16 Adsorption of Metal Ions and Complexes on Aluminosilicate Minerals B. A. Goodman
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The Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen AB9 2QJ, Scotland Adsorption of metal ions and complexes on the various types of aluminosilicate mineral is briefly reviewed along with contributions made by several spectroscopic methods to understanding the nature of adsorbed species. A knowledge of the chemical forms of adsorbed species is an important preliminary to any understanding of their reactivities in either natural or artificial situations and, although significant progress has been made in some systems, there is clearly still a great deal of work necessary in order to characterize fully the environments of many adsorbed species. Examples of the types of reaction that may be carried out specifically by metal-exchanged clays are given and serve as illustrations of the importance of such species in natural systems and of the tremendous potential that such systems have in performing novel chemical reactions. The
surfaces
other
cases
usually of,
compensated
equivalent
adsorption (which play
the
clays the
and
is
science
toxic
surface
of
areas)
of
importance agricultural
models of
often
Therefore,
nature
of
the
i n many
areas
of
industries,
and c o n s t r u c t i o n of adsorption
ions, the
complex adsorbent
have
of
and waters
an influence
and
for clay
systems.
is
adsorption
charge
mobility
and i n
charge
involving
opposite
in soils
a charge
surface
importance
the
clay.
the
carry
Any
i n natural
c a n have the
and
of metal
properties
ions
properties
to the engineering
adsorption
with,
regulating
species
great and
Theoretical the
i n
processes of
of
minerals exist.
are of particular
surface
properties
chemical
may
by a s s o c i a t i o n
role
adsorbed
adsorption
centres
amounts
high
major
chemical
aluminosilicate
processes
have a
beneficial of
o f many reactive
Clay ions
such
minerals minerals with
both
and the nature
on the p h y s i c a l and an understanding
of
species
on
science
through
adsorbed ranging
from
environmental
industries. been
formation
reviewed
along
with
and the i n f l u e n c e
and s o l u t i o n
of
pH o n a d s o r p t i o n
0097-6156/ 86/ 0323-0342S06.00/ 0 © 1986 American Chemical Society
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
16.
GOODMAN
processes take
a
in
a
number
there
is
Adsorption
on Aluminosilicate
Minerals
previous
ACS
(1).
of
chemical
cheraisorption,
or may
3-dimensional
growth
discussed detail sites
at
simple species the
in
of
cannot
be
that from
a
attention
and
of
some
energy
are
value
energy
nuclear
resonance
or
spin
is
+
information and to
on
liquids spin
with
1/2)
of the
priniple
electron
unpaired
of
observed
whilst
is
related
also
spin
echo
is
whose
performing to is
amenable
spectroscopy spectroscopy
to
the
are in
study
of
surface
electrons
occur
at
these
sorption
there
are
the
solid has
that
Again
spin
and
also
spectroscopy.
X-ray
involving
sensitive and
of a is
the
ESEM
electron
produce
a
decay
neighbouring IR
OH)
and
techniques and
Raman
and
IR
In
the
and
adsorbed
involving
valence
IR
enough
regions have to
solid-state
be
of
the
absorptions of
value
samples
amenable
photoelectron
is
transition
applications
species
inner-shell
ESR
observed
vibrations
near
being
usual remove
essentially
samples.
(particularly
where
are
case to
Transitions and
to
resonance
wide-ranging
instances are
liquid
solids
is
excitation.
of
molecular
groups
liquid-
pulses
these
it
environment(s)
this
nature
UV-visible
many
of
states provides
Both
case
is
the
with
latter
transitions
of
organic).
the
frequencies
photoacoustic probes
in
studies.
investigated,
of
by
spin and
resonance
in
and
Raman
(UV)-visible
(54.7°)
resonance
and
series
All
concerned
(particularly and
a
atoms.
molecules spectrum
by
particular
characterization
nuclear
electron
determined
and
information.
ENDOR
of
review
spectroscopy.
transitions
chemical
ESR s p e c t r o s c o p y
modulated shape
a
order
(ENDOR)
nucleus.
former
the have
paramagnetic
(IR)
field
angle"
that
the
that
or
nuclear
the
"magic
probed. an
spin
resonance
solution-like
states,
NMR i n
in
except
being
next-nearest-neighbour are
NMR
spin
ESR and
the
produce
to
electron(s)
combination
curve
and
this
magnetic
environment
effects
In
in
and Mossbauer
although at
will
most
adsorption.
between
external
rapidly
and
ultra-violet
studied,
sample
review
virtually
infra-red
chemical
similar between
(ESEM), and
of
obtained
mentioned
double
spectroscopy
an
cover
electron
spin
this
to one
number
c a n be
radiation
be
anisotropic in
that
(NMR),
a
and
a of
usage.
