Effect of Denitration with Sucrose on Property and Structure of Calcinate of Simulated PWR High-level Liquid Waste

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 highlevel 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. Xray 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. Xray 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 (FTIR) and Xray 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.