Freundlich, Langmuir adsorption isotherms and kinetics for the removal of malachite green from aqueous solutions using agricultural waste rice straw

Malachite (N-methylated diamino triphenyl methane), a green menace, is extensively being used as dye for colouring silk, leather and paper. It is carcinogenic and catalyzes allergic problems. In this work agricultural waste rice straw as adsorbent was employed to remove Malachite green from aqueous solutions. Effects of pH, concentration of the dye, temperature and adsorbent dosage was determined for maximum removal of dye. Equilibrium isotherms for the adsorption of the dye were well fitted to the Freundlich and the Langmuir isotherm models. Thermodynamic parameters, Gibb's free energy (ΔG°;), change in enthalpy (ΔH°) and change in entropy (ΔS°) have revealed spontaneous and endothermic nature of adsorption process. Kinetic measurements established that the adsorption of Malachite green over rice straw follows first-order kinetics