Xie Guoliang, Sheng Jie, Wang Jiayu, Yang Tian, Zhou Gaojie, Ma Jiayu, Hu Yanran, Gu Qixiong, Hao Weiduo, Jiao Kun, Sun Yuyong, Huang Zhen
School of Civil Engineering & Architecture, Tongling University, Tongling, Anhui 244000, China; State Key Laboratory of Oil and Gas Reservoir Geology and Exploration, Chengdu University of Technology, Chengdu 610059, China.
School of Civil Engineering & Architecture, Tongling University, Tongling, Anhui 244000, China.
Sci Total Environ. 2024 Aug 10;937:173533. doi: 10.1016/j.scitotenv.2024.173533. Epub 2024 May 25.
Pore type and pore structure evolves systematically across continuous black shale weathering profile. However, the extend and process of pore structure change is still an enigma. In this study, we try to unveil the pore structure evolution during weathering process through studying Cambrian Hetang shales in southern China. Fourteen shale samples, from protolith zone (PZ), fractured and weathered shale zone (FWZ), and saprolite zone (SZ), were collected to elucidate how porosity and pore structure develop during black shale weathering under subtropical condition. Through low pressure argon (Ar) gas adsorption (LP-ArGA), high pressure mercury intrusion (HPMI), nuclear magnetic resonance(NMR) and field emission scanning electron microscope (FESEM) observation, the results reveal significant differences in physical properties and pore structures among the PZ, FWZ, and SZ samples. Specifically, compared to PZ, FWZ and SZ samples are characterized by higher clay mineral content, lower organic matter (OM), and the absence of carbonates and pyrite. Total porosity, determined through HPMI and NMR, exhibits a gradual increase from PZ (6.70 % and 6.41 %) to FWZ (20.47 % and 13.45 %) and SZ (23.22 % and 12.48 %). Ar adsorption isotherms indicate a change in pore type from predominantly ink-bottle and slit-shaped in the PZ to mainly slit-shaped in FWZ and SZ. Integrated analysis of LP-ArGA, HPMI, NMR and SEM observation suggests a substantial decrease in the contribution of micropores to total pore volume (PV) and a concurrent increase in larger pores (meso-macropores) with the increase of weathering intensity. This results in smoother surfaces of micro-transition pores but rougher surfaces of macropores. Changes in mineralogy composition during weathering play a crucial role in influencing pore structure of shales and further accelerating the release and migration of toxic elements in black shale. Our study provides the essential theoretical foundation for the remediation of soil and water environmental pollution caused by black shale weathering.
孔隙类型和孔隙结构在连续的黑色页岩风化剖面上系统地演化。然而，孔隙结构变化的程度和过程仍然是个谜。在本研究中，我们试图通过研究中国南方寒武系荷塘页岩来揭示风化过程中的孔隙结构演化。采集了来自原岩带（PZ）、破碎风化页岩带（FWZ）和腐泥土带（SZ）的14个页岩样品，以阐明在亚热带条件下黑色页岩风化过程中孔隙度和孔隙结构是如何发展的。通过低压氩气（Ar）气体吸附（LP - ArGA）、高压压汞法（HPMI）、核磁共振（NMR）和场发射扫描电子显微镜（FESEM）观察，结果表明PZ、FWZ和SZ样品在物理性质和孔隙结构上存在显著差异。具体而言，与PZ相比，FWZ和SZ样品的特点是粘土矿物含量较高、有机质（OM）较低，且不存在碳酸盐和黄铁矿。通过HPMI和NMR测定的总孔隙度从PZ（6.70%和6.41%）逐渐增加到FWZ（20.47%和13.45%）和SZ（23.22%和12.48%）。Ar吸附等温线表明孔隙类型从PZ中主要为墨水瓶形和狭缝形转变为FWZ和SZ中主要为狭缝形。LP - ArGA、HPMI、NMR和SEM观察的综合分析表明，随着风化强度的增加，微孔对总孔隙体积（PV）的贡献大幅降低，同时较大孔隙（中 - 大孔）增加。这导致微过渡孔隙表面更光滑，但大孔隙表面更粗糙。风化过程中矿物组成的变化在影响页岩孔隙结构以及进一步加速黑色页岩中有毒元素的释放和迁移方面起着关键作用。我们的研究为修复黑色页岩风化造成的土壤和水环境污染提供了重要的理论基础。
