Eco-Friendly Synthesis of Mg-Al-CO3 Layered Double Hydroxides from Seawater Desalination Brine and Their High-Efficiency Adsorption of Congo Red Dye from Aqueous Solutions

Synthetic azo dyes comprise over 70% of the world’s textile wastewater discharges, making the design of highly efficient remediation materials a well-aligned target for sustainable development goals. This study addresses this challenge through a novel ‘waste-to-value’ circular economy framework by synthesizing a robust Mg-Al-CO 3 layered double hydroxide (LDHs) using the industrial Seawater Reverse Osmosis (SWRO) desalination brine as a zero-cost magnesium reservoir. Firstly, native Ca 2+ impurities were selectively removed by Na 2 CO 3 precipitation to ensure the purity of the material, then a controlled co-precipitation process with aluminum precursors was performed. The structural, textural and morphological properties of the brine derived LDHs were well characterized by XRD, FTIR, ICP-OES, SEM, TEM and EDS analyses. The engineered material was then used for the selective removal of Congo Red (CR) as a representative recalcitrant azo dye, the most industrially used. The equilibrium data were well described by Langmuir and Toth monolayer models with a very good maximum adsorption capacity of 292 mg g −1 . The kinetic profiles followed a pseudo second-order model, with almost similar mass transfer rate and capacity in the saline groundwater (salinity 700 mg L −1 ) doped with CR. Thermodynamic parameters (ΔH°= 35.2 kJ mol −1; Ea = 36.5 kJ mol −1 ) validated a thermally activated, spontaneous and endothermic mechanism driven by collaborative electrostatic surface attraction, hydrogen bonding and interlayer ion-exchange. Moreover, competitive binary assays with Methylene Blue presented an absolute selectivity towards anionic species. The material showed excellent structural robustness and economic feasibility, achieving more than 80 percent removal efficiency after five consecutive adsorption-desorption cycles with a 1 M NaOH regeneration agent. Finally, analysis of the ICP-OES effluent after adsorption showed no leaching of toxic secondary metals (Al = 0.08 mg L −1 ; Mg = 2.60 mg L −1 ), ensuring rigorous environmental safety well under international water quality standards. These findings make the brine-derived LDHs an elite, safe, reusable and highly cost-effective candidate for scalable textile effluent decontamination. Environmental implications This work introduces a high-impact, environmentally friendly strategy that addresses two critical environmental hazards: the disposal of hypersaline desalination brine and the persistence of organic dyes in wastewater. Seawater brine, is here the precursor for the synthesis of Mg-Al-CO 3 layered double hydroxides (LDHs), significantly reducing brine-related environmental risks and reliance on non-renewable raw materials. The LDHs demonstrate outstanding adsorption performance toward Congo Red dye, enabling efficient removal of a toxic pollutant from aqueous systems. This study establishes a waste-to-resource pathway that minimizes environmental burden, mitigates hazardous discharges, and advances scalable solutions for sustainable desalination and hazardous wastewater treatment.