Metal ion free watermelon (Citrullus lanatus) rind as adsorbent for the removal of lead and copper ions from aqueous solution

Chemically protonated watermelon rind (PWR) was evaluated as a low-cost and efficient adsorbent for the removal of Pb2+ and Cu2+ ions from aqueous solution. Protonation of watermelon rind (WR) was carried out with 0.1 M HCl as protonating agent. The adsorption process was found to be spontaneous and exothermic in nature. Kinetic investigations suggest that the present system follows pseudo-second-order kinetic model and rate-limiting step is not chemical reaction. The maximum loading capacity of PWR was found to be 116.2 and 39.2 mg g(-1) for Pb2+ and Cu2+ ions, respectively. FTIR and energy dispersive X-ray analyses supported the sorption of metal ions onto PWR. The results suggested that WR can be an effective adsorbent for the removal of heavy metal ions from aqueous solution.