Low-emission cement clinker precursor production, enabled by electrolytic extraction of calcium from waste cement

We report here the electrochemical production of cement clinker precursor, containing calcium derived from the electrolytic decomposition of waste cement. Our "cement recycler" contains a cement electrolyzer, coupled to a cement digestion vessel, and a Ca(OH)₂ isolation vessel. The cement electrolyzer creates acid and base equivalents, and converts waste cement into Ca(OH)₂ and SiO₂. The electrolyzer was demonstrated at current densities up to 300 mA cm^-2 to produce yields higher than 80% for Ca(OH)₂. We experimentally verified a 99.8% reduction in CO₂ emissions when using fresh waste cement, and an 80% reduction when using aged cement (enriched in CO₂ due to atmospheric carbonation) from a demolition site. Our cement recycler bypasses the need for virgin limestone and could cut global CO₂ emissions by nearly 1 Gt annually, while also helping divert substantial waste cement from landfills.