Sustainable synthesis of hydrated magnesium carbonates from industrial wastes via CO2 mineralization

Nesquehonite and hydromagnesite are hydrated magnesium carbonates (HMCs) that can play important roles in cementitious systems due to their seeding effects and contributions to microstructural development. This study presents a novel CO 2 mineralization strategy for producing high-purity nesquehonite and hydromagnesite using two industrial by-products: reject brine and paper sludge ash (PSA). The developed process involved precipitating magnesium from reject brine using PSA, followed by wet carbonation to form Mg(HCO 3 ) 2 solution and carbonated PSA (CPSA). Nesquehonite and hydromagnesite were produced by drying Mg(HCO 3 ) 2 solution at 50 °C and 105 °C, respectively. Characterization results confirmed the high purity and distinct microstructures of the produced HMCs. Isothermal calorimetry demonstrated that CPSA showed potential as a supplementary cementitious material in Portland cement-based mixes, while HMCs performed as effective seeds in Na 2 CO 3 -activated slag cement. The proposed method achieved 85.5% recovery degree of magnesium; moreover, it offers CO 2 sequestration potential through storage in HMCs while reducing alkali costs compared to conventional methods. Overall, this process provides a feasible route for waste valorization and CO 2 mineralization, while highlighting key scale-up considerations including brine variability, impurity tolerance, and energy demand associated with water removal during drying. • Novel CO 2 mineralization strategy, producing nesquehonite and hydromagnesite from reject brine and paper sludge ash (PSA). • Magnesium from reject brine wet carbonated to form Mg(HCO 3 ) 2 solution and carbonated PSA (CPSA). • CPSA used as SCM in PC-based mixes, while HMCs performed as effective seeds in Na 2 CO 3 -activated slag cement. • Proposed method achieved 85.5% recovery degree of magnesium, providing economic benefits through reduced alkali costs. • Process offers a feasible solution for waste utilization, CO 2 sequestration, and cement performance enhancement.