• Resources Recycling
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• v.15 no.3 s.71
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• pp.20-29
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• 2006

This study was carried out for to recover the purified crystalline gypsum from phosphogypsum by means of using it's crystallographical Properties. The dehydration of hydrated phosphogypsum to $\alpha$-hemihydrate is completed with the 2 hours treatment of it in $99^{\circ}C$ waterrs. The purified crystalline gypsum having the maximum size of $200{\mu}m$ was obtained by 325# wet screening after recrystallization of the $\alpha$-hemihydrate gypsum at the condition of $Na_2SO_4$ 10 wt%, slurry density 20%, $pH\;5{\sim}6,\;65^{\circ}C$ and 4hr. In this process, the yield of gypsum was 93.9% and its grade was 99%.

• Resources Recycling
• /
• v.15 no.3 s.71
• /
• pp.46-57
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• 2006

This study was carried out for the purpose of recovering the refined gypsum from waste phosphogypsum. The refined gypsum was recovered as a under product of 325 mesh wet screening followed by dehydration and hydration stage. The influence of dehydration temperature and time, dehydration rate, aging time, slurry density of hydration and sonication time on the yield and grade of gypsum were investigated. The refined gypsum of $94{\sim}96%$ grade is recovered in 95% yield by wet screening after selective dehydration and hydration process, from the phosphogypsum. For the better separation efficiency of gypsum, it is recommended to treat the phosphogypsum at the conditions of as follows; 6hr's dehydration at $140^{\circ}C$, hydration slury density of $3{\sim}10%$, hydration temperature of $20{\sim}30^{\circ}C$, hydration time of 2hr. In additions, addition of sodium citrate 0.005M and sonication of $5{\sim}10min.$ are effective for increase the recovery of gypsum. On the other hand, aging the dehydrated gypsum 16 hours or longer make decrease the recovery of gypsum remarkably.