Biosorption of Pb<sup>2+</sup> and Cr<sup>2+</sup> Using <i>Moringa Oleifera</i> and Their Adsorption Isotherms

Abstract

In the last three decades attention has been paid on environmental management caused by toxic materials such as heavy metals whose levels have risen due to increased anthropogenic activities. Conventional methods for waste treatment are numerous, some of which are expensive and sometimes inefficient. A search for cheaper and environmentally friendly method of treatment using natural products has taken a central stage in the recent past. Moringa oleifera seed powder was investigated with a view of using it as a low cost biosorbent for the removal of toxic heavy metals from wastewater. Fourier transform Infrared (FT-IR) analysis was done for characterization of Moringa oleifera seeds powder. Batch biosorption experiments of Pb2+ and Cr2+ with respect to contact time, pH, particle size, adsorbent dosage, effect of pretreatment and adsorption isotherms were studied. FT-IR showed the presence of –NH, -OH, -COOH functional groups in the biomass. The maximum biosorption capacity was observed at pH 5 for both metals, with the particle size of adsorbent of 0.250 mm and high adsorbent dosage of 0.6 g. The order of modification for Pb2+ was CaCl2 > NaOH > KMnO4 > HCl, while that of Cr2+ was KMnO4 > CaCl2 > HCl > NaOH. Although the data fitted into both the Langmuir and Freundlich adsorption isotherms high correlation coefficients of about 1.00, the Langmuir gave better results than the Freundlich. The results suggest that Moringa oleifera seeds have potential application in Pb2+ and Cr2+ decontamination from aqueous effluents and that pretreatment further enhances biosorption.