High-value added utilization of magnesium resource in brine via indirect CO2 mineralization to synthesize MgCO3 3H2O whiskers for excellent flame retardant

Direct discharge of seawater desalination brine causes ecological imbalances in marine environments and wastage of chemical resources, and CO2 is the predominant greenhouse gas driving global warming. In this work, we propose a combined and highly-efficient treatment strategy of seawater desalination brine and CO2, where NH4HCO3 as an indirect carbon source is employed to convert Mg2 + from seawater desalination brine to MgCO3 3H2O whiskers. The utilization ratio of Mg 2+- is 100 %. The synthesized MgCO3 3H2O whiskers possess the finest diameter of 500 nm and satisfactory aspect ratio of 60, compared with those reported in the literature. The purity and yield of the product are 99.61 % and 100 %, respectively. The remaining (NH4)2CO3 in the mother liquor could reabsorb CO2 to regenerate NH4HCO3 for recycling. The synthesized MgCO3 3H2O whiskers could significantly enhance the mechanical properties of epoxy resin. Notably, the addition of MgCO3 3H2O whiskers promote formation of the expansion structure during combustion, which effectively inhibits transfer of heat, oxygen, and smoke production. The residue MgO exerts a promoting effect on crosslinking and carbonization of char residue, and acts as a barrier against the transfer of heat and pyrolysis products. Consequently, the obtained composite exhibits the improved flame retardancy with V-0 grade and increased limiting oxygen index to 30.2 %. This work simultaneously realizes the complete extraction and high-value added utilization of Mg2+ from seawater desalination brine as well as the highly-efficient conversion of CO2, and demonstrates that MgCO3 3H2O whiskers are an ideal candidate for flame retardants in practical applications.