Preparation of Porous CaCO3·MgO Powder from Dolomite via Na3PO4-Assisted Calcination

Structural stability and pore control of the resulting products remain challenging during dolomite calcination due to the complex crystal structure of dolomite, limiting the quality and performance of the final products. This paper systematically investigated how calcination parameters governed the structure of Na3PO4-bearing dolomite derivatives in low temperature regions. The results revealed that controlled calcination of dolomite enabled the synthesis of hierarchically porous partially decomposed dolomite (PDD), consisting of a porous Mg-calcite framework and MgO nanospheres anchored to the pore networks. Magnesium retention in Mg-calcite was governed by temperature-time interplay, balancing kinetic trapping and thermodynamic expulsion. MgO coarsening followed temperature-dependent pathways. At 550 °C, low temperature enabled controlled MgO growth (59–73 nm), while 650 °C triggered sintering-dominated fusion (160 nm). At ≤550 °C, nano-MgO dispersion stabilized mesopores, whereas ≥600 °C MgO coarsening accelerated meso-macro pore transformation, culminating in sintering-induced collapse. Correspondingly, specific surface area underwent a gradual decline at lower temperatures, in contrast to the rapid decline at 650 °C. By revealing how thermal processing governs phase evolution and microstructure, this work identifies the key conditions for optimization of the microstructure and Mg content of PDD composites.