Practical and thermodynamic constraints on electromicrobially accelerated CO mineralization.

By the end of the century, tens of gigatonnes of CO will need to be removed from the atmosphere every year to maintain global temperatures. Natural weathering of ultramafic rocks and subsequent mineralization reactions can convert CO into ultra-stable carbonates. Although this will draw down all excess CO, it will take thousands of years. CO mineralization could be accelerated by weathering ultramafic rocks with biodegradable lixiviants. We show that if these lixiviants come from cellulosic biomass, this demand could monopolize the world's biomass supply. We demonstrate that electromicrobial production technologies (EMP) that combine renewable electricity and microbial metabolism could produce lixiviants for as little as $200 to $400 per tonne at solar electricity prices achievable within the decade. We demonstrate that EMP could make enough lixiviants to sequester a tonne of CO for less than $100. This work highlights the potential of this approach and the need for extensive R&D.