Equilibrium, thermodynamic and kinetic studies on removal of chromium, copper, zinc and arsenic from aqueous solutions onto fly ash coated by chitosan

• The modification of fly ash using chitosan.
• Fly ash coated by chitosan as an adsorbent for the removal of heavy metal ions.
• The adsorbents were characterized using the FTIR, SEM, BET and XRD methods.

The objective of this work was to examine the effectiveness of fly ash coated by chitosan (FAICS) as an adsorbent for the removal of heavy metal ions from aqueous solutions. The adsorption isotherms, effect of initial concentration, pH, contact time, temperature and adsorbent dosage were investigated. In this work the characterization of synthesized adsorbents is also presented. The adsorbents were characterized using the FTIR, SEM, BET and XRD methods. The process kinetics was evaluated by the pseudo first order, the pseudo second order and the intraparticle diffusion models. Batch kinetic data from the experimental investigations on the removal of heavy metal ions from aqueous solutions using FAICS have been well described by the pseudo second order model. The adsorption data for Cr(III,VI), Cu(II), Zn(II) and As(V) were fitted well with the Freundlich isotherm model. The adsorption capacities of FAICS(8:1) for Cr(III,VI), Cu(II), Zn(II) and As(V) were equal to 36.22 mg/g, 28.65 mg/g, 55.52 mg/g and 19.10 mg/g, respectively. The thermodynamic parameters such as enthalpy, entropy and free energy of adsorption of metal ion-FAICS systems were determined. It was found that the process is endothermic, favourable and spontaneous in nature. The results showed the highest efficiency in the case of adsorption of Zn(II) onto FAICS(8:1).

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