A Monash University team has developed a method of filtering salt ions from seawater that could revolutionise water desalination and purification techniques, and also provide a source of lithium for batteries.
The technology is based on metal-organic frameworks (MOFs), a material that has the largest internal surface area of any known substance compared to its volume, enabling it to collect greater levels of ions such as sodium and lithium from water than current techniques.
Dr Huacheng Zhang, professor Huanting Wang and associate professor Zhe Liu and their team at Monash University, in collaboration with Dr Anita Hill of CSIRO and Professor Benny Freeman from the University of Texas, recently discovered that MOF membranes could replicate the filtering function of organic membranes to selectively collect ions.
In recent years, MOF research has been aimed at the removal of hydrogen and carbon dioxide, but the Monash team developed a membrane structure aimed at removing salts and lithium ions, both of which are prevalent in saltwater.
Extracting the ions in the past has been based on creating a pressure differential across the membrane, but the MOF developed by the Monash project uses a small electrical potential to drive the ions to a collection point, therefore using significantly less energy than a pressure-based system.
Still in its early stages of research, Professor Wang said there was potential for the MOFs to be more cost-effective and efficient than current water desalination techniques by slashing energy consumption by as much as 2-3 times and processing water at a much faster rate. The membranes can also be reused once the ions have been extracted.
“We can use our findings to address the challenges of water desalination, instead of relying on the current costly and energy intensive processes,” Professor Wang said.
“This research opens up the potential for removing salt ions from water in a far more energy efficient and environmentally sustainable way.
There’s also the potential for the technology to be used as a novel way to harvest lithium.
“We’ll continue researching how the lithium ion selectivity of these membranes can be further applied,” Professor Wang said.
“Lithium ions are abundant in seawater, so this has implications for the mining industry that currently use 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’s Dr Anita Hill said the research offered real-world uses for the 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,” Dr Hill said.
For communities that rely on water with a high level of salts, such as bore water, the development of MOFs may present a solution for cleaner, safer, more reliable water sources.
Professor Wang said with further research, there was potential to create a system that removes a number of ions in one process by stacking successive membranes with ion selectivity into one system.
The next step in the research is to look into the viability of creating “real life” membranes for commercial applications.
- See the paper here.