Mechanism of lead adsorption from aqueous solutions using an adsorbent synthesized from natural condensed tannin

Adsorption is a method for removing lead from wastewater. The adsorption of lead on a new adsorbent synthesized from natural condensed tannin has been investigated using a series of batch adsorption experiments. The study on the adsorption mechanism indicates that the adsorbent performed in aqueous solutions as an ionic exchanger whose end group was sodium ion (Na⁺). One lead (II) ion (Pb²⁺) was adsorbed onto the adsorbent by taking the place of two Na⁺ ions. The maximum exchangeable Na⁺ present on the adsorbent was measured with the proton titration experiments and it was up to 1.0mmolNa⁺g^-1 dry adsorbent. To a significant extent, pH influenced the extraction of lead from aqueous solutions. The lead removal efficiency was up to 71%, 87% and 91% with initial solution pH at 3.0, 3.6 and 4.2, respectively. The Langmuir equation fitted the adsorption isotherm data well. The maximum adsorption capacity of lead calculated was 57.5, 76.9 and 114.9mgleadg^-1 dry adsorbent at initial solution pH of 3.0, 3.6 and 4.2, respectively. Therefore, the adsorbent does offer favorable characteristics in lead removal from acidic wastewater.