surface
transitions
in
and
have forms
task
In
of the
in addition
approaches. information
the
can
the
of
in
external
chemical
formidable
techniques
electron
modulation
the
minerals
a
techniques
resonance
photoelectron
concerned
(usually
on
with
of
rarely
is
their
of
photoacoustic
spectroscopy,
variations
onto
exist
studies
considered
chemical nature
solutions
electromagnetic
various
EPR),
echo
spectroscopy, NMR
in
the
magnetic
(ESR
electron
techniques of
understanding
This
of
is
our
the
of
precipitation
improve of
their
deal
resultant problem
be
conventional
great
the The
i.e.
addition
not
adsorbed
examples
range
potential
increasing
by a
with
In
and w i l l
required
spectroscopic
some
Spectroscopic complete
is
can
whether
surface,
species.
surface
since
involved.
achieved
on
and
Also,
those
however,
variety
to
occurs
information
mineral
surface
and
knowledge
pH.
metals
cases,
focus
order
processes
physisorption.
molecular
volume)
need
adsorption
solution
amounts
specific
in
we
of
solid
new
Sorption
d i s t i n c t i o n being
the
case
the
a
(this
especially
composition,
with
adsorption
However,
which
broadest
the
on
of
processes
conditions,
in
occur
Sposito
here.
adsorption
the
reaction
between
by
publication
with
not,
precipitation distinguishing
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forms,
343
to
can
study
spectrosopy
electrons.
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
It
in be by
(XPS) has
344
G E O C H E M I C A L PROCESSES AT M I N E R A L S U R F A C E S
applications
to
information in
on
sorption
investigations creates
situations.
the
to
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very
a
insensitive produce the
a
with
and
volume). of
texts
The
nature
As
far
as
minerals (i)
of
carry
a
cage
surfaces
hours
the
the
of
type
of
in
the
the
various
interested
chemical
Doppler
but
by are
is
solid
approach It
even
experiment.
chapter is
only
spectroscopy
is an
days)
to
Fe-57
is
However,
of
Ambe
of
is
nucleus
examples
its
generated
purposes,
methods
reader
velocity
Information
(or
in the
from
being
source
s e n s i t i v i t y and
given
the
can
be
use
of
et
al.
(this
beyond
the
scope
referred
to
some
of
the
literature.
surfaces
divided
properties into
layer
negative
(ii)
are
practice
processes.
practical
radioactive
adsorption
increase
many
most
transitions
decaying
nucleus
sorption
the
and
expanding
greatly
to
vacuum
practical
occurring
conventional
involving greater
a
Mossbauer
this
clay
may b e
the
for
details
in
the
to
In
nucleus
suitable
Sb-119
article
many
In
requiring
by
high
with
precursor. of
solid-state a
energy
nucleus
absorber
for
the
state
radioactive
often
to
into
spectrum.
a
environment as
provides technique
concerned
by
spectrum.
also
valuable
results
modulating
applications
much
Further
this
very
a
sample
states,
excited
spectrum and,
studies
performed Co-57
method isotope
sorption
the
material its
single
only
to
by
a
limited
the
is
excited
and
it
relating
emitted
chemical
in
in
obtained
state,
unknown
of
electromagnetic
suitable
the
limited
the
is
contribute
the
and
radiation
of on
materials using
of
ground
decay
provided
elements making
however,
spectroscopy
ground
of
is,
difficulties
radiation
excited by
Insertion
region
energy
of
It
the
Mossbauer
"tf-ray
number
chemical nature,
studies.
nuclear
exciting
large
and
possible
between the
a their
their charge
structures, surface over
structures,
accessible
are
3 general
a
only
to
such
area very
such
on
as
range
can
generally
pHs,
which
molecules
which
and which
of
zeolites, or
aluminosilicate
smectites,
solvation
wide
as
ions
concerned, groups:-
below
have a
internal
certain
size,
and (iii)
structures
by
chemical natures
the
The either which at
surface
from is
pH
the
especially amounts
or
from
under
different
that,
unless
an
kaolins
impurities
on
oxide-like a l . ,
is
have
taken
kaolinite source. (J3)
In
the
solely
may
a
low
of
in
been
of
the
Bolland
et
on
the
principal
mistakenly
with
a of
number x-ray
small surface
during
kaolin
the
minerals
have
structural
basis
of
high
a l . ,
dissolution of c a n be
The
mineral for
The
problems,
presence with
reported
contrast
zeolites.
