Collaborative Research: Coupled Effects of Density, Microstructure, and Ion Selectivity for Clay Membranes

About This Grant

This award will support research that advances fundamental understanding of bentonite clay, promoting the progress of science and contributing to national infrastructure and water security needs. Bentonite is a natural clay mineral with a unique ability to act like a semi-permeable membrane, slowing the movement of chemicals while still allowing water to pass through. This special property can affect the performance of engineered containment systems for municipal, agricultural, nuclear, and mining wastes. Bentonite membrane behavior is also being leveraged for emerging technologies in water treatment, desalination, carbon storage, and osmotic power generation. However, engineers do not fully understand the mechanisms behind this behavior due to limited experimental data to validate existing models or apply them in design practice. The research will quantify how the structure and behavior of bentonite influence its ability to control chemical movement and water flow. Results will help improve the design and performance of infrastructure that relies on bentonite, supporting national prosperity and welfare through more effective and resilient engineering solutions. In addition, the award will support workforce development through training and mentoring of undergraduate and graduate students, as well as STEM outreach to educate and inspire the next generation of college students to pursue engineering. The goals of the research are to investigate interrelated effects of ion selectivity, porosity, and microstructure on bentonite membrane behavior, and to characterize the impacts of these effects on the performance of infrastructure and engineered systems that utilize bentonite. Our current understanding of the significance and persistence of membrane behavior in these systems is hindered by limited availability of experimental data. For example, although the filtration efficiency of bentonite membranes is known to be sensitive to membrane density and the types and concentrations of chemical species being filtered, the vast majority of previous studies have focused on low-density barriers and electrolyte solutions containing only monovalent salts. The experimental program will include measuring chemical transport rates, membrane efficiency, and pore size distributions in bentonite specimens of different densities and solution chemistries. The research will expand the existing database of physico-chemical and transport properties of bentonite membranes, so that theoretical models for coupled water and chemical flows through these membranes can be validated over a wider range of conditions expected in real-world applications. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.