Hypersaline brine produced by fracking has left us in trouble, but a new process could help dry it up

Seemingly miraculous innovations have helped quench the ever-increasing thirsts of our industrial society. Need more energy? Fracture it from deep rocks. Fresh water? Desalinate ocean flows. Precious metals? Leach them from low-grade ores that were previously unmineable.

But these and other wonders leave us in the lurch, awash in a sea of ​​hypersaline brine. This “brine” – wastewater containing much higher levels of salt than seawater and often contaminated with pollutants – is a byproduct of these and other industrial processes, and is a problem.

“Disposal of brine solutions containing total dissolved solids greater than 60,000 mg l−1 poses technical, environmental and economic hurdles that remain mostly unresolved,” said Arup SenGupta, PC Rossin Professor of Civil Engineering. and environmental studies at Lehigh University.

However, a new approach developed by SenGupta and visiting researcher Hao Chen (then a PhD student) represents a step forward in cleaning up and even potentially releasing valuable resources hidden in super-salty water. The work is published in the journal Natural water.

Current methods

Current methods of processing this byproduct often compound the environmental damage inherent in industrial processes.

• Pumping hypersaline brine into the ocean is a common practice in coastal desalination plants, but it can disrupt deep-sea ecosystems.
• Wastewater from indoor industrial facilities often evaporates in the sun in huge, open ponds, but this process is inefficient, weather-dependent, and prone to concentration of contaminants that threaten both groundwater and surrounding environments.
• Pumping brine from deep wells was a common practice, but it has been banned in many areas due to the ecological and geological damage it causes.
• Other methods such as multi-stage thermal distillation and membrane distillation have some advantages, but also require large energy inputs to generate heat and are prone to scale buildup and irreversible fouling or to contamination of equipment.

Developing methods to concentrate brine to levels conducive to the collection of crystallized solids has become a priority of the U.S. Department of the Interior and other global water agencies.

Crystallized solids can more easily be disposed of, reused for industrial processes, and even “mined” for precious metals, including lithium.

A new solution

SenGupta and Chen developed a new process, evaporative ion exchange (EIX), to concentrate brine at room temperature using air humidity and ion exchange. Unlike existing methods, EIX avoids scaling and clogging, and is much faster than natural evaporation thanks to its efficient design.

It uses a polymer ion exchange resin bead, a type of gel with a high concentration of charged functional groups or atoms whose electrical charge binds with oppositely charged ions. When the pearl comes into contact with water, the internal pressure of the resin allows it to quickly absorb water while rejecting salts and other compounds.

“This phenomenon is similar to forward osmosis, but no semi-permeable membrane physically exists. Instead, the ion exchanger-water interface acts as a semi-permeable membrane and absorbs the water is very fast,” SenGupta said.

When subsequently exposed to dry air, the resin releases water into the air through evaporation at room temperature without the need for external heat input.

“This cycle can be repeated, allowing the resin to continually concentrate solutions at room temperature,” SenGupta said. “The process is rapid and the entire energy requirement is provided by the ambient air.”

The base resin used in the study was Purolite A502P, a commercially available ion exchange resin for drinking water systems. The researchers doped the material with zirconium dioxide (ZrO₂) nanoparticles to guarantee its density and prevent the resin from floating.

The experience

To test the process, the researchers conducted experiments using both synthetic hypersaline brine created in the laboratory and hypersaline water collected from gas well sites in the Marcellus Shale region of Pennsylvania and New Jersey. . In addition to salt, the Marcellus sample contained high concentrations of barium cations, strontium cations, and calcium ions.

The EIX beads were placed in a bed, which was then filled with brine until the resin reached saturation. The bed was drained of brine, then the resin was exposed to blown, unheated air for evaporation, and the total volume and total dissolved solids (TDS) of the remaining brine were measured. This cycle was then repeated using the remaining brine.

• After the completion of three cycles, the volume of the remaining synthetic brine was reduced by a factor of almost three, and the TDS of the remaining synthetic brine was increased by a factor of almost three.
• Cycles carried out with identical polymer beads but without ion exchange functional groups made it possible to obtain an increase in the TDS of the synthetic brine of less than 20%.
• After four cycles performed with the Marcellus sample, the concentrations of barium, sodium, and chlorine were concentrated beyond the solubility limit, resulting in direct crystallization of the barium chloride and sodium chloride salts.
• The processes did not result in scaling or fouling of the resin, and experiments indicated the ability to concentrate and recover lithium from natural hypersaline.

“The most remarkable finding of this study is the precipitation/crystallization of salts from hypersaline water from a Marcellus gas well after four EIX cycles at room temperature,” SenGupta said. “According to the literature, no other brine concentration process achieves incipient crystallization at room temperature.”

SenGupta said the benefits of the process make him optimistic about the potential to scale the process for widespread use. The next steps would be to run a pilot system and record its process parameters and energy benefits compared to other high-temperature processes.

“The EIX process does not require the manufacturing of any specialized materials for process scale-up,” SenGupta said. “It does not require heat or a major energy source. It can be quickly expanded.”