Dithionite Inhibits Iron(III) (Hydr)oxide Formation during Olivine Dissolution Advancing Simultaneous CO ₂ Mineralization and Nickel Recovery

Increasing CO₂ concentration poses significant global challenges, impacting both environmental and human health. As we strive for a carbon-neutral energy technology transition, the demand for critical elements (<i>e.g.,</i> nickel and cobalt) continues to increase, while high-grade ores are depleting. Combining CO₂ mineralization with the recovery of critical elements from low-grade ores offers an innovative solution. Olivine, a magnesium-rich ultramafic with trace amounts of critical elements, is a promising mineral; however, its impurities, such as iron (Fe(III)), hinder the dissolution of Ni and Mg from olivine, reducing its carbonation and critical element recovery. To address this challenge, this study examined Ni dissolution from San Carlos olivine at high temperatures and high CO₂ pressure. We found that iron(III) (hydr)oxide layers impeded olivine dissolution; however, with sodium dithionite (Na₂S₂O₄), a reducing agent, olivine dissolution is significantly improved by preventing iron(III) (hydr)oxide formation. With Na₂S₂O₄, within 24 h, Mg and Ni dissolution from olivine increased 2.85-fold and 2.66-fold, respectively, compared to samples without Na₂S₂O₄. After seven cycles, with solutions replaced every 24 h, 98.9% of the total Mg and 84.6% of the total Ni were recovered. This approach enhances olivine's CO₂ mineralization and improves the sustainability of critical element supply.