GUO Jingfei, ZHOU Ziwei, LIU Like, SHAO Tianqi, WANG Lianghui, CHEN Song
(School of Materials Science and Engineering, Southwest Jiaotong University, Chengdu 610000, Sichuan, China)

Abstract:  In order to avoid the volatilization of Cs during the sintering process at high temperatures, volcanic ash-based geopolymer with target composition close to that of pollucite Cs(AlSi₂O₆) was formulated at 200 ℃ by mild hydrothermal method to immobilize Cs as waste material. The impact of sodium nitrite on structure and immobilization performance of the simulated 137Cs geopolymer solidified body under hydrothermal conditions was studied. The influence of hydrothermal conditions on the existence of sodium nitrite in the geopolymer solidified body was also discussed. It was found NaOH played a key role in the immobilization of Cs, which promoted the formation of pollucite structure under hydrothermal conditions through alkali excitation, thereby reducing the concentration of Cs⁺ in PCT. In addition, the anion leaching concentration measured with ion chromatography (IC) also showed that the sodalite formed during the hydrothermal process had a certain immobilization effect on the ions. However, under the conditions of this study, sodalite was only compatible with (NO₃)^- but not directly compatible with (NO₂)^-. Therefore, the form of hydrothermally synthesized geopolymer was selective for the treatment with salt in sodium-salt waste.

Key words:  hydrothermal; pollucite; volcanic ash; sodium-salt waste; sodium nitrit