Adsorption and desorption studies of Congo red using low-cost adsorbent: activated de-oiled mustard

The feasibility of using an agricultural by-product-activated de-oiled mustard (ADM), as an adsorbent in the removal of azo dye, Congo red was evaluated in a batch adsorption process. The adsorption characteristics of Congo red onto ADM were investigated with respect to the changes in initial pH of dye solutions, contact time, initial dye concentration and temperature. The dye adsorption equilibrium was rapidly attained after 20 min of contact time. The Freundlich, Langmuir and Tempkin adsorption models were applied to experimental equilibrium data and isotherm constants were calculated using linear regression analysis. The thermodynamic parameters proved that the present adsorption process was feasible, spontaneous and endothermic in nature in the temperature range from 30 to 50°C at 303 K (30°C). The kinetic studies confirm the first-order process for the adsorption reaction and also play an important role in finding out half-life of the adsorption process and rate constants for both the adsorbents. The mechanism of the adsorption process was determined from the intra-particle diffusion model. Regeneration of the saturated columns has been made by eluting NaOH solution and more than 90% dye has been recovered.