Acid leaching process of an ultramafic mine tailing for indirect CO2 mineralization

The extraction of divalent metals from ultramafic mine tailings for indirect CO₂ mineralization is a promising strategy for large-scale carbon sequestration. This study investigates the acid leaching process of an ultramafic nickel tailing, rich in magnesium silicates, using hydrochloric acid and citric acid. The aim was to evaluate the leaching efficiency of key metals, including magnesium, calcium, and iron, under varying operational conditions such as acid concentration, solid-to-liquid ratio, temperature, and multi-stage leaching. The experimental results show that both acids effectively leach the target metals, but with differing efficiencies. HCl demonstrates higher leaching efficiency, particularly for magnesium and iron, while citric acid shows moderate efficiency, especially for magnesium. The efficiency of metal extraction declines with higher solid-to-liquid ratios due to reduced surface area for leaching. Temperature impacts both acid systems differently; in the HCl system, it can reduce efficiency for some elements, while in the citric acid system, it can enhance efficiency for others. The findings suggest that both HCl and citric acid can be utilized for the acid leaching step in indirect CO₂ mineralization, with HCl offering higher extraction efficiencies and broader applicability to various metals.