Once considered an intractable byproduct of vital industrial processes, waste salt is rapidly emerging as a versatile and indispensable component in the global shift towards sustainable energy. Engineers worldwide are pioneering innovative methods to transform this environmental challenge into a suite of solutions, ranging from critical mineral extraction to advanced energy storage, positioning waste salt as a crucial “missing link” for a cleaner, more resilient energy future.
The Unseen Challenge: The Growing Problem of Waste Salt
Industrial activities such as desalination, chemical manufacturing, mining, and food processing generate billions of tons of waste salt annually, often in the form of concentrated brines. Disposing of these high-salinity byproducts poses significant environmental threats, harming ecosystems when released into oceans or freshwater sources. The increasing demand for fresh water through desalination only exacerbates this issue, creating an ever-larger volume of brine waste. However, within this challenge lies a hidden opportunity: these brines and salt deposits are rich in resources and properties that are invaluable to the energy transition.
Turning Brine into Bounty: Critical Mineral Extraction
The accelerating demand for critical minerals—essential for electric vehicles, renewable energy infrastructure, and electronic devices—has driven researchers to explore unconventional sources. Waste brines are proving to be a surprising treasure trove.
From Desalination Waste to Battery Gold
Brines from desalination plants, natural salt lakes, and other industrial waste streams contain valuable minerals such as lithium, magnesium, manganese, neodymium, and dysprosium. These elements are vital for manufacturing batteries, permanent magnets in wind turbines, and other green technologies. Extracting these minerals from concentrated waste streams can be more economical and sustainable than traditional terrestrial mining, potentially reducing recovery costs by over 50%.
Innovations in Brine Processing
New technologies are revolutionizing critical mineral extraction from brines. Researchers at the Pacific Northwest National Laboratory, for instance, have developed a saline solution-based method to selectively recover valuable elements like manganese, magnesium, neodymium, and dysprosium from e-waste and brines. These methods exploit the unique properties of metals to form solids at different rates, significantly speeding up separation processes from typical 30 hours to just four hours in some cases. Membrane-based separation processes are also being developed to efficiently process various minerals, including lithium and rubidium salts, from waste brine, offering faster and more sustainable alternatives to methods like solar evaporation ponds, which contribute to water loss in sensitive ecosystems like the Great Salt Lake.
Salt’s Role in Energy Storage: Thermal Batteries and Hydrogen Hubs
Effective energy storage is paramount for integrating intermittent renewable energy sources like solar and wind into the grid. Salt, in various forms, offers compelling solutions for both heat and gas storage.
Thermal Energy Storage (TES): Banking Heat with Salt
Waste salt has garnered significant interest as a low-cost, efficient medium for thermal energy storage (TES), effectively functioning as a “thermal battery.” Companies like Waste Salt Technologies LLC are actively working on commercializing products that use repurposed waste salts to store thermal energy. These systems can capture heat from various intermittent sources, such as solar thermal systems or curtailed grid power, and release it as process heat (with efficiencies around 90%) or convert it into electricity (around 40% efficient). This technology addresses the mismatch between energy generation and demand, providing a stable and continuous heat source for industrial processes and contributing to a 100% renewable power grid. Molten salt storage systems, in particular, boast high heat storage density, low cost, and long lifespans, making them suitable for applications ranging from concentrated solar power plants to industrial waste heat recovery and grid peak shaving.
Underground Caverns for Hydrogen and CO2 Storage
Beyond thermal applications, extensive underground salt deposits offer immense potential for large-scale energy and emissions management. Research highlights that these geological formations can serve as secure holding tanks for hydrogen gas and sites for permanent carbon dioxide (CO2) storage. Salt caverns are naturally impermeable, making them ideal for storing gases. This capability is critical for expanding hydrogen as a clean energy carrier, as hydrogen requires significantly more storage space than natural gas for comparable energy output. Co-locating hydrogen production with CO2 storage in surrounding porous rock formations, particularly in regions with abundant salt domes like the Texas Gulf Coast, presents a synergistic approach to decarbonization.
Powering the Future: Green Hydrogen and Osmotic Energy
Engineers are also leveraging salt’s inherent properties to generate electricity and produce clean fuels.
Saltwater Electrolysis for Clean Hydrogen
Producing “green hydrogen” from water electrolysis, powered by renewable electricity, is a key strategy for decarbonizing energy systems. While traditional electrolysis requires ultrapure freshwater, researchers are making strides in direct saltwater electrolysis. This advancement is crucial given the scarcity of fresh water and the abundance of seawater. Challenges such as electrode corrosion by chloride ions are being addressed through innovative approaches, including forward osmosis and the use of semi-permeable membranes to filter water before electrolysis. Electrochemical salt splitting is another emerging technology that uses electricity to separate salts, regenerating acids and bases, and producing clean water, thereby supporting circular economy principles in industrial wastewater treatment.
Harvesting Blue Energy from Salinity Gradients
Osmotic power, also known as “blue energy,” harnesses the energy released when freshwater and saltwater mix across a semi-permeable membrane. This pressure difference can drive turbines to generate electricity without combustion or emissions. Recent developments, such as Japan’s first osmotic power plant in Fukuoka, integrate with existing infrastructure like desalination plants, utilizing their concentrated brine waste to enhance efficiency. These plants demonstrate the practical viability of osmotic energy, offering a stable, weather-independent renewable energy source with significant global potential.
Beyond the Obvious: Other Salt-Enabled Energy Solutions
The versatility of salt extends even further, touching upon several other critical areas of the energy transition.
Geothermal Enhancement
Salt’s excellent thermal conductivity can be harnessed in next-generation geothermal energy systems. Engineers are exploring how salt formations can efficiently channel heat from warmer underlying rocks to produce geothermal power, contributing to a more diversified renewable energy portfolio.
Nuclear Waste Transformation
In the nuclear sector, molten salt technologies are emerging as a game-changer for waste management. Companies like Moltex Energy are developing processes like “Waste to Stable Salt” (WATSS) that can transform nuclear waste into stable salt forms and even convert it into clean, dispatchable energy. This not only dramatically reduces waste volumes but also eliminates long-lived radioactive elements, providing a commercially viable alternative to conventional disposal methods.
Saline Ice Power
In a surprising breakthrough, researchers have discovered that bending salty ice can generate electricity. This nascent technology, while still in its early stages with challenges in durability and efficiency, opens up possibilities for generating clean energy in cold regions and from engineered saline ice structures, potentially transforming ice from a winter nuisance into a valuable power source.
The Road Ahead: Challenges and Opportunities in Salt Utilization
While the potential of leveraging waste salt and natural salt deposits is immense, challenges remain. Scalability and economic viability need further demonstration for many of these technologies. The long-term stability and efficiency of some processes, such as direct saltwater electrolysis, require continued research to overcome issues like electrode corrosion. Furthermore, careful management of any residual waste from brine processing is essential to ensure a net positive environmental impact.
Despite these hurdles, the collaborative efforts of engineers, researchers, and industries are rapidly unlocking the multifaceted potential of salt. By repurposing an abundant “waste” product and harnessing the unique geological properties of salt formations, these innovations are paving the way for a more circular economy and robust, sustainable energy infrastructure, effectively turning an environmental problem into a cornerstone of the energy transition.
