Thermodynamic analysis of separation of alloying elements in recycling of end-of-life titanium products

The separation and control of undesired elements are key to recycling scrap or end-of-life (EoL) metal products, as the quality of regenerated metals is often impaired by contamination from the alloying elements in the scrap. However, little is known of their removability or controllability because they are normally absent in the production of primary metal from natural ore. Here, the distribution ratios of 31 kinds of alloying element among the metal, slag, and gas phases in the re-melting of EoL titanium products were quantitatively discussed. Our results clarified that the typical titanium alloying elements – Al, Fe, and V – are essentially uncontrollable in re-melted titanium by oxidation or evaporation. This suggests that the mixing of commercially pure titanium (CP-Ti) and other titanium alloys should be avoided. Hence, the development of new technologies to separate alloying elements from titanium scraps for sustainable titanium recycling is highly anticipated.

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► We predicted the distributions for various impurity elements in molten titanium.
► Only Mg and some rare earth metals can be removed to the slag phase by oxidation.
► Ag, Mg, Mn, Na, Mg, and Zn can be removed owing to their high evaporation pressures.
► Al, Fe, Mo, Nb, Sn, V, and Zr, strongly tend to remain in the molten titanium.