When wastewater is polluted with heavy metals, it’s usually expensive and messy to decontaminate. But a new type of material, designed to precisely pull copper ions from water, demonstrates how water treatment could become more affordable—and how wastewater could become a way to sustainably source important metals.
While the process to clean wastewater today pulls out everything—including nutrients and essential minerals, not just contaminants—at once, forming a toxic sludge, the new technology, developed as a prototype by a team at the Department of Energy’s Lawrence Berkeley National Laboratory, targets and traps just the copper ions. “It’s kind of like a crystal sponge,” says Jeff Urban, the director of the Inorganic Nanostructures Facility in the Berkeley Lab’s Molecular Foundry and senior author of a new journal article about the technology. “When you put it into water, it opens up. Instead of grabbing everything, this is a sponge that’s very specific to copper because of the size of the pores and the stickiness of the pores for copper.”
The material, called ZIOS (zinc imidazole salicylaldoxmine), is durable enough that it could be used in the acidic water coming from a copper mine. When it’s filled with copper, the copper can be removed, and then it can be reused again. The scientists started with copper because it was easier to target; copper, while a nutrient in small doses, is dangerous at higher levels in water. “There are global regions for which elevated levels of copper in the groundwater are a big issue,” he says.
The material can also be designed to capture other metals in water—lithium, for example, which is a key material for making the batteries used in electric cars and renewable energy storage. “We view this as kind of a template for an overall strategy for doing targeted and precision separations,” Urban says. Wastewater treatment plants could eventually use filters that precisely capture different materials simultaneously, pulling each material out in a different channel. Done at a large scale, it could become one source for new materials without the environmental impacts of mining.
The technology is both faster and less expensive than other methods of removing pollutants. “The starting materials are cheap,” he says. “And it has a good lifetime, so you’re not paying to replace it.”