Abstract: The slagiron system which was formed in meltingseparation process of the prereduction niobium concentrate of Bayan Obo with electric furnace was taken as a research object. The variation rule of the distribution ratio of niobium and phosphorus between the slag and iron during the meltingseparation process was investigated by experiment. The results showed that the distribution ratios of niobium and phosphorus decreased with the increase of w［C］， and w［C］should be controlled below 342% at end point of the meltingseparation process. The niobium oxides was reduced to NbC at the slagiron interface when carbon dissolved in iron saturated. The distribution ratios of niobium and phosphorus decreased with the increase of temperature， the temperature should be controlled at 1450℃ in the meltingseparation process. The distribution ratios of niobium and phosphorus increased with the increase of w(FeO)，and w(FeO)should be 585% at end point of the meltingseparation process. The distribution ratios of niobium and phosphorus increased with the increase of the optical basicity of the slag， the addition of MgO in slag greatly decreased the distribution ratio of phosphorus.

Key words: meltingseparation, niobium, phosphorus, slag, iron, distribution ratio