Energy-efficient calcination-free mg cement recovered from desalination brine

Abstract

Conventional ordinary Portland cement (PC) or magnesium-based cements' production typically involves energy-intensive calcination. In this work, the recovery of calcination-free Mg(OH)₂-based low carbon cements from reject brine was demonstrated, addressing the global challenge of carbon neutrality. The use of electrochemical approach can reduce energy intensity by 52–78 % compared to PC, lowering it to 0.87–1.93 MWh per ton of Mg(OH)₂, while eliminating 0.56 MWh (2.0 GJ) per ton of MgO required for calcination, targeting net carbon emissions of −0.31-0.41 ton CO₂/ton. To enhance production efficiency and quality, the nanostructure of Mg(OH)₂ was tailored using urea as a nano modifier and cross-linker in the harvesting process. At an optimum modifier dosage, Mg(OH)₂ particles aligned with high surface exposure, thus presenting greater reactivity, pore volume and specific surface area. Thermogravimetric (TG), X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses performed on Mg(OH)₂ revealed the optimum modifier content. The use of this Mg(OH)₂ as a binder in carbonated samples revealed dypingite and nesquehonite as the main reaction products. The performance of Mg(OH)₂ as a binder was influenced by its properties, which were dependent on the urea dosage. A critical modifier dosage of 0.2 mol/L yielded brucite with the highest SSA and reactivity, translating to the highest strength among all samples. The underlying mechanism could be attributed to the interlocking and synergistic effects arising from the optimal co-existence of rosette-like dypingite and rod-like nesquehonite.