The biosorption process of Zn (II) ions in industrial wastewater was investigated using derived composite biosorbents from walnut and snail shells. Composite adsorbents were produced by activating walnut shell carbon (WSC) with phosphoric acid to obtain acid-treated walnut shell carbon (AWSC) and WSC and AWSC were independently impregnated on chitosan to produce walnut shell carbon impregnated on chitosan (WSCC) and acid-treated walnut shell carbon impregnated on chitosan (AWSCC) respectively. The removal efficiencies of Zn (II) ions from synthetic wastewater using the prepared adsorbents were determined. The effects of operational parameters on Zn (II) ions adsorption were investigated. The adsorption data of Zn (II) ions were analysed using Langmuir, Freundlich and Temkin isotherms. The Langmuir isotherm fitted the adsorption data excellently for the derived composite biosorbents, giving an indication of monolayer coverage on the derived composite biosorbents and the determination coefficients were close to unity. Also, the maximum adsorption capacities of 3.1104, 3.8052, 16.4474 and 17.6991 mg/g were obtained for WSC, AWSC, WSCC and AWSCC at pH=5, 1 g of adsorbent dosage, Zn (II) ions initial concentration of 30 mg/L, contact time of 2 h, agitation speed of 150 rpm, particle size of 60 BSS and temperature of 30°C. The kinetic modelling of Zn (II) ions adsorption showed that pseudo second-order kinetic model gave the best fit amongst the investigated kinetic models. The adsorption of Zn (II) ions on the prepared adsorbents was film-diffusion controlled. The experimental results of this study showed that acid-treated walnut shell carbon impregnated on chitosan has the potential to be applied as alternative efficient low-cost biosorbent in the remediation of heavy metal contamination in wastewater. The thermodynamic parameters indicated that the adsorption of Zn (II) ions on the derived composite biosorbents was exothermic, endogonic, favourable, non-spontaneous with changes in enthalpy (, negative), entropy [, nearly zero (though negative)], and Gibbs free energy (, positive), for all the prepared adsorbents.
Key words: Adsorption, biosorbents, chitosan, isotherm, kinetic models, film diffusion.
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