A facile method of transforming FGD gypsum to α-CaSO4·0.5H2O whiskers with cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solution

Abstract

A facile method to transform flue gas desulfurization gypsum (FGD gypsum) to α- calcium sulfate hemihydrate (α-HH) whiskers with high aspect ratios mediated by cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solutions was studied. Addition of KCl facilitated the dissolution of calcium sulfate dihydrate (DH) and created a much higher supersaturation, which could come into being a larger driving force for the phase transformation from DH to α-HH. CTAB as the crystal modifier can significantly promoted 1-D growth of α-HH whiskers along the c axis and the presence of 0.25% CTAB (by weight of FGD gypsum) resulted in the increase of the average aspect ratio of α-HH whiskers from 28.9 to 188.4, which might be attributed to the preferential adsorption of C16H33(CH3)3N+ on the negative side facets of α-HH crystal.

Crystallization Kinetics of α-Hemihydrate Gypsum Prepared by Hydrothermal Method in Atmospheric Salt Solution Medium

“…The results show that the crystallinity of α-HH got higher with the increase of time and temperature, and the solution of α-HH quantity increased. In this study, the XRD peak of the α-HH sample (Corresponding to different crystallization temperatures) was very consistent with the XRD peak of the α-HH sample published in previous references [25,32,33]. The effect of the reaction temperature on the crystallinity of the sample is terminated in Table A1 in the appendix.…”

Inhibition of calcium sulphate hemihydrate crystallization under simulated conditions of phosphoric acid evaporation

“…Several studies have been done on modifying phase transformation gypsum to bassanite in glycerol-water solutions. [21][22][23] Driven by complexation, both malic acid and sodium dodecyl sulphate (SDS) were observed preferentially adsorbing to the more Ca 2+ dense planes intersecting the c-axis of crystals, reducing the average aspect ratio. [21,23] Cetrimonium bromide (CTAB), on the other hand, appeared to instead adsorb to the planes parallel to the c-axis rich in SO 4 2À , reducing the crystal aspect ratio instead.…”

“…[21,23] Cetrimonium bromide (CTAB), on the other hand, appeared to instead adsorb to the planes parallel to the c-axis rich in SO 4 2À , reducing the crystal aspect ratio instead. [22] However, the surrounding media has a large impact on the way that additives interact with crystals, particularly in regard to additive conformation and (de) protonation. In reverse microemulsions, CTAB and SDS altered bassanite similarly, with the exception that at higher CTAB/H 2 O ratios CTAB appeared to adsorb and slow all crystal faces, resulting in decreased aspect ratios.…”

Effects of Cationic Polyacrylamide on Hydrothermal Formation of Ultralong α‐CaSO4·0.5H2O Whiskers

“…obtained α‐CaSO 4 ·0.5H 2 O whiskers with tunable aspect ratio by using succinic acid as the morphology modifier. The effective use of other organic additives such as sodium dicarboxylates, cetyltrimethyl ammonium bromide (CTAB), malic acid, and ethylene glycol has also been reported . The morphology modification effects of these organic species were generally attributed to their selective adsorption onto different facet of the α‐CaSO 4 ·0.5H 2 O crystals.…”