Structural Characteristics Of Amorphous Calcium Sulfate: Evidence To The Role Of Water Molecules

Amorphous calcium sulfate (ACS) is intimately involved in the crystallization of calcium sulfate minerals, a major contributor to sulfur sequestration and a technological hindrance of scale formation, but its structural characteristics remain largely undiscovered. Here, we studied the structure of ACS nanoparticles captured under low CaSO4 concentration conditions. The ACS nanoparticles have a proto-gypsum property ranging from short-range to medium-range order, and water molecules are key structural constituents that are in a disordered state and 8-fold coordinated with Ca in the first coordination shell. More importantly, on a molecular scale, we give evidence concerning the energetic role of water molecules in promoting ions transport, molecule rearrangement, and development of a local coordination environment that facilitates structural evolution of ACS. This work reveals some important structural characteristics of ACS and has significance in providing a better understanding of the crystallization and biomineralization of water-bearing minerals.