Determination and Analysis of the Solubility of CaSO₄·2H₂O and α-CaSO₄·0.5H₂O in Formamide Aqueous Solutions at T = 303.15–363.15 K

Abstract

The solubility of calcium sulfate dihydrate (DH) and α-calcium sulfate hemihydrate in formamide aqueous solutions with 0–13 m formamide at temperatures from 303.15 to 363.15 K was measured by the dissolution equilibrium method. Formamide has a solubilization effect similar to the salt effect; the solubility of calcium sulfate dihydrate and α-calcium sulfate hemihydrate first increases significantly as the concentration of formamide aqueous solution increases. When the solubility reaches the maximum value, it decreases gradually. The modified Apelblat–Jouyban–Acree model shows good agreement with experimental values; hence, it may be suitable in describing the solubility of calcium sulfate dihydrate and α-calcium sulfate hemihydrate in the formamide aqueous solution at the temperatures ranging from 303.15 to 363.15 K under 88.35 kPa. On comparing the solubility of calcium sulfate dihydrate and α-calcium sulfate hemihydrate in the formamide aqueous solution, it was found that the solubility of α-calcium sulfate hemihydrate is lower than that of calcium sulfate dihydrate, being above 8.3418 and 3.7286 mol·kg–1 when the temperatures are 353.15 and 363.15 K, respectively, which is beneficial to the conversion of calcium sulfate dihydrate into α-calcium sulfate hemihydrate.

Solubility and Physical Properties of α-Calcium Sulfate Hemihydrate in NaCl and Glycerol Aqueous Solutions at 303.15, 323.15, and 343.15 K

“…Compared with formamide aqueous solution, 24 NaCl has the same properties as formamide, which makes the solubility of calcium sulfate increase first and then decrease. Compared with the solubility of DH in the NaCl−glycerol−H 2 O system, 25 the effect of glycerol and NaCl on the solubility of α-HH is the same as that on DH.…”

“…Our group has studied the solubility of DH and α-HH in a formamide aqueous solution and DH in a glycerol−sodium chloride aqueous solution. 24,25 Therefore, in this paper, we studied the solubility behavior of α-HH in a NaCl−glycerol−H 2 O system with 0−6 molality (m) NaCl and 30−80 wt % glycerol at 303.15, 323.15, and 343.15 K. The relationship among solubility, density, viscosity, and NaCl concentration was established by a polynomial equation.…”

“…Because the solubility and crystal morphology of calcium sulfate change by adding an organic solvent, it is necessary to study the solubility of calcium sulfate in an organic solvent–salt–H 2 O system. Our group has studied the solubility of DH and α-HH in a formamide aqueous solution and DH in a glycerol–sodium chloride aqueous solution. , …”