Chemical speciation of long-lived radionuclide technetium-99 and

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Chemical Speciation of Long-lived Radionuclide

Technetium-99 and its Environmental Behaviour

Keli ang Shi
DTU-PhD
Octo ber 2012
Thesis for the Degree of Doctor of Philosophy
Center for Nuclear Technologies,
Department of Chemistry, Technical University of Denmark

Chemical speciation of long-lived radionuclide technetium-99
and its environmental behaviour

Keliang Shi

To be presented with the permission of the Department of Chemistry for public criticism in DTU,
th
Roskilde, Denmark on 29 October, 2012.
Supervisor
Senior scientist Xiaolin Hou
Center for Nuclear Technologies, Technical University of Denmark
Roskilde, Denmark

Co-supervisors
Senior scientist Per Roos
Center for Nuclear Technologies, Technical University of Denmark
Roskilde, Denmark

Professor Wangsuo Wu
School of Nuclear Science and Technology, Lanzhou University
Lanzhou, China

Opponents
Senior scientist Helge Egsgaard
Department of Chemical and Biochemical Engineering, Technical University of Denmark
Roskilde, Denmark

Professor lan W. Croudace
University of Southampton, National Oceanography Centre
Southampton, UK

Dr. Florence Goutelard
French Alternative Energies and Atomic Energy Commission, Division of Nuclear Energy
France

ii
Abbreviations
AMS accelerator mass spectrometry
CF concentration factor
EARP enhanced actinide removal plant
EDTA ethylenediaminetetraacetic
EXAFS extended X-ray absorption fine structure
HC holding coil
HPLC high performance liquid chromatography
ICP-MS inductively coupled plasma mass spectrometry
LSC liquid scintillation counter
NAA neutron activation analysis
PUREX plutonium uranium recovery by extraction
RIMS resonance ionization mass spectrometry
SC separation column
SD standard deviation
SERS surface enhanced raman spectrometry
SI sequential injection
SP syringe pump
SV selection valve
TBP tri-butylphosphate
TEVA tetravalent actinides
TIMS thermal ionization mass spectrometry
TiOA tri-iso-octylamine
UV ultraviolet
XAS X-ray absorption spectrometry

iii
Resume
På grund af højt fissionsudbytte, høj mobilitet og lang halveringstid anses technetium-99 for at være
blandt de vigtigste radioaktive isotoper til sporstofanvendelser i havmiljøet og at have væsentlig
betydning i forbindelse med radioaktivt affald. Undersøgelser af metoder til at bestemme technetium
og dens kemiske former er derfor vigtige for at forstå, hvorledes technetium opfører sig i miljøet.
Denne afhandling sigter mod at udvikle analytiske metoder til hurtig og præcis bestemmelse af den
99
samlede mængde Tc i miljøprøver (f.eks. makroalger, jord og havvand) samt bestemmelse af kemiske
former, som technetium forekommer på i makroalger. Afhandlingen omfatter desuden anvendelser
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af Tc som et oceanografisk sporstof til at undersøge havstrømme og havforurening i kystområder ved
at bruge makroalger som bioindikator.
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Analytiske metoder til at bestemme Tc i forskellige miljøprøver så som makroalger og havvand er
blevet etableret. Metoder til forbehandling af forskellige prøvetyper er blevet undersøgt omfattende
foraskning, syreoplukning af faste prøver samt fældning af technetium med jernhydroxid for store
prøver af havvand. En ny fremgangsmåde er udviklet til at separere og oprense technetium fra
99
prøvematricer og interferende stoffer med efterfølgende bestemmelse af Tc ved induktivt koblet
plasma massespektrometri (ICP-MS). Stabiliteten af technetium ved tør-foraskning af faste prøver og
våd-foraskning af væskeopløsninger af prøver er undersøgt i lys af de særlige kemiske egenskaber ved
technetium, og herved er procedurer til forbehandling blevet fastlagt. Teknikker til ekstraktions-
kromatografi med TEVA-kolonner er anvendt til at fjerne interferenser af rutenium og molybdæn. Det
er blevet undersøgt, hvorledes technetium, rutenium og molybdæn fæstnes på og udtrækkes fra TEVA
-
jonbyttere, og i forbindelse hermed er en mulig mekanisme til at kontrollere fæstnelse af TcO4 ved
+
forskellige koncentrationer af H blevet afledt. Med brug af to små TEVA-kolonner (1.5 mL hver) er
4 5
der for miljøprøver opnået dekontaminationsfaktorer på over 10 for molybdæn og over 10 for
rutenium samt genfinding af technetium på 60-95%. Med ICP-MS analyseteknik er opnået en
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detektionsgrænse på 1.5 mBq for Tc. De analytiske metoder har vist sig at være pålidelige og er
anvendt med succes til analyser af miljøprøver.
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En analysemetode til at bestemme kemisk speciering af Tc i makroalger er blevet udviklet.
Forskellige kemiske former for technetium blev separeret med biokemiske teknikker og bestemt med
ICP-MS efter forbehandling af prøver og oprensning af technetium med ekstraktions-kromatografiske
-
teknikker. Ud over TcO4 blev der fundet mest technetium i makroalgernes bio-makromolekyler så som
algin, pigment, cellulose mm. Forskellige bindinger af technetium med disse bio-makromolekyler blev
udledt.
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Sæsonbetingede variationer i koncentrationer af Tc i makroalger (Fucus) blev undersøgt ved at
analysere månedlige tangprøver indsamlet ved danske kyster. Mulige årsager til disse sæsonvariationer
blev undersøgt. Koncentrationsfaktoren for overførsel af technetium til makroalger blev fundet at være
konstant og ikke variere med tidspunkt for indsamling. Resultaterne indikerer, at makroalger kan
iv
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anvendes som en pålidelig bioindikator til at overvåge niveauer af Tc i havvand og til at vurdere
tidsmæssige variationer samt spredning af forurening i marine systemer.

