pH dependence of sorption of Cd²⁺, Zn²⁺, Cu²⁺ and Cr³⁺ on crude water and sodium chloride extracts of <i>Moringa stenopetala</i> and <i>Moringa oleifera,/i>

Abstract

The ability of crude water and sodium chloride extracts of partially defatted powder of Moringa stenopetala (MS) and Moringa oleifera (MO) to remove heavy metals (Cd2+, Zn2+, Cu2+ and Cr3+) from
single ion solution was investigated. At initial metal concentration of about 4 ppm, the extracts showed complete sorption for Cd2+, Zn2+ and Cr3+ ions at pH above 7.8, 4.0 and 4.0, respectively, at a dose of 1.0 ml of sorbent in 9.50 ml of metal solution. Cu2+ sorption increases slightly with pH to about 60% for MS at pH 6 and then becomes constant up to pH 8 when sorption rises to completion. Preliminary
characterization of the actual powder by proton nuclear magnetic resonance showed clear presence of amide (-CO-N-H), benzenoid (Ar-H), saturated alkyl and unsaturated fragments in both MS and MO. The mass spectrum showed the presence of amino (R-NH2) fragments. The remarkable heavy metal sorption ability of M. stenopetala and M. oleifera could thus be attributable to, among other mechanisms,
coordination or complex formation between the metal cations and pH dependent oxygen and nitrogen anionic sites of the Moringa proteins.