Single-Crystal Regular Hexagonal Microplates of Two-Dimensional α-Calcium Sulfate Hemihydrate Preparation from Phosphogypsum in Na₂SO₄ Aqueous Solution

Abstract

Large quantities of solid waste phosphogypsum (PG) not only occupy the farmland but also cause severe pollution to the surrounding environment. The most effective way to achieve a high-value utilization of PG is to prepare α-calcium sulfate hemihydrate (α-HH) with various morphologies. In this study, we developed a simple and Cl-free one-pot synthetic strategy to effectively transform PG into single-crystal α-HH regular hexagonal microplates (RHMPs) in Na 2 SO 4 aqueous solution at 98 °C assisted with sodium citrate (TSC). Na 2 SO 4 plays a role in accelerating the transformation rate, whereas TSC regulates the crystal habit of α-HH from rod to regular hexagonal plate. The rate of DH−α-HH transformation in aqueous solutions can be effectively controlled by regulating water activity (α H 2 O ), which decreases with the increase in Na 2 SO 4 concentration. Crystal habit control is attributed to the strong preferential adsorption of citrate ions to the ( 001) and ( 002) top facets of α-HH by chemical adsorption. The paste made from the obtained α-HH RHMPs deserves higher dry compressive/bending strength of 46.1/15.2 MPa, which is comparable with that of α-HH prepared by other methods. Our work provides a simple and low-corrosiveness strategy to transform PG into α-HH RHMPs with excellent mechanical property, thus showing great promise for a wide range of challenging reuse of solid waste in environmental protection.

Preparation of α-High-Strength Hemihydrate from Flue Gas Desulfurization Gypsum in AlCl3–MgCl2 Solution at Atmospheric Pressure

“…thickness of 17 and 3 μm, respectively. A similar shape of HH crystals was reported by Sun et al,18 but they used sodium citrate as a crystal modifier in concentrated Na 2 SO 4 media. It is also observed that the concentrations of AlCl 3 solution have little effect on the crystal morphology of the final HH solid.4.1.2.…”

“…The effects of metal ions such as Na + , K + , Mg 2+ , Cu 2+ , Al 3+ , and Fe 3+ on the crystal morphology and size of calcium sulfate whiskers in aqueous HCl solutions were also investigated. , The results revealed that Al 3+ ions resulted in bigger and shorter crystals of HH . Additives of succinic acid, sodium citrate, and maleic anhydride proved to be more effective morphology modifiers for crystals of α-HH.…”

“…15,16 The results revealed that Al 3+ ions resulted in bigger and shorter crystals of HH. 16 Additives of succinic acid, 17 sodium citrate, 18 and maleic anhydride 19 proved to be more effective morphology modifiers for crystals of α-HH.…”

Effects of Co Doping on the Growth and Photocatalytic Properties of ZnO Particles

“…There are several methods available for controlling morphologies at present, such as the sputtering deposition technique [ 12 ], chemical vapor deposition [ 13 ], pulsed laser deposition [ 14 ], and the co-precipitation process [ 15 ]. Among these methods, the aqueous solution method appears more favorable in an economical and large-scale production [ 16 , 17 , 18 ]. Particles with specific crystal facets and complex corrugated particles with tips also have good photocatalytic activity and dispersion properties [ 19 , 20 , 21 , 22 ].…”

Self-Symmetrical 3D Hierarchical α-Calcium Sulfate Hemihydrate Twin-Flowers Composed of Microplates as a Renewable Material for Water Separation from Water-in-Oil Emulsion

“…19 Recently, controlling the morphology of HH crystals has attracted much more attention in the scientific community because of the morphology-dependent properties, such as mechanical strength, filtration rate, packing density, and so on. 21 So far, great progress has been made in the synthesis of HH with well-defined morphologies such as whiskers, 22 wires, 23 long columns, 24 rods, 25 plates, 26 and granule. 27 These morphologies are all evolved from a one-dimensional (1D) structure.…”