Controllable Synthesis and Formation Mechanism of Spherical MgCO ₃ Prepared Using MgCl ₂ ·6H ₂ O and Urea via a Deep Eutectic Solvent Method

Controllable spherical anhydrous MgCO₃ remains a significant challenge that restricts its wider application. A green and efficient strategy for morphology-regulated anhydrous MgCO₃ was investigated using an ethylenediaminetetraacetic acid (EDTA)-modified deep eutectic solvent (DES). Uniform spherical particles with an average size of 12.78 μm were obtained at 160 °C for 1 h and grew to 15.03 μm after 2.5 h. At 180 °C, spherical anhydrous MgCO₃ formed within 0.5 h, with the particle size increasing from 12.95 to 20.13 μm as the reaction was extended. The characteristic reflections at 2θ = 32.6°, 42.9°, and 53.9° were observed with no detectable impurities. The absence of the IR band near 1640 cm^-1 and a residual mass of 47.6% after heating to 600 °C under N₂ further verified the anhydrous nature and high purity. The spherical MgCO₃ exhibited a smaller peak shift of the (104) plane during heating and a higher <i>T</i>_5% value, indicating superior thermal stability over its cubic counterpart. The main formation mechanism is that EDTA can strongly chelate Mg²⁺, displace its coordinated water molecules, and regulate ion release, thereby changing the growth mechanism from interface-reaction-controlled to diffusion-controlled, which promotes isotropic spherical growth. It provides an environmentally benign route for controlled MgCO₃ synthesis.