Synthesis of Calcium Monosulfoaluminate

For the synthesis of calcium monosulfoaluminate, reagent-grade materials were used:

Calcium carbonate (CaCO₃, Eksparas, Lithuania), with purity ≥ 99.0 wt.% of CaCO₃;

Aluminium hydroxide (Al(OH)₃, Honeywell, Germany) with purity ≥ 99.0 wt.% of Al(OH)₃;

Gypsum (CaSO₄·2H₂O, Lach–Ner, Poland), which consisted of 27.07 wt.% of Ca, 20.64 wt.% of S, and other substances (up to ~ 1% wt.%).

The composition of the initial mixture was prepared based on ye`elimite (Ca₄Al₆O₁₂(SO₄) stoichiometry. Calcium oxide (CaO) was obtained from calcium carbonate calcinated at 950 °C temperature for 1 h (the loss on ignition ~ 42.9%), where the quantity of free CaO was equal to ~ 98.2 wt.%. Meanwhile, the aluminium oxide (Al₂O₃) was prepared by dehydration of aluminium hydroxide at 475 °C temperature for 4 h (the loss on ignition ~ 34.2%). Both mentioned substances were sintered in an electric muffle furnace SNOL 8.2/1100 (Umega group, AB, Lithuania).