Removal of lead from aqueous solutions by condensed tannin gel adsorbent

Lead has caused serious environmental pollution due to its toxicity, accumulation in food chains and persistence in nature. In this paper, lead removal from aqueous solutions was investigated using condensed tannin gel adsorbent synthesized from a natural tannin compound. It is found that the adsorption is strongly affected by pH values of aqueous solutions. Within pH range of 3.5-6, when initial lead concentration is 100 mg/L, removal efficiency is more than 90%. Adsorption equilibrium is reached within 150 minutes. The adsorption isotherm fits well with the Langmuir equation, by which the saturated adsorption uptake of 190 mg Pb²⁺ /g dry tannin gel adsorbent is obtained. By means of thermodynamics analysis, it is revealed that the process is exothermic and the adsorption heat is up to 38.4 kJ/mol. With respect to high efficiency, moderate pH requirement and minimized second pollution, the tannin gel adsorbent exhibits a promising potential in the removal of lead from wastewater.