Correlating particle size distribution and thermal decomposition of intensely ground limestone and dolostone with microstructure and structural changes.

Abstract

An extensive investigation in limestone and dolostone ground in a planetary ball mill was achieved bearing in mind the different paths often observed in particle size reduction and agglomeration between these rocks and their increasing use in ultrafine size ranges for eco-friendly engineering applications. Two samples ground (dry) in a planetary ball mill up to 32 h were examined using laser scattering, physisorption, electron microscopy, X-ray diffraction, infrared spectroscopy and thermal analysis. Static hardness and crystal grain sizes were measured in parent rock specimens. For limestone, the apparent grinding limit (12 µm) was reached after 1 h, and no changes were observed in lattice strain, crystallite size and infrared bands related to CO32- vibration modes. For dolostone, these properties changed significantly when the grinding limit (6 µm) was achieved (8 h). Calcite-aragonite transformation was mostly observed in intensely ground dolostone. The activation energy for thermal decomposition of calcite and dolomite was correlated with lattice strain and particle agglomeration. The lower grinding rate noticed for dolostone was attributed to its refined grain size. Distinct energy dissipation mechanisms were portrayed once the grinding limit was reached: agglomeration and deagglomeration cycles in limestone; plastic deformation and growth of strong agglomerates in dolostone.