Adsorption of Cadmium onto Orange Peels: Isotherms, Kinetics, and Thermodynamics

Abstract

Batch adsorption of Cd (II) onto orange peel, a residue of the fruits processing industry, has been studied. Equilibrium isotherms, kinetic data, and thermodynamic parameters have been evaluated. Equilibrium data fit well with Langmuir isotherm model. The kinetic data were found to follow the pseudo-second-order model. The negative ΔHº value indicates the exothermic nature of the adsorption process. Orange peel was shown to be a promising adsorbent for Cd (II) removal from aqueous solutions. Nomenclature A Constant describing the energy of interaction between solute and adsorbent surface; β Desorption constant (g/mg) during any experiment; C 0 Initial concentration (mg/l); CeEquilibrium concentration (mg/l); K F & n Freundlich constants; k 1 Pseudo first-order adsorption rate constant (l/min); k 2 Pseudo second-order adsorption rate constant (g/mg. min); K D Distribution coefficient (cm 3 .g -1) K L Langmuir constants (L mg -1); k id Intraparticle diffusion rate constant (min -1); MWeight of adsorbent (mg); q Adsorption capacity,(mg of Cd (II) /g adsorbate); q e Adsorption capacity at equilibrium, (mg of Cd (II) /g adsorbate); q max Maximum adsorption (mg of Cd (II) /g adsorbate); q t Adsorption capacity at time t, (mg of Cd (II) /g adsorbate); R Gas constant (8.314 J/mol/K); Rc Percent of Cd (II) adsorbed (mg/g); ReThe removal efficiency of Cd (II) (mg/g); r 2 Correlation coefficient TTemperature (K) tContact time (min); V Volume of the solution; α Initial adsorption rate (mg of Cd (II)/g adsorbate. min);