Isotherms, kinetics and thermodynamic studies of adsorption of Cu2+ from aqueous solutions by Mg2+/K+ type orange peel adsorbents

Orange peel (OP) was used as raw material to prepare two novel adsorbents: MgOP (Mg2+ type orange peel adsorbent) and KOP (K+ type orange peel adsorbent). FTIR and SEM were used to characterize the adsorbents. Effects of pH, solid/liquid ratio, time and metal ion concentration on the Cu2+ adsorption by these two adsorbents were investigated. The isotherms data were analyzed using the Langrnuir, Freudlich, Temkin and Dubinin-Radushkevich models. Langmuir model provides the best correlation for the adsorption of Cu2+ by both MgOP and KOP. and the mono-layer adsorption capacity for Cu2+ removal by MgOP and KOP are 40.37 and 59.77 mg/g, respectively. The adsorbed amounts of Cu2+ increased with the increase in contact time and reached equilibrium within 20 min. The kinetics data were analyzed using four adsorption kinetic models: the pseudo-first and second-order equations, the Elovich equation and intraparticle diffusion equation. Results show that the pseudo-second-order equation fits the experimental data very well. Thermodynamic studies showed the spontaneous and exothermic nature of the adsorption of Cu2+ by MgOP and KOP. (C) 2009 Elsevier B.V. All rights reserved.