Water's role in the circular economy

To boost supply chains, scientists at the US Department of Energy’s Argonne National Laboratory have been looking at ways to recover valuable materials from water and have now published details about the various mechanisms by which critical materials can be extracted from diverse water streams.

Water represents one underexplored avenue of acquiring many of the materials needed for decarbonisation. According to Seth Darling, Chief Science and Technology Officer for Argonne’s Advanced Energy Technologies directorate, different types of water offer different kinds of material resources.

​“The oceans are such a tremendous resource because the total quantities of many valuable and important materials are vast, but they are also highly dilute,” he said. ​

“Wastewater has also been in need of reframing. We want people to see that wastewater is not truly waste; rather, it’s rich with all sorts of valuable stuff.”

Darling also noted groundwater aquifers and geothermal brines as other possible sources of valuable materials. These materials include lithium, which is increasingly in demand for electric vehicle batteries and could be used to help decarbonise our economy. ​

“Lithium is in the ocean and in geothermal brines; you’d extract it differently from these two sources but it’s important to understand which is cheapest, has the smallest environmental impact and enables secure supply chains,” Darling said. ​“For many other materials, water is underexplored as a source, and that’s something we’re paying increasingly more attention to.”

The technologies that Darling and his colleagues are exploring to extract critical materials from different types of water range from the traditional (like membranes) to the innovative (like interfacial solar steam generators).

Omar Kazi, a PhD student in molecular engineering at the University of Chicago working with Darling, is studying methods to concentrate wastewater streams to recover valuable materials. ​

“Getting rid of the water through evaporation is an energy-intensive and slow process,” Kazi said. ​“In geothermal brines, it can take years for water to evaporate to be able to recover the lithium that’s contained in them, which creates a huge bottleneck. The question we are asking is, how we can make the water evaporate faster?”

One way to do that could be through the use of porous photothermal materials, which convert light to heat efficiently. These light absorbers act like a black T-shirt that heats up on a sunny day. That heat is transferred to the water directly at the interface with the surrounding air, significantly accelerating evaporation.

A paper based on the study, ​‘Material design strategies for recovery of critical resources from water’, appeared online in Advanced Materials.

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