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 Pb 2+ /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.

Removal, Recovery and Recycle of Gold (III) from Aqueous Solution Using Persimmon Tannin Gel

In order to recover much amount of gold, gold removal-recovery cycle was examined using immobilized persimmon gel, which could remove much amount of gold (III) from the tetrachloroaurate solution at 30°C. Removal of gold has proceeded different 2 mechanisms stages. At first, gold (III) was adsorbed rapidly on the surface of the persimmon gels until 2 hours and reached adsorption equilibrium. After that, the amount of gold removed was re-increased slowly and also reached equilibrium until 48 hours. The amount of gold removed was affected by the pH of the solution. The amount of Au removed was the highest at pH 5, which was decreased with decreasing or increasing the pH of the solution. The amount of gold removed (mol/g-dry wt. gels) was increased with increasing the gold concentration in the solution, whereas gold removed ratio was decreased. Gold removed ratio was increased with increasing the amount of persimmon gel used, whereas the amount of removed Au (mol/g-dry wt. gels) was decreased. Gold removal-recovery cycles were also examined in detail.