• Grinding treatment is significantly more effective than increasing concentration or adding tailings in enhancing the workability of hemihydrate phosphogypsum (HPG) slurry.
• The study provides the first direct evidence of the transformation from robust embedded structures to soft stacking structures, explaining the mechanism behind workability improvement.
• Practical recommendation: grinding HPG for 20 minutes and mixing with 0–200wt% phosphorus tailings achieves satisfactory workability and mechanical performance.
• The findings offer a low-cost, green solution to prevent pipe plugging and ensure stable transportation of HPG-based filling materials in underground mining applications.