高庙子膨润土中蒙脱石碱性溶蚀的矿物学证据

高放废物地下处置库运营过程中，衬砌混凝土在地下水作用下产生的强碱性溶液，会扩散进入膨润土缓冲屏障，长期将使屏障性能发生退化。采用不同 pH 值的 KOH 溶液模拟衬砌混凝土溶出的碱性溶液，在室内进行为期一年的常温接触扩散试验，开展X射线荧光光谱（X-ray fluorescence spectroscopy，简称XRF）、X射线衍射（X-ray diffraction，简称 XRD）、扫描电镜（scanning electron microscope，简称 SEM）和能谱（energy dispersive spectrometry，简称 EDS）试验，研究强碱性溶液缓慢扩散对高庙子膨润土矿物的影响。XRF试验结果表明，当 KOH 溶液的 pH>12.6时，膨润土中 Si 元素的含量开始减少，即含Si 矿物蒙脱石、石英、方石英等发生了溶解；同时，K元素含量增多，表明膨润土与碱溶液发生离子交换反应，溶液中大量的K⁺进入蒙脱石层间。XRD 试验结果表明，在 pH=12.6时，蒙脱石矿物的 001峰开始右移、变宽，峰值强度大大减弱；在pH>13时，衍射角θ整体向右偏，晶面间距由原始膨润土样的1.385 3 nm（13.853 Å）减小为1.221 0 nm（12.210 Å），表明蒙脱石矿物晶层被压缩。随着 KOH 溶液 pH 值增大，膨润土中蒙脱石、石英等矿物的含量明显减少，长石类矿物的含量逐渐增加，伊利石和斜发沸石的含量也呈现略微增多的趋势。SEM 试验结果表明，随着溶液 pH 的增大，蒙脱石部分晶层会发生重叠，进而产生部分裂隙和孔洞，加速蒙脱石的溶蚀进程。在为期一年的接触扩散试验中，pH=13.8的 KOH 溶液扩散深度超过7.5 mm，并且在碱溶液与膨润土接触面上观察到新生成的伊利石微晶，证实强碱性溶液会导致蒙脱石溶解及伊利石化。

Mineralogical evidence of alkaline corrosion of montmorillonite in GMZ bentonite

During the operation of underground repository of high-level radioactive waste, the highly alkaline solution generated by groundwater corroding lining concrete will diffuse into the bentonite buffer barrier, resulting in the degradation of barrier property. The KOH solution with different pH values was used to simulate the alkaline solution, and a one-year contact diffusion test at room temperature was conducted. Then, X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrometry (EDS) were performed to investigate the effect of slow diffusion on the mineralogy of bentonite. The XRF test results show that when the pH of KOH solution was greater than 12.6, the content of silicon began to decrease, that is, montmorillonite, quartz, cristobalite and other Si-containing minerals in bentonite were dissolved. At the same time, the content of K increased, indicating that the bentonite had an ion exchange reaction with the alkaline solution, a large amount of K⁺ ions in the solution entered the montmorillonite crystal layer. The XRD test results show that the 001 peak of montmorillonite mineral started to shift to the right at pH=12.6, the peak widths widened, and the peak intensity reduced considerably. When the pH>13, the crystal interlayer space decreased from 1.385 3 nm (13.853 Å) to 1.221 0 nm (12.210 Å), indicating that the crystal layer of montmorillonite was compressed. With the increase of the pH value, the content of minerals such as montmorillonite and quartz decreased significantly, and the contents of illite, clinoptilolite and feldspar minerals increased slightly. The SEM test results show that part of the montmorillonite crystal layer overlapped with the pH of the solution increasing, and then some cracks and holes were generated. As a result, the cracks can accelerate the dissolution of montmorillonite. In the one-year contact diffusion test, the diffusion depth of the KOH solution with pH=13.8 exceeded 7.5 mm, and the newly formed illite crystallites were observed on the contact surface between the alkaline solution and the bentonite. It is confirmed that the strong alkaline solution will cause montmorillonite dissolution and illitization.