You are quite right, EVs don't remove CO2 from the air or the ocean, and posters ought to bare that in mind when they accuse the Sami of blocking planet saving technologies. There is however, a simple fix for removing CO2 from the ocean (thus reversing ocean acidification) and sequestering it on the ocean floor, but there is not really any saleable consumer product from it, so it doesn't easily fit any market based solution, so there is not much interest in it.

https://www.ispatguru.com/calcination-of-limestone/

The Availability of Limestone and Other Raw Materials for Ocean Alkalinity Enhancement

Stefano Caserini, Niccolò Storni, Mario Grosso

First published: 09 May 2022

https://doi.org/10.1029/2021GB007246

Citations: 5

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Abstract

The work assesses the availability and localizations of different raw materials suitable for ocean alkalinity enhancement (OAE), like limestone, olivine, magnesite and brucite, since several billion tons of rocky materials are needed to achieve meaningful results for carbon sequestration through OAE. Resources of carbonates are immense and widespread around all continents. Availability of pure carbonates is still very large (outcrop area 4.1 million km²) and is not a constraint for the large-scale development of OAE. Outcrops of pure carbonates within 10 km from the coastline and below bare ground or scrub/shrub, preferred for the logistics of exploitation, account for about 70,000 km², and could provide about 5,000 Gt of limestone. These values increase by a factor of 3 and 8 within 50 and 100 km from the coastline, respectively. Potential resources of olivine, less easily identifiable from the geological data, are estimated in the order of a few hundred billion tons and could provide only a minor contribution to ocean-based carbon removal strategies. A comparison with the current level of world extraction of mineral raw materials is also provided. The annual production of limestone, estimated to be more than 6.6 Gt from deposits scattered all around the world, is about 9% of the world production of mineral raw materials (around 44 Gt yr⁻¹), and is of the same order of magnitude as coal (7.3 Gt yr⁻¹). The annual productions of magnesite (29 Mt yr⁻¹), olivine (8.4 Mt yr⁻¹) and brucite (1.5 Mt yr⁻¹) are two orders of magnitude lower.

Key Points

• Pure carbonate potential resources are of several trillion tons and are not a constraint for the development of global-scale ocean liming

• A large part of pure limestone resources is located nearby the coastline, in area with no to low vegetation cover, mainly in North Africa and Iran

• The global limestone yearly production is similar to that of coal, thus the needed upscale is far lower than for olivine, magnesite and brucite

Plain Language Summary

The ongoing acidification of the oceans due to the increase of carbon dioxide (CO₂) concentration in the atmosphere and the consequent increased uptake by the sea can be tackled by adding alkaline compounds under controlled conditions. Since this promotes a number of reactions in the carbonate system which ultimately results in a drawdown of atmospheric CO₂, the enhancement of ocean alkalinity can also contribute to the global effort of limiting global warming, and it is widely studied in the literature among the CO₂ removal technologies. A limiting factor can be the worldwide availability of alkaline materials to be used for such a scope. The paper shows that the global availability of pure carbonates is vast, although unevenly distributed, and it could largely satisfy the requirement for large-scale development of ocean alkalinization. The required up-scaling of limestone production compared to the current level is much lower than what would be needed for other raw materials that could be used, such as olivine, magnesite and brucite. Moreover, a large fraction of pure limestone resources that could be exploitable is located nearby the coastline, in areas without or with low vegetation cover, which favors the logistics related to the exploitation.