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2019 - Sustainable Industrial Processing Summit & Exhibition
23-27 October 2019, Coral Beach Resort, Paphos, Cyprus
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    Slag Basicity Variation at Block Smelting for the Recycling of Tantalum
    Dominik Hofer1; Stefan Luidold1; Tobias Beckmann2;
    1MONTANUNIVERSITAET LEOBEN, Leoben, Austria; 2H.C.STARCK TANTALUM & NIOBIUM GMBH, Laufenburg, Germany;
    PAPER: 228/Recycling/Regular (Oral)
    SCHEDULED: 14:00/Sat. 26 Oct. 2019/Adonis



    ABSTRACT:
    Tantalum rich ores containing oxidic minerals like tantalite or columbite are primarily mined by artisanal and small scale practices. [1] Major sources located in countries around the African Great Lakes like Congo and Rwanda control global output with a 60 % share. [2] Direct treatment of concentrates with a Ta<sub>2</sub>O<sub>5</sub> content higher than 25 % takes place via leaching followed by liquid-liquid extraction. Recycling, chlorination and processing of low grade residues, slags, sludges or dusts represent aspiring alternatives accounting for approximately 30 % of the tantalum world production. [3] The pyrometallurgical manufacturing of synthetic tantalum concentrate (syncon) in a multi-stage process constitutes an established procedure for various input materials. [4] Within this study, the first step (smelting and reduction) is recreated in a small scale induction furnace as well as a DC-EAF. Huge amounts of high melting slag comprising mostly Al<sub>2</sub>O<sub>3</sub>, CaO, MgO, SiO<sub>2</sub>, TiO<sub>2</sub> and ZrO<sub>2</sub> arise whilst Nb and Ta concentrate in the metal phase. Previous flow behaviour investigations [5] and viscosity calculations reveal low viscous slag to be crucial for good metal/slag separation at elevated CaO content. Therefore, a variation of slag basicity is tested for further process optimization and to attain technical standard regarding treatment time, tapping procedure and slag composition of < 0.2 % Ta<sub>2</sub>O<sub>5</sub>. Accumulation of value components was successfully realized and validated by SEM/EDX. Thus, yield, energy saving potential and other process adjustments for the syncon production can be investigated at the laboratory scale before upscaling to industrial quantity.

    References:
    [1] Killiches F. et al.: Sorgfaltspflichten in den Lieferketten von Zinn, Tantal, Wolfram und Gold. DERA Deutsche Rohstoffagentur Commodity TopNews 46, 2014.
    [2] Reichl C., M. Schatz and G. Zsak: World Mining Data. Minerals Production, 2017.
    [3] Andersson K., K. Reichert and R. Wolf: Tantalum and Tantalum Compounds: Ullmann's Encyclopedia of Industrial Chemistry (2000), 1-15.
    [4] Schulenburg F., H. Rossel and U. Bartmann: Tantalrecycling: Thiel, Thome-Kozmiensky et al. (Hg) 2017 - Recycling und Rohstoffe, 137-154.
    [5] Hofer D. et al.: Influence of CaO/SiO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> Ratio on the Melting Behaviour of SynCon Slags. In: Minerals, Metals and Materials Society, TMS Annual Meeting & Exhibition (Hg.): TMS 2019 148th Annual Meeting & Exhibition supplemental proceedings. Cham: Springer, 1139-1148.