Studies On The Sorption Behaviors Of Strontium And Cesium Onto Sandy Soil

It is important to study the sorption behaviors of strontium and cesium onto the surface soil of a nuclear waste disposal repository for the performance and safety estimation of the repository. In this thesis, the sandy soil, collected from the earth surface of a pre-selected site for nuclear waste disposal, was pretreated and characterized, and its physical and chemical properties were also measured. The effects of solid-to-liquid ratio, initial sorbent concentration, pH of the solution, ionic strength, HA and temperature on the sorption behaviors of strontium and cesium onto sandy soil were investigated using a batch method in detail. The sorption isotherms of strontium and cesium were simulated by Langmuir, Freundlich, L-F and D-R models. The following results and conclusions were obtained:1. The sorption percentage of strontium onto sandy soil increased with solid-to-liquid ratio, but decreased with initial strontium concentration increasing. The distribution coefficient of strontium decreased with solid-to-liquid ratio and initial strontium concentration increasing. The sorption of strontium increased with pH values increasing, and was hardly independent of ionic strength. The dominant sorption mechanism of strontium might be surface complcxation.2. The sorption percentage of cesium onto sandy soil increased with solid-to-liquid ratio, but decreased with initial cesium concentration. The distribution coefficient of cesium increased with solid-to-liquid ratio, but decreased with initial cesium concentration. The sorption of cesium was independent of pH below pH～7, increased greatly in the pH range of 7-8, and maintained high level above pH～8. The sorption of cesium decreased with ionic strength increasing, and the competing ability of cations followed an order K+>Mg2+>Na+>Ca2+. The sorption of cesium might be mainly dominanted by ion-exchange.3. The sorption ability of the sandy soil for cesium was stronger than for strontium. The sorption of strontium and cesium onto sandy soil was an exothermic and spontaneous process. The sorption behaviors of strontium and cesium were both interpreted in terms of Freundlich isotherm model, and the sorption behavior of strontium was also simulated by L-F and D-R isotherm models very well.