Removal of Acid Blue 40 from Aqueous Solution by Teak Leaf Litter Powder: Kinetics, Thermodynamics and Equilibrium Study

The equilibrium, kinetics and thermodynamics of the feasibility of using teak leaf litter powder (TLLP) to remove anionic Acid Blue 40 (AB40) dye from aqueous solution was investigated. Dye removal was influenced by contact time, TLLP dosage as well as concentration, pH and temperature of AB40 solution. Optimum removal of dye occurred at low TLLP dosage, acidic pH, and low dye concentration. Adsorption data fit well both Langmuir and Dubinin-Radushkevich isotherms and the maximum monolayer capacity of the adsorbent was 80.64 mg g^-1 at pH 2 and 303 K. The kinetics of dye removal was best suited to the pseudo-second order model. The spontaneous and exothermic process was influenced by both intraparticle diffusion and liquid film diffusion but the latter was the rate-controlling step. The values of adsorption free energy (E), change in enthalpy (ΔH°) and entropy (ΔS°) were: 7.07 kJ mol^-1, -15.99 kJ mol^-1 and -42.77 J mol^-1 K^-1. TLLP may be a promising low-cost adsorbent for treating wastewaters containing AB40 and other anionic acid dyes.