Extraction of Rare Earth Metal Oxide Inclusion Particles in Steel

Abstract

The conventional recovery technology is not economically viable due to the low rare metal concentration in industrial scraps. It is expected that iron- and steelmaking process can recover rare metals as a high-concentration ore substitute. For efficient enrichment of rare earth metal (REM) in this process, the establishment of the thermodynamic values related to REM deoxidation of molten iron is required. To obtain precise thermodynamic data, the concentration of elements solved in the metal sample should be determined separately from that in the inclusions, which is suspended in molten iron. Therefore, a stable extraction method for REM oxide in iron was investigated.

From the dissolution behavior of Sm₂O₃, Nd₂O₃ and Dy₂O₃ reagents in various eluents, 2 v/v% triethanolamine-1 w/v% tetramethylammonium chloride-methanol (2%TEA) is most suitable for the extraction of REM oxide. From the analysis using SEM-EDX and SEM-WDX, REM oxide in Fe-0.2 mass% REM alloy was identified as REM₂O₃ containing a small amount of MgO and FeO. From the relationships between the total O concentration and the insoluble O concentration calculated from insoluble REM concentration, the REM oxide inclusions in Fe-REM alloy could be extracted precisely by the electrolysis with 2%TEA.