Bio-Accelerated Weathering of Ultramafic Minerals with Gluconobacter oxydans

Abstract

Ultramafic rocks are an abundant source of cations for CO2 mineralization (e.g., Mg) and elements for sustainability technologies (e.g., Ni, Cr, Mn, Co, Al). However, there is no industrially useful process for dissolving ultramafic materials to release cations for CO2 sequestration or mining them for energy-critical elements. Weathering of ultramafic rocks by rainwater, release of metal cations, and subsequent CO2 mineralization already naturally sequesters CO2 from the atmosphere, but this natural process will take thousands to hundreds of thousands of years to remove excess anthropogenic CO2, far too late to deal with global warming that will happen over the next century. Mechanical acceleration of weathering by grinding can accelerate cation release but is prohibitively expensive. In this article we show that gluconic acid-based lixiviants produced by the mineral-dissolving microbe Gluconobacter oxydans accelerate leaching of Mg2+ by 20x over deionized water, and that leaching of Mg, Mn, Fe, Co, and Ni further improves by 73% from 24 to 96 hours. At low pulp density (1%) the G. oxydans biolixiviant is only 6% more effective than gluconic acid. But, at 60% pulp density the G. oxydans biolixiviant is 3.2x more effective than just gluconic acid. We demonstrate that biolixiviants made with cellulosic hydrolysate are not significantly worse than biolixiviants made with glucose, dramatically improving the feedstock available for bioleaching. Finally, we demonstrate that we can reduce the number of carbon atoms in the biolixiviant feedstock (e.g., glucose or cellulosic hydrolysate) needed to release one Mg2+ ion and mineralize one atom of carbon from CO2 from 525 to 1.