| The safety and reasonable treatment of radio-waste is a key faetor for the Chinese nuelear power program. It is very important to study the adsorption activity of radioactive nuclides on buffer/backfill materials. In this paper, the purified GMZ bentonite was selected as the experimental material and Nd(Ⅲ) 、Ce(Ⅳ) 、Sr(Ⅱ) were adsorption object for simulation nuclide. The structure and basic properties of the GMZ bentonite was characterized in detail by advanced analytical techniques. Adopted static batch type adsorption and single factor experiment method focused on the various influence factors such as solid-liquid ratio, p H, initial concentration, ionic strength and temperature on the adsorption performance of simulation nuclide on GMZ bentonite; Discussed kinetic and thermodynamic analys at different time and temperature,respectively. The main purpose of this paper was to study the adsorption mechanism of simulation nuclide on bentonite and to evaluate the possible application of bentonite as a backfill material in nuclear waste repository in real work. According to the experimental results, the conclusions were got as follows:(1) Prepared the purified bentonite, characterized these samples using SEM,XRD, etc, investigated the chemical compositions, mineral structures and surface morphology of the samples.(2) Researched adsorption of radionuclides on bentonite samples as a function of bentonite dosage. The removal percentage of radionuclides increased with an increasing amount of bentonite dosage in the suspension. However, the distribution coefficient decreases with increasing clay dosage.(3) Investigated adsorption of radionuclides on bentonite as a function of p H and ionic strength. The results showed that ion exchange or outer-sphere surface complexation may be the main adsorption mechanism of Nd( Ⅲ)on bentonite at p H<6, whereas inner-sphere surface complexation may be the main adsorption mechanism at p H>6. The adsorption of Ce(Ⅳ) is strongly depended on the p H,which means surface complexation may be the main adsorption mechanism of Ce( Ⅳ) on bentonite. The adsorption of Sr( Ⅱ) is strongly depended on the p H and ionic strength. Ion exchange or outer-sphere surface complexation contributes mainly to Nd(Ⅲ) sorption on bentonite.(4) Researched adsorption of radionuclides on bentonite samples as a function of contact time. The adsorption was quickly to achieve the adsorption equilibration, and the time to achieve the adsorption equilibrium was about 1~4 hours; The adsorption of radionuclides on bentonite was fastest to achieve equilibrium and its adsorption capacity was the largest. The kinetic adsorption of radionuclides on bentonite samples could be described well by a pseudo-second-order model.(5) Studied adsorption of radionuclides on bentonite as a function of temperature and calculated thermodynamic parameters(Δ H°, Δ S° and ΔG °). The adsorption of Nd( Ⅲ) on bentonite was an endothermic and spontaneous process, and an exothermic process for the adsorption of Ce( Ⅳ)on bentonite, an endothermic and spontaneous process for the adsorption of Sr( Ⅱ) on bentonite. The adsorption isotherms of radionuclides could be described by Langmuir models. This phenomenon indicates that there is no interaction between the sorbate molecules and the adsorption is localized in a monolayer. |
PDF Full Text Request