Sorption of zinc and lead on coir

Pilot tests have shown that coir (fibres from Coco nucifera) is suitable as a metal ion sorbent. Batch sorption experiments were carried out with Zn and Pb to quantify the sorption kinetics, the pH dependence of the sorption, sorption isotherms at pH 3.0 and pH 5.6, and desorption. Unground and unmodified coir was used and the metal concentrations ranged between 0 and 0.015 mM (1000 μg/l) for Zn and 0 and 9.7 × 10 ^-4 mM (200 μg/l) for Pb. The pH maximum was 4.5 (91%) for Zn and 2.5 (97%) for Pb. Pb had a higher sorption affinity than Zn, and the affinity was higher at pH 5.6 than at pH 3.0. The isotherms could be represented by the Freundlich, but not by the Langmuir models in the concentration range tested. Desorption experiments demonstrated that less than 1% and 13% of the sorbed Pb and Zn, respectively, could be desorbed at pH 5.6 during 2 h.