SPECIATION AND REACTIVITY OF CHROMIUM(III) OLIGOMERS IN

136 Pages·2002·2.45 MB·English

by  Judah Friese

SPECIATION AND REACTIVITY OF CHROMIUM(III) OLIGOMERS IN
ALKALINE SYSTEMS.

BY
JUDAH ISAAC FRIESE

A dissertation submitted in partial fulfillment of the
requirements for the degree of

DOCTOR OF PHILOSPHY

WASHINGTON STATE UNIVERSITY
Department of Chemistry

MAY 2002
To the faculty of Washington State University:

The members of the Committee appointed to examine the dissertation of
JUDAH ISAAC FRIESE find it satisfactory and recommend that it be accepted.

_________________________________
Chair

_________________________________

_________________________________

_________________________________

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ACKNOWLEDGEMENTS
There are many people who I wish to thank for the support,
encouragement, guidance, and friendship during my graduate tenure. Dr. Sue B
Clark for her advice, guidance and patience with working with me. She gave me
the chance to travel nationally and internationally to present my graduate work
and to continue my education. I have enjoyed working in her lab, and will
remember by graduate years with fondness.
I would like to thank Ms. Susan Bentjen for her enthusiastic attitude and
helpfulness. If something did not work, if something could not be found, or if
Microsoft Word was not formatting correctly, she is the go to person. She is the
one who gets things done, and made graduate studies a lot easier.
I would also like to thank the past and present members of the Clark group
from whom I have received support: Minfang Yeh, Steve LaMont, Andrew
Maddison, Stacey Loyland-Asbury, Matt Douglas, Hiromu Kurosaki, Carrie
Gillaspie, Zhichang Zhang, Erin Finn, and Tammy Orshiro. Special thanks must
be extended to Ben Ritherdon. He and I work very well together on many
projects and was a good friend. Labwork has not been as funny without him.
I would like to thank my family for their love and support: Mom and dad,
mom and dad Swanson, Josh, Seth, Amanda, Rachel, Katie, Joel, Jacob, and
Hannah.
My wife Amanda has always been supportive, and agreed to move
halfway across the country for me to pursue graduate school at WSU. Her
support has been unwavering. Thank you.

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I would finally like to thank the U.S. Department of Energy’s Environmental
Management Science Program for funding this project.

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SPECIATION AND REACTIVITY OF CHROMIUM(III) OLIGOMERS IN
ALKALINE SYSTEMS

