ECO-FRIENDLY BIOCHARS FOR THE ADSORPTION OF HEAVY METALS FROM AQUEOUS PHASE

Abstract

Adsorption is a unique and promising method for the removal of heavy metals from aqueous environment using cost-effective and readily available materials. This study examined mono and simultaneous adsorption of cadmium (Cd), mercury (Hg) and lead (Pb) onto biochars produced from groundnut and shea nut shell biomass feed stocks at pyrolysis temperatures of 350 ± 5 ºC and 700 ± 5 ºC. Fifty mg/l of heavy metal ion with 2 g/ 50 ml of adsorbent dosage were leached at constant room temperature of 24 ± 0.5 ºC in laboratory and constant contact time of 72 min. A total of 126 elutes (consisting of 54 mono, 54 binary and 18 ternary samples) were obtained from the batch experiments and conveyed to the Ecological Laboratory of University of Ghana, for the analysis. The removal efficiency of Hg was almost 100%, Cd and Pb were higher than 99.50% and 99.10%, respectively in monocomponent system by groundnut and shea nut shell biochars. The experiment showed that shea nut shell biochars had the strongest affinity for heavy metal ions in the mono aqueous phase. In the binary system of Cd and Hg the removal efficiency were above 99.70% and 100%, respectively. The ternary experiment showed the order of adsorption of Pb2+ > Hg2+ > Cd2+ for Cd, Hg and Pb ions onto groundnut and shea nut shells biochars. The fast pyrolysis temperature and type of biochar showed a slight increase in the adsorption efficiency of metal ions but the increase was not statistically significant (p > 0.05). The study revealed that Langmuir adsorption isotherm was the best fit model for heavy metal ion adsorption onto biochars in the batch experiment. The interactive effects of binary and ternary metal systems onto biochars were either antagonistic or synergistic in nature. Based on these results, it is therefore recommended that further competitive adsorption study on these biochars should be undertaken for accurate estimation of adsorption in natural environments.