Adsorption of Heavy Metals from Wastewaters Using Adonosia digitata Fruit Shells and Theobroma cacao Pods as Adsorbents: A Comparative Study

Abstract

In this study, adsorption of heavy metal ions using activated carbon from Adonsonia digitata fruit shells and Theobroma cacao pods was carried out to comparatively evaluate their effectiveness as adsorbents for the purpose of removing Pb2+ and Cd2+ from synthetic wastewaters. Adosonia digitata fruit shells (ADFS) were collected within Yola and its environs, Adamawa State, Nigeria, whereas Theobroma cacao pods (TCP) were collected from the divisional office of the Cocoa Research Institute of Nigeria (CRIN) in Ikom, Cross River State, Nigeria. Both samples were crushed resulting in particle sizes of about 300-450 µm and the physicochemical as well as the adsorption properties of the activated carbon produced from both adsorbents were studied. Effects of some process parameters have been investigated in this study as well by following a batch adsorption technique at 32 ± 2oC. The percentage removal of Pb2+ and Cd2+ was found to increase with the decrease of the initial concentration of metal ions and to increase with the increase of the contact time and the adsorbent dose. The monolayer adsorption capacity, Qo for Pb(II) was found to be 41.20 mg/g and 29.89 mg/g for ADFS and TCP, respectively, whereas the monolayer adsorption capacity Qo for Cd(II) was found to be 34.39 mg/g and 25.10 mg/g for ADFS and TCP, respectively. In conclusion, it was observed that activated ADFS had a higher monolayer adsorption capacity for Pb2+ and Cd2+ than activated TCP.