动力堆模拟高放废液的甲醛脱硝及脱硝过程中的沉淀行为

Formaldehyde Denitration and Precipitation Behavior During Denitration of Power Reactor Simulated High-Level Liquid Waste

两步法玻璃固化工艺中,高放废液可通过化学脱硝达到降低酸度的目的,常用的化学脱硝剂有甲酸、甲醛、蔗糖等。以甲醛为化学脱硝剂,对动力堆模拟高放废液进行脱硝及脱硝过程中沉淀行为进行研究。模拟高放废液在90℃、脱硝比例为1.0~2.0范围内进行脱硝,对脱硝后各物质运用电感耦合等离子发射光谱(ICP-OES)、X射线荧光光谱(XRF)、扫描电镜-能谱分析(SEM-EDS)、Raman光谱、X射线衍射(XRD)、热重分析仪(TG)进行分析。结果表明:脱硝后废液中NO_(3)^(-)含量明显降低,随脱硝比例增大,NO_(3)^(-)的含量逐渐降低,甲醛含量增加。脱硝过程中出现由Zr、Mo、La、Ce、Nd、Fe、Te、Pr、Cs、Sm、Cr、Sr、Y、Co、Ni组成的沉淀,沉淀的形成有两个过程:一个过程为形成颗粒状的结晶物Ln_(2)Zr_(3)(MoO_(4))_(9)(Ln=La、Ce、Nd、Pr、Eu、Sm)和MoO_(2);另外一个过程为形成由O、Fe、Zr、Mo、Te构成的无定形粉末物质;脱硝产物的热分解主要发生在约360℃以下。

In the two-step vitrification process, the high-level liquid waste can be reduce acidity by chemical denitration, and the commonly used chemical denitration agents are formic acid, formaldehyde, sucrose, etc. In this paper, the denitration of simulated high-level liquid waste and the precipitation behavior in the denitration process was studied with formaldehyde as the chemical denitration agent. The simulated high-level liquid waste was denitrated at 90 ℃ with denitration ratio in the range of 1.0 to 2.0. After denitration, each substance was analyzed by ICP-OES, XRF, SEM-EDS, Raman, XRD and TG. The results show that the content of nitrate in the waste stream after denitration is significantly reduced, and the content of nitrate gradually decreases and the content of formaldehyde increases with the increase of denitration ratio. The precipitation consisting of Zr, Mo, La, Ce, Nd, Fe, Te, Pr, Cs, Sm, Cr, Sr, Y, Co, Ni appeares in the denitration process. The precipitation is formed by two processes, one process is the formation of granular crystals Ln_(2)Zr_(3)(MoO_(4))_(9)(Ln=La, Ce, Nd, Pr, Eu, Sm) and MoO_(2);the other process is the formation of an amorphous powder substance consisting of O, Fe, Zr, Mo, and Te. The thermal decomposition of denitration products mainly occurs below about 360 ℃.