Nº

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COMUNICAÇÃO TÉCNICA

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Nº 174136.1

Didymium obtainment from rare earth oxides produced in Araxá, Brazil João Batista Ferreira Neto

Fernando Jorge Gomes Landgraf Gerhard Ett

Celia Aparecida Lino Santos Andre Luiz Nunis da Silva João Ricardo Filipini da Silveira Fabiana Yamasaki Martins Vieira Maciel Santos Luz

Palestra apresentado no 24.International Workshop on Rare-Earth and Future Permanent Magnets and their Applications, Munique Alemanha, 2016

A série “Comunicação Técnica” compreende trabalhos elaborados por técnicos do IPT, apresentados em eventos, publicados em revistas especializadas ou quando seu conteúdo apresentar relevância pública.

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Didymium obtainment from rare earth oxides

produced in Araxá, Brazil

J. B. Ferreira Neto

1

_{, P. Wendhausen}

2

_{, F. J. G. Landgraf}

1

_{, G. Ett}

1

_{, C. A. L.}

Santos

1

_{, A. L. N Silva}

1

_{, J. R. F. Silveira}

1

_{, F. Y. M. Martins}

1

_{and M. S. Luz}

1

_{Laboratory of Metallurgical Processes, Institute for Technological Research}

(IPT), Sao Paulo – SP, Brazil

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OUTLINE

- RE Market and initiatives in Brazil

- Neodymium and Didymium oxide reduction

- Experimental

- Results and Discussion

- Conclusions

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Fonte: U.S. Geological Survey, Mineral Commodity Summaries, January 2015 RE Oxide basis

World Reserves of RE

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Tailings of Nb ore extraction - CBMM

Xenotime (1% de RE, mainly Y) – Taboca

Mining - Minsur

Serra Verde Mining of the Mining Ventures Brazil group (city of Minaçu – GO)

Mineral % Bariopyrochlore 4 Limonite, goethite 36 Barite 20 Magnetite 16 Gorceixite 6 Monazite 4 Ilmenite 5 Quartz 4 Others 5 Total 100

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CBMM invested ~US$ 15 million:

- Concentration plant (3.000 t/y)

- Solvent Extraction Plant (~5 t/y)

- Lanthanum Oxide

- Cerium Oxide

- Heavy RE oxides

- Didymium Oxide

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Ore

Concentrate

Oxide

Metal (Nd,Pr)

Alloy

Powder

Sintering/magnet

CBMM

Knowledge at

universities and

research

institutes

CBMM/IPT project

(Jun/14 – Jun/16)

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Electrolysis

Cyclic

Voltammetry

Metalothermic

reduction

Routes investigated

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- Nd

₂

O

₃

+ 3 Ca = 2 Nd + 3 CaO

Molten Salt: CaCl

₂

High Ca and CaO solubility

Metalothermic Reduction

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Metalothermic Reduction

Experimental conditions

- 5 kg CaCl

₂

- 500 g Didymium oxide

- Argon atmosphere

- T = 1050°C (> Tm Nd and Pr)

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Metalothermic Reduction

Results:

- Yield: 90% (reduction)

Weight %

Al

0.16 Si

0.08 Mg

0.37 Ca

0.77 Pr

49.5 Nd

49.1 REE

0.02 NdxAly

C – 440 ppm (Ca source)

O – 20 ppm

ICP-MS

Ca and Mg can be removed

by vacuum treatment

Mg, Ca < 20 ppm after

vacuum treatment

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Cyclic Voltammetry

Cyclic voltammogram of LiF-CaF

₂

-NdF

₃

-Nd

₂

O

₃

system at 200 mV/s

-2.00 -1.75 -1.50 -1.25 -1.00 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 C u rre n t d e n si ty (A/ cm²) Potential (V/Pt) LiF-CaF 2-NdF3-Nd2O3, 200 mV/s well-formed peak (-1,70V/Pt) Nd3+_{+ 3e}-_{= Nd}0 Li+_{, Ca}2+_ions reduction peak Oxidation peak -1,7 -1,6 -1,5 -1,4 -1,3 -0,6 -0,4 -0,2 0,0 0,2 0,4 0,6 C u rre n t d e n si ty (A/ cm²) Potential (V) LiF-CaF₂-PrF₃-Pr₆O₁₁, (200 mV/s) Pr4+ + e -> Pr3+ Pr3+ + 3e -> Pr

Cyclic voltammogram of LiF-CaF

₂

-PrF

₃

-Pr

₁₁

O

₆

system at 200 mV/s.

Experimental conditions:

• Graphite crucible

• Cathode: Mo

• Anode: Graphite

• Reference Electrode: Pt

• T = 900°C

Mo C

Tc

Pt

wv

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Electrolysis

Experimental conditions:

• 14 kg LiF-CaF

₂

-NdF

₃

-PrF

₃

• T: 1020 - 1050 °C

• Didymium oxide: 420 g

• I = 80-150 A; V = 3,5 – 5 V

• Current density:

- Cathode: 0,3-0,5 A/cm

2 - Anode: 4-6 A/cm

2 Gas analyses

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Electrolysis

Stable operation

Anodic effect

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Electrolysis

_{Weight %}

Al

0.009-0.015

Mg

0.02-0.5

Ca

0-0,02

Pr

7-44

Nd

58-92

O

0.002 REE

0.1 Pr can be controlled by

PrF

₃

/NdF

₃

ratio in molten salt

Source: CaF

₂

• Gas generated: 0,18 to 0,3 kg of CO2 equivalent (CO +

CO

₂

)/kg of Didymium

CO/CO

₂

ratio = 3-4

• Current Efficiency ~70%

• Energy consumption (only DC current source): 3,5 – 4,5

kwh/kg Didymium

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Conclusions

Calciothermic reduction

- Batches of metallic didymium were obtained by calciothermic reduction (> 98,5%)

- Main impurities of Didymium: Al, Si, Mg, Ca and C

- Ca and Mg can be removed by vacuum treatment

Cyclic voltammetry

- The cyclic voltammograms (LiF-CaF

₂

-NdF

₃

-Nd

₂

O

₃

, LiF-CaF

₂

-PrF

₃

-Pr

₁₁

O

₆

and LiF-CaF

₂

-NdF

₃

-PrF

₃

-Nd

₂

O

₃

-Pr

₆

O

₁₁

) showed that Nd ions are reduced in a one-step process, whereas Pr ions

are reduced in a two-step process.

Electrochemical reduction

- Metallic didymium > 99% was produced by Electrolytic reduction

- The electrochemical process is stable if the oxide concentration in molten salt is

appropriately controlled (controlling the oxide feeding rate and the electric parameters

of electrolytic process – V and I).

- Anodic gases (CO and CO

₂

) are produced during the electrolytic process and PFC can also

be generated.

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