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Immobilization
mechanism of radioactive borate waste in phosphate-based geopolymer waste forms
(2022)
Byoungkwan Kim, Jaehyuk Kang, Younglim Shin, Tae-min Yeo,
Wooyong Um
Journal of
Cement and Concrete Research Volume 161, November 2022, 106959
DOI : https://doi.org/10.1016/j.cemconres.2022.106959
ABSTRACT
The solidification of radioactive borate waste (BW), which contains a
high concentration of boron ions using cement waste forms is challenging
because soluble borate hinders the cement hydration reaction. Here, BW was
immobilized using a phosphate-based geopolymer, and the phase change of BW in
the geopolymer was inves- tigated. The geopolymers could solidify BW up to 50
wt% depending on the water content and heat curing conditions. In geopolymers
cured at high temperatures (60 and 90 ◦ C), the
7-day compressive strength increased as the BW waste loading increased up to 40
wt%. Heat curing promoted geopolymerization and the precipitation of amorphous
boron phosphate, leading to an increase in the compressive strength. The
formation of a new amorphous boron phosphate phase was confirmed by performing
XRD, MAS NMR, and SEM analyses of the geopolymers and reaction products. These
results can improve our understanding of the immobilization mech- anism of BW
in phosphate-based geopolymers. |
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