Ferritin Protein Nanocages for Selective Separation and Recovery of Critical Metals

Recycling critical metals from waste streams is increasingly important to meet the rising demand for clean energy technologies and reduce the environmental impact of ore mining. A key step in this process is the selective separation and recovery of high-grade metals from waste leachates containing complex metal mixtures; however, current strategies are limited by high chemical, energy, and resource consumption, substantial financial costs, and production of hazardous byproducts. Herein, we report the pioneering use of ferritin – self-assembling protein nanocages with porous, hollow structures and supercharged inner surfaces – as a high-efficiency biosorbent for eco-friendly, selective metal recovery from mixtures. Ferritin nanocages adsorbed cobalt (Co2+), nickel (Ni2+), and lithium (Li+) primarily through electrostatic interactions, localizing the adsorbed metal cations within their cavities. Adsorption isotherms indicated significantly more effective adsorption of Co2+ and Ni2+ compared to Li+, enabling efficient Co2+/Ni2+ separation from Li+. Leveraging ferritin's ability to concentrate adsorbed metal cations within cavities enabled selective recovery of Co2+ as nearly 95% pure solid carbonate salts from Co2+-Li+ mixtures through single-step precipitation under mild conditions, while Li+ remained in solution. This research opens new avenues for using ferritin nanocages in selective metal separation and recovery from waste streams via simple, environmentally benign adsorption-precipitation processes.