Sorption of Tc(IV) in Saline Solutions – II. Sorption on MX-80, Illite, Shale and Limestone in Na-Ca-Cl Solutions

Shinya Nagasaki^1,*, Zhiwei Zheng¹, Jianan Liu¹, Jieci Yang¹, Tammy (Tianxiao) Yang²

¹McMaster University, 1280 Main Street West, Hamilton, ON, L8S 4L7, Canada
²Nuclear Waste Management Organization, 22 St. Clair Ave. East, 4th Floor, Toronto, ON, M4T 2S3, Canada

Received 2024-04-26 ; Revised 2024-05-27 ; Approved 2024-06-11

Abstract

Technetium has been identified as an element of interest for the safety assessment of a deep geological repository for used nuclear fuel. In this study, the sorption of Tc(IV) onto MX-80 bentonite, illite, and shale in ionic strength (I) 0.1 – 6 mol/kgw (m) Na-Ca-Cl solutions at pHm = 4 – 9 and limestone at pHm = 5 – 9 was studied. Tc(IV) sorption on MX-80 increased with pHm from 4 to 6, reached the maximum at pHm = 6 – 7, and then gradually decreased with pHm from 7 to 9. Tc(IV) sorption on illite gradually increased with pHm from 4 to 7, and then decreased as pHm increased. The sorption properties of Tc(IV) on shale were quite similar to those on illite. Tc(IV) sorption on limestone slightly increased with pHm from 5 to 6 and then seemed to be constant at pHm = 6 – 9. Tc(IV) sorption on all four solids was independent of ionic strength (0.1 – 6 m). The 2 site protolysis non-electrostatic surface complexation and cation exchange model successfully simulated the sorption of Tc(IV) onto MX-80 and illite and the optimized values of surface complexation constants were estimated.

Key Words : Technetium(IV), Sorption, MX-80 bentonite, Illite, Shale, Limestone