Sustainable synthesis of Ca–Al hydrocalumite via acid leaching and hydrothermal crystallization

This study investigates the synthesis of a Ca–Al hydrocalumite-type layered double hydroxide (LDH) from calcite and MK through acid leaching, alkaline precipitation, and hydrothermal crystallization. The objective was not only to assess the feasibility of this route from minimally processed mineral precursors, but also to identify the conditions governing selective hydrocalumite (HC) formation in a Ca–Al system. The effects of HCl concentration, aging time, aging temperature, pH during aging, crystallization time, and crystallization temperature were systematically examined. X-ray diffraction results showed that phase formation strongly depends on the balance between precursor dissolution, release of calcium and aluminum species, and suppression of silica-related secondary reactions. The most favorable conditions were obtained with 1 M HCl, 30 min aging at 45 °C, pH 11.5, and hydrothermal crystallization at 50 °C for 18 h. Under these conditions, the synthesized product exhibited the most pronounced HC reflections, with limited formation of katoite, anorthite, and residual calcite. FTIR and TG/DTA analyses supported the formation of a hydrated Ca–Al hydrocalumite-type phase containing carbonate species. Compared with a commercial reference, the synthesized material displayed a finer and more homogeneous particle size distribution, a more open @lamellar morphology, and lower specific surface area and porosity, while maintaining strong basicity and buffering capacity in aqueous media. These results demonstrate that HC can be successfully obtained from simple mineral resources, provided that synthesis parameters are carefully controlled, and open the way for more economical and accessible preparation routes for Ca–Al layered materials.