Abstract
Arsenic is a potent carcinogen whose presence in groundwater poses a persistent global public health threat. While groundwater treatment mitigates arsenic exposure, it generates concentrated arsenic-rich by-products that are universally considered economic and environmental burdens. However, arsenic is experiencing a renaissance. Both the United States and European Union have classified arsenic as a critical raw material (CRM) due to the role of metallic arsenic [As(0)] in materials needed for digital infrastructure and clean energy systems. Bringing these two material flows together, we show that arsenic removed during groundwater treatment can be transformed into pure amorphous As(0) nanoparticles via a two-stage process of alkali extraction and selective reduction. The creation of valuable CRMs from carcinogenic treatment by-products is a potentially disruptive technology for the water sector that can alter global As(0) supply chains. Revenue from upcycled As(0) can also help improve the challenging economics of water treatment in marginalized arsenic-affected regions.