Development of a sulfidized zerovalent iron-geopolymer composite for the reductive immobilization of ReO4− (2025)

Chung-Seop Lee, Jinmo Ahn, Jaehyuk Kang, Wooyong Um

Journal of Environmental Management Volume 373, January 2025, 123575

DOI: https://doi.org/10.1016/j.jenvman.2024.123575

ABSTRACT

 A geopolymer waste form has become a suitable approach for the immobilization of the volatile technetium (Tc) due to the low curing temperature (<60 °C). However, the low retention and the high mobility of the anionic technetium (TcO4−) remain challenging due to the charge repulsion stemming from the negative charges of the geopolymer surface and the anionic TcO4−. Herein, a geopolymer composite containing sulfidized nanoscale zerovalent iron (S-nZVI) was developed to reductively immobilize ReO4− (used as a non-radioactive surrogate for TcO4−). With low S-nZVI addition (≤4.0 wt%), S-nZVI particles are homogeneously dispersed in the geopolymer paste, resulting in stable mechanical strength of the S-nZVI/GP composite (>33.02 MPa). Moreover, the S-nZVI/GP composite showed a lower leaching rate of Re than the geopolymer without adding S-nZVI under the same leaching conditions. Apparently, the presence of S-nZVI enhanced the reductive condition of geopolymer slurry, converting ReO4− to a lower oxidation state species including ReS2 during geopolymerization, and causing the decrease of Re leachability from 1.04 × 10−7 to 3.42 × 10−11 cm2 s−1. This new type of S-nZVI/GP composite is expected to expand the application of a geopolymer binder in the radioactive waste management field of the nuclear industry.