Coupling acid neutralization and resource recovery to scale ocean alkalinity enhancement

Ocean Alkalinity Enhancement (OAE) is a promising carbon dioxide removal (CDR) strategy with the theoretical potential to sequester gigatons of atmospheric CO₂ each year. Electrochemical 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, carbon-neutral strategies for HCl disposal. Here, we 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.