This study describes and demonstrates key steps in a carbon-negative process for manufacturing cement from widely abundant seawater-derived magnesium (Mg) feedstocks. In contrast to conventional Portland cement, which starts with carbon-containing limestone as the source material, the proposed process uses membrane-free electrolyzers to facilitate the conversion of carbon-free magnesium ions (Mg2+) in seawater into magnesium hydroxide [Mg(OH)2] precursors for the production of Mg-based cement. After a low-temperature carbonation curing step converts Mg(OH)2 into magnesium carbonates through reaction with carbon dioxide (CO2), the resulting Mg-based binders can exhibit compressive strength comparable to that achieved by Portland cement after curing for only 2 days. Although the proposed "cement-from-seawater" process requires similar energy use per ton of cement as existing processes and is not currently suitable for use in conventional reinforced concrete, its potential to achieve a carbon-negative footprint makes it highly attractive to help decarbonize one of the most carbon-intensive industries.
Keywords: carbon negative; cement; electrochemistry; magnesium; seawater.