Low-Alkali CO2 Mineralization Pathways Using Cement Kiln Dust and Desalination Brine

Population growth and industrial expansion have intensified environmental degradation, with water scarcity and carbon emissions emerging as pressing global challenges. In arid regions, seawater desalination is widely adopted to meet freshwater demand, but it generates a concentrated waste stream-reject brine-rich in divalent ions such as Ca2+ and Mg2+. Simultaneously, the cement industry produces large volumes of cement kiln dust (CKD), an alkaline by-product often discarded as waste. This study presents an integrated approach that simultaneously addresses reject brine management, CO2 sequestration, and CKD valorization through mineral carbonation. Under optimal leaching conditions (100 g/L CKD, 15 minutes), over 98% of Mg2+ was removed from the brine, and Ca2+ concentrations increased to 6.82 g/L. CO2 bubbling into the treated brine resulted in carbonate precipitation, yielding products with mixed mineralogy. While phase-pure calcite was obtained in most cases, nesquehonite (MgCO3•3H2O) also formed. Scanning electron microscopy and X-ray diffraction analyses confirmed distinct morphologies and compositions. Product yield ranged from 1.55 to 2.81 g/L, and calcium concentrations in the final solution remained relatively high, indicating incomplete precipitation of the product. These findings show that while CKD alone cannot ensure complete CaCO3 recovery, it substantially reduces the need for synthetic alkalis. The findings demonstrate a sustainable pathway for CO2 capture and waste valorization, contributing to circular economy efforts in the water and construction sectors.