Efficient Concentration of PB From Water by Reactions With Layered Alkali Silicates, Magadiite and Octosilicate
Donhatai Sruamsiri, Thipwipa Sirinakorn, Makoto Ogawa
Abstract
Abstract Human health problems are often related to contamination of the aqueous environment by toxic metal ions. In the present study, two layered alkali silicates (magadiite and octosilicate) were examined to assess removal of Pb 2+ from aqueous solutions in terms of quantity and kinetics. The ion-exchange reaction between the silicates and aqueous solutions of lead(II) acetate at various concentrations was examined at room temperature for 24 h. The adsorption isotherms were H-type, showing the strong interactions between Pb 2+ and the silicates. The amounts of Pb 2+ adsorbed were as much as 1.23 mmol Pb/g magadiite and 2.32 mmol Pb/g octosilicate, which are larger than the reported values for various ion exchangers. They were larger than the theoretical cation exchange capacities (2.2 and 3.7 meq/g for magadiite and octosilicate, respectively), suggesting that the collection of Pb 2+ included the precipitation as basic lead salts in addition to the ion exchange. The adsorption isotherms for magadiite and octosilicate fitted the Langmuir equation with correlation coefficients, R 2 , of 0.9991 and 0.9972, respectively. The adsorption of Pb 2+ onto the layered alkali silicates from acidic aqueous solution was examined to obtain smaller amounts of adsorbed Pb 2+ (0.32 mmol Pb/g magadiite and 0.34 mmol Pb/g octosilicate), confirming the important role of pH on the surface charge of the layered silicates in terms of ion exchange. The adsorption of Pb 2+ reached equilibrium within 5 min for magadiite while it took 60 min for octosilicate. The difference was in the particle morphology; smoother diffusion of Pb 2+ was possible through flower-shaped aggregates of particles of magadiite.