NSF Award
2413770
Minerals that are insoluble in water tend to deposit on the interior walls of water pipelines, forming mineral scales that are extremely difficult to remove. Consequently, mineral scale presents a costly challenge for industrial processes such as membrane desalination, heating and cooling systems, natural resource production, and papermaking. The most common mineral scale is calcium carbonate, found in eggshells, chalk, and the skeletons of shellfish. Current methods to remove this and other water-insoluble scales involve harsh acids or other environmentally unfriendly chemicals. Thus, there is a need for more benign and effective treatments. However, developing such treatments requires understanding the chemical and physical mechanisms by which these treatments dissolve scale. To address this knowledge gap, this research project will test whether a class of organic molecules called citrates, often derived from lemon juice, combined with inorganic salts can serve as environmentally friendly treatments to remove calcite, the most stable and problematic form of calcium carbonate. This research builds on the team’s history of collaboration and expertise in identifying the mechanisms by which sustainable biopolymers dissolve other types of mineral scales. The expected outcomes of this project include the development of design rules for environmentally friendly treatments for calcium carbonate and other insoluble mineral scales, ultimately leading to reduced costs for scale treatment across multiple industries. The project team will disseminate these results at national meetings and conferences in Houston, where scale control poses a significant problem for local industries. Additionally, they will develop new activities on scale dissolution to complement their ongoing outreach efforts for K-12 students and their parents through the University of Houston STEM Zone Saturday event and the public at the annual Houston Energy Festival.<br/><br/>This project aims to elucidate the mechanisms that control modifier-driven dissolution of mineral scale under quiescent and flow conditions. As a model system, the team will study the dissolution of calcite, the thermodynamically stable form of the ubiquitous calcium carbonate mineral scale. The research plan integrates the team members’ complementary expertise in microfluidics, transport phenomena, crystal engineering, and molecular simulation to test the overarching hypothesis that careful selection of modifier chemistry for scale control can drive calcite dissolution. The plan includes three specific aims: (1) determine the mechanisms by which organic and inorganic modifiers dissolve calcite; (2) examine the effects of flow on modifier-calcite interactions and scale dissolution; and (3) identify cooperative effects between modifiers on dissolution. Optical and atomic force microscopy experiments will be used to quantify bulk and mesoscopic dissolution of calcite in the presence of two classes of modifiers, citrate derivatives and salts, and in quiescent and flow conditions relevant for practical applications. Complementary molecular simulations will characterize the modifier-calcite interactions and their effects on the dissolution mechanisms and kinetics. Finally, these methods will be applied to examine how interactions between the organic (citrate-based) and inorganic (alkali and alkaline earth metals) modifiers enhance or hinder calcite dissolution. Together, these studies will develop a fundamental understanding of the chemical factors that control calcite dissolution. This project will thus pave the way for new environmentally friendly chemistries to dissolve this problematic scale and establish general principles for identifying and designing chemical agents to dissolve mineral scales. Further, these results may provide insight into the mechanisms controlling the formation of calcium carbonate in the environmental carbon cycle, which is relevant for biomineralization, regulation of sea alkalinity, and emerging CO2 sequestration technologies, as well as in pathological diseases such as kidney stones and atherosclerosis. Thus, the new mechanistic understanding of calcite crystal growth and dissolution may have broader relevance for natural, biological, and synthetic calcification pathways.<br/><br/>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.
