Study On Mo-containing Borosilicate Glass And Glass-ceramic

The deposition and isolation of the nuclear waste for protecting the ecosystem is anurgent problem to be solved currently.Glass and glass ceramic immobilization has been widely studied in the world for nuclear waste treatment,among which borosilicate glass immobilization is widely used and the only industrial application method.As one of the most abundant fission products in high-level radioactive waste,Mo has a high content in power reactor HIGH-LEVEL radioactive waste,but it has a very low solubility（～1mol%）in borosilicate.This low solubility will lead to glass phase separation,and thus precipitate water-soluble yellow phase,resulting in the reduction of curing effect of the cured body.Based on this,this paper to improve the solubility of Mo in borosilicate glass and chemical stability as the goal,using X-ray diffraction（XRD）,Scanning Electron Microscopy（SEM）,Energy Spectrum Analysis（EDS）,Fourier Transform Infrared Spectroscopy（FTIR）,Raman spectroscopy,Nuclear Magnetic Resonance（NMR）and chemical stability test,studied the different alkali metal and simulation of nuclide composition such as Ce on the solubility of Mo in boron silicate glass,glass crystallization,Influence of glass structure and chemical stability.On this basis,the phase,crystallinity and chemical stability of molybdenum-tungsten-calcium mineral glass ceramics prepared by different formulations and different processes were investigated.The optimum process and formula for preparing molybdenum-tungsten-calcium mineral phase glass ceramics were obtained.It provides the theoretical basis for the industrial production and application of the immobilization of Mo and Ce high-level radioactive waste and obtains the following conclusions.（1）The effect of different alkali metals on Mo solubility in ordinary borosilicate glass was investigated.The experimental results show that the solubility of Mo in borosilicate increases with the decrease of ionic radius of alkali metal,but excessive monovalent alkali metal（Li）with small radius will also cause phase separation of glass,resulting in the requirements of solidified body is not up to standard.Based on the demands on solving the phase separation problem of the solidified body and further improve the solubility of Mo,and then design and explore the substitution of Li₂O Na₂O in high alumina borosilicate glass for Mo solubility experiment.Through this experiment,it is proved that Li₂O replacing Na₂O can increase the solubility of Mo in high alumina borosilicate glass to 5 mol%,and the final preparation of the maximum solubility of Mo in the glass solidified sample is not separated phase.Comparing the two experiments,it is found that Li₂O replacing Na₂O in high alumina borosilicate glass is more favorable for improving the solubility of Mo than that in ordinary borosilicate glass.The normalized leaching rates of Mo and B were about10^-4g·m^-2·d^-1and 10^-3g·m^-2·d^-1,respectively.（2）The influence of simulated Ce on high-alumina and high-molybdenum glass shows that the solubility of Mo in glass increases first and then decreases with the increase of Ce O₂content,and the solubility of Mo and Ce reaches the maximum when the Ce content is 10mol%（Mo>4.5 mol%,Ce>10 mol%）.The solubility of Mo and Ce is much higher than that of ordinary borosilicate glass.The chemical stability test results showed that the 28-day normalized leaching rates of Mo and B were stable at the order of 10^-3g·m^-2·d^-1,while the normalized leaching rates of Ce were basically lower than the detection line,indicating that the cured glass has good curing ability for Mo,Ce and B.（3）In the study of glass ceramics,it was found that the Ce-5.0 sample with the highest crystallization strength of Ca Mo O₄had no hetero phase formation after the initial heat treatment,which was suitable for the preparation of glass ceramics.Through the exploration of different heat treatment processes,it was found that the temperature was increased to 600 ^oC at a heating rate of 5 ^oC/min for 2h,and then continued to rise to 1400 ^oC at a heating rate of 5 ^oC/min for 2h.At last,the glass ceramics prepared by cooling to 680 ^oC at a cooling rate of 5 ^oC/min and holding for4h had no other precipitated phase and reached the maximum crystallinity.The inclusion capacity of Mo and Ce in vitreous ceramics is 4.75 mol%and 5 mol%,respectively.In addition,the normalized leaching rate of heat-treated glass ceramics in deionized water is significantly lower than that of glass samples without heat treatment for the same formula.This shows that the chemical stability of the glass ceramic samples after heat treatment is higher than that of the glass samples prepared by one-step melting method.