Techne
tium is a long lived (2.13 × 10
5 a), be
ta emi
tting radionuclide which is a groundwa
ter con
taminan
t a
t a number o
f nuclear
facili
ties
throughou
t the world. I
ts environmen
tal behaviour is primarily governed by i
ts redox s
ta
te. Under oxic condi
tions i
t forms
the highly soluble per
techne
ta
te
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ttp://www.sciencedirect.com/cache/MiamiImageURL/B6VDG-4R5F00V-1-14/0?wchp=dGLzVlz-zSkWW" alt="View the MathML source" title="View the MathML source" align="absbottom" border="0" height=17 width="52"/> ion; under reducing condi
tions i
t forms
the poorly soluble, reduced
forms o
f Tc, par
ticularly
the Tc(IV) ion which is expec
ted
to precipi
ta
te as hydrous TcO
2 above i
ts solubili
ty limi
t (10
−9 mol l
−1 a
t ![](h<font color=)
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ti
ties/223c.gi
f" al
t="no
t, ver
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ti
tle="no
t, ver
t, similar" border="0">pH 7) or
to be s
trongly sorbed
to mineral sur
faces a
t lower concen
tra
tions. Thus
the redox cycling behaviour o
f Tc is predic
ted
to be key
to i
ts environmen
tal behaviour in
the na
tural and engineered environmen
t. Here
the resul
ts o
f a series o
f X-ray absorp
tion spec
troscopy (XAS) experimen
ts which examine
the oxida
tion s
ta
te and coordina
tion environmen
t o
f Tc in a range o
f es
tuarine, aqui
fer and
freshwa
ter sedimen
t suspensions, and in an environmen
tally relevan
t amorphous Fe(II) phase under bo
th reduced and reoxidised biogeochemical condi
tions are presen
ted. In reduced sedimen
ts and
the amorphous Fe(II) phase prior
to reoxida
tion, XAS resul
ts show
tha
t Tc was re
tained as hydrous TcO
2-like phases across all samples. Under air reoxida
tion, experimen
ts showed signi
fican
t (up
to 80%) remobilisa
tion o
f Tc
to solu
tion as
f="/science?_ob=MathURL&_method=retrieve&_udi=B6VDG-4R5F00V-1&_mathId=mml27&_user=1067359&_cdi=5982&_rdoc=1&_acct=C000050221&_version=1&_userid=10&md5=f0f15a358112ca5669ec5d8ebf6c453a">
ttp://www.sciencedirect.com/cache/MiamiImageURL/B6VDG-4R5F00V-1-15/0?wchp=dGLzVlz-zSkWW" alt="View the MathML source" title="View the MathML source" align="absbottom" border="0" height=16 width="40"/>. In pre-reduced
freshwa
ter sedimen
ts, aqui
fer sedimen
ts and
the amorphous Fe(II) phase oxidised wi
th air, XAS indica
ted
tha
t Tc remained associa
ted wi
th
the solids as hydrous TcO
2-like phases. By con
tras
t, in air reoxidised es
tuarine sedimen
t XAS analysis sugges
ted
tha
t bo
th hydrous TcO
2-like phases and
f="/science?_ob=MathURL&_method=retrieve&_udi=B6VDG-4R5F00V-1&_mathId=mml28&_user=1067359&_cdi=5982&_rdoc=1&_acct=C000050221&_version=1&_userid=10&md5=224c47893f6f9d77e2c8d3ce2feb2198">
ttp://www.sciencedirect.com/cache/MiamiImageURL/B6VDG-4R5F00V-1-16/0?wchp=dGLzVlz-zSkWW" alt="View the MathML source" title="View the MathML source" align="absbottom" border="0" height=16 width="40"/> were re
tained wi
thin
the sedimen
t. Finally, when microbially-media
ted NO
3 reoxida
tion occurred in es
tuarine and aqui
fer sedimen
t slurries, experimen
ts showed compara
tively low (<8%) remobilisa
tion o
f Tc
from solids over similar
timescales
to air reoxida
tion experimen
ts, whils
t XAS again showed
tha
t bo
th hydrous TcO
2-like phases and
f="/science?_ob=MathURL&_method=retrieve&_udi=B6VDG-4R5F00V-1&_mathId=mml29&_user=1067359&_cdi=5982&_rdoc=1&_acct=C000050221&_version=1&_userid=10&md5=f9baaebf81c5f54d99bc0386cdcc3da8">
ttp://www.sciencedirect.com/cache/MiamiImageURL/B6VDG-4R5F00V-1-17/0?wchp=dGLzVlz-zSkWW" alt="View the MathML source" title="View the MathML source" align="absbottom" border="0" height=16 width="40"/> were re
tained wi
thin
the sedimen
t. By con
tras
t, in
the amorphous Fe(II) phase, al
though NO
3 reoxida
tion again led
to low (<4%) remobilisa
tion o
f Tc
from solids, XAS analysis showed
tha
t Tc was re
tained as hydrous TcO
2-like phases alone. These resul
ts are discussed in
the con
tex
t o
f the redox cycling behaviour o
f Tc in
the na
tural and engineered environmen
t.