Negative emission enabled by combining ocean alkalinity enhancement and waste concrete upcycling

Electrochemical ocean alkalinity enhancement (OAE) is a promising technology for negative carbon emissions, but the resulting dilute acid stream poses a disposal challenge. This study presents an innovative method to neutralize this acid using recycled concrete aggregates (RCA) while simultaneously producing high-quality aggregates for new construction. A rotary drum reactor facilitates the reaction by reducing the acid concentration from 0.5 M to 0.1 M HCl and lowering the RCA water absorption from 6.8% to 0.5-1%. The remaining 0.1 M acid is further neutralized to near-neutral pH by reaction with RCA fines. The effects of pre-carbonation on RCA and the scalability of this method are also discussed. Integrating waste concrete upcycling with electrochemical OAE has the potential to achieve hundreds of megatons of negative CO2 emissions annually, while diverting gigatons of construction and demolition waste from landfills, thus generating significant revenue through reduced disposal fees and the production of valuable aggregates.