Thermochemical Study of Calciothermy of Scandium Compounds EMC 2017, Leipzig. June 26th Thermochemical Study of Calciothermy of Scandium Compounds M. Sc. Brinkmann, Frederic; Dr.-Ing. Arnold, Alexander; M. Sc. Milicevic, Ksenija; Prof. Dr.-Ing. Friedrich, Bernd

Approach to metallothermic Scandium reduction 1/27 Thermochemistry Reduction mechanisms Suitable reducing agents Scandium compounds Metal yields Process parameters Kinetics Activation energy Reaction time Pressure Phase separation Process layout Crucible material Furnace layout Use of reaction enthalpy Theoretical and experimental investigations

Metallothermic Sc reduction processes 2/27 Halide reduction Oxide reduction State of the art: ScF3 is reduced by pure Ca at 1550 °C -1600 °C [1-3] Produced Sc metal is contaminated by Ca and Ta or Mo (crucible material) Further purification includes distillation and sublimation Zn may be added to lower melting point [1] Harata et al. [4]: Sc2O3 reduction with Ca unfeasable Addition of Al as collector metal leads to Sc reduction and collection in the metal phase

Thermochemistry of Scandium - I 3/27 xA +F2 = z AxFy xA +O2 = z AxOy Scandium compounds are thermodynamically very stable Pure substances (a = 1): RE-oxides are more stable than CaO and Al2O3; RE-fluorides are more stable than AlF3, but less stable than CaF2 -> Metallothermy is unfeasable for pure Sc2O3

Sc-Zn phase diagram 4/27 However, Sc melting point is fairly high (1814 K) Liquidus temperature may be decreased with Zn addition

Methodology – „Klärkreuze“ „Klärkreuze“ method: Proposed by W. Guertler almost 100 years ago [5] Determining the reaction outcome within a ternary (or quarterny) system Draw connections between all known compounds on the ternary system frame 5/27 B A X B2X BX AX

Methodology – „Klärkreuze“ 6/27 Determining intersection points Determining which line shows equilibrium at intersection point Example: Intersection 1 A – B2X or B – AX? Experiment or thermochemical simulation 2 B + AX = B2X + A Therefore, the connection B – AX may be cancelled B A X B2X BX AX 1 2 3

„Klärkreuze“ - Example 7/27 B B2X BX A + B + B2X AX + B2X + BX AX + BX + X A + AX + B2X A X AX

Thermochemical simulation tool „FactSage 7.0“ 8/27 FactSage 7.0 uses thermochemical databases that contain parameters for Compounds (Gibbs energy as a function of T and p) Solutions (Gibbs energy as a function of T, p and composition) By minimizing the Gibbs energy of a system that is determined by a given set of constraints, equilibrium conditions are calculated

FactSage 7.0 results 9/27 Databases used: FactPS FToxid FTlite

Sc-Ca-Zn-F system – triangulation at 1300 K 10/27 ScF3 can be reduced by Ca but not by Zn Ca-Zn can be considered to lower alloy melting point

Sc-Ca-Zn-F system – tetradration at 1300 K 11/27 Ca-Zn alloys as reducing agent: reduction path always passes CaF2 – ScZn sub system Thus, reduction results in a ScZn alloy

Summary ScF3 reduction by Ca/Zn 12/27 Ca consumption is always 0.59 g / g ScF3 Sc yield is at 100 % Sc product is diluted by Zn

Sc-Ca-Zn-O system – triangulation at 1300 K 13/27 Sc2O3 cannot be reduced by Zn nor Ca However, intermetallic compounds in the system Ca-Sc-Zn exist Possible reduction in the quaternary system – tetraedration needed

Sc-Ca-Zn-O system – tetradration at 1300 K 14/27 Sc2O3 cannot be reduced by Zn nor Ca Ca-Zn alloys are candidates for reduction Reduction outcome is a ScZn alloy

Summary Sc2O3 reduction by Ca/Zn 15/27 Reducing alloy Ca consumption Zn consumption Sc in product [wt.-%] [g/g Sc2O3] Ca - Ca3Zn 1.744 0.949 26.37 Ca5Zn3 0.970 37.74 Ca0,6Zn0,4 0.872 40.74 CaZn 1.420 31.432 CaZn2 2.840 18.64 CaZn5 7.101 8.4 Diluted by Zn and Ca Diluted by Zn Minimum Ca consumption is 0.872 g / g Sc2O3 At least 0.949 g Zn is necessary for complete oxide reduction Highest Sc content in metal product is 40.74 wt.-%

Sc-Ca-Al-F system – triangulation at > 1150 K 16/27 ScF3 can be reduced by Ca and Al Pure Sc can only be achieved by Ca Al3Sc is the reduction product of ScF3 and Al: ScF3 + 4 Al = Al3Sc + AlF3

Sc-Ca-Al-F system – tetradration at > 1150 K 17/27 Reduction with Al-Ca alloys: ScF3 is reduced by Ca Al addition yields Al-Sc compounds Compounds depend on Al addition (Ca:Al ratio)

Sc-Ca-Al-O system – triangulation at 1300 °C 18/27 No thermochemical data for AlScO3 In order to understand the Al-Sc-O system. tetraedration is necessary

