Production of Scandium and Al-Sc Alloy

Transcription

1 Production of Scandium and Al-Sc Alloy Masanori Harata a, Takao Nakamura b Hiromasa Yakushiji c, Toru H. Okabe a a The University of Tokyo b Chiba Institute of Technology c Pacific Metals Co., Ltd. 1

2 Production of Scandium and Al-Sc Alloy 1. Introduction 2. Metallothermic reduction 3. Molten salt electrolysis 4. Summary 2

3 Scandium? One of the rare earth elements Low density (2.99 g / cm 3 ) High chemical reactivity High price (10,000~ yen / g) Sc metal Al-Sc alloy Al-Sc alloy Halide lamp Bicycle frame MIG29 3

4 Crustal abundance of scandium Rank. Atomic number, Z Element Content of earth crust (%) Rank Atomic number, Z Element Content of earth crust (%) Rank. Atomic number, Z Element O Zn Si Ce Er Al Cu Sn Fe Y Ta Ca La U st abundant Content of earth crust (%) Na Nd K Co W Mg Sc Eu Ti Ho H N Tb P Nb I Mn Ga Tm F Pb Lu B S Pr Hg C Ag Sm Cl Gd Pt Dy Rh Ni Yb Au Scandium is the 31 st most abundant element in the earth crust. 4

5 Scandium-containing minerals Form Mineral name Content of Sc 2 (mass%) Thortveitite 25.0~48.3 Zircon 0.005~0.3 Silicates Beryl ~1.2 Garnet 0.02~0.4 Olivine ~0.02 Pyroxene ~0.04 Xenotime ~1.5 Phosphates Monazite 0.002~0.5 Apatite ~0.08 Davidite 0.02 Columbite 0.01~0.8 Uraninite 0.15~0.2 Wolframite 0.005~1.3 Oxides Magnetite 0.001~0.04 Hematite ~0.15 Titanomagnetit ~0.02 Ilmenite ~0.15 Rutile 0.005~0.16 Laterite 0.003~0.03 Thortveitite ore [(Sc, Y) 2 Si 2 O 7 ] ~48.3 mass%sc 2 Currently, Sc is recovered from rare earth ores or as a by-product from uranium mill tailings. Sc is distributed very widely among 800 different earthly species of minerals. Recently, possibility of recovering Sc from Ni laterite ore is focused. 5

6 Possibility of recovering scandium from nickel ore Ni ore containing Sc Pyrometallurgical process Matte/Metal Ni Pyrometallurgy Slag Containing Sc 2 Sc 2 in a slag can not be recovered. Hydrometallurgical process Leachant Ni and Co recovery Ni and Co Hydrometallurgy Ni ore containing Sc Leachant Sc 2 Sc 2 in leachant can be recovered at a low cost. 6

7 Purpose of this study Standard Gibbs energy of formation, ΔG f / kj mol Ellingham diagram Ti + O 2 = TiO 2 2/3 Sc + F 2 = 2/3 ScF 3 Ca + F 2 = CaF 2 4/3 La + O 2 = 2/3 La 2 4/3 Sc + O 2 = 2/3 Sc Temperature, T / K 4/3 Al + O 2 = 2/3 Al 2 2 Ca + O 2 = 2 CaO Fluorination: 973 K Sc 2 (s) + 6 HF (g) 2 ScF 3 (s) + 3 H 2 O (g) Reduction: ~1873 K 2 ScF 3 (l) + 3 Ca (g) 2 Sc (l) +3 CaF 2 (l) Disadvantage Conventional process The production cost is high because an expensive reaction apparatus is required for handling fluorides. Contamination from the crucible can not be prevented due to the high temperature reaction. Purpose of this study Development of a new process which can produce Sc metal or Al-Sc alloy directly from Sc 2 at low temperatures (~1273 K). 7

8 Production of Scandium and Al-Sc Alloy 1. Introduction 2. Metallothermic reduction 3. Molten salt electrolysis 4. Summary 8

9 The concept of metallothermic reduction Metallothermic reduction Reduction: 4Sc 2 (s) + 3 Ca (g) 2 Sc (s) + 3 CaSc 2 O 4 (s) Reduction and alloying: Sc 2 (s) + Al (l) + 3 Ca (g) Al-Sc alloy (l) + 3 CaO (s) Stainless steel reaction chamber Sc 2 (+ Al + CaCl 2 ) Ta crucible Ca vapor Temperature, T red = 1273 K Time: t red = 6 h Ca shots Ti sponge 9

10 Result (1) Sc 2 (+ Al) + Ca Reduction experiment in the absence of a collector metal Exp. A: Sc 2 (0.005 mol) + Ca (0.030 mol, vapor) Obtained sample Intensity, I (a.u.) Sc CaSc 2 O 4 Sc 2 JCPDS # JCPDS # JCPDS # Angle, 2θ / degree A complex oxide (CaSc 2 O 4 ) was formed and reduction was incomplete. Reduction experiment using a collector metal Exp. B: Sc 2 ( mol), Ca ( mol), Al (0.036 mol) Obtained Al-Sc alloy Intensity, I (a. u.) Al 3 Sc Al Al 4 Ca JCPDS # JCPDS # JCPDS # Angle, 2θ(degree) Sc 2 was successfully reduced to metallic Sc and alloyed in situ to form liquid Al-Sc alloy without forming CaSc 2 O 4. 10

