Method for producing cement retarder with salt gypsum

The invention provides a method for producing cement retarder with salt gypsum, which comprises: separating and removing sodium chloride solution from salt gypsum plaster to obtain salt gypsum containing water, adding water and rotating crystal excitant, and rotating crystal, filtering, washing and filtering to obtain dehydrate gypsum, and solid-phase product with average particle size of 35 to 45 micrometer, and salt content of 0.5 to 0.8 percent, and drying under the temperature of 120 DEG C to prepare cement retarder with salt content of 0.5 to 1.0 percent and average particle size of 30 to 40 micrometer. The invention takes gypsum brine salt-making by-product as raw material, can transfer anhydrous gypsum into dehydrate gypsum at short time during the purification process of raw material, thus effectively improving the separation and washing operation, after washing, using washing liquid to wash off substance such as sodium chloride and the like during the filter pressing process, and putting the washing