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In order to increase solubility of sulfur in borosilicate glass, SO42- ions in simulated high-level liquid waste (HLLW) with relatively high content of sulfur and sodium were pretreated by adding Ba(NO3)2 solution, and then borosilicate glass waste form was prepared by melt-quenching method. The effects of pretreated HLLW on the structure and leaching resistance were mainly investigated. The results show that the waste loading can be increased to 23% (mass fraction) without phase separation after the Ba(NO3)2 pretreatment. The normalized elemental mass loss of Na, B and Si of the HLLW-loaded samples are one order of magnitude lower than that of the pure borosilicate glass. Furthermore, the leaching resistance of the glass waste form has no significant change with increasing HLLW content. 11B and 29Si MAS NMR analyses indicate that part of BO3 transforms into BO4 structural units and a polymerization of the glass network occurs after HLLW addition. [ABSTRACT FROM AUTHOR]

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In order to supress the formation of yellow phase during vitrification, simulated high-level liquid waste(HLLW) with high content of sulfur and sodium were pretreated by adding Ba(NO3)2 solution, and then borosilicate glass waste forms were prepared by traditional melting method. The effects of pretreatment on the formation of yellow phase and its phase structure and microstructure were mainly investigated. The sulfur content retained in the glass waste forms before and after pretreatment were compared. The results show that SO2-4 ions in the simulated HLLW can be immobilized in BaSO4. The amount of yellow phase during the vitrification process can be markedly reduced by the pretreatment. For the generated yellow phase before pretreatment, the main constituents are Na2SO4 and LiNaSO4 along with a small amount of CaMoO4 and Na2CrMoO4. After pretreatment, the X-ray diffraction peak intensity of LiNaSO4 decreases and BaSO4, BaMoO4, and BaCrO4 phases appear. The sulfur content retained in the glass waste form before pretreatment decreases gradually with increasing temperature. The sulfur content retained in the glass waste form after pretreatment remains almost unchanged in the temperature range of 850-1 050 ℃, and decreases gradually with further increasing temperature. The pretreatment is helpful to improve the sulfur retention especially for the higher sulfate-bearing HLLW.