Reaction rate scaling in porous media in the transport controlled regime

本研究应用研究者发展的多孔介质中溶质运移理论来预测地球表面附近化学反应速率的时间依赖性。 例如，硅酸盐矿物的化学风化率对全球碳循环有重大影响，对气候变化、植被和土壤生产都有影响。 众所周知，地壳中的化学风化率随着时间的增加而迅速下降，随着观测时间尺度从数小时增加到数百万年，其下降幅度高达7个数量级（1千万倍）。这些风化过程是复杂的。一个完整的解决方案将需要同时处理颗粒表面和溶液中的各种化合物的化学平衡，试剂和反应产物通过多孔介质的运动，以及颗粒表面性质的变化。 研究人员应用了一个非常简单的假设，即风化速率与溶质运移速度成正比，他们知道如何预测。 没有试剂，反应就不会发生;不除去风化产物，反应就达到平衡并停止。 随着地表风化层的加深，将反应物种聚集在一起的传输路径变得更长和更曲折（即，它们在方向上表现出频繁的变化）。这项研究澄清了路径变得更加曲折的程度，从而使反应减慢了多少。此外，它提供了洞察如何曲折的路径相关的溶质运输可以改变。 调查人员的结果也可能适用于有毒化学品在地下的沉积和沥滤速率，使它们与我们环境面临的广泛威胁有关。农业径流中的营养物质迁移对河流、河口和近岸环境构成严重威胁。 另一方面，浅层地下有效的养分运输促进了工业化农业的成功。 因此，了解如何影响这些路径的曲折程度有助于优化农业和环境需求。目前的研究是相关的，不仅溶质在流体流动中的运输，而且还为不同的应用程序，如细胞有丝分裂，血液灌注在大脑中，色谱，过滤，二次采油，催化，填充床反应器的行为，建筑材料的降解，组织生理学，迁移和流行病学，泡沫中的热分散和原子的内部动力学。

This research applies a theory of solute transport in porous media developed by the investigator to predict the time dependence of chemical reaction rates near the earth's surface. Chemical weathering rates, for example, of silicate minerals, have significant impacts on the global carbon cycle, with implications for climate change, extinctions, and soil production. It is well known that chemical weathering rates in the earth's crust decrease rapidly with increasing time, diminishing by as much as seven orders of magnitude (a factor of 10 million) as the time scale for observation increases from hours to millions of years. These weathering processes are complex. A full solution would require simultaneous treatment of the chemical equilibration of various compounds on particle surfaces and in solution, the movement of reagents and reaction products through the porous media, and changes in the nature of the particle surfaces. Researchers apply the greatly simplifying assumption that weathering rates are proportional to solute transport velocities, which they know how to predict. Without reagents, the reactions do not occur; without removal of the weathering products, reactions reach equilibrium and cease. As the weathered layer of the surface deepens, the transport paths that bring reacting species together become longer and more tortuous (i.e., they exhibit frequent changes in direction). This research clarifies the degree to which the paths become more tortuous and thus how drastically the reactions are slowed. In addition, it provides insight into how the tortuosity of paths relevant for solute transport can be altered. Investigators' results may also applicable to rates of deposition and leaching of toxic chemicals in the subsurface, making them relevant to a wide range of threats to our environment. Nutrient transport in agricultural run-off can be a serious threat to streams, estuaries, and near-shore environments. On the other hand, efficient nutrient transport in the shallow subsurface enhances the success of industrial agriculture. Understanding of how to influence the tortuosity of such paths can thus aid in the optimization of agricultural and environmental needs. The present research is relevant not only for solute transport in fluid flow, but also for applications as diverse as cellular mitosis, blood perfusion in the brain, chromatography, filtration, secondary oil recovery, catalysis, the behavior of packed bed reactors, degradation of building materials, tissue physiology, migration and epidemiology, heat dispersion in foams and the internal dynamics of the atom.