent and occured as a result of isomorphic substitution. Mean free energies (ED) varied between 0.65 and 7.87 J/mol, and heats of sorptions (B) changed between 4 and 96 J/mol. These low energy values support the electrostatic interaction between surface and dye molecules. Organic dye adsorption showed Langmuirian character and in the presence of more than one adsorptive dye, adsorption capacities remained under individual adsorption capacity values because of competition. Adsorption kinetic showed second order reaction character. Using sodium humate, CaCl2 solution, and acid mixture solution as leach solutions desorption properties were examined. Higher desorption values were achieved by using 1% of sodium humate solution because of hydrophobic interactions and formation of H bonds.