Abstract
The use of nuclear energy is accompanied by the generation of radioactive waste, so the construction of radioactive disposal repository is necessary. In the backfilling process, the principal component of engineering barrier material is〝Bentonite〞. Because of it’s excellent sorption capabilities for cationic radionuclides and high-swelling property against the water to penetrate through the clay, it has been widely used in many countries. Among the nuclides of radioactive wastes that might migrate to living environment, Cesium ( Cs ) has the longest half-life for about 30 years. It may cause the most far-reaching effect on the biosphere. The migration of Cs+ should be supervised and controlled strictly. To evaluate and supervise the radioactive disposal sites in the near future, it will require more reports on this kind of research.In this study, in order to investigate the effect of alkylammonium salt of organic substances to the Cs+ adsorptive behavior, the adsorption experiments were performed with MX-80 clay treated with primary/ quaternary alkylammonium salt in amounts equivalent to cation exchange capacity (CEC). Firstly, the analytical methods of XRD、FTIR and BET were used for determining the structure and the surface properties of the clay, and the potentiometric titration experiment can establish the necessary parameters for the subsequent simulation. From the result of the adsorption experiment, the preliminary understanding of the Cesium ion adsorption behavior is obtained. This result pointed out that Na-MX80 had better Cs+ adsorption behavior than that of untreated MX80, especially in the acidic environment. Secondly, on the part of the modified clay, the clay modified by the primary alkylammonium salts had better adsorption effect than that by the quaternary alkylammonium salts. Particularly, the modified clays with number 16 carbon chain length of the ammonium salt showed poor adsorption result than that of the untreated MX80.Finally, the parameters established from the previous experiment results were linked up with MINEQL+ program and combined with double-layer model to simulate the adsorption of cesium ions on the clay surface. By observing the surface adsorption dissociation constants of different adsorption sites, we can discuss the adsorption behavior further.According to the results of modeling, the contribution of edge adsorption sites of the clays modified by the primary alkylammonium salts would increase with the carbon number of carbon chain, while the contribution of structural adsorption site decreased with the carbon number, especially decreasing most in 16-C; the contribution of edge adsorption sites of clays modified by quaternary alkylammonium salts slightly decreased with the carbon number of carbon chain. However, the contribution of structural sites remained in a low level, while there is a remarkable increase in 12-C.Furthermore, the measuring experiment of solid suspension( S.S.) exhibited that quaternary alkylammonium salts modified clay showed better effect than primary alkylammonium salts modified clay on reducing the solid suspension.