Integrated Recovery of Iron and Nickel from Olivine Ores Using Solvent Extraction: Synergistic Production of Amorphous Silica and Carbonates through pH Adjustment and Carbon Mineralization

Abstract

This study proposed a sustainable method for the concurrent recovery of metals from olivine minerals and carbon sequestration through carbon mineralization to address the challenges of climate change and critical mineral recovery for the renewable energy transition. It developed a comprehensive development in leaching processes, recovery of metals, and reagent recycling while assessing its economic benefits and environmental impact. Employing hydrometallurgical leaching, our approach facilitates the selective recovery of Ni²⁺ while converting Mg²⁺ into their carbonates. This approach is further refined through a stepwise technique that controls operating conditions to generate high-purity valuable products, enabling nearly 90% of Mg²⁺ and Ni²⁺ to be dissolved and converted to carbonates. This study evaluated various organic and inorganic acids for the leaching process, followed by Fe extraction and pH swing, to yield pure Fe salts and amorphous silica. Separately extracting iron from the solution significantly reduces the loss of valuable metals in subsequent stages by minimizing the coprecipitation of iron with silicon. A techno-economic assessment (TEA) was performed to evaluate the economic impact of removing iron before the solvent extraction of nickel. This analysis, based on mass balance flow comparisons, determined that the independent removal of iron is more profitable, resulting in the production of more and higher-value products. Ni²⁺ was selectively extracted from the leachate using Versatic 10, which forms a complex with nickel in the organic phase. The solution containing either a strong acid or a greener agent (i.e., gaseous CO₂) was effectively used to strip Ni²⁺ from the organic phase. Different polymorphs of Mg carbonates were produced under ambient conditions. The proposed process flow results in high-purity products suitable for use in various industries, which enhances the economy, facilitating the rapid adoption of this technology.