Biosorptive behaviour of Mango ( Mangifera indica) and Neem ( Azadirachta indica) bark for Hg 2+, Cr 3+ and Cd 2+ toxic ions from aqueous solutions: a radiotracer study

Abstract

Biosorption of Hg 2+ and Cr 3+ on dead biomass Mango ( Mangifera indica) and Neem ( Azadirachta indica) bark has been assessed at micro to tracer level concentrations from aqueous solutions employing the `radiotracer technique'. A high level of uptake of metal ions on these solid surfaces occurs within ca. 4 h of contact time reaching apparent saturation. The increase of sorptive concentration (10 −8 to 10 −2 mol dm −3), temperature (293–323 K) and pH (ca. 3 to 10) favoured the removal process of these ions; but in the case of Hg 2+ on Neem bark, there was seemingly no temperature effect. The uptake process follows first order rate law and obeys the Freundlich adsorption isotherm. Added anions and cations in the bulk solution inhibit to some extent the removal of these toxic ions. Similarly the inhibition in the uptake was also observed when both biomasses were irradiated by neutron and γ-rays prior to being employed as sorbents. No significant sorption of Cd 2+ was observed on these dead biomass solid surfaces under various physical–chemical conditions.