Biosorption potential of cocoa pod husk for the removal of Zn(II) from aqueous phase

• Cocoa pod husk (CPH) was used for the removal of Zn(II) from aqueous solutions.
• The Avrami model best predicted the biosorption kinetics of Zn(II) onto CPH.
• The biosorption equilibrium was better described by the Freundlich isotherm model.
• Thermodynamic studies showed the biosorption was spontaneous and endothermic.
• Presence of coions had adverse effect on the biosorption capacity of CPH for Zn(II).

The potential of cocoa pod husk (CPH) as a biosorbent for the removal of Zn(II) from aqueous solution in a batch system was studied. The effects of contact time, initial concentration of Zn(II), temperature, pH and presence of other metal ions were investigated. The biosorption was relatively fast at 30 °C and followed the Avrami kinetic model. The biosorption isotherm modeling showed that the equilibrium data fitted better to the Freundlich than the Langmuir model. The biosorption showed a pH dependent profile and optimum values at pH 6. Binary metal system experiments showed that the presence of coions had adverse effect on the biosorption capacity of CPH for Zn(II). The thermodynamic parameters indicated that the biosorption of Zn(II) on CPH was a spontaneous and endothermic process. High biosorption capacity obtained shows that CPH may be useful for the removal of Zn(II) from aqueous media.