X-ray observation of phosphorus vaporization from steelmaking slag and suppression method of phosphorus reversion in liquid iron

The behavior of phosphorus in CaO-SiO2-Al2O3-MgO-P2O5-FetO slag systems during solid Al and carbon deoxidation was investigated at 1873 K. Furthermore, an X-ray apparatus (vertical resistancetube furnace equipped with an X-ray inspector system, which enhances the real-time observation of the generated gas in slag) was introduced to confirm the possibility of the vaporizing phenomena of phosphorus from slag. The X-ray-assisted observations proved that phosphorus gas is produced from P2O5-containing slag during the deoxidation process and can be applied to suppress the reversion of phosphorus into the liquid iron by removing it into the air. The results of experiments between slag and metal showed that Al decreased the FetO and P2O5 contents in slag simultaneously because of the strong reducing power, but carbon decreased only the FetO content in slag to a certain extent without reducing the P2O5. For the prevention of the phosphorus-content increment in liquid iron during the deoxidation process, it was ascertained that the FetO content, the absorption site of phosphorus gas, should be decreased to some extent at the time of phosphorus generation. It could be proposed that it is the two-step deoxidation process that decreases the FetO content by carbon while maintaining the P2O5 content in the slag at a nearly constant level and then decreases the remaining P2O5 content quickly by vaporizing as a gas phase by Al, without considerable reversion of the phosphorus in hot metal.