Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4–NaCl

Wang, X., Yang, L., Zhu, X., & Yang, J. (2014). Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H2SO4–NaCl–H2O system. Particuology, 17, 42–48. https://doi.org/10.1016/j.partic.2013.12.001

Preparation of calcium sulfate whiskers from FGD gypsum via hydrothermal crystallization in the H₂SO₄–NaCl–H₂O system

Xiao Wang ^{a b}, Liushuan Yang ^b, Xinfeng Zhu ^b, Jiakuan Yang ^a *

a School of Environmental Science and Engineering, Huazhong University of Science and Technology (HUST), Wuhan 430074, China
b Department of Civil and Material Engineering, Henan University of Urban Construction, Pingdingshan 467036, China

10.1016/j.partic.2013.12.001

Volume 17, December 2014, Pages 42-48

Received 26 August 2013, Revised 28 November 2013, Accepted 6 December 2013, Available online 28 January 2014.

E-mail: jkyang@mail.hust.edu.cn; yjiakuan@hotmail.com

Highlights

• Calcium sulfate whiskers (CSWs) were prepared from purified FGD gypsum in H₂SO₄–NaCl–H₂O system.

• Crystallization of CSW could be controlled via the formulas of H₂SO₄ and NaCl.

• H₂SO₄ and NaCl have opposite effects on the solubility of FGD gypsum.

Abstract

Little attention has thus far been paid to the potential effect of solution composition on the hydrothermal crystallization of calcium sulfate whiskers prepared from flue-gas desulfurization (FGD) gypsum. When purified FGD gypsum was used as raw material, the morphology and phase structure of the hydrothermal products grown in pure water, H₂SO₄–H₂O, NaCl–H₂O, and H₂SO₄–NaCl–H₂O solutions as well as the solubility of purified FGD gypsum in these solutions were investigated. The results indicate that calcium sulfate whiskers grow favorably in the H₂SO₄–NaCl–H₂O system. When prepared using 10–70 g NaCl/kg gypsum −0.01 M H₂SO₄–H₂O at 130 °C for 60 min, the obtained calcium sulfate whiskers had diameters ranging from 3 to 5 μm and lengths from 200 to 600 μm, and their phase structure was calcium sulfate hemihydrate (HH). Opposing effects of sulfuric acid and sodium chloride on the solubility of the purified FGD gypsum were observed. With the co-presence of sulfuric acid and sodium chloride in the reaction solution, the concentrations of Ca²⁺ and SO₄²⁻ can be kept relatively stable, which implies that the crystallization of the hydrothermal products can be controlled by changing the concentrations of sulfuric acid and sodium chloride.

Graphical abstract

Keywords

FGD gypsum; Calcium sulfate whisker; Hydrothermal crystallization; Solution composition

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