v
Abstract
Because of the high fission yield, high mobility and long half-life, technetium-99 is considered to be
one of the most important radionuclides in environmental trace application as well as nuclear waste
management. The study on the determination of technetium and its speciation is therefore a key issue
for understanding its fate and behaviour in ecosystem. This thesis aims to develop series of analytical
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methods for rapid and accurate determination of total Tc in environmental samples (e.g., seaweed,
99 99
soil, and seawater), as well as speciation analysis of Tc in seaweeds. The application of Tc as an
oceanographic tracer to investigate seawater movement and coastal pollution using seaweed as a bio-
indictor was also investigated.
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Analytical methods of Tc for different environmental samples such as seaweed and seawater were
established. According to the types of sample, different pre-treatment methods including dry ashing
and acid leaching for solid samples as well as co-precipitation of technetium using ferrous hydroxide
from large volume water samples were investigated in details and a novel approach has been developed
to separate and purify technetium from sample matrix and other interferences prior to measurement
99
of Tc by inductively coupled plasma mass spectrometry (ICP-MS). Considering the special chemical
property of technetium, the stability of technetium during dry ashing of solid samples and evaporation
of sample solution was investigated and the corresponding pre-treatment procedures were proposed. To
remove the interferences of ruthenium and molybdenum, extraction chromatographic techniques using
TEVA column was applied. The sorption and elution behaviours of technetium, ruthenium and
-
molybdenum onto TEVA resin were investigated and a possible mechanism controlling TcO4 sorption
+
at different concentrations of H was deduced. With the application of two small TEVA columns (1.5
4 5
mL for each), decontamination factors of >10 for molybdenum and >10 for ruthenium and recovery
of 60-95% for technetium were achieved for different environmental samples. An absolute detection
99
limit of 1.5 mBq for Tc was obtained by ICP-MS measurement. The analytical methods were proved
99
to be reliable and have been successfully applied for the determination of Tc in environmental
samples.
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An analytical method for chemical speciation of Tc in natural seaweed has been developed. Different
species of technetium were separated using biochemical techniques and detected by ICP-MS after
sample pre-treatment and purification of technetium using extraction chromatographic technology.
-
Besides TcO4 , most of technetium was found in bio-macromolecules of seaweed, such as algin,
pigment, celluloses, etc. Possible binding modes of technetium with these bio-macromolecules were
deduced.
99
Seasonal variation of Tc concentration in seaweed (Fucus) was investigated by analysis of seaweed
samples collected monthly in Danish coast, and a possible mechanism driving its seasonal variation
was explored. The concentration factor of seaweed to technetium was found to be a constant and does
not vary with sampling date. The results indicate that seaweed can be used as a reliable bio-indictor to
vi
99
monitor the level of Tc in seawater and estimate the temporal variation and dispersion of pollution in
the marine system.
vii
Preface
This thesis was carried out at the Radioecology and Tracer Programme, Center for Nuclear
Technologies, Department of Chemistry, Technical Universtiy of Denmark (DTU) during 2009-2012
in partial fulfilment of the requirements for acquiring the Ph.D degree in Chemistry.
The thesis manily aims to establish analytical methods for rapid and accurate determination of
99
total Tc in environmental samples (e.g., seaweed, soil, and seawater), as well as speciation analysis
99 99
of Tc in seaweeds. The application of Tc as an oceanographic tracer to investigate seawater
movement and coastal pollution using seaweed as a bio-indictor was also investigated.

Roskilde, October 2012
Keliang Shi
viii