1. Phosphorus removal was demonstrated using sodium hydroxide coated slag.
2. Coated slag caused high pH of the solution and increased the removal efficiency.
3. When pH dropped below 8.0, phosphorus removal efficiency rapidly decreased.
4. Ca, Mg, Al, and Na ions were consumed in the precipitation-coagulation process.
5. The coarse-grained slag coated by sodium hydroxide showed significantly higher removal efficiency than the fine-grained slag without coating.
6. Enhanced removal efficiency was obtained by recycling the initial effluent.