Towards Sustainable Carbonate Synthesis: Mechanochemical Synthesis and In situ X-ray Powder Diffraction Studies

Alkaline-earth metal carbonates like magnesite (MgCO₃), dolomite (MgCa(CO₃)₂), and calcite (CaCO₃) are typically formed via atmospheric CO₂ carbonatization. For the synthesis of many carbonates, high pressures or temperatures are required. Unlike these methods, the mechanochemical synthesis of carbonates utilizes ball milling to apply mechanical energy, inducing structural and physicochemical changes and enabling chemical reactions through shear forces, abrasion, impact, and extrusion.[1]

This study investigates the mechanochemical synthesis of K₂Ca(CO₃)₂ polymorphs, specifically fairchildite and buetschliite, synthesized from CaCO₃ and K₂CO₃ in a shaker mill (Retsch MM400). The synthesis and phase transformation pathways were explored using both ex situ laboratory analysis and in situ X-ray powder diffraction, providing insights into reaction pathways and crystallographic transformations. The primary objective of this systematic investigation is to examine how variables such as milling frequency and water/hydroxyl content influence the transformation pathway between the structurally disordered high-temperature polymorph fairchildite and the thermodynamically stable polymorph buetschliite.[2]

This mechanochemical approach also opens pathways for synthesizing other carbonate systems, such as eitelite (Na₂Mg(CO₃)₂), dolomite (MgCa(CO₃)₂), and nyerereite (Na₂Ca(CO₃)₂). Similar studies can be conducted to investigate how variables like temperature, moisture, reactant ratios, and milling conditions influence their polymorphic transformations, providing broader insights into phase control across diverse carbonate systems.

References

1. Weidenthaler, C. In Situ Analytical Methods for the Characterization of Mechanochemical Reactions. Crystals 2022, 12, 345.
2. Kahlenberg, V., et al. Mechanochemical synthesis and transformation of the polymorphic double carbonates fairchildite and buetschliite, (K₂Ca(CO₃)₂): an in situ X-ray powder diffraction study. RSC Mechanochemistry, 2025, 2, 152.