Research will explore deionisation of salt water

Tuesday, 03 September, 2019

Research will explore deionisation of salt water

Assistant Professor Kyle Smith’s extensive research in the field of water desalination is exploring novel ways to deionise salt water, with a new research project funded by the US National Science Foundation.

With research published in the journal Water Research, the University of Illinois Mechanical Science and Engineering professor has generated promising results for energy-efficient desalination of alternative water resources. His newest work, spearheaded by his doctoral student Erik Reale, involves deionisation devices that can reversibly store and release cations using intercalation materials — a class of materials commonly used for rechargeable batteries. In particular, the study addresses the challenge of cycling intercalation materials with fast rates of electron, ion and fluid transport — features that are difficult to achieve simultaneously in a single system.

The research team fabricated optimised electrodes containing insulative Prussian Blue analogue particles and used them in an experimental cation intercalation desalination (CID) cell with symmetric electrodes. Compared with past CID demonstrations, the team witnessed a nearly 10-fold increase in the rate of salt removal at similar energy consumption levels.

“High salt removal rates are needed in electrochemical water treatment devices because smaller units can be constructed to achieve the same total production of treated water if salt can be removed faster,” said Smith. “Following that line of thinking, the capital cost to construct a system will be lower for a fixed water productivity level.”

In the new three-year National Science Foundation-funded research project, Smith will use battery materials to overcome the limitation in the volume of waste brine that is produced during water desalination using reverse osmosis (RO). Brine disposal has major environmental sustainability issues, including increased earthquakes when injected into the earth and danger to aquatic ecosystems when disposed of in bodies of water.

Although RO brine generation is dictated by the pressure driving force used (and thus imposes mechanical limitations), Smith plans to use electric fields to concentrate salt ions, which he said could concentrate salts to levels near saturation in solution.

Building on previous research

In 2016, the University of Illinois reported that Smith had discovered the technology that charges batteries for electronic devices could provide fresh water from salty seas. Smith developed a novel device — a saltwater-filled battery with electricity running through it — that deionised water using the least amount of energy possible at the time.

In 2017, Smith and his team took salt water desalination a step further, focusing on new materials to improve the economic viability and energy efficiency of the process in collaboration with Wetsus, the European Centre of Excellence for Sustainable Water Technology. The team created a battery-like device that uses electrodes made from a material that removed sodium ions, as well as potassium, calcium, magnesium and others — an important technological improvement because salt water and brackish waters often contain a mix of other salts like potassium, calcium and manganese chloride. This work was published in the journal Electrochimica Acta.

The present experimental work follows that published by Smith and his students using computational modelling of electrochemical transport to guide the design of battery-based desalination cells. The group has recently used quantum mechanical modelling, combined with experiments and thermodynamic analysis, to understand how the battery materials used in their desalination cells absorb sodium, magnesium and calcium at the atomic scale.

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