Arsenic is a double-edged sword. It is a known carcinogen found naturally at high levels in groundwater. But it is also an element that is critical for clean energy technologies such as solar cells.
Connecting those two flows, researchers have found a way to convert the arsenic in groundwater into pure arsenic nanoparticles that can be used in manufacturing. “The creation of valuable [critical raw materials] from carcinogenic treatment by-products is a potentially disruptive technology for the water sector that can alter global [arsenic] supply chains,” Kaifeng Wang and Case M. van Genuchten, geochemists at the Geological Survey of Denmark and Greenland, write in a paper published in the journal Science Advances.
Arsenic, which occurs naturally in rocks, soils, and water, is highly toxic. Long-term exposure to the element, typically because of contaminated groundwater, can cause a range of adverse health effects, including neurological impairment in children, cancer, cardiovascular disease and diabetes.
But the element is also useful in various clean energy technologies. It goes in the metal alloys used in batteries, for instance. And gallium arsenide semiconductors are vital for making high-efficiency solar cells and the high-performance computer chips that go in electronics and telecommunications devices.
Most of the world’s arsenic is mined and produced in China today. Because of the element’s use in technologies and its constrained supply chain, the US and the EU both list it as a critical raw material.
Arsenic usually exists in groundwater in the form of arsenate or arsenite ions. Around the world, treatment with iron oxide particles is an established way to remove these arsenic compounds from groundwater. The process creates a concentrated solid sludge that is difficult to dispose.
The Danish researchers came up with a two-stage chemical process to recover and reuse the arsenic in groundwater. First, they extract arsenic from the solid sludge using an alkali solution . The next step involves treating the extracted arsenic with a common sulfur-bearing chemical called thiourea dioxide. This process gives pure metallic arsenic nanoparticles.
“This work sets the foundation for rethinking the role of As treatment as a dual service that provides safe drinking water and generates local sources of critical raw materials,” the research duo writes.
Source: Kaifeng Wang and Case M. van Genuchten. Commodifying a carcinogen: Critical raw materials from arsenic-laden groundwater. Science Advances, 2025.
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