Enhancing the hydration reactivity of hemi-hydrate phosphogypsum through a morphology-controlled preparation technology

The mixed solution (36 wt% P2O5 and 20 mg·ml− 1 SO42 −) was prepared with phosphoric acid and sulfuric acid, and then heated to 95 °C. Apatite powders were slowly and evenly added into the mixed solution, and stirred at a speed of 135 r·min− 1. A certain mass of sulfuric acid was again poured into the reaction tank at a dropping speed of 4.5 g·min− 1. After 150 min of allowing crystals to grow, the slurry was filtered to obtain hemi-hydrate phosphogypsum having the stumpy crystals of type-α hemi-hydrated gypsum and high hydration reactivity.