| Sol-Gel technology was applied to synthesize porous silica gel by phase separation and supercritical drying. The structure property of synthesized porous silica gel were characterized by means of TG-DTA, SEM, FT-IR, Press Mercury Analyzer, Gas Adsorption Analyzer and so on. Discontinous process was applied to study the adsoptive property of porous silica gel to cerium ions, while the adsorptive property to uranium was studied using discontinuous process and dynamic adsorption test. High silica glass-ceramic solidification forms wraping the simulating element cerium are synthesized by sintering porous silica gel at lower temperature, which was analyzed by TG-DTA, XRD, SEM, leaching test and so on. Research results are as follows:Porous silica gel could be successfully fabricated by phase separation and supercritical drying. That one fabricated by phase seperation is a kind of light porous material which has the structure of contimous pore and network with high porosity, high skelen density, low apparent density, the pore size distribution of main mesopore and micropore, the basic structure unit of Si-O-Si and surface of a large number of hydroxyl groups and organic groups. Porous silica gel synthesized by phase separation has good thermal stability as the basic structure features are not changed significantly after heat-treatment at high temperature, while porous silica gel prepared by supercritical drying has sponge-like network structure and poor thermal stability. In summary, porous silica gel synthesized by phase separation has better performance than that synthesized by supercritical drying, so that our works were focoused on the adsorption-separation properties and solidification-enbeding properties of porous silica gel fabricated by phase separation in the studing of the separation-solidification of simulative High Radioactive Level of Liquid Waste.Porous silica gel synthesized by phase separation has fine adsorptive capacity to cerium and uranium, while a longer equilibrium adsorptive time to cerium was obtained. The adsorptive properties of porous silica gel to cerium and uranium are affected by sorbents' quantity for a given initial concentration of cerium and uranium. Adsorptive mechanism of cerium and uranium on porous silica gel was more physic adsorption than chemical adsorption, and the main adsorption mechanism are different in different stage of the adsorptive reaction. The adsorptive properties of porous silica gel to uranium are affected by the pH value in solution, which are better in neutral and weak acid solution, while poorer in strong acid solution at pH<5.0. The adsorptive property parameters of porous silica gel to uranium are different when the initial concentration of uranium in solution is changed. The equilibrium adsorptive capacity increase with increasing the initial concentration of uranium in solution, while the equilibrium adsorptive rate and ratios decrease. When the species and states of other ions in solution are different, the adsorptive capacity of porous silica gel are also changed. Trivalent ions have greater influence on the adsorptive capacity of porous silica gel, while divalent and monovalent ions no influence. It keeps to Langmuir equation orderliness and quasi-Second order kinetic equation that porous silica gel adsorbed uranium. Therefore, uranium in the surface of porous silica gel is monolayer adsorption, and adsorption reaction is not a simple surface reaction process but the combination of a variety of reactions, which not only occurs on the surface of porous silica gel but also occurs in the grains. Dynamic adsorptive property are greatly influenced by the flow rate of solution.The dynamic equilibrium adsorptive capacity increases with decreasing the flow rate, while the migration rate of uranium is gradually reduced.High silica glass-ceramic solidification forms immobilizing cerium could be successfully synthesized by sintering in lower temperature not melting at higher temperature. Appearance character, compaction and density of solidification forms relate with the sintering temperature. Solidification forms are conducive to being sintered and the optimum sintering temperature is about 1150℃～1250℃. Cerium in the form of CeO2 crystals uniformly distribute in the high silica glass matrix. The results of leaching test show that high silica glass synthesized by sintering porous silica gel at the lower temperature has a good immobilizing performance. The normalized leaching rate of elements is significantly less than that of the current borosilicate glass solidification forms which have been applied to industry now. |
PDF Full Text Request