Abstract:
Denitration treatment is required before the high-level liquid waste vitrification, conventional denitration agents are formic acid, formaldehyde, sucrose, etc. According to the denitration effect of sucrose, a simulated PWR highlevel liquid waste rotary calcination experiments were conducted to investigate the effects of temperature and ratio of sugar to nitrate on the properties and structure of the calcinate. Xray fluorescence spectrometer (XRF) analysis indicates that temperature and ratio of sugar to nitrate has significant effects on denitration, when temperature ≥500 ℃ and ratio of sugar to nitrate ≥1∶8, N content (mass fraction) is lower than the detection limit, C content is <1.42%. Scanning electron microscope (SEM) images show that sucrose can make the calcinate form a loose foam shape, and then form dense particle agglomerates under high temperature and rotation. Xray diffractometer (XRD) spectrum reveals that when the temperature ≥500 ℃ and ratio of sugar to nitrate ≥1∶8, the degree of crystallization of the calcinate significant increases, and zirconium lanthanum oxide, barium strontium molybdenum oxide and yttrium cerium oxide are formed. Thermogravimetric/derivative thermogravimetric (TG/DTG) curves present that the calcination process is divided into the following three stages: the evaporation of free water and bound water, the decomposition of nitrate and sucrose, and the decomposition and calcination of inorganic salts. Fourier transform infrared spectrometer (FTIR) and Xray photoelectron spectroscopy (XPS) analysis results reveal that the characteristic functional groups of sucrose, such as C—O—C, C—C, C—OH, and NO-3 gradually disappear at high temperature producing metal hydroxide, carbonates as an intermediate product further decomposes into metal oxides. The characteristic functional groups of C—O—C, C—C, C—OH and NO-3 of sucrose gradually disappear at high temperature, and may generate metal hydroxides and carbonates as intermediate products, are further decomposed into metal oxides.