Duret et al. (2026): Slaking quicklime with seawater for open-ocean alkalinity enhancement: Technical feasibility and cost implications
Manon Tiphaine Duret, Connor Clark and Kenton Heidel, IN: Frontiers in Climate, https://doi.org/10.3389/fclim.2026.1824086
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, the authors 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. The authors also developed a simple transport cost model to compare land-slaked Ca(OH)₂ transport vs. transport and onboard slaking of CaO.