Molecular Simulation Of Uranyl Adsorption On（001）surfaces Of Na-montmorillonite

With the rapid development of nuclear technology and industry inthe world， how to safely dispose the large amount of waste that isproduced by the nuclear industry has been paid close attention. Uraniumis the central element in the nuclear fuel cycle，as fuel of nuclear reactorsand as major component of the final waste. It is highly mobile and readilycomplexates with organic and inorganic matter. Therefore，uranium andits decay products are hazardous pollutants of the environment. The deepgeological disposal is now regarded as the most effective way and widelyaccepted for the safe high level radioactive waste disposal in the wold.Bentonite has excellent properties such as retardant nuclides frommigration and low permeability and so on，and also is widely distributedin natural environment，so it is usually chosen as the buffer and backfill material in the deep geological disposal of high level radioactive waste.Here we use molecular simulation technique， apply molecularmechanics，Monte Carlo method and molecular dynamics simulation，main focus on the behavior of uranium absorption on（001）surface ofNa-montmorillonite surfaces of interlayers with different water layers.The major content is as follows：（1）We apply Materials Studio molecular simulation software tobuild model of Na-montmorillonite， optimize its four types usingmolecular mechanics， compare the changes then find as more waterlayers are forced into the system，the layer spacing，volume and betaangle of Na-montmorillonite all increase，but its density decreases. Theincreasing layer spacing well prove the swelling nature.（2）We use Monte Carlo method to calculate adsorption amount，adsorption energy and isosteric heats of uranyl ions adsorption on（001）surface of Na-montmorillonite at300K and100k Pa， uranyl ionsadsorption tendency is find to crease obviously as the water layers isincreased. Adsorbed uranyl ions gather above Na-montmorillonite TOTand around water molecules， further more around water molecules.Isosteric heats dates show that Na-montmorillonite has great property ofadsorbing uranyl ions in both physical and chemical adsorption.（3）We use molecular dynamics simulation to study the absorptionbehavior characteristics of uranyl ions adsorption on（001）surface of Na-montmorillonite，then find the sorption ability of Na-montmorillonitefor uranyl ions decreases as the water layers is increased. The adsorptionmechanism of uranyl and sodium ions adsorption are both ion exchange.On（001）surface of Na-montmorillonite，both uranyl and sodium ions arehydrated with two shells. Besides from the equilibration snapshot wediscover sodium and uranyl ions both equally lie on each side ofNa-montmorillonite，it indicate montmorillonite can make its two sidecharge balance.（4）The adsorption ability of Na-montmorillonite whose interlayerwith one，two and three water layers，to uranyl ion，sodium ion and watermolecule weaken as in order. Usually，Na-montmorillonite of interlayerwith two water layers has strong adsorption ability while comparing withNa-montmorillonite of interlayer with one or three water layers.