D’Ascanio et al. (2025): Coupling acid neutralization and resource recovery to scale ocean alkalinity enhancement
Rocco D’Ascanio, Mojtaba Fakhraee, Nicolas Theunissen, Joachim AR Katchinoff, Matthew D Eisaman and Noah J Planavsky, IN: CDR.Xiv, https://doi.org/10.70212/cdrxiv.2025401.v1
Electrochemical ocean alkalinity enhancement (OAE)—where seawater alkalinity is increased by removing hydrochloric acid (HCl)—has attracted particular interest, but the viability of this approach at climate-relevant scales hinges on the development of low-cost, carbonneutral strategies for HCl disposal. Here, the authors demonstrate a two-step bench-scale process that addresses this challenge by first neutralizing HCl using common mafic and ultramafic rocks, and then recovering valuable products from the resulting solutions. This process can yield co-products such as amorphous silica and nickel/cobalt hydroxides, while converting HCl into a saline solution that can be discharged to the ocean without reversing alkalinity gains. A technoeconomic case study in Washington State, USA, estimates the cost of acid neutralization at < $25 per tonne of CO₂ removed via OAE, with the potential for future net profitability as co-product purities improve.