Selective Dissolution of Magnesium from Ferronickel Slag by Sulfur-Oxidizing Mixotrophic Bacteria at Room Temperature

Due to the significant magnesium content, ferronickel slag is potentially a secondary magnesium resource and a subject for CO 2 fixation. The current techniques require high energy consumption and involve physical and chemical processes. The biohydrometallurgical method can be applied to extract magnesium from ferronickel slag to minimize the energy required. However, the information about bioleaching magnesium from slag is still limited. Also, it is essential to investigate the selectivity of magnesium over iron dissolution because iron is also one of the major elements in the slag. In this study, ferronickel slag was subjected to bioleaching experiments using sulfur-oxidizing mixotrophic bacterium ( Citrobacter freundii ) at ambient conditions, which was capable of producing organic acid and secreting extracellular polymeric substances and utilizing iron and sulfur as energy sources. The effect of pulp density (75–150 g/L), particle size fraction (less than 74 μm to 105–149 μm), and elemental sulfur addition (0–15 g/L) on magnesium recovery was investigated. The experimental results showed that the bacterium could improve the dissolution of magnesium-bearing minerals in the slag. Increasing pulp density, particle size fraction, and elemental sulfur concentration were detrimental to the selectivity of magnesium over iron. The highest selectivity of 0.90 was reached in the biotic system using a size fraction