studies on sorption of congo red from aqueous solution onto soil

the aim of this study was to investigate the congo red sorption on soil from the region of iasi (ne of romania). the effects of contact time, temperature, sorbent dose and initial dye concentration on soi sorption were investigated. the results show that the amount adsorbed of congo red on soil increase with increasing dye concentration, temperature and contact time. the experimental data were analyzed using the pseudo-first order lagergren model, the pseudo-second order model and intraparticle diffusion model. experimental results show that the dye sorption process follows the pseudo-second-order kinetic model. intraparticle diffusion studies indicated that the adsorption mechanism was not exclusively controlled by the diffusion step. the equilibrium sorption data were interpreted using langmuir, freundlich and tempkin models and the results were best described by freundlich isotherm. it was indicative of the heterogeneity of the sorption sites on the soil particle. thermodynamic analysis of the congo red sorption on studied soil indicates that the system is spontaneous and exothermic in nature.