Effect of direct charging of hot recycled slag on hot metal pretreatment dephosphorization in a dephosphorization furnace

Industrial experiments were carried out to investigate the effect of the direct charging of hot recycled slag (DCHRS) on hot metal pretreatment dephosphorization in a dephosphorization furnace. The bulk compositions of semi-steel and slag show that a better dephosphorization effect could be achieved by applying the DCHRS process in the dephosphorization furnace. Compared with the bulk compositions in normal heats, the mean contents of phosphorus in the semi-steel and total Fe in the final slag were decreased by 0.006 and 1.93 wt.%, respectively, with an increase of approximately 6 °C in the semi-steel temperature. According to mineralogical observations, the dephosphorization slags in normal heats and test heats were similar in petrographic constituents, but the metal loss was markedly decreased in the DCHRS process. Thermodynamic calculations show that even though the dephosphorization slag in the DCHRS process had the same dephosphorization capacity as that in the normal refining process, the phosphorus distribution between slag and hot metal in the new process was slightly higher and closer to the reaction equilibrium. Meanwhile, proper operating conditions, including slag basicity, total Fe content in the final slag, bath temperature, slag formation and slag volume, were optimized to improve the dephosphorization efficiency under the condition of the DCHRS process. The consumption of lime, light-burnt dolomite and oxygen during blowing was significantly decreased by the DCHRS process.