Interaction and stabilization of organic radioactive waste in geopolymer

2023 Fiscal Year Annual Research Report

• Project/Area Number: 21K04207
• Research Institution: Hokkaido University
• Principal Investigator: Y Elakneswaran 北海道大学, 工学研究院, 准教授 (60769090)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: Cement chemistry / Geopolymer / Radioactive waste / Oil

Outline of Annual Research Achievements

In this research, the appropriate control of organic liquids in geopolymers was studied. Initially, an alkali-activated solution (with a molar ratio of K2O:SiO2:H2O of 1:1:13, containing K2SiO3 and KOH) was mixed with a lubricant (FBK Turbine 32, ENEOS) and a cationic surfactant (CTAB) to form an emulsion. Subsequently, metakaolin-based geopolymers were synthesized within the emulsion (with an Al:Si molar ratio of 1:1). The interaction mechanism between the oil emulsion and the geopolymer (with or without surfactant) was evaluated using zeta potential analysis, paste slump flow, scanning electron microscopy (SEM), compressive strength tests, and total organic carbon analysis.
Based on the experimental results, metakaolin-based geopolymers exhibited no capacity to solidify oil independently. However, with the assistance of CTAB, they successfully solidified oil ranging from 10% to 50% content. CTAB altered the surface charge of the oil from negative to positive, facilitating interaction with the oppositely charged surface of the geopolymer. Nonetheless, the compressive strength of the resulting composite decreased with increasing oil content due to heightened porosity. Over time, as hydration products filled the pores, the strength gradually improved. After immersing the geopolymer-oil composite in water for 90 days, the detected level of organic carbon in the water gradually approached the maximum value of 0.2%. This suggests that the surfactant tightly bound the oil within the geopolymer.