Insight into Influence of Glycerol on Preparing α-CaSO₄·1/2H₂O from Flue Gas Desulfurization Gypsum in Glycerol–Water Solutions with Succinic Acid and NaCl

Abstract

The conversion of CaSO4·2H2O (DH) to CaSO4·1/2H2O (HH) was facilitated by increasing glycerol content from 55% to 85% in glycerol–water mixtures; the average length and diameter of produced α-HH crystals decreased from 60.97 to 7.21 μm and from 15.21 to 5.17 μm, respectively, resulting in a decrease in the average aspect ratio from 4.06 to 1.41. The phase transformation was reduced dramatically from 30 to 3 h. As glycerol content increased in the mixtures, an increase in α-HH maximal relative supersaturation and decrease of ion diffusion rate were hypothesized as explanations for the morphology change in the alpha-hemihydrate (α-HH) produced. The kinematic feasibility of FGD gypsum transition to α-HH in the mixed solutions with the increase of glycerol should also be attributed to the enhancement of maximal relative supersaturation for α-HH precipitation.

Preparation of α-calcium sulfate hemihydrate from industrial by-product gypsum: A review

“…Although the phase transition kinetics was unfavorable, trace amounts of non-lattice cations (such as Na + , K + , Cu 2+ , Zn 2+ , Mn 2+ , and Mg 2+ ) as phase transition accelerators could shorten significantly the time of transformation from DH to HH, of which Na + has the best performance (Jiang et al, 2013). Additionally, Guan et al (2017;2019b) further studied the role of glycerol during the transition of HH from FGD gypsum in the mixture of glycerol and water, and found that in addition to reducing the water activity it could also control the crystal morphology and particle size of α-HH by surface adsorption and adjusting relative supersaturation. At present, this method is still in the laboratory exploration stage, and during its industrialization process, researchers still need to solve many problems, such as alcohol recycling and washing water recovery.…”

Effect of Molecular Structure of Organic Acids on the Crystal Habit of α-CaSO4·0.5H2O from Phosphogypsum

“…Many studies have proven that some organic acids can be used as a crystal modifier to regulate the crystal shape of α-CaSO 4 •0.5H 2 O particles. For instance, the short hexagonal prism α-CaSO 4 •0.5H 2 O, with an aspect ratio of 1.0-1.4, could be obtained by adding succinic acid (C 4 H 6 O 4 ) [15][16][17][18] [20]. In the presence of maleic acid (C 4 H 4 O 4 ), the crystal habit of α-CaSO 4 •0.5H 2 O evolved from a needle-like whisker to a short equiaxial crystal [21].…”

Aspect ratio-controlled preparation of α-CaSO4·0.5H2O from phosphogypsum in potassium tartrate aqueous solution

“…[21][22][23] However, the high-concentration salt solutions can lead to serious equipment corrosion. 24,25 The reverse microemulsion and alcohol-water strategies that require a large amount of surfactants such as CTAB, SDS and organic alcohols such as ethylene glycol and glycerine. 26,27 Although these surfactants and organic alcohols are advantageous for the synthesis of a-CaSO 4 $0.5H 2 O crystals with various morphologies and sizes, the close adsorptions to the surface of a-CaSO 4 $0.5H 2 O crystals cause great trouble for subsequent separation and cleaning.…”