Study On The Sorption Of Pb(Ⅱ) And Th(Ⅳ) Onto Gaomiaozi Bentonite

Bentonite is a kind of clay mineral which is abundant in our country.It has unique sandwich structure,which has the good exchangeability and sorption capacity.Bentonite has lots of advantages in the treatment of wastewater,such as simple process,high efficiency and low cost.Because of its special physicochemical properties,it is considered as one of the most promising candidates for use as a buffer material in the geological disposal systems for high-level radioactive waste(HLW).In this thesis,sorption of Pb(â…¡) and Th(â…£) on Gaomiaozi bentonite were studied by batch technique,and the mechanisms were also discussed.The sample of Gaomiaozi bentonite was characterized by using acid-base titration, XRD and FTIR in detail.The sorption behavior of Pb(â…¡) and Th(â…£) from aqueous solution to Gaomiaozi bentonite was investigated as a function of contact time,pH,fulvic acid(FA) and humic acid(HA),solid content,ionic strength,foreign ions and temperature. The results indicated that the sorption of metal ions on bentonite was quickly and several hours were enough to achieve the sorption equilibration.The sorption was strongly dependent on pH and ionic strength.The sorption was mainly dominated by surface complexation at high pH values and by ion exchange at low pH values.HA has strong positive influence on the sorption of Pb(â…¡) and Th(â…£) on bentonite at low pH values.The sorption isotherms were simulated by the Langmuir,Freundlich,and Dubinin-Radushkevich(D-R) models respectively.The sorption isotherms of Pb(â…¡) and Th(â…£) was simulated by Langmuir model very well.The thermodynamic parameters(â–³H~0,â–³S~0 andâ–³G~0) for the sorption of Pb(â…¡) and Th(â…£) on bentonite were determined at different temperatures.The thermodynamic data indicated that the adsorption reaction was exothermic and the process of sorption was favored at high temperature.Sorption mechanism of Pb(â…¡) and Th(â…£) on bentonite was discussed and the results indicated that the sorption of Pb(â…¡) and Th(â…£) on Gaomiaozi bentonite was mainly dominated by surface complexation,and cation exchange also contributed partly to sorption at low pH values.The results suggested that Gaomiaozi bentonite was suitable as a sorbent material for the recovery and sorption of radionuclides and heavy metal ions from aqueous solution.