Sc-Ca-Al-O system – triangulation at 1300 °C 19/27 Zacharov (1985): N = 1 + Mk + Mik + 2 (Ck + Cik) Here: N = 19 sub systems Only one tetraedration exists Sc reduction with Al results in an intermetallic AlxScy phase and AlScO3

Summary Sc2O3 reduction by Al/Ca 20/27 Ca/Al ratio [mol/mol] Sc products Sc content in product [wt.-%] Ca consumption [g Ca/ g Sc2O3] Al consumption [g Al/ g Sc2O3] 0.5 Al3Sc 35.71 0.872 1.174 0.6 Al3Sc, Al2Sc 39.99 0.978 1 Al2Sc, AlSc 52.62 0.578 2 AlSc, AlSc2 68.96 0.293 100 % Sc yield is possible with the shown ratios By using Ca and Al as reducing agent, Sc activity in the product is strongly reduced Intermetallic products depend on Ca/Al ratio

Sc-Mg-Zn-F system – triangulation at ≥ 1300 K 21/27 ScF3 reduction with Mg is possible For every g Sc, 0.811 g Mg is necessary 2 ScF3+3 Mg = 2 Sc+3 MgF2

Sc-Mg-Zn-F system – tetraedration at T ≥ 1300 K 22/27 Subsystems: ScF3-MgF2-ZnF2-F ScF3-MgF2-ZnF2-Zn ScF3-MgF2-Sc-ScZn MgF2-Mg-Sc-ScZn MgF2-Mg-MgZn2-ScZn ScF3-MgF2-MgZn2-Zn MgF2-MgZn2-ScZn-Zn Different products are formed when alternating Mg/Zn ratios

Sc-Mg-Zn-O system – triangulation at < 1050 K 23/27 Sc2O3 cannot be reduced by either Zn nor Mg Unclear which compounds are stable in the Mg-Sc-Zn system Calculations indicate a ternary compound (red dot) Thermodynamic data for ScZn2 in the temperature range is false Further calculations are done at T > 1300 K

Sc-Mg-Zn-O system – tetraedration at T ≥ 1300 K 24/27 Subsystems: Sc2O3-MgO-ZnO-O Sc2O3-MgO-ZnO-Zn Sc2O3-MgO-MgZn2-Mg Sc2O3-MgO-MgZn2-Zn Sc2O3-MgZn2-ScZn-Zn Sc2O3-MgZn2-ScZn-Mg Sc2O3-Sc-ScZn-Mg Sc2O3 reduction with Mg/Zn or Mg is not possible

Summary I: Sc2O3 25/27 Sc2O3 Sc2O3 reduction is not feasable with pure substances Ca-Zn and Ca-Al alloys allow reduction and dilution 100 % yield is thermodynamically possible Reduction with Al results in intermetallic Al- Sc compounds and AlScO3 Recommended processing Pure Sc Al-Sc alloys Sc2O3 + CaxZny ScxZny (Tliq > 748 K) CaO (Tliq: 2853 K) Distillation Sc Zn AlxScy (Tliq > 1468 K) Sc2O3 + Ca + Al CaO (Tliq: 2853 K) Slag additives

Summary II: ScF3 ScF3 26/27 ScF3 is not as stable as Sc2O3 Reduction with pure Ca or Mg is possible Al3Sc is formed during reduction with pure Al Recommended processing Pure Sc Al3Sc alloy Al-Sc alloys ScF3 + 4 Al ScF3 + Al + Ca ScF3 + 1.5 Ca / Mg Sc (Tliq: 1814 K) CaF2 / MgF2 (Tliq > 1529 K) Al3Sc (Tliq: 1593 K) AlF3 (Tsub: 1533 K) AlxScy (Tliq > 1468 K) CaF2 (Tliq: 1696 K) AlF3 (Tsub: 1533 K)

Outlook 27/27 Results will be used to design reduction experiments Transfer to „ScAlE“ project Kinetics and practicability have not yet been considered Process parameters Slag design Co-reduction of Al2O3 and ScF3 / Sc2O3 to be investigated

Thank you for your attention! EMC 2017, Leipzig Thank you for your attention!

Literature [1] Spedding, F. H.; Croat, J. J. (1973): Magnetic properties of high purity scandium and the effect of impurities on these properties. In: The Journal of Chemical Physics 58 (12), S. 5514–5526. [2] Beaudry B.J., Gschneidner, JR.: Preparation and basic properites of the rare earth metals. In: Eyring Gschneidner (Hg.): Handbook on the physics and chemistry of rare earths, Bd. 1, S. 173–232. [3] Daane, A. H.; Spedding, F. H. (1953): Preparation of Yttrium and Some Heavy Rare Earth Metals. In: Journal of the Electrochemical Society 100 (10). [4] Harata, M.; Nakamura, T.; Yakushiji, H.; Okabe, T. H. (2013): Production of scandium and Al–Sc alloy by metallothermic reduction. In: Mineral Processing and Extractive Metallurgy 117 (2), S. 95–99. [5] Guertler, G. (1920): Observations of theoretical metallurgy (german). In: Metall und Erz, 17 (8), S. 192–195