Precipitation behaviour of simulated high-level liquid waste during the denitration process based on two-step vitrification

Abstract

In the two-step vitrification process, it is necessary to first reduce the acidity of the waste before calcination. In this study, the influence of formic acid as a denitration agent on the precipitation behavior of a simulated high-level liquid waste during denitration was investigated. The denitration process was conducted at a temperature of 90℃, and the denitration ratio ranged from 1.0 to 2.0. The denitration products were analyzed using various techniques including ICP-OES, XRF, SEM-EDS, Raman, and XRD. The results revealed a significant decrease in nitrate content after denitration when the denitration ratio was between 1.0 and 2.0. As the denitration ratio increased, the nitrate content progressively decreased, while the formic acid content increased. A denitration precipitate containing elements such as Zr, Mo, La, Ce, Nd, Fe, Te, Pr, Cs, Sm, Sr, Y, Co, and Ni was observed. The content of each component and the morphology of the precipitate were found to be correlated with the denitration ratio. Crystallization of MoO2 and Ln2Zr3(MoO4)9 (Ln = La, Ce, Nd, Pr, Sm) in the precipitation occurred when the denitration ratio was between 1.0 and 1.2. On the other hand, predominantly rod-shaped particles (Ln(HCOO)3, Ln = La, Ce, Pr, Nd, Sm) were formed when the denitration ratio was 1.4 or higher.