Removal of Leishman stain from aqueous solutions using natural clay of Qulapalk area of Kurdistan region of Iraq

The rate of the adsorption process was found to follow the pseudo second-order kinetics, which was found to be increased with the increase of temperature. The activation parameters Ea, ΔH∗ and ΔS∗ were found to be 37.94 kJ mol−1, 35.34 kJ mol−1 and 148.02 J mol−1 K−1 respectively. The sorption isotherm fitted to both Freundlich and Langmuir isotherm models. High adsorption capacity was recorded for the current natural clay (455.37 mg/g) toward methylene blue. Equilibrium thermodynamic parameters ΔH°, ΔS° and ΔG° indicated that the adsorption processes was spontaneous and endothermic in nature.