Adsorption of heavy metals (lead and chromium) by Calliandra surinamensis chaff

Adsorption is one of the most effective ways of removing heavy metals such as Cu, Zn, Pb etc from media. This research work investigated the adsorption efficiency of Calliandra surinamensis pod chaff (Powder Puff flower) for the removal of heavy metals from their aqueous solutions using its chaff as the absorbent. C. surinamensis chaff was activated using ZnCl2 solution in water. The activated carbon obtained was characterized in terms of functional groups present in the carbon using FTIR which gave the infrared spectra of the activated carbon of the sample material. The impact of varying adsorption parameters such as pH of the solution, adsorbent dosage, particle size of the adsorbent and contact time on the amounts of lead and chromium removed from their solutions were evaluated to determine the maximum amounts of the metals adsorbed by changing the initial concentrations of the metals from 10 to 50 mg/l in solution. Analysis of variance was also done to determine the effects of varying process variables on the amounts of metals adsorbed. Increase in the process variables considered, pH, adsorbent dosage, particle size and contact time led to a corresponding increase in the amounts of lead and chromium adsorbed according to the order 10<20<30<40<50 mg/l. However, chromium was more adsorbed than lead as pH, adsorbent dosage and contact time increased while lead was more adsorbed with increasing particle size. Analysis of variance showed a p-value > 0.05 for pH and >0.10 for contact time showed that the variation in pH and contact time were not significant on the amounts of lead adsorbed by the adsorbent. While the p-value <0.005 for pH and adsorbent dosage and <0.05 for particle size showed that variations in adsorbent dosage and particle size are significant on the amounts of lead adsorbed. Also, for chromium, a p-value of 0.0145, 0.0001 and 0.0034 for pH, adsorbent dosage and particle size respectively showed that variations in pH, adsorbent dosage and particle size were significant on the amounts of chromium adsorbed by the adsorbent, while a p-value of 0.1679 for contact time showed that variation in contact time has no significant effect on the amount of chromium adsorbed by the adsorbent. In conclusion, C. surinamensis activated carbon is a promising and environmental friendly adsorbent for the treatment of aqueous solutions laden with heavy metals of lead and chromium.