charge. the
former
minerals,
present
minerals
surfaces
concluded,
net
either
reactions The
smectite
sometimes
from
Thus of
in
arise
structure,
pH d e p e n d e n t .
important
decomposition
circumstances.
charge LIm e t
have
is
dominate
can
arise
situations
account
which be
also charge
that
minerals
protonation/deprotonation
may
partial
Both
by
groups
cases
undetected
experiment.
negative
these
determined
substitution within
to
surface
are
aluminosilicate
considered
minerals
in
of or
properties
surfaces.
cation
surface
latter of
with
of
charge
charge
generally
determination difficulties
their
independent,
Is
whereas
adsorption of
isomorphous
oxide/hydroxide
mechanism
to
whose
shown
Al,
the
attributed of
natural
diffraction
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
16.
GOODMAN
(XRD)
and
cation
Adsorption
chemical
exchange
external
surface
The
CEC of
of
e.g. with
underestimate
the
fully
theoretical exclusion
model
has
recently
of
The
like
concentrations distinguish
be
between such
as
but
requiring
the
calculations
rationalize
acid
type
demonstrate
Lewis
pyridine
by
sites
and could
surfaces.
However, frequently
groups
in
on
information surfaces
investigations
of
Cu(II)
ionic
broadening exchange Cu the
(12) of
sites.
Recent
levels
of
adsorption that
the sites
Mn(II) that
most of
was
and
this of
the
type cross
Bronsted
of N-15 enriched followed
hydroxyl
by
groups
mineral
of
hydroxyl
that
in
on the
occurs
the
has
been
surface
For
minerals.
of
of
sites the
preferentially
than
arise
dipolar divalent
surfaces.
the clay
The with
sheet,
with
edge
and C u ( I I )
h a s shown
that
associated
for oxide
measurements at
and
dependent
Cd(II)
dependence
the
talc The
with
orientation
the plane
for
from ESR
example,
was n o t a s s o c i a t e d
From these
sites
kaolinite,
on t h e m i n e r a l
4 - 8 . 5 (13) pH
of
the exchange
the
a n d much l o w e r
reactions. pH
of
adsorption range
however,
adsorption
to
exchange
pH
reversible
ions.
h u m i d i t y were
the
and nature
consistent
11-12 Â apart
cation
work
i n this
to of
published
c a n be o b t a i n e d
exchanged
each
perpendicular
the
metals, Is
in
spectra
about
axis
precipitation
edge
Mn
minerals
paramagnetic
and
low r e l a t i v e
that
montmorillonite
for
the
principal
suggesting
zeolites
the technique
on the o r i g i n
demonstrate
being
at
is
groups
i n the characterization of
of
adsorbed
substitutions
ions
spectra
10,11)
Quantum
been
Silylation with
IR
minerals.
results
pyrophyllite
spectroscopy
in
conditions
used
by
difficult,
hydroxyl
can distinguish
be
not
i n an attempt
have
the surface
also
Total
does
adsorption
are
displacement (£) ·
of
surfaces
in resolving
under
spinning
presumably
(e.g.
the
from
surface
papers
a probe
By the
(6)
used
molecules
n-butylamlne as
IR
Experimental adsorption
of
NMR
assumed.
solid
absorptivities.
been
adsorbent
N-15
and
c a n be d i s t i n g u i s h e d
molar
some
the
potentials
but t h i s
sites.
and
angle"
used
used
from
of
co-ion
that
generally
measurements
by t h e s y s t e m a t i c
unenriched
(8,9)
hydroxyl
with
and "magic
acid
most
sites
recently
example,
NMR h a s b e e n
silica
acid
deriving
from
suggest
on
simple
characterization.
t h e u s e o f NMR s p e c t r o s c o p y
For
polarization
Si-29
have
aluminosilicates,
problem.
and
these
is
titration,
t h e i n t e r a c t i o n mechanisms
Lewis
of
by
quantitative
determination
as
layers
a
for
(b)
work
sites
grossly
problem
constant
i n mineral
and Lewis
pyridine,
(5),
acidic
problem
Bronsted
have
present
the
interface
this
surfaces
of
sometimes
this
the
g.
i n s o l u t i o n when
of
observed
measurements
developed
results
determined
mechanical
amorphous
been
constant-charge
can
spectroscopy
which
The
fundamental
may
t o overcome
m o n t m o r i l l o n i t e and I l l i t e
a
bases,
area
adsorption
2
the
impurities,
0 - 1 meq/100
the c l a y - s o l u t i o n
characterization
represents
the
for
much o f
smectite
from
i s exposed
In an attempt
potentials
n o t behave
of
that
N
that
from
ranging
surface
measurements.
surfaces do
area
expanded.
procedures,
smectites
345
Minerals
(CEC) a r i s e s
kaolinite
assessment
double-layer
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extraction
capacity
difficulties, are
on Aluminosilicate
at
with
minerals
i t was
the constant
on low or
argued
potential
range.
