Predictive thermodynamic models for liquid-liquid extraction of single, binary and ternary ...

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Iowa State University Capstones, Theses and
Retrospective Theses and Dissertations
Dissertations
1977
Predictive thermodynamic models for liquid-liquid
extraction of single, binary and ternary lanthanides
and actinides
Ying-Chu Hoh
Iowa State University
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Recommended Citation
Hoh, Ying-Chu, "Predictive thermodynamic models for liquid-liquid extraction of single, binary and ternary lanthanides and actinides
" (1977).Retrospective Theses and Dissertations. 5827.
https://lib.dr.iastate.edu/rtd/5827
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HOH, Ying-Chu, 1943-
PREDICTIVE THERMODYNAMIC MODELS FOR
LIQUID-LIQUID EXTRACTION OF SINGLE,
BINARY AND TERNARY LANTHANIDES ABD
ACTINIDES.
Iowa State University, Ph.D., 1977
Engineering, chemical
Xerox University i\/licr0films,
Ann Arbor, Michigan 48106
Predictive thermodynamic models for
liquid-liquid extraction of single, binary
and ternary lanthanides and actinides
by
Ying-Chu Hoh
A Dissertation Submitted to the
Graduate Faculty in Partial Fulfillment of
The Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Department: Chemical Engineering and Nuclear Engineering
Major: Chemical Engineering
Approved
Signature was redacted for privacy.
Ma]or Work
Signature was redacted for privacy.
For the Major Department
Signature was redacted for privacy.
For the Gradpate College
Iowa State University
Ames, Iowa
1977
ii
TABLE CF CONTENTS
Page
SOHENCLATUPE iV
INTFOCUCTION 1
LITESATUBE SEVIFW U
Liquid-Liquid Extraction of Lanthanides by
Organcphosphorus Compounds 4
Liquid-Liquid Extraction of Actinides by
Organcphosphorus Compounds 10
Lanthanide Complexes in Aqueous solution 17
Actinile Complexes in Aqueous Solution 22
Liquid-Liquid Extraction of Nitric Acid by
Tri-n-butyl Phosphate 25
BASIC THEORY 29
The Theory of Mononuclear Complexes Equilibria 29
DEVELOPMENT OF THERMODYNAMIC LIQOID-LIQniD EXTRACTION
MODELS 44
Lanthanide Nitrate Complexes for Single, Binary
and Multiccmponent Systems 47
The case of neodymium nitrate complexes 47
The case of cerium nitrate complexes 54
Actiniie Nitrate complexes for Single, Binary
and Multicompcnent Systems 59
The case of plutonium (IV) and neptunium (IV)
nitrate complexes 59
EXPERIMENTAL PROCEDURES 66
Materials 66
Preparation of the Rare Earth Stock Solutions 66
Equilibrium Studies 67
i-ii
Separation Factor Studios 71
Icn SelACtivA Electrode Measurements 71
Simple Linear Pegression Analysis 79
DISCUSSION OF BFSULTS 81
Application of Published Data to the Thermo-
Dynamic liquid-liquid Extraction Models 81
Th?. system neptunium nitrate-nitric acid-water
-TEP-benzene 81
The system plutonium nitrate-nitric acid-water
-TBP-toluena 85
Th 2 system cerium nitrate-nitric acid-water
-TEP-tenzene 91
The system neodymium nitrate-ytterbium nitrate-
-nitric acid-water-TBP-carbon tetrachloride 99
HDEHP Solvent Extraction Analysis 104
The system lanthanum nitrate-sodium nitrate-
nitric acid-water-HDEHP-Amsco 104
The system neodymium nitrate-sodium nitrate-
nitric acid-water-HDEHP-Amsco 122
The system lanthanum nitrate-neodymium nitrate-
nitric acid-water-HDEHP-Amsco 132
The system lanthanum chloride-neodymium nitrate-
nitric acid-water-HDEHP-Amsco 138
The system lanthanum nitrate-neodymium nitrate-
samarium nitrate-nitric acid-water-HDEKP-Amscc 145
CONCLaSICNS AND RECOMMENDATIONS 154
EIBLIC6RAPHY 158
ACKNOWLEDGMENTS 170
APPENDIX: DEVELOPMENT OP THE PSEEICTIVE THEEMOCYNAMIC
MODEL EQUATION FOR MORE THAN ONE ETTPACTABLE SPECIE 171
iv
NOMENCLATURE
a activity of particular specie
i
a degree of formation of a particular ion
i
B ligand
E overall electrode voltage (millivolts)
E reference electrode voltage (millivolts)
a
F Farady's electrochemical constant