11 Result (2) Sc 2 + Al + Ca +CaCl 2 Reduction experiment using a collector metal and flux Exp. C: Sc 2 ( mol), Ca ( mol), Al (0.036 mol), CaCl 2 ( mol) Obtained Al-Sc alloy Intensity, I (a.u.) Al Al 3 Sc Al 4 Ca JCPDS # JCPDS # JCPDS # Angle, 2θ / degree Metallic phase was easily separated from slag phase. EPMA analysis (a) Aluminum (b) Scandium (c) Calcium Al 3 Sc Al 4 Ca 11

12 Production of Scandium and Al-Sc Alloy 1. Introduction 2. Metallothermic reduction 3. Molten salt electrolysis 4. Summary 12

13 The concept of molten salt electrolysis Electrolysis Cathodic reaction : Sc 3+ (in salt) + 3 e - Sc (l, in Al) Anodic reaction : C (s) + x O 2- (in salt) CO x (g) + 2x e - Overall reaction : Sc 2 (in salt) + C (s) 2 Sc (in Al)+ CO x (g) e - Sc 2 Carbon electrode (anode) T = 1173 K Molten salt Solid Sc 2 particle CaCl 2 + Sc 2 molten salt Al liquid electrode (cathode) e - O e - O 2- Al liquid electrode 13

14 Molten salt electrolysis (XRD, EPMA) Sectioned sample Analysis area 5 mm EPMA analysis (a) Aluminum Intensity, I (a.u.) XRD analysis Angle 2θ/ degree (b) Scandium Al Al 3 Sc (c) Calcium JCPDS # JCPDS # Al 3 Sc Sc segregated at the surface of the sample. 14

15 Molten salt electrolysis (XRF) XRF results of the samples obtained after the electrolysis. Exp. # Molten salt system Current, i /A Time, t /s Al Sc Ca Fe d-1 1 CaCl mol%Sc <0.01 d-1 2 CaCl mol%Sc <0.01 <0.01 d-2 1 CaCl 2-2mol%Sc d-3 1 CaCl 2-2mol%Sc d-4 1 CaCl 2-2mol%Sc <0.01 d-5 1 CaCl 2-4mol%Sc d-6 1 CaCl 2-4mol%Sc d-7 1 CaCl 2-4mol%Sc d-8 1 CaCl 2-4mol%Sc d-9 1 CaCl 2-8mol%Sc <0.01 d-9 2 CaCl 2-8mol%Sc d-10 1 CaCl 2-8mol%Sc Surface of the sample was analyzed. 2 Section of the sample was analyzed. Al-Sc alloy with low Ca contamination (<0.65 mass%) was successfully produced by electrolysis of CaCl 2 -Sc 2 molten salt. 15

16 Evaluation of current efficiency Calculated mass of Sc in the sample, w Sc / g (a) CaCl 2-2mol%Sc 2 molten salt A 1 A Theoretical maximum ε = 100% Calculated mass of Sc in the sample, w Sc / g (b) CaCl 2-4mol%Sc 2 molten salt 0.25 A 0.5 A 1 A Theoretical maximum ε = 100% Calculated mass of Sc in the sample, w Sc / g Electrical charge Q / C (c) CaCl 2-8mol%Sc 2 molten salt A Theoretical maximum Electrical charge Q / C ε = 100% Electrical charge Q / C w Sc = w Al-Sc C Sc w Sc : Mass of Sc in the sample. w Al-Sc : Mass of the sample obtained after electrolysis. C Sc : Concentration of Sc in the sample determined by XRF. Current efficiency of each sample varied widely. In some experiment, current efficiency was more than 100%. 16

17 Summary For producing Sc and Al-Sc alloy directly from Sc 2 at low temperatures, metallothermic reduction and molten salt electrolysis were conducted. Metallothermic reduction When Al was used as a collector metal for the reduction of Sc 2, metallic Sc was successfully obtained directly from Sc 2 and alloyed in situ to form liquid Al-Sc alloy. When aluminum was used as a collector metal, excess calcium remained in the alloy sample in the form of Al 4 Ca. Molten salt electrolysis It was difficult to evaluate the current efficiency of electrolysis because Sc segregated around the surface of the Al-Sc alloy sample. Al-Sc alloy(0.81~32.31 mass%) with low calcium impurity(~0.69 mass%) was successfully produced by the electrolysis of CaCl 2 -Sc 2 molten salt. 17

18 Future Process of high performance Al alloy production e - V Sc 2 Al A Carbon electrode (anode) CO x (g) Cathodic reaction: Sc 3+ (in salt) + 3 e - Sc (l, in Al) Anodic reaction: C (s) + x O 2- (in salt) CO x (g) + 2x e - Overall reaction: Sc 2 (in salt) + C (s) 2 Sc (in Al)+ CO x (g) CaCl 2 + Sc 2 molten salt Al-Sc liquid alloy Al-Sc liquid alloy with low Ca 18