Solvent Extraction of Europium (III) from a Nitric Acid Solution
Annette Hein (Casper College)
Faculty Advisors: Dr. William Cross, Dr. Michael West
Theory
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?
Size Reduction
Leaching
Solvent
Extraction
Stripping
[Eu]
initial
Extraction according to Cytec data sheet (Cytec 2014):
𝐸𝑢3+ (𝑎𝑞) + 3𝐻𝐿(𝑜) ↔ 𝐸𝑢𝐿3 (𝑜) + 3𝐻 + (𝑎𝑞)
Generalized reaction:
𝐸𝑢𝐴𝑚+ (𝑎𝑞) + 𝑛𝐻𝐿(𝑜) ↔ 𝐸𝑢𝐴𝐻(𝑛−𝑚) 𝐿𝑛
Distribution coefficient:
𝐸𝑢𝐴𝐻(𝑛−𝑚) 𝐿𝑛
(𝑜)
𝐷=
𝐸𝑢𝐴𝑛+
[Eu]
final
Δ [Eu]
[H+] final
Conclusions
Δ [HL]
[HL] final
log(D)
(𝑜)
pH
final
[HL]
initial
Log(H+/HL)
+ 𝑚𝐻 + (𝑎𝑞)
n = slope of log(D)
vs. log(H+/HL)
Equilibrium constant:
+ 𝑚
𝐸𝑢𝐴𝐻(𝑛−𝑚) 𝐿𝑛
[𝐻 ]
(𝑜)
𝐾𝑒𝑞 =
𝐸𝑢𝐴𝑚+ [𝐻𝐿]𝑛
[Eu]
initial
If we assume that m = n, rearranging gives:
𝐻+
log(𝐷) = −n log
+ log(𝐾𝑒𝑞 )
𝐻𝐿
[Eu]
final
pH
initial
pH
final
[H+]
initial
[H+]
final
Δ [Eu]
Δ [H+]
m = Δ [H+]/Δ [Eu]
Use in Industry
Organic
Results and Discussion
Materials: Eu stock solution,
kerosene, Cyanex 572 extractant,
HNO3 and NaOH for titrations.
Experimental conditions:
• Temp = 25 ⁰C
• 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
100
90
80
70
60
50
40
30
20
10
0
•
•
•
•
Aqueous
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
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-earthcrisis/#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.
pH50 ≈ 0.8
1.5
0.0
1.0
2.0
3.0
R² = 0.996
1.0
Equilibrium pH of aqueous solution
• 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?
Log(D)
Extraction 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).
0.5
95% confidence
interval for slope:
n = 3.85 ± 0.06
0.0
-0.5
Equilibrium pH = 0.6-1.1
-1.0
-1.5
-1.1
-0.9
-0.7
-0.5
7
6
5
4
3
2
Experimental: n = 3.85
Cytec: n= m = 3
1
0
Acknowledgments
Log([H+]/[HL])
8
H+ per Eu extracted
Methods
% Eu extracted
Image credits: Retrieved June 22, 2014, from
http://www.technologyreview.com/featuredstory/423730/the-rare-earth-crisis/#comments
• 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).
Equilibrium pH = 2.3 - 2.6
• 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.
Error bars are based on uncertainty of ± 5% in pH and final Eu concentration.
This work was made possible by the
National Science Foundation REU
Back to the Future Site DMR1157074
Thanks to Dr. Kenneth Han, Dr. Alfred
Boysen, Mr. Kelsey Fitzgerald, Mr. Ian
Markon, and Mr. Nathan Madden for
help and advice.