Novel method of ocean alkalinity enhancement using ikaite and other hydratedcarbonate minerals

Removing large volumes of CO₂ from the atmosphere, as well as rapid and deep emission reductions, may be required to meet the goals of the Paris Agreement. This has catalyzed recent attention on carbon dioxide removal (CDR) approaches that can remove more CO₂ from the atmosphere than they emit. The oceans absorb approximately 25% of the CO₂ that is emitted to the atmosphere, which causes acidification and adds to the stress experienced by some shell-forming organisms. A relatively inexpensive process for creating a hydrated calcium carbonate, ikaite, could be used to mimic the effect of natural carbonate weathering. This process uses high pressure CO₂ (~15 bar) in an aqueous reactor to dissolve crushed limestone within minutes. The calcium rich water is passed to a low-pressure reactor (~0.1 bar) that evolves and recycles gaseous CO₂ and forces the precipitation of ikaite over 30 – 80 minutes at temperatures <15°C. Experimental results suggest complete dissolution of ikaite can increase seawater alkalinity and thus potentially ameliorate the effects of ocean acidification. The focus of this study is on material characterisation and geochemical kinetics. In particular, we are using Raman spectroscopy coupled with X-Ray Diffraction for identification of the materials synthetically formed and we are exploring experimentally the precipitation and dissolution kinetics of ikaite and other hydrated carbonate minerals such as amorphous calcium carbonate (ACC). Preliminary results show that ikaite might be a precursor of ACC and synthetic can be stable for days at low temperature (sufficient time to be added to the ocean) and that it dissolves in seawater and stoichiometrically increases alkalinity.

            This technology could be scaled up to have a meaningful impact on climate change, and the costs could be comparable to other CO₂ removal approaches. That is possible within the next 20 to 30 years, particularly as the raw materials are abundant.