Coupling Mineral Carbonation and Ocean Liming

Abstract

The process by which basic/ultrabasic silicate minerals (e.g., olivine) are reacted with CO2 to produce solid carbonate minerals (“mineral carbonation”) has been suggested as a method to sequester carbon dioxide from point sources into stable carbonate minerals. Alternatively, the addition of lime (produced from calcining carbonate minerals) to the surface ocean (“ocean liming”), which results in an increase in ocean pH and a draw-down of atmospheric CO2 has been proposed as a “geoengineering” technology, which stores carbon as dissolved alkalinity in the surface ocean. Combining these approaches, in which the magnesium carbonate minerals produced from mineral carbonation are used as a feedstock for ocean liming (mineral carbonation-ocean liming; MC–OL), may reduce the limitations of individual technologies while maximizing the benefits. Approximately 1.9 metric tons of magnesium silicate (producing 0.7 ton of magnesium oxide) are required for every net ton of CO2 sequestered. A total of 0.7 ton of CO2 is produced from this activity, 70% of which is high-purity (>98%) from calcining and potentially amenable for geological storage. The technology can be conceptually viewed as an alternative to direct air capture and swaps ambient CO2 for high-purity point source CO2. MC–OL requires approximately 4.9 and 2.2 GJ of thermal and electrical energy ton–1 of CO2 sequestered. MC–OL has less demand for geological storage; only 0.5 ton of CO2 needs to be injected for every ton of CO2 removed from the atmosphere. However, manipulation of ocean chemistry in this way potentially creates an additional environmental impact (localized elevated pH or co-dissolution of trace metals) and requires additional attention.