Preparation of α-High-Strength Hemihydrate from Flue Gas Desulfurization Gypsum in AlCl₃–MgCl₂ Solution at Atmospheric Pressure

Abstract

An industrially feasible process was proposed to produce α-calcium sulfate hemihydrate (α-HH) from FGD gypsum without any additives. In this process, an AlCl 3 solution was used to promote the conversion of calcium sulfate dihydrate (DH) to hexagonal prismatic α-HH with high strength at atmospheric pressure. The phase transition kinetics of FGD gypsum was experimentally investigated under conditions: AlCl 3 (2−2.5 m), MgCl 2 (0−0.4 m) existing in raw FGD gypsum, and the solid−liquid ratio (or solid content %) range of 0.1−2 at 363 K. It was found that increasing the concentrations of MgCl 2 in AlCl 3 solution accelerated the conversion. The uniform large hexagonal prism HH product was obtained at the folowing optimal conditions: 2.5 mol/kg AlCl 3 , 0.4 mol/kg MgCl 2 , solid−liquid ratio of 2, and equilibration time of 2 h at 363 K. The phase diagram of the AlCl 3 -MgCl 2 -H 2 O system was determined by measuring solubility of solids. The E-NRTL activity model was used to construct the phase transition diagram of CaSO 4 in AlCl 3 −MgCl 2 media and to judge the stable range of DH and HH.

New Process for Na2CO3 Production from Na2SO4 Based on Modeling the Na2SO4–(NH4)2SO4–MEA–MEG–H2O System

“…In Figure , we present a novel process that effectively separates Na 2 SO 4 and (NH 4 ) 2 SO 4 . If required, ammonia gas recycling is accomplished by the decomposition of ammonium sulfate using low-grade limestone (CaCO 3 ), − in which alpha-type calcium sulfate hemihydrate (CaSO 4 ·0.5H 2 O) can be produced. , As noted above, in order to recycle ammonia, the Solvay process generates a substantial amount of wastewater and solid waste residues. However, our new process provides a feasible solution to these environmental issues while generating commercially viable products: soda ash, ammonium sulfate, or even high-strength gypsum.…”

Process for the Remediation of Titanogypsum (Red Gypsum) Using Weak Acid and CaCl2 to Produce Saleable α-Gypsum and FeCl2·4H2O

“…2:1 m HCl and 3 m FeCl 2 ) shows that within 2 h DH has been almost completely transformed into hexagonal prismatic HH with an average column length of 50 μm, whose morphology is required for α-high-strength gypsum. 21 Although calcium sulfate hemihydrate becomes coarser after 6 h, AH is still very limited. The addition of 1 m CaCl 2 into the solution of 1 m HCl and 3 m FeCl 2 , as shown in Figure 4 (no.…”

Unveiling the organic acids with auxiliary functional groups effect on α‐hemihydrate gypsum: Ab initio calculations

“…This important gel material boasts a low aspect ratio, exceptional mechanical strength, and biocompatibility. 14 Numerous studies have highlighted the strong correlation between the crystal morphology and size of α-HH and its mechanical properties. [15][16][17] Specifically, it has been observed that α-HH crystals with a lower aspect ratio demonstrate superior mechanical strength when compared to needle-shaped or higher aspect ratio crystals.…”

“…However, the most promising and lucrative application thus far has been the conversion of PG into α‐hemihydrate gypsum (α‐HH, CaSO 4 ·0.5H 2 O). This important gel material boasts a low aspect ratio, exceptional mechanical strength, and biocompatibility 14 …”