Dual Valorization of Mine Tailings for Critical Metal Extraction and Carbon Capture via Organic Acids

Abstract The growing demand for critical elements (CEs) and carbon removal solutions creates opportunities to valorize mine waste. We investigate the organic acid-enhanced extraction of critical elements from wollastonite-rich tailings while assessing carbon dioxide (CO2) mineralization potential. Tailings were obtained from a mine in New York and contained aluminum, calcium, iron, magnesium, manganese, and titanium in wollastonite, pyroxene, garnet, and feldspar phases. Flow-through dissolution experiments at 40 and 80 °C using citric, formic, and oxalic acids (0.001–0.1 M), coupled with online pH, temperature, and pressure monitoring, were conducted, and the data were used to validate a multimineral kinetic model based on population balance equations, aqueous geochemistry, and ligand-dependent dissolution rate laws. Formic and oxalic acids achieved superior extraction, with formic acid particularly efficient for calcium─enabling coupled CEs recovery and CO2 mineralization. The ligand-promoted rate laws show a kinetic order of 0.5–1 with respect to formate activity for all minerals. Moreover, comparison of the estimated rates with previous works shows up to 1 order of magnitude faster dissolution in the presence of 0.1 M formic acid, reaching a plateau around pH 4 as the formate activity becomes constant. Overall, our multimineral kinetic framework demonstrates that model complexity should match element distribution, with mineral-specific kinetic models required for elements concentrated in distinct phases. In this way, the proposed approach provides a predictive tool to support sustainable tailings valorization.