LAUSR

Abstract The hydrothermal method is efficient in synthesizing alpha calcium sulfate hemihydrate (α-CSH) particles from flue gas desulfurization gypsum. This study investigates the effects of LiCl·H2O solution with different carboxylates on the conversion process. Under optimal operating conditions, hexahedral column shaped crystals are obtained to verify the feasibility of this process. Results reveal that carboxylates especially disodium ethylenediamine tetraacetate (EDTA disodium) in conjunction with LiCl influences crystal morphology and nucleation. A fairly concentrated LiCl·H2O solution (over 2 M) with EDTA disodium (over 0.01 M) shortens reaction time and reduces particle size. Each crystal plane presents a balanced growth rate to create column objects because of the complexation reaction between EDTA disodium and calcium ions. The results of X-ray diffraction coupled with thermogravimetry and differential scanning calorimetry confirm that α-CSH is the only product.