“Supergreen” Renewables: Integration of Mineral Weathering Into Renewable Energy Production for Air CO2 Removal and Storage as Ocean Alkalinity

Abstract:

Excess planetary CO₂ and accompanying ocean acidification are naturally mitigated on geologic time scales via mineral weathering. Here, CO₂ acidifies the hydrosphere, which then slowly reacts with silicate and carbonate minerals to produce dissolved bicarbonates that are ultimately delivered to the ocean. This alkalinity not only provides long-term sequestration of the excess atmospheric carbon, but it also chemically counters the effects of ocean acidification by stabilizing or raising pH and carbonate saturation state, thus helping rebalance ocean chemistry and preserving marine ecosystems. Recent research has demonstrated ways of greatly accelerating this process by its integration into energy systems. Specifically, it has been shown (1) that some 80% of the CO₂ in a waste gas stream can be spontaneously converted to stable, seawater mineral bicarbonate in the presence of a common carbonate mineral – limestone. This can allow removal of CO₂ from biomass combustion and bio-energy production while generating beneficial ocean alkalinity, providing a potentially cheaper and more environmentally friendly negative-CO₂-emissions alternative to BECCS. It has also been demonstrated that strong acids anodically produced in a standard saline water electrolysis cell in the formation of H₂ can be reacted with carbonate or silicate minerals to generate strong base solutions. These solutions are highly absorptive of air CO₂, converting it to mineral bicarbonate in solution. When such electrochemical cells are powered by non-fossil energy (e.g. electricity from wind, solar, tidal, biomass, geothermal, etc. energy sources), the system generates H₂ that is strongly CO₂-emissions-negative, while producing beneficial marine alkalinity (2-4). The preceding systems therefore point the way toward renewable energy production that, when tightly coupled to geochemical mitigation of CO₂ and formation of natural ocean “antacids”, forms a high capacity, negative-CO₂-emissions, “supergreen” source of fuel or electrcity.

1) http://pubs.acs.org/doi/pdf/10.1021/es102671x

2) http://pubs.acs.org/doi/full/10.1021/es800366q

3) http://www.pnas.org/content/110/25/10095.full.pdf

4) http://pubs.acs.org/doi/abs/10.1021/acs.est.5b00875