Calcium oxalates are naturally occurring biominerals and can be found as a byproduct of some industrial processes. Recently, a new and green method for carbon capture and sequestration in stable calcium oxalate from oxalic acid produced by carbon dioxide reduction was proposed. The reaction resulted in high-quality weddellite crystals. Assessing the stability of these weddellite crystals is crucial to forecast their reuse as solid-state reservoir of pure CO₂ and CaO in a circular economy perspective or, eventually, their disposal. The thermal decomposition of weddellite obtained from the new method of carbon capture and storage was studied by coupling in-situ high-temperature X-ray powder diffraction and thermogravimetric analysis, in order to evaluate the dehydration, decarbonation, and the possible production of unwanted volatile species during heating. At low temperature (119–255 °C), structural water release was superimposed to an early CO₂ feeble evolution, resulting in a water-carbon dioxide mixture that should be separated for reuse. Furthermore, the storage temperature limit must be considered bearing in mind this CO₂ release low-temperature event. In the range 390–550 °C, a two-component mixture of carbon monoxide and dioxide is evolved, requiring oxidation of the former or gas separation to reuse pure gases. Finally, the last decarbonation reaction produced pure CO₂ starting from 550 °C.

Epitaxial growth is a long-standing crystallization phenomenon of great technological interest. Here, we present the use of a new methodology approach making full use of the concept of adhesion energy between two different crystal phases, A and B. This is achieved by using (i) the traditional crystal-chemical fit between A and B; (ii) the extensive use of Bollmann's approach to the 2D-lattice coincidences; (iii) the most accurate methods of calculation of the specific adhesion energy of A/B. We illustrate the approach with two case studies: (i) how epilayers of inorganic and monoclinic Li₂CO₃ (zabuyelite) can modify the crystal habit of the CaCO₃ polymorphs, calcite (rhombohedral) and aragonite (orthorhombic); (ii) how a complex organic substance like sericin (silk fibroin like protein-SFLP) could stabilize aragonite and calcite, the most diffuse CaCO₃ polymorphs, simply reproducing and mimicking in the laboratory what nature does.

2D and 3D epitaxies of the main {010}, {001} and {100} forms of deposited bassanite (CaSO₄·0.5H₂O) on {10.4} calcite (CaCO₃) as a substrate are described to provide a theoretical crystallographic background for the replacement of calcite by bassanite both in nature and in the laboratory and by weathering linked to cultural heritage. First, epitaxy in the third dimension, perpendicular to the investigated interfaces, has been verified in order to establish whether adsorption/absorption can occur (as anomalous mixed crystals) at the bassanite/calcite epi-contacts. Secondly, and by applying the Hartman–Perdok method, 2D lattice coincidences have been obtained from the physical-geometric matches of bonds running in the common directions within the elementary slices facing the substrate/deposit interfaces. This research represents the second and more detailed part of a wider program extended to the epi-interactions between the following pairs: (i) {010}-gypsum/{10.4}-calcite (just published); (ii) bassanite/{10.4}-calcite (the present work); and (iii) anhydrite (CaSO₄)/{10.4}-calcite (coming soon).

3D-epitaxy of the {010} pinacoid of deposited gypsum (CaSO₄·2H₂O) on the substrate {10.4} calcite rhombohedron is described, in order to give a theoretical background to the replacement of calcite with gypsum both in the laboratory and by weathering in nature. 2D-lattice coincidences are geometrically obtained from the matching of periodic bond chains (PBCs) running within the elementary slices facing towards the substrate/deposit interfaces. The epitaxy in the third dimension, perpendicular to the interfaces, has been verified as well, to establish if ad/absorption occurs (anomalous mixed crystals) at the calcite/gypsum contact. This research represents the reticular part of a wider program extended to the epi-interaction among the gypsum/calcite, gypsum/bassanite (CaSO₄·1/2H₂O) and gypsum/anhydrite (CaSO₄) couples.