Synthesis of hydroxyapatite coating material from waste steelmaking slag

The aging of the global population has resulted in a significant increase in the incidence of bone and joint defects. Hydroxyapatite (HAP) exhibits remarkable biocompatibility and other advantageous properties. Consequently, it is extensively employed as a surface coating for titanium and various other substrates, including stainless steel and ceramics, to address joint defects. This application of HAP in the context of orthopedic repair is of significant importance in the field of biomedical engineering. Currently, the preparation of industrial-grade HAP mainly relies on chemically pure reagents, leading to the excessive consumption of natural mineral resources and making it difficult to reduce the production cost. Steel converter slag, as the main solid waste of steel converter steelmaking, has a Ca content of 40% - 60% which exists mostly in the water-soluble phase, making it an ideal source of Ca for HAP preparation. This study was carried out for the selective extraction of Ca from steel slag, the synthesis of steel slag-derived nano-HAP microsphere powders, and the preparation of related coatings. The results demonstrate that the selective leaching of Ca can be achieved by employing a 0.5 mol/L acetic acid solution, controlling the liquid-to-solid ratio at 5:1, and conducting the leaching process at 45 ℃ for 30 min. Moreover, well-dispersed spherical nano HAP particles were prepared via the template-assisted hydrothermal synthesis method. Among the tested spraying distances, 70 mm gave the best bonding strength, but coating uniformity was not yet satisfactory. A novel process of HAP coating material preparation from steel slag was proposed in this work.