Seawater may make CarbFix CO2 sequestration technique more feasible in water-deficient countries

By using seawater instead of freshwater, the CarbFix method of sequestering CO2 can be used off the coast of West India, Saudi Arabia, Western USA, Siberia and Kamchatka, where there are large reserves of basalt that is very suitable for using the CarbFix technique.

In a paper published in the journal Geochimica et Cosmochimica, post-doctoral researcher Martin Voigt and colleagues explain why they hypothesized about the possibility of using saltwater:

Over millions of years, the interaction of marine basalt with percolating seawater in low-temperature ocean floor hydrothermal systems leads to the formation of calcite and aragonite. The presence of these minerals in marine basalts provides evidence for substantial CO₂ fixation in these rocks.

In Iceland, CarbFix involves capturing CO2 from steam emanating from a geothermal plant, dissolving it in freshwater and injecting it into the subsurface in basalt. Reactions of the CO2-rich solution with basalt rich in iron, calcium and magnesium leads to mineralization of the CO2 into carbonate minerals within two years.

The drawback is that 25 tonnes of freshwater are required for each tonne of C02-dissolved liquid. Although this water can be reused, it is obviously a limiting factor in countries with limited supplies of water.

Enter Voigt et al. Their experiments using seawater instead of freshwater were albeit carried out in the laboratory rather than in the sea itself, but they conclude:

Notably, at pCO₂ of tens of bars, magnesite will form, limiting the formation of Mg-rich clays, which might otherwise compete for the Mg cation and pore-space in the submarine basaltic crust. This suggests that the injection of CO₂-charged seawater into subsurface basalts can be an efficient and effective approach to the long-term safe mineral storage of anthropogenic carbon.

https://www.sciencedirect.com/science/article/pii/S0016703721003379?dgcid=author

Magnesite is a carbonate mineral.

This summer, experiments will begin with injecting seawater into boreholes at the Reykjanes geothermal power station on Iceland’s southwest coast. This power station uses seawater for cooling purposes.

I have written several articles on CarbFix, such as this one for BBC Future and this one for Energy Monitor. But developments occur frequently at CarbFix, so if anyone wants an article on the latest developments, let me know.