A facile method of transforming FGD gypsum to \u03b1-CaSO4\xb70.5H2O whiskers with cetyltrimethylammonium bromide (CTAB) and KCl in glycerol-water solution

Qingjun Guan,Wei Sun,Yuehua Hu,Zhigang Yin,Changping Guan

doi:10.1038/s41598-017-07548-3

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.

Highlights

Flue gas desulfurization gypsum (FGD gypsum), which is mainly composed of CaSO4·2H2O (DH), is the industrial waste residue produced by limestone-gypsum wet process of flue gas desulfurization technology
As KCl concentration increased, α- calcium sulfate hemihydrate (α-HH) generated by FGD gypsum would continue to dehydrate and be more transformed into anhydrous calcium sulfate (AH)
Conclusion α-HH whiskers with high aspect ratios could be prepared by using FGD gypsum in glycerol-water solutions with cetyltrimethylammonium bromide (CTAB) and KCl under facile conditions

Summary

Introduction

Flue gas desulfurization gypsum (FGD gypsum), which is mainly composed of CaSO4·2H2O (DH), is the industrial waste residue produced by limestone-gypsum wet process of flue gas desulfurization technology. The gypsum can be used as the raw material of a cement retarder[1], or processed to the building gypsum (β- CaSO4·0.5H2O)[2] or high-strength gypsum (α- CaSO4·0.5H2O)[3, 4] All of these products are low value-added. Few research was carried out to explore the preparation of α-HH whiskers with high aspect ratios by use of FGD gypsum under facile conditions. We introduced a facile method to prepare α- CaSO4·0.5H2O (α-HH) whiskers with small diameters and high aspect ratios by use of FGD gypsum in glycerol-water solutions. CTAB and KCl were used as the crystal modifier and phase transformation accelerator, respectively, and the corresponding mechanism was studied

Methods

Results

Conclusion