Adsorption Equilibrium, Kinetics and Thermodynamics of Methylene Blue from Aqueous Solutions using Date Palm Leaves

Abstract

The ability of Date palm Leaves powder (DPLP) to remove methylene blue (MB) from aqueous solutions by the biosorption process has been studied. Biosorption studies were carried out at different initial dye concentration, contact time, initial solution pH, biosorbent dosage, the particle size of (DPLP) and temperature. Biosorption data were modeled using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich adsorption isotherms. The results showed that equilibrium was reached within 160min. The used biosorbent gave the highest adsorption capacity at pH 6.5. Equilibrium data of the biosorption process fitted very well to the Temkin model (R2=0.994). The maximum adsorption capacity, Langmuir's qmax, improved from 43.103 to 58.14mg/g as the temperature increased from 30 to 60°C. The enthalpy ΔH° and entropy ΔS° values were respectively estimated at 8.098kJ mol−1 and 12.97J K−1 mol−1 for the process. Three simplified kinetic models including a pseudo-first-order equation, pseudo-second-order equation and intraparticle diffusion equation were selected to follow the adsorption process. Kinetic parameters, rate constants, equilibrium sorption capacities and related correlation coefficients, for each kinetic model were calculated and discussed. It was shown that the adsorption of methylene blue (MB) could be described by the pseudo-second order equation (R2= 0.996), methylene blue is slowly transported via intraparticle diffusion into the particles and is finally retained in micropores, suggesting that the adsorption process is presumable a physisorption.