Researchers from Monash University, CSIRO and The University of Texas have discovered a cost-effective solution to filtering salt and metal ions from water utilising metal-organic frameworks, which could be used for desalination.
Metal-organic frameworks (MOFs) have the largest internal surface area of any known substance and the sponge-like crystals can be used to capture, store and release chemical compounds.
The researchers have discovered that MOF membranes have the ability to mimic the filtering function, or ‘ion selectivity’, of organic cell membranes.
MOFs have the potential to remove salts from seawater and separate metal ions, offering a new approach for the water and mining industries, according to the researchers.
Currently, reverse osmosis membranes are responsible for more than half of the world’s desalination capacity, and the last stage of most water treatment processes, yet these membranes have room for improvement by a factor of two to three in energy consumption. They do not operate on the principles of dehydration of ions, or selective ion transport in biological channels and therefore have significant limitations.
In the mining industry, membrane processes are being developed to reduce water pollution, as well as for recovering valuable metals. For example, lithium-ion batteries are now the most popular power source for mobile electronic devices, however at current rates of consumption, there is rising demand likely to require lithium production from non-traditional sources, such as recovery from salt water and waste process streams.
If economically and technologically feasible, direct extraction and purification of lithium from such a complex liquid system would have profound economic impacts.
Monash University Faculty of Engineering Associate Dean (International) and Department of Chemical Engineering, Professor Huanting Wang, said the results of the research may lead to a less expensive way of desalinating water for consumption.
“We can use our findings to address the challenges of water desalination. Instead of relying on the current costly and energy intensive processes, this research opens up the potential for removing salt ions from water in a far more energy efficient and environmentally sustainable way,” Mr Wang said.
Mr Wang said while desalination is an obvious application of this new technology, there are also many different ways it can be applied, particularly in regards to lithium selectivity.
“This is just the start of the potential for this phenomenon. We’ll continue researching how the lithium ion selectivity of these membranes can be further applied.
“Lithium ions are abundant in seawater, so this has implications for the mining industry that currently uses inefficient chemical treatments to extract lithium from rocks and brines. Global demand for lithium required for electronics and batteries is very high.
“These membranes offer the potential for a very effective way to extract lithium ions from seawater, a plentiful and easily accessible resource.”
CSIRO Executive Director of Future Industries, Dr Anita Hill, said the research offers another potential real-world use for MOFs, which have been heralded as a “next-generation material”.
“The prospect of using MOFs for sustainable water filtration is incredibly exciting from a public good perspective, while delivering a better way of extracting lithium ions to meet global demand could create new industries for Australia,” Dr Hill said.
