Phosphate tailings, rich in calcium, magnesium, and phosphorus, are conventionally processed through roasting and leaching. We propose two-stage ammonium-salt leaching as a new separation method for calcined phosphate tailings. In the first stage, calcium extraction reached 84.67% through Box-Behnken-optimized ammonium chloride leaching (20 °C, NH₄Cl/tailings mass ratio of 0.98, liquid-solid ratio of 9.78, pH 8.5, 40 min), following internal diffusion-controlled kinetics (Eₐ = 2.24 kJ/mol), as described by: 1–2(1–x)–3(1–x)^2/3=3.7234×10^–2exp(–2.2436×10³/RT)t. The second stage achieved 95.21% magnesium leaching via Box–Behnken-optimized ammonium sulfate conditions (85.14 °C, (NH₄)₂SO₄/residue ratio of 1.2, liquid-solid ratio of 12.1, pH 7, 60 min), exhibiting chemical-reaction-controlled kinetics (Eₐ = 37.58 kJ/mol), described by: 1–(1–x)^1/3=3.4099×10³exp(-3.7584×10⁴/RT)t. The near-neutral leaching system facilitates reagent regeneration via ammonia recovery, mitigating equipment corrosion and diminishing chemical consumption, whilst co-producing high-value-added products - namely, Type 96 calcium hydroxide (HG/T 4120-2024) and Type II-B magnesium hydroxide (HG/T 3607-2024). The residual slag can be directly utilized as flotation feed for phosphorus recovery, ensuring complete tailings valorization without secondary waste generation.