Bioleaching of olivine and enstatite with formation of Mg-oxalate mediated by engineered Gluconobacter oxydans.

Carbon mineralization using ultramafic rocks is a promising approach for long-term carbon dioxide removal. Here, we investigate whether a genetically engineered strain of Gluconobacter oxydans (B58 ∆pstS, P112:mgdh) can simultaneously achieve carbon mineralization and bioleach critical elements. Olivine and enstatite were bioleached at low-temperature conditions (30 °C) and with 5% pulp density. Direct G. oxydans-mineral contact promotes Fe2+ oxidation and leads to higher leaching efficiency compared to leaching with a cell-free biolixiviant. Importantly, G. oxydans facilitates the precipitation of magnesium oxalate, a compound with twice the carbon storage capacity of magnesite. Oxalic acid was detected in the G. oxydans-produced biolixiviant, and solid-phase Mg-oxalate formed most efficiently at low pH. SEM and XRD analyses reveal extensive olivine dissolution and secondary coating by Mg-oxalate and amorphous silica, which may inhibit further leaching. Mass balance calculations show that G. oxydans leached up to 75% of the Mg hosted in the starting materials, while only 11% of leached Mg reacted to sequester carbon as Mg-oxalate after 15 days. The enhanced sequestration potential of Mg-oxalate combined with bioaccelerated critical element leaching to offset costs represents a promising opportunity for global carbon storage that is worthy of further investigation. (193/200).