Uptake and desorption of nickel(II) using polymerised tamarind fruit shell with acidic functional groups in aqueous environments

Abstract

The sorption potential of formaldehyde polymerised tamarind fruit shell (FPTFS) containing acidic functional groups for the treatment of Ni(II) ions from aqueous solutions has been investigated. The adsorbent was characterised by infrared spectroscopy and scanning electron microscopy. Operating parameters affecting Ni(II) adsorption were investigated by the batch technique. Maximum Ni(II) sorption was found to occur at an initial pH of around 6. Kinetic studies showed that the amount adsorbed increased with initial Ni(II) concentration and the equilibrium was established in 180 min. The kinetic data were analysed using the Lagergren pseudo-first-order, Ritchie second-order and modified Ritchie second-order equations, and showed better fit with the modified Ritchie second-order equation. Equilibrium data were analysed by Langmuir, Freundlich, Sips and Toth isotherm models and the Sips model best defined the isotherm. The adsorption of Ni(II) was endothermic in nature (ΔHads: 45.93 kJ/mol) with an increase in entropy (ΔSads: 245.67 J/mol/K) and a decrease in Gibbs free energy (ΔGads:−28.52 to−35.67 kJ/mol) in the temperature range 30–60 °C. The reduction in adsorption capacity with an increase in ionic strength and isosteric heat of adsorption (ΔHx: 24.85 kJ/mol) revealed an ion exchange mechanism for Ni(II) adsorption. The adsorption efficiency of FPTFS towards Ni(II) removal from a nickel-plating industry wastewater sample was investigated and quantitative removal of 100 mg/L of Ni(II) in 1 L of industrial wastewater was possible with 6 g of FPTFS. The spent, nickel-laden FPTFS was regenerated by 0.1 M HCl and four adsorption/desorption cycles were performed. The results indicated that FPTFS exhibited considerable potential for application in the removal of Ni(II) ions from aqueous solutions.