The understanding of mixing-controlled reactive dynamics in heterogeneous porous media remains limited, presenting significant challenges for modeling subsurface contaminant transport processes and for designing cost-effective environmental remedial efforts. The complexity of accurately observing, measuring, and modeling mixing-limited reactive transport has led to inadequate exploration of these critical processes. This study investigates the mixing and reaction kinetics affected by stagnant zones, which are commonly found in alluvial aquifers-aquitards and fracture-matrix systems. By conducting experiments involving conservative and bimolecular reactive transport through porous media within translucent chambers filled with two sizes of glass beads and under varying flow rates, we explored the effects of grain size and hydrodynamic conditions. Using a high-resolution camera, we monitored the concentration changes of conservative and reactive tracers, with subsequent interpretation through three-dimensional numerical simulations. The outcomes revealed the emergence of distinct mixing interfaces within both mobile and stagnant zones, culminating in a bi-peaked plume formation. Notably, the mixing and reaction times in media containing stagnant zones were found to be approximately 10 times longer than in homogeneous media. These findings, through experimental and modeling efforts, advance our understanding of mixing-limited reactive transport phenomena within heterogeneous media, underscoring the significant role of stagnant zones—a topic previously underexplored.

中文翻译：

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非均相多孔介质中混合限制反应输运的实验和建模见解：停滞区的作用


对非均相多孔介质中混合控制反应动力学的理解仍然有限，这给模拟地下污染物迁移过程和设计具有成本效益的环境修复工作带来了重大挑战。准确观察、测量和模拟混合受限反应传递的复杂性导致对这些关键过程的探索不足。本研究调查了受停滞带影响的混合和反应动力学，停滞带常见于冲积含水层-滞水层和裂隙-基质系统。通过在充满两种尺寸的玻璃珠的半透明腔室内进行涉及多孔介质的保守和双分子反应性传输的实验，在不同的流速下，我们探索了晶粒尺寸和流体动力学条件的影响。使用高分辨率相机，我们监测了保守示踪剂和反应示踪剂的浓度变化，随后通过三维数值模拟进行解释。结果显示，在移动区和停滞区内都出现了不同的混合界面，最终形成了双峰羽流。值得注意的是，发现在包含停滞区的介质中的混合和反应时间比在均质介质中长约 10 倍。通过实验和建模工作，这些发现促进了我们对异质介质中混合受限反应传输现象的理解，强调了停滞区的重要作用——这是一个以前未被充分探索的话题。