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
GEOCHEMICAL PROCESSES AT MINERAL SURFACES
346
Adsorption
of
metal
Selectivity
of
variety
factors,
of
on
minerals
adsorption
can
the
vary
most
form
of
the
adsorbate,
external
solution
and
the
investigation.
contributing
to
interpreting examples the
the
from
the of
Exchange divalent identical
at
reversible
the
exchange
found
to
with when with
this
sodium-trace
the
metal
exchanging
ions
are
of
ion
analysis
structures work
may
the
related data
involving action
ions
have
exchange range
strong
halloysite The
has
(19). Ni
When by
the
the
much
less
reported
has
clay
been
to
half
of
solutions
montmorillonite follow In
(23).
competition
preferentially to
Na
and
Κ but
a
smaller
anion,
sulphate
and
species
uranyl
roughly
with
and
being
preference
over
strong Mg,
have
at
to
very of
been
increasing
clay
alkaline a
and
by the
adsorption
curves alkali
to
(20,21),
solutions
the
in
ions
equal
solutions for
of was
nitrate of
a Ni
This
solutions
Isotherms
there
with of
(22).
CEC
of
adsorption
nitrate.
adsorbing
nitrate
with
adsorbed,
as
exert
adsorption
although
CEC f o r
the
cation,
minerals
form
acetate
from
the
strength,
pairs
the
Langmuir-type
adsorption relative
the
of
Ca-saturated with
the
reported
and
wide
individual
medium c a n
ionic
Ion
in
of
a
changing
particular
e.g.
with
of
with
where
a
the
solution
neutral
form
for
(17,18).
obtained
activity
variously
approaching
was
of
uranium
concentrations, U
that
nitrate
sulphate
on
dominant to
in
of
for
one
for
ions
the
Zn
No
exchange
that
desorbing
fluctuation
for
of
than
latter
suggest and
trends
behaviour,
Na-
from
tactoid
this
charge.
cases
increasing
with
formation
Adsorption
approximately uranyl
was
reduction
montmorillonite of
with
relative
for
strength
adsorption
occurred
smectites adsorbing
although
selectivity
In
of
was
Ion
also
(JUS),
formation
on
When
and
and
adsorption
(15).
shown
the
phase
exchange
consistent are
ionic
on
decreased
consequent
CEC
There
high
sulphate
solution.
followed
and
depressed
explained
conditions,
been
principles,
undergoing
on
energies
phase.
has
exchange
the
described
specific
influence
adsorption
was
the
a
nature
kaolinites
greater
hydration
it
exchanger
been
in was
mass-action
ions
when
metal
exchange
adsorption.
adsorption
successfully
conditions.
show
ion
of
trace
mixture
the
virtually
coefficient
the
an
has
ideal
the
approximation
coefficient
significant by
poor
experimental
experimental minerals e.g.
a
different
selectivity
from of
it
of
several
be
non-ideal,
ideal that
selectivity
deviation
trivalent
is
data,
and
selected
stoichiometric
the
thermodynamic
an
factors
for to
were
of in
as
charge,
dissimilarity
equation of
unequal
(14)
found
produces
as
exchange
of
the
mass
of
to
the
illustrations
selectivity
metal
exchange
behaves
and
reactions
of
in
mineral
understanding
as
a
and
processes.
fraction the
the
section,
produced
described
according
influence
degree to
amount
cation
that
and
was
that,
montmorillonite an
0.01 than
Adsorbability
was
on
Cd
Pickering
but
on
exchange
particularly
often,
have
on
a
types
metals
(27)
pH r a n g e ion
formation
have
Sr
the
Co.
ligands
effect
the
loading
ligands
trace
Inskeep
which
there
Cd a n d
the
and
to
different
distibution of
ion.
different
Co
chloride
in
pH,
increased
that
hydroxy-Al
simple
distribution
levels
with
suggesting
solvated
due
to
or
concentrations
result
concentrations,
loading
coefficient
a
as
clay
Cd,
in a
montmorillonite
(14,24)
widely
from
CdCl^"",
Their
salt
low
salt
increasing
concentrations. very
type
free
of
with
increase as
Co o n
the
with
lower
the
with
on
adsorption
high was
possibly the
groups
investigated
to
of
interpreted
consistent
Cd
347
Minerals
adsorption
solutions
been
moderate
solutions
clay
work,
was
of
the been
hydroxyl
from
Adsorption
of
has
other
adsorbability
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5-6
structural
montmorillonite
(26) .
on Aluminosilicate
was
complex. with
pH u p
were
found
excess
respectively,
behaviour
controlling on
hydroxy
ions
complexation
of
process
species
with
the
of
The to to Mg
of
its
i l l i t e
was
apparently
particular is
to
greater
surface
controlled the
âmerican Chemical Society Library In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
by
ligands.
