Slaking quicklime with seawater for open-ocean alkalinity enhancement: Technical feasibility and cost implications

[Geoengineering News]

https://www.frontiersin.org/journals/climate/articles/10.3389/fclim.2026.1824086/abstract

Authors: Manon Tiphaine Duret, Connor Clark, Kenton Heidel

19 May 2026

Abstract

Scalable carbon dioxide removal (CDR) solutions, such as ocean alkalinity enhancement (OAE), are necessary to mitigate climate change. One OAE approach is open-ocean liming, consisting in distributing hydrated lime (Ca(OH)₂) to increase seawater alkalinity and thereby long-term carbon storage in the ocean. Large-scale deployment would require transporting and distributing substantial quantities of Ca(OH)₂, making logistics a non-negligible component of total implementation costs. Most OAE studies to date assume the transport of Ca(OH)₂ rather than quicklime (CaO). However, CaO is denser, contains ~20% more alkalinity per unit mass, and has superior bulk handling properties compared to Ca(OH)₂. If technically feasible, transporting CaO and slaking it onboard using seawater could therefore reduce logistics costs. Here, we experimentally assess the feasibility of slaking CaO with artificial seawater. Slaking efficiencies and kinetics were comparable between seawater and deionized water, with CaO reactivity explaining more variance than solution composition. Seawater slaking produced secondary minerals, including likely brucite (~5 wt% of slurry) and gypsum (~0.3 wt%), but their formation is unlikely to reduce OAE efficiency under recommended alkalinity distribution practices. We also developed a simple transport cost model to compare land-slaked Ca(OH)₂ transport vs. transport and onboard slaking of CaO. Under conservative bulk-shipping assumptions, onboard slaking could reduce transport and port handling costs by 4 to 21 % per tCO₂ removed relative to Ca(OH)₂ transport. Overall, seawater slaking appears technically feasible and economically advantageous for OAE implementation, and supports the integration of slaking systems into bulk carriers for potential deployment at scale.

Source: Frontiers