Structural characteristic and formation mechanism of hemihydrate calcium sulfate whiskers prepared using FGD gypsum--颗粒学报PARTICUOLOGY

Zhang, X., Ran, L., Wang, X., Jin, B., Zhang, J., Li, S., & Yang, L. (2022). Structural characteristic and formation mechanism of hemihydrate calcium sulfate whiskers prepared using FGD gypsum. Particuology, 62, 98-103. https://doi.org/10.1016/j.partic.2021.04.010

Structural characteristic and formation mechanism of hemihydrate calcium sulfate whiskers prepared using FGD gypsum

Xiaoting Zhang, Lingwei Ran, Xiao Wang ^*, Biao Jin, Jianwu Zhang, Shanying Li, Liushuan Yang

Department of Civil & Material Engineering, Henan University of Urban Construction, Pingdingshan 467036, Henan, China

10.1016/j.partic.2021.04.010

Volume 62, March 2022, Pages 98-103

Received 10 March 2021, Revised 8 April 2021, Accepted 20 April 2021, Available online 9 May 2021, Version of Record 17 November 2021.

E-mail: 30010906@hncj.edu.cn

Highlights

• HH-CSWs were synthesized from FGD gypsum at different holding times.

• Holding time increased sample's diffraction peaks intensity and aspect ratio.

• H₂O channel's shape and size in sample are different with reported data.

• H₂O released as Ca–O–H bonds broken, formed novel Ca–O–S bonds in HH-CSWs crystals.

Abstract

Hemihydrate calcium sulfate whiskers (HH-CSWs) were hydrothermally synthesized in a sulfuric acid solution at 120 °C for different holding times (20, 40, and 60 min). The phase structures and morphologies were characterized by XRD and SEM, respectively. The XRD pattern of the sample under 60 min was refined via the Rietveld fitting method. The structure models of the HH-CSW sample under a 60-min holding time was established based on Rietveld fitting results. No difference in the positions of diffraction peaks was determined. The as-prepared holding time increased the intensity and aspect ratio of the diffraction peaks of both samples. In the prepared HH-CSW structure, Ca–O polyhedron is a 12-sided polyhedron similar to that in the gypsum structure; the Ca atom is located in two positions in the one-unit cell; the H₂O channel along the c-axis similar is O-shaped and bigger than that in hexagonal and monoclinic CaSO₄·0.5H₂O structures. Therefore, although the prepared HH-CSW crystals’ structure are similar to that of the reported hexagonal and monoclinic CaSO₄·0.5H₂O structures, they are not the same. The formation mechanism of HH-CSW from flue gas desulfurization (FGD) gypsum is discussed based on the analysis of gypsum structure.

Graphical abstract

Keywords

FGD gypsum; HH-CSW; Rietveld method; Crystal structure

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