Generating sustainable cement material from seawater with low-cost ultrafiltration (UF) membrane electrolysis

Abstract

Membrane electrolysis offers a promising avenue for in-situ generation of hydroxide ions (OH−), facilitating the recovery of magnesium (Mg2+) and calcium (Ca2+) ions from seawater as alkaline earth hydroxide precipitates. This process paves the way for an alternative greener method in the production of raw materials for cement manufacturing compared to limestone mining. Despite its potential, the application of conventional ion migration membranes, such as anion exchange membrane (AEM) and cation exchange membrane (CEM), is hampered by their high cost and low mechanical quality, posing significant barriers to industrial scalability. In this work, we introduce the utilization of commercially available high mechanical strength ultrafiltration (UF) membrane within a two-chamber electrochemical system, repurposing it as an ion migration membrane due to its distinct advantages in terms of simplicity and relative cost-efficiency than conventional AEM. This research demonstrates that the UF membrane exhibited a comparable performance to AEM in terms of OH− production. Both membranes achieved 97–99 % removal of Mg2+ and Ca2+ within 3 h at a current density of 8 mA/cm2 and maintained comparable migration rate of SO42− ion. Compared to AEM, a notable distinction of the UF membrane is its reduced migration rate of Cl− ions, resulting in lower membrane discoloration/oxidation. Furthermore, the investigation reveals that utilizing a Na2SO4 solution as an alternative anolyte, despite being slower for OH− production, offers economic advantages and facilitates higher selective recovery of Mg2+ over Ca2+. The end products of this process, MgO and CaO, are viable raw materials for cement production, underscoring a sustainable and low carbon approach compared to conventional limestone mining of cement production.