Adsorption of copper ions onto acid-modified Aframomum africanum shell: Isotherm and kinetic studies

Abstract

In this work, copper ions have been successfully removed from aqueous solution using the acid-modified Aframomum africanum shell (MAAS) as an adsorbent. The adsorbent was characterized using Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM). The aframomum africanum shells were also characterized before and after being modified with the acid to determine their pH at the point of zero charge (pHpzc). The MAAS was found to have the pHpzc of 4.77. In batch experiments, the adsorption capacity of MAAS was investigated as a function of pH of solution, adsorbent dosage, contact time, initial copper ion concentration and agitation speed. The results revealed that at pH solution of 9, adsorbent dosage of 5 g/L, contact time of 30 min, initial Cu(II) ion concentration of 50 mg/L and at an agitation speed of 250 rpm, the maximum Cu(II) ion adsorption capacity of MAAS was 31.25 mg/g. The adsorption kinetic data and the isotherm data were also studied to find the suitable models of Cu(II) removal. The kinetic data and the isotherm data of Cu(II) removal by MAAS was found to follow the pseudo-second order kinetics model (R² = 0.999) and the Langmuir isotherm model (R² = 0.990), respectively. Therefore, the outcome suggested that the shells of Aframomum africanum can be utilized as an economical and efficient adsorbent to eliminate Cu(II) from aqueous solution.