Solvent Extraction of Europium (III) from a Nitric Acid SolutionAnnette Hein (Casper College)

Faculty Advisors: Dr. William Cross, Dr. Michael West

Conclusions

• The experimental results do not support the stoichiometric coefficients for H+ and for the ligand presented in the manufacturer’s literature.

• This suggests that some Eu ions are extracted according to a reaction that differs from that suggested by Cytec.

• The pH50 and associated isotherm found in this study agrees well with that presented by the manufacturer (Cytec 2014).

References• Bourzac, K. (2011, April 19). The rare earth crisis. MIT Technology Review.

Retrieved June 22, 2014, from http://www.technologyreview.com/featuredstory/423730/the-rare-earth-crisis/#comments

• Deng, Q., Jin, Y., Wang, Q., Zhao, R., Pan, N., Zhai, F., et al. (2012). New cyclen derivative ligand for thorium(IV) separation by solvent extraction. Journal of Radioanalytical Nuclear Chemistry, 295, 125-133.

• Cytec Inc (2014). Cyanex 572 solvent extraction reagent product data sheet. Retrieved July 2, 2014 from http://www.cytec.com/sites/default/files/files/CYTEC_CYANEX_572_FINAL.pdf

• Han, K., Fuerstenau, M. (2003). Hydrometallurgy and solution kinetics. Principles of mineral processing. Englewood, CO: Society for Mining, Metallurgy, and Exploration, Inc.

This work was made possible by the National Science Foundation REU Back to the Future Site DMR-1157074 Thanks to Dr. Kenneth Han, Dr. Alfred Boysen, Mr. Kelsey Fitzgerald, Mr. Ian Markon, and Mr. Nathan Madden for help and advice.

Acknowledgments

Introduction

• This project focused on extraction of Eu (III) from aqueous solution, using Cyanex 572.

• China dominates supplies of rare earth elements, so methods of processing are being researched in the US (Bourzac 2011).

Research questions:• Relationship between solution pH

and percent extraction? • Stoichiometry of the reaction?

LeachingSize Reduction

Solvent Extraction Stripping

Use in Industry

MethodsExtraction procedure: agitate extractant in organic phase with Eu in aqueous phase, measure equilibrium pH and aqueous Eu concentration (Deng et al 2012, Han and Fuerstenau 2003).

Materials: Eu stock solution, kerosene, Cyanex 572 extractant, HNO3 and NaOH for titrations.

Experimental conditions: • Temp = 25 C⁰• Nitric acid stock solution• O:A volume ratio = 1:1• Contact time = 15 min• Cyanex 572 conc. = 30% by

volume in kerosene• Initial Eu conc. = 100 ppm

TheoryExtraction according to Cytec data sheet (Cytec 2014):

Generalized reaction:

Distribution coefficient: Equilibrium constant:

If we assume that m = n, rearranging gives:

Organic

Aqueous

0.0 0.5 1.0 1.5 2.0 2.5 3.00

102030405060708090

100

Equilibrium pH of aqueous solution

% E

u ex

trac

ted

pH50 ≈ 0.8

-1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

R² = 0.995886265096244

Log([H+]/[HL])

Log(

D)

95% confidence in-terval for slope:n = 3.85 ± 0.06

Equilibrium pH = 0.6-1.1

Results and Discussion• Good extraction occurs at pH > 1.1. • Poor extraction occurs at pH < 0.6.• The pH50 is about 0.8. • Precipitation was observed at pH ≥ 6.5

• Each Eu (III) ion is, on average, reacting with more than the predicted n = 3 ligands.

• Are some Eu (III) ions reacting with 3 and others with 4 ligands?

0

1

2

3

4

5

6

H+

per

Eu

extr

acte

d

Cytec: n= m = 3

Equilibrium pH = 2.3 - 2.6

Experimental: n = 3.85

• More H+ ions are being released per Eu ion than the predicted m = 3.

• Experimental error makes it difficult to establish the exact H+/Eu ratio.

• Within error, it is possible that m = n.

Image credits: Retrieved June 22, 2014, from http://www.technologyreview.com/featuredstory/423730/the-rare-earth-crisis/#comments

Error bars are based on uncertainty of ± 5% in pH and final Eu concentration.

Δ [Eu]

Δ [HL]

[HL] initial

[Eu] initial

[Eu] final

pH final

log(D)

[H+] final

[HL] final

Log(H+/HL)

n = slope of log(D) vs. log(H+/HL)

Δ [Eu] Δ [H+]

pH initial

[Eu] initial

[Eu] final

pH final

[H+] final

m = Δ [H+]/Δ [Eu]

[H+] initial