Effective utilization of calcareous soil towards the removal of methylene blue from aqueous solution

Abstract

Color is the main attraction of any fabric industry. No matter how excellent its constitution, if unsuitably colored it is bound to be a failure as a commercial fabric. Manufacture and use of synthetic dyes like methylene blue (MB) for fabric dyeing has therefore become a massive industry today. Soil is widely used as adsorbent for removing toxic pollutants from their aqueous solutions due to its wide availability and cost efficiency. In this work, the feasibility of employing calcareous soil to remove MB, a cationic dye from its aqueous solutions was investigated. The entire process has been done through batch operation. Percentage removal was greater for dilute solutions, but the absolute amount of MB adsorbed by the calcareous soil at equilibrium increased with an increase of the initial concentration. The kinetics of the adsorption process was analyzed by pseudo-first-order, pseudo-second-order, intraparticle diffusion, surface mass transfer, and Elovich models. The first four mechanisms seem to be significant in the rate controlling step. Equilibrium adsorption was investigated by Freundlich, Langmuir, Temkin, and D–R isotherms. The Langmuir equation (R 2 = 0.982) fitted to equilibrium data better than all the tested isotherm models. The dimensionless separation factor (R L) was low (0.00007) indicating favorable adsorption of MB on to calcareous soil. Thermodynamic activation parameters such as ∆S°, ∆G°, and ∆H° were also calculated and results revealed that the adsorption process is a favorable exothermic and can be spontaneous in nature. Finally, it can be concluded that calcareous soil can be an effective low-cost adsorbent for removal of cationic dye from waste effluents.