Salt migration, a phenomenon observed in both natural and industrial environments, refers to the accumulation and movement of salt crystals from evaporating solutions onto surfaces. Once they begin to amass, the crystals ascend, dispersing from the solution. This migratory behavior, as noted by researchers, can lead to damage or be utilized positively, depending on circumstances. Recent findings published on June 30 in the journal Langmuir mark the first demonstration of salt migration at a single-crystal level and beneath the meniscus of a liquid.
“This study not only clarifies how salt migration initiates, but also examines the reasons and timing of its onset,” states Joseph Phelim Mooney, a postdoctoral researcher at the MIT Device Research Laboratory and a co-author of the study. “We aspire that this depth of understanding aids others, whether they are addressing water shortages, conserving ancient murals, or crafting longer-lasting infrastructure.”
This research is pioneering in visually depicting how salt crystals develop and interact with surfaces below a liquid meniscus, a concept theorized for decades but never truly captured or validated at this scale. It provides essential insights that could influence a broad spectrum of fields — including mineral extraction, desalination, anti-fouling coatings, membrane design for separation technologies, and even art preservation, where salt damage poses a significant risk to cultural heritage.
In applications related to civil engineering, for instance, this research can elucidate the reasons and timing behind the growth of salt crystals across surfaces like concrete, stone, or construction materials. “These crystals can apply pressure leading to cracking or flaking, ultimately diminishing the long-term resilience of structures,” says Mooney. “By identifying the exact moment when salt starts to migrate, engineers can more effectively devise protective coatings or drainage systems to combat this degradation.”
In the realm of art conservation, where salt can severely damage murals, frescoes, and ancient artifacts—often developing beneath the surface before damage becomes visible—this research can assist in recognizing the specific conditions that trigger salt movement, empowering conservators to take action sooner and with greater precision to safeguard heritage items.
The journey of this research began during Mooney’s Marie Curie Fellowship at MIT. “I was focused on enhancing desalination systems and quickly encountered [salt accumulation as] a significant barrier,” he explains. “[Salt] was ubiquitous, covering surfaces, obstructing flow paths, and undermining the efficiency of our designs. I came to realize we lacked a complete understanding of how or why salt begins to migrate across surfaces in the first place.”
This experience motivated Mooney to collaborate with colleagues to explore the fundamentals of salt crystallization at the air–liquid–solid interface. “We aimed to zoom in to observe the moment when salt starts to move, so we utilized in situ X-ray microscopy,” he remarks. “What we discovered offered us a completely new perspective on surface fouling, material degradation, and controlled crystallization.”
The new findings may indeed facilitate improved management of crystallization processes essential for extracting salt from water in zero-liquid discharge systems. They can also help clarify the mechanisms of scaling on equipment surfaces and potentially bolster emerging climate technologies that rely on smart regulation of evaporation and crystallization.
The work also supports applications in mineral and salt extraction, where salt migration can represent both a challenge and a chance. In these scenarios, Mooney states, “by mastering the precise physics governing salt formation at surfaces, operators can enhance crystal growth, increasing recovery rates and minimizing material losses.”
Co-authors of the paper include fellow researchers from the MIT Device Lab: Omer Refet Caylan, Bachir El Fil (currently an associate professor at Georgia Tech), and Lenan Zhang (currently an associate professor at Cornell University); as well as Jeff Punch and Vanessa Egan from the University of Limerick; and Jintong Gao from Cornell.
The research was carried out using in situ X-ray microscopy. Mooney describes a pivotal moment for the team when they observed a solitary salt crystal anchoring itself to a surface, initiating a cascading growth reaction.
“While this had been speculated upon, our capture of this moment on X-ray for the first time felt like witnessing the critical instant where everything changes — the ignition points of a self-sustaining process,” Mooney notes. “Even more astonishing was what transpired afterward: The salt crystal didn’t merely grow to occupy the available space. It penetrated the liquid-air interface and reshaped the meniscus, establishing ideal conditions for the subsequent crystal. This subtle, recursive mechanism had never been visually documented before — and observing it in real-time profoundly altered our understanding of salt crystallization.”
The paper, “In Situ X-ray Microscopy Unraveling the Onset of Salt Creeping at a Single-Crystal Level,” is currently available in the journal Langmuir. The research was conducted in MIT.nano.