f fugacity of a particular specie
i
I ionic strength of solution
k stoichiometric overall stability constant
i
K distribution coefficient
d
K liquid-liquid extraction equilibrium constant
e
K effective liquid-liquid extraction equilibrium
1 constant
K* K /K3
1 1 e
K K /K
M-N 1H IN
K» K» /K*
H-H 1H IN
K activity coefficient quotient
r
k selective constant
X
n metallic ion
m molarity of a particular species in solution
n ligand number
0 the ratio of the organic concentration to the ligand
concentration in the aqueous phase
r activity coefficient of a particular specie
i
S ideal gas constant
s separation factor for species M and N
H-H
T absolute temperature, °R
T thermodynamic overall stability constant
kn
T thermodynamic stepwise stability constant
sn
X mole fraction of particular specie
i
Z Charge of particular ion
i
Subscripts
K refers to the aqueous phase
i refers to ith species
n number of ligand ions in a complex
0 refers to organic phase
R refers to resin phase
± refers to mean
E refers to equilibrium conditions
I refers to initial conditions
0 refers to standard state
T refers to total
I I refers to activity
( ) refers to concentration
1
INTRODUCTION
The lanthanide and actinide elements constitute two
families of metals which often exhibit very similar chemical
behavior. The similarity is most easily observed with the
cations in oxidation state III, the most common one for all
the elements of the lanthanide series and for the trans­
uranium elements of the actinide series.
Liquid-liquid extraction is one of the most important
techniques for the quantitative separation of lanthanide or
actinide elements which are similar in properties. Until
recently, fundamental solvent extraction chemistry studies
were usually carried out at tracer concentrations for the
lanthanide elements. The actual chemistry of the reactions
involved in solvent extraction at macro-concentraticn is
extremely complicated due to many unknown factors.
Due to the lack of precise information, the solvent
extraction of the lanthanides and actinides from an aqueous
salt solution to organophosphorus compounds has been somewhat
difficult to thermodynamically analyze for a number of
reasons. First, during the extraction, a considerable amount
of hydrogen ions are liberated into the aqueous phase when
the acidic organophosphorus compound is the extractant.
Therefore, for the extraction of a single component
lanthanide or actinide salt, the final equilibrated aqueous
2
phase will form a binary electrolyte solution which contains
the remaining lanthanide or actinide ions, the hydrogen ions,
and the ligands. Second, there is considerable difficulty in
determining the neutral organcphosphorus compound
concentration such as tri-n-butyl phosphate (TBP) in the
coextraction of nitric acid and water into the organic phase.
Third, at relative high concentrations, the lanthanide and
actinide ions form a series of complexes with a ligand;
M+3, MB+2, MB+i, and MB in the aqueous phase, where B
2 3
represent a ligand. This make the system more complicated.
Fourth, until recently, the extraction mechanism of
lanthanides at higher concentraction was not well defined.
The objectives of this investigation are:
(1) To review the progress achieved in the field of
liquid-liquid extraction of lanthanides and actinides from
aqueous salt solution by organophosphorus compounds such as
di- (2-ethylhexyl) phosphoric acid (HDEHP) and TEP,
(2) To develop thermodynamic models for single, binary,
and multicomponent systems and to quantitatively describe and
predict the equilibrium relationships for liquid-liquid
extraction of lanthanide and actinide nitrates by
organophosphorus compounds (TBP and HDEHP);
(3) To make optimal use of the published data in
literatures for relating the lanthanide and actinide nitrates
complex formation in the aqueous phase to the liquid-liquid