The use of chitosan-grafted cocoa husk char (CCH) and unmodified cocoa husk char (CH) as adsorbents for the removal of Cr6+ and Pb2+ were studied. The adsorption efficiencies were compared with that of the commercial activated carbon (GAC F-300). Energy Dispersive X-ray spectroscopy (EDS) was used to determine the elemental compositions of the adsorbents while Scanning Electron Microscope (SEM) was used for the surface texture and morphological characteristics of the cocoa husk. The study optimised metal ion concentration, adsorbent dosage, agitation time and adsorbent particle size for the removal of the metals from simulated wastewater using Atomic Absorption spectroscopy (AAS) and removal efficiencies were calculated. Langmuir and Freundlich models were employed to study the adsorption pattern. The equilibrium experimental data results of Pb2+ fitted well to Langmuir and Freundlich the two adsorption isotherms. The coefficient of correlation (R2) for both models falls within 0<R2<1. The experimental data obtained from the sorption of Cr6+ by the adsorbents, except CH, fitted Langmuir model than Freundlich model. The Langmuir isotherm fits the experimental data than Freundlich isotherm for Cr6+ sorption by the CCH modified cocoa husk and the activated carbon except the unmodified cocoa husk. The study concluded that cocoa husk, an agricultural waste material, have potential as an adsorbent to remove toxic heavy metal like chromium and lead from industrial waste water. Modification of this waste with chitosan also enhances its performance in the removal of the metals.
Key words: Adsorption, cocoa husk, chitosan, heavy metal, atomic absorption spectroscopy, isotherm.