Enhanced Ca²⁺/Mg²⁺ Leaching and CO₂ Sequestration in Serpentine and Olivine upon <i>Ramichloridium apiculatum</i>

Bioleaching pretreatment enhances the mineral carbonation reaction, which has the advantages of being green, environmentally friendly, and pollution-free compared to physical and chemical methods. In this paper, serpentine and olivine were pretreated with two different contact modes by Ramichloridium apiculatum. The effects of fungal pretreatment on the leaching rules of Ca2+ and Mg2+ and the CO2 sequestration characteristics of the two minerals were investigated. The leaching results indicated that under the action of R. apiculatum, the concentrations of Ca2+ and Mg2+ in the fermentation broth significantly increased. Compared with the sterile experiment, the concentrations of Ca2+ and Mg2+ in serpentine and olivine increased by 14.56 and 11.94 times and 26.36 and 15.38 times, respectively. The leaching yields of Ca2+ in serpentine and olivine direct contact leaching experiments were 1.57 and 2.24 times higher than those in indirect contact leaching experiments, while the leaching yields of Mg2+ were 2.79 and 2.04 times, respectively. Scanning electron microscopy (SEM) showed that the mechanical damage caused by the direct contact between hyphae and minerals led to the obvious destruction of the structure. Then, the mineral carbonation experiment results showed that the CO2 sequestration content of serpentine and olivine reached 0.61 and 0.97 mol/kg after leached by fungus pretreatment, respectively, which increased 2.77 and 5.71 times compared to the sterile treatment, respectively. Fungus enhances mineral carbon sequestration characteristics through two processes, including the promotion of Ca2+ and Mg2+ leaching to increase the probability of M2+ binding with carbonate ions in the solution, and fungal cell walls and metabolites could act as carbonate precipitation templates by chelating free Ca2+ and Mg2+.