The influence mechanism of citric acid on the morphology of hydrothermal product by the desulfurization of gypsum
The calcium sulfate hemihydrate crystals were prepared from raw materials of desulfurized gypsum and citric acid by using the hydrothermal method.The effect of citric acid on the morphology of calcium sulfate hemihydrate crystals and its reaction mechanism were studied based on the characterization of the crystal by using the XRD,FTIR and so on.The results show that C6H6O7-and C6H7O7 in solution not only could be adsorbed through chemical adsorption on planes and reacted with Ca2+on the(020),(400)and(204)planes of the calcium sulfate hemihydrate crystal to have formed the calcium citrate for precipitation,but also could be adsorbed on the(204)plane of the crystal by electrostatic adsorption,when citric acid dosage was 0.20％.In addition,the mutual adsorption between C6H8O7 and citrate ion on surface of the calcium sulfate hemihydrate crystal by the association interaction of carbon chains and the hydrogen bonding interaction of hydroxyls resulted in the coating of C6H8O7 on surface of the calcium sulfate hemihydrate crystal.This is unfavorable to the precipitation of growth units such as SO2-on surface of the crystal.It will result in the transformation of its morphology from the fibrous to hexagonal prismatic crystals.When the doseage of citric acid was greater than 0.20％,citric acid was existed mainly in the form of C6H8O7 in solution.Thus,the association effect and hydrogen bonding interactions between C6H8O7 and citrate ion on the surface of calcium sulfate hemihydrate played dominant roles,which was unfavorable to the growth of the(020)and(400)planes of the calcium sulfate hemihydrate crystal and resulted in the transformation of its morphology from fibrous to hexagonal prismatic ones.
dosage of citric acidcalcium sulfate hemihydrate crystalcrystal morphologyeffect mechanism
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