Removal of Cd, Cr, and Pb from aqueous solution by unmodified and modified agricultural wastes

The adsorption of cadmium (Cd), chromium (Cr), and lead (Pb), widely detected in wastewater, by unmodified and modified banana stalks, corn cob, and sunflower achene was explored. The three agricultural wastes were chemically modified with sodium hydroxide (NaOH), in combination with nitric acid (HNO3) and sulfuric acid (H2SO4), in order to improve their adsorptive binding capacity. The experiments were conducted as a function of contact time and initial metal ion concentrations. Of the three waste materials, corn cob had the highest adsorptive capacity for Pb than Cr and Cd. The NaOH-modified substrates had higher adsorptive capacity than the acid modified samples. The chemical treatment invariably increased the adsorption capacity between 10 and 100 %. The Langmuir maximum sorption capacity (qm) of Pb was highest (21–60 mg g−1 of banana, 30–57 mg g−1 of corn cob, and 23–28 mg g−1 of sunflower achene) and that of Cd was least (4–7 mg g−1 of banana, 14–20 mg g−1 of corn cob, and 11–16 mg g−1 of sunflower achene). The qm was in the order of Pb > Cr > Cd for all the three adsorbents. The results demonstrate that the agricultural waste materials used in this study could be used to remediate water polluted with heavy metals.