Leaching behavior and microstructure of phosphorus in converter slag

• Published in: Journal of iron and steel research, international Vol. 31; no. 7; pp. 1646 - 1660
• Main Authors: Zhou, Chao-gang, Li, Jin-yue, Chen, Qing-gong, Yang, Yin-ye, Gong, Wei, Ai, Li-qun, Wang, Shu-huan, Ma, Bei-yue
• Format: Journal Article
• Language: English
• Published: Singapore Springer Nature Singapore 01.07.2024
• Subjects: Applied and Technical Physics; Engineering; Machines; Manufacturing; Materials Engineering; Materials Science; Metallic Materials; Original Paper; Physical Chemistry; Processes; Acid leaching; Phosphorus; Solid solution; Slag structure; Dephosphorization converter slag
• DOI: 10.1007/s42243-024-01175-9
• ISSN: 1006-706X

Converter slag is a by-product of the steelmaking process and contains a large amount of Ca, Fe, P and other elements. If the phosphorus in the converter slag can be effectively extracted, the resulting phosphorus can be used as a phosphate fertilizer. Phosphorus in converter slag is mainly enriched in 2CaO·SiO 2 –3CaO·P 2 O 5 (C 2 S–C 3 P) solid solution and is easily dissolved in water. Therefore, acid leaching method was used to dissolve the solid solution to extract phosphorus in converter slag, so as to realize the recycling of phosphorus resources in converter slag. The leaching behavior of three actual converter slags from different steel mills in acid leaching solutions composed of citric acid, sodium hydroxide, hydrochloric acid and deionized water was studied by X-ray diffraction, scanning electron microscopy combined with energy dispersive spectrometry, Fourier transform infrared spectroscopy and Raman spectroscopy to reveal the change in object image structure as well as SiO 4 and PO 4 tetrahedron before and after acid leaching. The results show that only a small amount of phosphorus in converter slag with too low basicity is enriched in C 2 S–C 3 P solid solution, resulting in poor leaching effect. When the converter slag has a high basicity, the removal effect of phosphorus is 70.64%–81.88%. In addition, when the basicity of converter slag is roughly the same, the dephosphorization effect of slag with high FeO content is relatively poor. And acid leaching will cause depolymerization behavior of SiO 4 and PO 4 tetrahedron, so that the mole fraction of Q 0 (Si) (asymmetric stretching vibration of Si–O bond in SiO 4 tetrahedron with bridge oxygen number of 0) and NBO/Si (non-bridging oxygen in silicate tetrahedra) will increase. Phosphate-containing solids can be obtained from the solution after acid leaching through static precipitation, and the solids have the potential to make phosphate fertilizers.