Interactions of Pb(II), Cd(II) and Cr(VI) with Neem (Azadirachta indica) leaf powder: kinetics and thermodynamics

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Neem leaf powder (NLP) is made from the leaves of the Neem tree (Azadirachta indica) for removing Pb(II), Cd(II) and Cr(VI) from water. The powder (surface area 21.45 m²/g), was used at pH ∼7.0 and pseudo first and second orders, Elovich equation, intra-particle and liquid film diffusion models were used to test the kinetics. The interactions mostly followed a second-order model involving transfer of the cations from the surrounding liquid film to the surface of the adsorbent particles. The interactions were exothermic and spontaneous. Enthalpy, entropy and Gibbs energy changes show a high potential of NLP as a biosorbent for metal ions.