CTAB modification bentonite for enhanced Re adsorption and diffusion suppression

Abstract

Abstract 99Tc is a crucial high-yield fission product, characterized by its radiotoxicity, extended half-life, high solubility, and significant mobility in the environment. On the other hand, Re is employed as a substitute for Tc due to its analogous properties and non-radioactive nature. Bentonite is commonly used as a backfill material in repositories for high-level radioactive waste storage; however, it exhibits minimal adsorption capacity for Re(Tc). This study aims to enhance the adsorption capability of bentonite for Re(Tc) through modification with Cetyltrimethylammonium Bromide (CTAB). Modified bentonite exhibits excellent adsorption performance under various conditions, primarily driven by the interaction between the ReO4 − anion and the pyridinium ring of the CTA+. Its primary adsorption mechanism involves a chemical precipitation reaction between ReO4 − and CTA+. The adsorption capacity is approximately 30 times that of unmodified bentonite, and the adsorption process is characterized by spontaneous low-temperature chemical monolayer adsorption. Experimental results of the modification indicate that high-temperature and alkaline modification conditions contribute to enhanced adsorption capacity, with an optimal modification time of approximately 30 h and a maximum modifier addition of 250 % of the bentonite’s cation exchange capacity (CEC). Additionally, the incorporation of modified bentonite into natural bentonite significantly inhibits the diffusion behavior of ReO4 −. These findings highlight the substantial improvement in the adsorption capacity of bentonite for Re(Tc) through batch modification, leading to reduced mobility of ReO4 − within backfill materials.