Abstract

By Judah Isaac Friese, Ph.D.
Washington State University
May 2002

Chair: Sue B. Clark

The chemistry of trivalent chromium (Cr(III)) in alkaline systems is very
complex due to the formation of hydrolyzed species. The chemistry of Cr(III)
under such conditions is of recent interest due to the need to remove it from
highly alkaline high level radioactive waste (HLW). Treatment by simple caustic
leaching has not been successful, where as oxidative leaching by various
oxidants yields inconsistent results. Development of a chromium(III) removal
process has been hampered by the lack of understanding of its fundamental
chemistry in alkaline systems.
In this research, several separation methods have been developed to
study the speciation of Cr(III) over a range of pH. Ion exchange (IX) is a method
that separates species based on their overall net charge. Cr(III) oligomers have
increasing charge, the monomer (+3), dimer (+4), trimer (+5) and tetramer (+6)
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and were separated in macroscopic amounts by IX. Each fraction of oligomer
eluted from the column was analyzed by UV-VIS spectroscopy.
Capillary electrophoresis (CE) is a microscale technique that separates
Cr(III) oligomers under a variety of chemical conditions. CE is also a method that
separates species based on charge density. A separation protocol based on an
indirect method of detection was developed isolate monomeric, dimeric, trimeric
tetrameric and higher oligomers. Order of elution by CE supports the triangular
configuration of the trimer.
Oxidation of Cr(III) with peroxydisulfate is one aspect of reactivity that was
studied in alkaline systems. Separate kinetic studies of the monomer, dimer,
trimer, and tetramer were performed by placing each oligomer is base and
adding the oxidant. A mechanism for oxidation is proposed. Peroxydisulfate has
several advantages and disadvantages as an oxidant for leaching from HLW. In
base, it is a powerful oxidant, but the rate of reaction slows as hydroxide
concentration is increased. It also may oxidize the actinides to more soluble
forms along with Cr(III).
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Table of Contents
ACKNOWLEDGEMENTS....................................................................................iii
Abstract.................................................................................................................v
Table of Contents................................................................................................vii
List of Tables .......................................................................................................ix
List of Figures.......................................................................................................x
Chapter 1: Intorduction to Chromium Chemistry...................................................1
Introduction....................................................................................................1
The Chemistry of Trivalent Chromium...........................................................4
Speciation Techniques ..................................................................................5
Cr(III) Speciation............................................................................................9
Cr(III) reactivity............................................................................................11
Focus of this Thesis and Attribution.............................................................12
Chapter 2: Chromatographic Separation and Characterization of Hydrolyzed
Cr(III) Species.....................................................................................................27
Abstract .......................................................................................................27
Introduction..................................................................................................28
Experimental................................................................................................31
Ion Exchange...............................................................................................32
Data Analysis...............................................................................................36
Results and Discussion ...............................................................................37
Conclusions.................................................................................................43
Acknowledgements......................................................................................44
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Chapter 3: Kinetics and Mechanism of the Oxidation of Chromium(III) Oligomers
by Peroxydisulfate Under Alkaline Conditions ....................................................56
Abstract: ......................................................................................................56
Introduction..................................................................................................57
Experimental Section...................................................................................58
Results.........................................................................................................60
Discussion...................................................................................................65
Chapter 4: The Speciation of Cationic Cr(III) Oligomers as a Function of pH and
Aging Time..........................................................................................................85
Abstract .......................................................................................................85
Introduction..................................................................................................86
Experimental................................................................................................88
Results and Discussion ...............................................................................90
Chapter 5: Conclusions.....................................................................................107
Appendix I: Estimating the Charge Density of Cr(III) Oligomers.......................114
Appendix II: Observed Rate Constants for the Oxidation of Cr(III) with
Peroxydisulfate...........................................................................................119
viii
List of Tables
Chapter 1 Tables
Table 1 - Best Basis Inventory Estimates for Waste Components in Tank
241-C-104, 241-T-201 and 241-T-204................................................19,20
Table 2 - Variation in the Rates of Hydrolytic Processes .........................21
Table 3 - General Speciation Techniques................................................22
Table 4 - Characteristics of the Absorption Spectra of Cr(III) Species.....23
Chapter 2 Tables
Table 1 - Recovery of Cr(III) from the ion exchange columns..................47
Table 2 - Estimated volumes and charge densities for the various Cr(III)
species.....................................................................................................48
Chapter 3 Tables
Table 1 – Resolved rate constants for the oxidation of individual Cr(III)
species with peroxydisulfate.....................................................................71
Table 2 – Rate constants for the oxidation of unseparated Cr(III) species
.................................................................................................................72
Table 3 – Activation parameters for the oxidation of unseparated Cr(III)
species.....................................................................................................73
Chapter 4 Tables
Table 1 – Concentrations of total cationic Cr(III) species.......................100
Table 2 – Estimates of changes in the concentrations of cationic Cr(III)
species as a function of time..................................................................101

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List of Figures
Chapter 1 Figures
Figure 1 - Solution Structures of Cr(III) Oligomers...................................24
Figure 2 - UV-VIS Spectra of Oligomeric Species....................................25
Figure 3 - ESR Spectra of Oligomeric Species........................................26
Chapter 2 Figures
Figure 1 - Solution Structures of Cr(III) Oligomers...................................52
Figure 2 - Chromatograms for the elution of 51Cr-labeled Cr(III) oligomers
by ion exchange.......................................................................................53
Figure 3 - Capillary electrophoresis electropherograms using indirect
detection on the Cr(III) oligomer fractions separated by ion exchange ....54
Figure 4 - Electropherogram for a hydrolyzed solution of Cr(III)...............55
Chapter 3 Figures
Figure 1 - Structures of Cr(III) species.....................................................76
Figure 2 - Typical kinetic data at low and high base.................................77
Figure 3 - The dependence of observed rate constants on peroxydisulfate
concentration at 0.10M NaOH and 35.6oC...............................................78
Figure 4 - The dependence of observed rate constants for the slow
reaction pathway (k ) on peroxydisulfate concentration at 0.01M NaOH
2obs
and 35.6oC...............................................................................................79
Figure 5 - Hydroxide dependence on resolved rate constants.................80
Figure 6 - The dependence of observed rate constants on peroxydisulfate
concentration for a mixture of Cr(III) species at 1.0M NaOH....................81
Figure 7 - The dependence of observed rate constants on peroxydisulfate
concentration for a mixture of Cr(III) species at 5.0M NaOH....................82
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