The influence of retarders in the hydration process of phosphogypsum
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Abstract:
The influence of retarders on the hydration process of phosphogypsum is investigated by determining setting time，intensity of hardened anhydrite，hydration rate，hydration temperature increase and the degree of solution supersaturation in combination with observing by scanning electron microscope. The results indicate that S〖JP+5〗G-10 and citric acid retarder can adapt to phosphogypsum well; pH value has a great influence on the retarding effect，5.1 and 6.0 are the best pH values for the effect of S〖JP+5〗G-10 and citric acid in plaster of phosphogypsum respectively. However，citric acid dosage should not exceed 0.1% or the amount of doped-SG-10 should not more than 0.2%. Both S〖JP+5〗G-10 and citric acid lead to a delay in the hydration heat evolution and significantly decrease the hydration ratio in the early stage and the ratio of recede limited in the final hydration.It can also partly change the hydration kinetics process of phosphogypsum at the same time. Initial liquid concentration and over-saturation of phosphogypsum are less than the blank sample after adding retarder，while liquid phase ion concentration and decreased ratio of over-saturation simultaneously are sharply depressed in the hydration reaction process. S〖JP+5〗G-10 causes the large crystal sizes，but it has a minor effect on the crystal morphology of dehydrate. Adding citric acid result in a large influence on the dehydrated crystal morphology of phosphogypsum.
