An approach to leach phosphorus from slag was applied to commercial fertilizers made from steelmaking slag, which has relatively coarse grains. After leaching at pH 3 with citric acid, about 60% of the P 2 O 5 had been dissolved, but the dissolution ratio of MnO was less than 30%. The separation index, calculated from the dissolution ratio of P 2 O 5 divided by that of MnO, was 2.1. In addition, the dissolution ratio of the solid solution was 90% or greater. However, 25% or more of the matrix was also dissolved. To improve the selectivity of leaching, the mineralogical phases comprising the matrix were synthesized, and their leaching behaviors were investigated. The results indicate that it is important to eliminate the glassy phases and to change the valence state of iron in its oxides to 3 + to suppress the dissolution of the matrix. Finally, a synthesized slag, containing only Fe 2 O 3 as the only iron oxide, was prepared by slow cooling, and leaching tests were conducted. About 99% of the P was dissolved, but the dissolution ratio of Mn was less than 10%. In addition, the separation index increased to 14.1. In this case, the dissolution of the matrix was suppressed, and almost all the solid solution phase was dissolved.
This study focused on the use of molten oxide electrolysis (MOE) as a low-cost, clean, continuous separation method suitable for incorporation into actual steelmaking processes. We discussed interfacial behavior from molten iron to slag by anodic polarization of the copper-containing carbon-saturated molten iron (metal phase)–molten oxide (slag phase) interface and investigate the operating mechanism of MOE. The basic constant potential electrolysis between the metal phase (Fe-10 wt% Cu-5.0 wt% C) and slag phase (27 wt% CaO-27 wt% SiO2-45 wt% Al2O3-1.0 wt% CaS) by maintaining 1–2 V vs. Pt at 1773 K in an Ar atmosphere is described. When polarized, a high concentration of dispersed Cu-rich phase was detected locally near the metal–slag interface but not in the phase center of the metal. At the metal–slag interface, the energies of the Fe-rich and Cu-rich phase–slag interfaces decreased due to electric capillarity, and the Cu-rich phase distributed near the interface.
The hold‐up of molten pig iron and slag melt in the coke packed bed of blast furnace (BF) causes a decrease of void between coke lumps and inhibits gas permeability. Smooth dripping of those liquids in the coke bed is desirable to keep the productivity of BF. Herein, the conditions for smooth flowing of molten iron on coke surface are calrified, and the falling angles of Fe‐C and actual pig iron droplets on coke and graphite are measured at high temperature. It is found that Fe‐C droplet easily slids down on coke because of small falling angle, and the falling angle of actual pig iron is even smaller, while those droplets adhere to a graphite substrate. The carbon in iron has only a small effect on the static contact angle with coke, but has a great influence on the falling angle. From the viewpoint of the roughness of coke surface, the variation of static contact angle and falling angle is discussed.
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