In the present work, the effect of dephosphorization endpoint temperature on the dephosphorization of hot metal was studied for the double slag converter steelmaking process under the conditions of low temperature and low basicity by the industrial experiments. In the temperature range of 1350–1450 °C, with an increasing dephosphorization endpoint temperature, the dephosphorization ratio and phosphorus distribution ratio first increase and then decrease. The phosphorus content in hot metal first decreases and then increases at the end of dephosphorization. At the dephosphorization temperature range of 1385–1410 °C, the dephosphorization ratio is higher than 55%, the P₂O₅ content in the dephosphorization slag is 3.93–4.17%, the logL_P value is 1.76–2.09, the value of $P_{\mathrm{CO}}^{\mathrm{P}-\mathrm{C}}$ of the selective oxidation reaction of carbon and phosphorus is 53–80 Pa, and the $a_{\mathrm{FeO}}$ value is 0.284–0.312. The path of phosphorus in hot metal entering the P-rich phase of dephosphorization slag can be reasonably inferred as: hot metal → Fe-rich phase → P-rich phase. Under the present industrial experimental conditions, the dephosphorization and rephosphorization reactions are in dynamic equilibrium at 1413 °C. Considering the experimental results and thermodynamic calculation results of industrial experiments by the double slag dephosphorization process, the optimal temperature range for intermediate deslagging is about 1400–1420 °C.

The kinetic investigation of the dephosphorization in the new double slag converter steelmaking process was carried out based on the coupled reactions model combining with a heat balance temperature model for the 220-ton industrial experiment. The calculated results of [%C], [%Si], [%P] in the hot metal, and the slag compositions are in good agreement with the experimental results. When the heat balance temperature model is applied, the P prediction results are better rather than those predicted by using the fixed temperatures. The calculated phosphorus distribution ratio increases with the refining time, while the phosphate capacity shows a downward trend due to the decrease in slag basicity and the increase in temperature. The rate-controlling step of the dephosphorization is determined to be the mixed control of the mass transfer of P in the hot metal and P₂O₅ in the slag. As the initial Si concentration is increased, the interfacial oxygen activity required for starting the dephosphorization is increased, leading to the delay of the dephosphorization start time.

In this paper, the influence of the Fe₂O₃ addition amount on the dephosphorization of hot metal at 1623 K with the slag of the low basicity (CaO/SiO₂) of about 1.5 was investigated by using high-temperature laboratorial experiments. With increasing the Fe₂O₃ addition amount from 5 to 30 g, the contents of [C], [Si], [Mn] and [P] in the hot metal at the end of dephosphorization are decreased and the corresponding removal ratios increase. In dephosphorization slags, the phosphorus mainly exists in the form of the nCa₂SiO₄–Ca₃(PO₄)₂ solid solution in the phosphorus-rich phase and the value of coefficient n decreases from 20 to 1. Furthermore, the oxygen potential and activity at the interface between the slag and hot metal are increased. When the oxygen potential and the oxygen activity at the interface are greater than 0.72 × 10⁻¹² and 7.1 × 10⁻³, respectively, the dephosphorization ratio begins to increase rapidly. When the Fe₂O₃ addition amount is increased to 30 g, the ratio of the Fe₂O₃ addition amount to theoretical calculation consumption is around 175%, and the dephosphorization ratio reaches the highest value of 83.3%.

In the present work, the effect of the basicity at the lower range from 0.98 to 2.13 on dephosphorization of hot metal at 1623 K was studied through high-temperature laboratorial experiments. With the increase of the basicity from 0.98 to 2.13, the P and C contents in hot metal rapidly decrease and increase at first, and then gradually decrease and increase, respectively. From the scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD) results, with the increase of the basicity, the phase containing the high P content changes from the matrix phase into the phosphorus (P)-rich phase. Under the present experimental conditions, the P-rich phase can only be precipitated from the liquid slag when the basicity is higher than 1.55, which is a benefit to the dephosphorization. As the Raman intensity of the P-O-Ca structure unit in the P-rich phase is significantly higher than that of the P-O-Si structure unit, most of the phosphorus in the P-rich phase exists in the P-O-Ca structure unit and a small amount of phosphorus exists in the P-O-Si structure unit. With the increase of the basicity of the dephosphorization slag, the activity coefficient of P₂O₅, ${\gamma }_{{(\mathrm{P}}_2{\mathrm{O}}_5)}$ , in the liquid phase decreases, while the basicity in the liquid phase increases.