Synopsis :It is quite important to reveal the microscopic reaction mechanisms and the role of the solid and liquid phases in the solid CaO coexisting flux in the hot metal dephosphorization process. In the present study, solid CaO piece and FeO x -CaO-SiO 2 -P 2 O 5 slag with various FeO x and P 2 O 5 contents, and CaO/SiO 2 ratios of the slag were reacted at 1573 and 1673K. The interface between solid CaO and molten slag was observed and analyzed by SEM/EDS. Microscopic reaction mechanisms between solid CaO and molten slag was discussed with changing reaction times, slag compositions and temperatures. The CaO-FeO x phase adjacent to solid CaO, and the CaO-SiO 2 or CaO-SiO 2 -P 2 O 5 solid phase coexisting with the FeO x -CaO-SiO 2 liquid slag next to the CaO-FeO x phase were observed for all slag compositions, temperatures and reaction times. Phosphorus was condensed as 2CaO · SiO 2 -3CaO · P 2 O 5 phase more easily in the case of higher CaO/SiO 2 ratio and higher FeO x content in slag. There was a linear relationship between P 2 O 5 content in 2CaO · SiO 2 -3CaO · P 2 O 5 phase and the distance from CaO-FeO x phase to 2CaO · SiO 2 -3CaO · P 2 O 5 phase. The P 2 O 5 content increased from CaO-FeO x boundary toward bulk slag, and P 2 O 5 content in the condensed phase near the CaO-FeO x phase increased with increasing reaction time. This P 2 O 5 concentration gradient tended to diminish. These results suggest that the condensation of phosphorus as 2CaO · SiO 2 -3CaO · P 2 O 5 phase was controlled by P 2 O 5 diffusion from bulk slag to reaction interface, not by absorption of P 2 O 5 into 2CaO · SiO 2 particle.
Synopsis :Steelmaking slag is recycled and reused, but its utilization is restricted due to its chemical properties. On the other hand, steelmaking slag is considered to be a promising resource of iron and phosphorus in Japan. In this work, reduction of (Fe t O) and (P 2 O 5 ) in steelmaking slag and recovery of iron and phosphorus resources were investigated with the aim of developing a new recycling process for steelmaking slag. In order to investigate the effect of slag basicity (%CaO/%SiO 2 ) and Fe t O content in slag on phosphorus separation from steelmaking slag, steelmaking slags were reduced by carbonaceous material at high temperature by using an induction furnace. From the results, the effects of slag composition, temperature and oxygen partial pressure on phosphorus separation from steelmaking slag were discussed.
Synopsis :The effects of temperature (1473-1873K) and slag composition (CaO/SiO 2 ϭ1.2-4.0) on reduction of (Fe x O) and (P 2 O 5 ) in steelmaking slag by carbon with mechanical stirring were investigated in laboratory-scale experiments. The results were summarized as follows.1) The reduction ratios of (Fe x O) and (P 2 O 5 ) in steelmaking slag obtained in this research were 0-98% and 3-98%, respectively. These values were highly dependent on both slag basicity and the reduction temperature.2) (P 2 O 5 ) was reduced by carbon and concentrated in iron, which was obtained by reduction of (Fe x O). Higher reduction ratios of (P 2 O 5 ) exceeding 50% were obtained under the condition that the activity of (Fe x O) in the slag was less than 0.01. The (P 2 O 5 ) reduction ratio decreased as the equilibrium phosphorus partition ratio between slag and metal calculated by slag composition and temperature increased.3) From the phosphorus mass balance before and after experiments, 1-29 mass% of unidentified phosphorus was confirmed. The ratio of unidentified phosphorus increased as the equilibrium P 2 gas partial pressure calculated with an equation for the gaseous dephosphorization reaction increased. The mechanism of (P 2 O 5 ) reduction in steelmaking slag was discussed based on the results of phosphorus distribution and observation of the reduced slag by EPMA analysis.
Steelmaking slag is recycled and reused, but its utilization is restricted due to its chemical properties. On the other hand, steelmaking slag is considered to be a promising resource of iron and phosphorus in Japan. In this work, reduction of (Fe t O) and (P 2 O 5 ) in steelmaking slag and recovery of iron and phosphorus resources were investigated with the aim of developing a new recycling process for steelmaking slag. In order to investigate the effect of slag basicity (%CaO/%SiO 2 ) and Fe t O content in slag on phosphorus separation from steelmaking slag, steelmaking slags were reduced by carbonaceous material at high temperature by using an induction furnace. From the results, the effects of slag composition, temperature and oxygen partial pressure on phosphorus separation from steelmaking slag were discussed.
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