Acacia karroo charcoal lumps were used for the biosorption of Ni(II) and Zn(II) from an aqueous solution using batch mode. The effect of various parameters viz., solution pH, adsorbent dose, contact time and initial metal concentrations were studied. Freundlich and Langmuir isotherm models were applied to the batch equilibrium data. The maximum biosorption capacity (qmax) for Ni(II) and Zn(II) was found to be 9.0 and 7.99 mg g−1 at pH 6.0 and 4.0 respectively. Experiments were performed to study the kinetics of Ni(II) and Zn(II) biosorption and the data obtained was best fitted to the pseudo-second-order kinetic model. Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) changes were also calculated and the observed values supported the spontaneity of the biosorption process. The exhausted adsorbent was regenerated three times using 0.1 N NaOH and its regeneration capacity was evaluated. These results illustrate that A. karroo charcoal lumps hold good potential for removing heavy metals ions from aqueous solution and could be used for desalinating metal ions from industrial wastewater.

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