Sorption of Tc(IV) in Saline Solutions – I. Sorption on MX-80 and Granite in Ca-Na-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 2024-05-20 ; Approved 2024-06-13

Abstract

Technetium-99 is identified as an element of interest for the safety assessment of a deep geological repository for used nuclear fuel. The sorption behavior of Tc(IV) onto MX-80 and granite in Ca-Na-Cl solutions of varying ionic strength (0.05 – 1 mol/kgw (m)) and across a pHm range of 4 – 9 was studied in this paper. Sorption of Tc(IV) was found to be independent of ionic strength in the range of 0.05 to 1 m for both MX-80 and granite. Sorption of Tc(IV) on MX-80 increased with pHm from 4 to 7 and then decreased with pHm from 8 to 9. Sorption of Tc(IV) on granite gradually increased with pHm from 4 to 8 and then became almost constant or slightly decreased with pHm from 8 to 9. A 2 site protolysis non-electrostatic surface complexation and cation exchange sorption model successfully simulated sorption of Tc(IV) on MX-80 and granite. Optimized values of surface complexation constants (log K0) are proposed

Key Words : Technetium (IV), Sorption, Granite, MX-80, Saline, 2SPNE SC/CE model