Stability and leaching resistance performance of SAC repair and solidification materials exposed to gamma irradiation

Abstract

Sulphoaluminate cement (SAC) has great application prospect in the solidification of radioactive borate liquid waste and repair of its transport system, which could not avoid being impacted by the gamma irradiation environment. Whereas, the impact mechanisms and change of leaching resistance of SAC with and without borate are still ambiguity, corresponding to solidification and repair case. In this work, the stability of ettringite with and without borate, AH3 gel and C-A-S-H gel exposed to an 60Co gamma irradiation environment with the dose of 1.0 M Gy is investigated deeply by the characteristics of MAS-NMR and X-ray photoelectron spectroscopy, also the change of leaching resistance of SAC is discussed. The experimental results show that gamma irradiation induces the slight decomposition of channel and structural water, and leads to its structural relaxation. Surprisingly, the existence of borate decreases the decomposition degree of these two types of water and improves the stability of ettringite. The gamma irradiation reduces the transformation of AH3 gel to gibbsite crystal for SAC matrix, increases the disorder degree of silicate phase attached to AlO4 tetrahedral environment and accelerated hydration of ye’elimite. Totally, the changes of the main skeleton structures of ettringite, AH3 gel and C-A-S-H gel are not noticeable, which still has great stability exposed to gamma irradiation. In addition, gamma irradiation would deteriorate with little degree the leaching resistance of SAC wasteform and increase its mechanical performance, which still meets environmental safety requirements.