Corrosion of GMZ bentonite by diffusion of strong alkaline solution
ZHANG Huyuan1，2，TONG Yanmei2，JIA Quanquan2#br#
(1. Key Laboratory of Mechanics on Disaster and Environment in Western China，Ministry of Education，Lanzhou University，Lanzhou，Gansu 730000，China；2. School of Civil Engineering and Mechanics，Lanzhou University，Lanzhou，
Gansu 730000，China)
Abstract：In the underground repository of high-level wastes，strong alkaline cementitious material dissolved by groundwater from the lining concrete will penetrate into bentonite buffer，resulting in a certain degradation of the performance of the buffer barrier. A diffusion cell was particularly designed to simulate the diffusion process of KOH solution into compacted GMZ bentonite specimens，so to investigate the possible changes in clay minerals and microstructure under elevated temperature for the purpose of long-term evaluation of GMZ bentonite buffer in China. Totally，24 sets of KOH diffusion tests were conducted on bentonite specimens with an initial dry density of 1.80 g/cm3，covering combinations of pH = 12.6，13.0 or 13.5，temperature of 30 ℃ or 60 ℃ and reaction time of t = 7，14，21 or 28 d. As soon as diffusion tests terminated，bentonite specimens were disassembled to carry out X-ray diffraction(XRD) and scanning electron microscopy(SEM) analysis. Research results verify that the dissolution loss of montmorillonite in bentonite has a positive correlation with pH and temperature and that the dissolution mainly concentrate within 0‐2 mm from the contact surface with a max drop from original 44.4% to 25.9%. The alkaline dissolution of wing-like gels generated originally during bentonite hydration is responsible for the montmorillonite dissolution. Bentonite microstructure damage resulted from alkaline solution moderates with increasing the diffuse depth from the contact surface，accompanied by a decrease of the apparent porosity. Macro fissures on the contact surface are visible by naked eyes，aggregate destroy occurs within 0–4 mm from the contact surface but the microstructure almost keeps changeless while deeper than 4mm. With respect to the long term chemical evolution of bentonite barrier，further attention should be paid to solution chemistry，hydraulic condition and time scale of mineral-solution reactions.
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2020, Vol. 39 
