Evaluation of metal oxides and activated carbon for lead removal: Kinetics, isotherms, column tests, and the role of co-existing ions.

Activated carbon (AC) is commonly used in faucet and pitcher filters for lead (Pb(II)) removal in homes. This study evaluated the Pb(II) removal performance of AC and metal oxides (e.g. Fe(OH)3 and TiO2), as well as the co-existing ions' effect on Pb(II) removal. Results showed that metal oxides had higher adsorption capacity (28.9-51.5 mg/g) than AC (21.2 mg/g). Pb(II) was inner-spherically adsorbed onto both AC and metal oxides surfaces. Among various metal ions, calcium (Ca(II)) demonstrated dramatic effects on Pb(II) removal ability of AC, while it had no effect on Pb(II) adsorption by metal oxides. This difference resulted from the inner- and outer-sphere adsorption of Ca(II) on AC and metal oxides, respectively. The presence of orthophosphate (orth-P) and sulfate enhanced Pb(II) removal by those three adsorbents, whereas carbonate and silicate had negligible effect on Pb(II) adsorption. Interestingly, while the orth-P was usually used as corrosion inhibitor because of the formation of lead-phosphate coprecipitate, we found that the enhanced effect of orth-P on Pb(II) removal was mainly due to the synergistic adsorption. This study provides valuable information for the selection of effective adsorbents for Pb(II) removal and is helpful for understanding the roles of co-existing ions on it.