Method for preparing alpha-type semi-hydrated gypsum from undisturbed phosphogypsum under low reaction medium dosage

The invention relates to a method for preparing alpha-type semi-hydrated gypsum from undisturbed phosphogypsum under the condition of low reaction medium dosage, which comprises the following specific steps: 1) uniformly mixing water and a plasticizer, adding into the undisturbed phosphogypsum, adding a passivator, uniformly stirring and aging to obtain high-flow phosphogypsum slurry; (2) adding a salt medium into the high-flow-state phosphogypsum slurry, uniformly stirring, and heating for crystal transformation reaction to obtain alpha-type high-strength gypsum slurry with high solid content; and 3) performing spray drying on the alpha-type high-strength gypsum slurry with high solid content to obtain the alpha-type semi-hydrated gypsum. According to the method, the plasticizer is added to release water in pores of the phosphogypsum, so that the utilization rate of the water is increased, the alpha-type semi-hydrated gypsum is prepared by reaction under the condition of lower water-gypsum ratio, the water c