Removal of heavy metals from aqueous solutions using cocoa pod husk

Abstract

In this study, the potential use of Cocoa Pod Husk (CPH) as biosorbent for the removal of Zn(II) and Cr(VI) was investigated. The surface morphology of CPH was investigated using Scanning Electron Microscopy (SEM) and Fourier Transform Infra Red Spectroscopy (FTIR). The results shown CPH undergo some changes in structure, and functional groups before adsorption and after adsorption indicated adsorption process took place. The effects of adsorption time, adsorbent dosage, particle size and initial heavy metals concentration on CPH adsorption for Zn(II) and Cr(VI) were investigated during adsorption study. The results show that the amount of heavy metals adsorbed on CPH increased with initial heavy metals concentration, adsorbent dosage and adsorption time. For Zn(II) and Cr(VI), the adsorption rate is optimal at adsorbent size 150μm, adsorption period as long as 180 minutes, adsorbent dosage of 0.5g and 600mg/L initial heavy metals concentration. Langmuir and Freundlich adsorption models were used to evaluate the isotherm constant. The equilibrium data for all heavy metals fitted well with Langmuir Isotherm equation giving maximum capacity of adsorption at 111.11mg/g and 90.91 mg.g for Zn(II) and Cr(VI) respectively. The modelling of kinetics of heavy metals adsorption onto CPH was investigated using Pseudo First Order model and Pseudo Second Order model. Zn(II) and Cr(VI) fitted well with Pseudo Second Order.