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348
GEOCHEMICAL PROCESSES AT MINERAL SURFACES
Montmorillonite, i n contrast, appeared to behave as an ion-exchanger with results being Interpreted i n terras of competition between a l l p o s i t i v e l y charged solution species for the adsorption s i t e s . The retention of Cu by allophane i s enhanced by phosphate regardless of the sequence of Cu and phosphate adsorption, although Cu has been found to have no e f f e c t on the simultaneous and subsequent adsorption of phosphate on surface bound Cu (32). ESR results suggest that the Cu binds to surface A10H groups of the allophane i r r e s p e c t i v e of the presence of phosphate and i t was proposed that the enhanced Cu retention was the result of the formation of a ternary complex by the binding of phosphate to the a x i a l position of the surface-bound Cu i o n . The formation of polymeric metal ions on mineral surfaces readily occurs i n nature and aluminosilicate clay minerals i n t h e i r natural state are often associated with surface coatings of iron and/or aluminium oxides. Mossbauer spectroscopy has been used extensively i n the i d e n t i f i c a t i o n and characterization of such iron oxide species In minerals (e.g. 33), but l i t t l e work has been carried out on the s i m i l a r aluminium oxide species. However, the production of hydroxy-aluminium i n t e r l a y e r s i n expanding layer minerals, possibly involving the Al^O^OH^ "*" ion, has received considerable attention (34). The polymeric cations p a r t i a l l y neutralize the charge of the aluminosilicate sheets, which, therefore, exhibit a reduced CEC, but at the same time the i n t e r l a y e r ions function as p i l l a r s which prevent the mineral from collapsing on heating. Thus structures resembling those of z e o l i t e s are formed and have attracted interest because of their molecular sieve and c a t a l y t i c properties. Hydroxy-magnesium interlayers also occur extensively i n p h y l l o s i l i c a t e s . Such interlayers can be prepared s y n t h e t i c a l l y (35,36) by t i t r a t i n g MgCl and NaOH into a suspension of a layer s i l i c a t e mineral, although the extent of i n t e r l a y e r formation Is strongly dependent on pH and the nature of the mineral (37). 7
Characterization of chemical forms of adsorbed metal ions Information on the nature of the chemical environment of trace metal ions adsorbed on clay minerals can be obtained by a number of spectroscopic methods, but the p r i n c i p a l applications have used either XPS or ESR spectroscopy, or one of i t s related techniques, such as ENDOR and ESEM spectroscopy. With XPS i t i s possible to obtain good a n a l y t i c a l information on the amount of metal adsorbed and, i n favourable cases, to i d e n t i f y the chemical form of that metal. Oxidation states are readily determined and I t can be shown, for example, that adsorption of Co(II) on manganese oxides results i n oxidation to Co(III) (38,39), whereas adsorption of Co(II) on z i r c o n i a and alumina leads to the formation of cobalt(II) hydroxide (40). With Y-type z e o l i t e s hexaaquacobalt(II) i s adsorbed as Co(II), and cobalt(III) hexaamraine i s adsorbed as Co(III). The XPS spectrum of Co(II) adsorbed on c h l o r i t e was consistent with the presence of the hexaaquacobalt(II) ion f o r pH 3-7 and indicated that no cobalt(II) hydroxide was present (41). With k a o l i n i t e and i l l i t e , Co i s adsorbed as Co(II) over the pH range 3-10 (39,42), i t being bound as the aqua Ion below pH 6 and as the hydroxide above pH 8. Measurements involving Pb have
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
16.
GOODMAN
Adsorption
shown
that
(43),
whereas
Results
adsorbed the
(44)
adsorbed
indicate
chroraium(III) structure state.
is
able
and As
those
an
differences Mg
compounds,
such
magnesium
Downloaded by COLUMBIA UNIV on October 6, 2014 | http://pubs.acs.org Publication Date: November 13, 1987 | doi: 10.1021/bk-1987-0323.ch016
be
has on
made
aqueous
their
natural
solution
their
methods
for
only
a
small
much
of
the
the
and
Auger
exchangeable
and
typical
in
short
equilibrium
supercages.
low
ionic
resembles
are
the
set
small of
ESR
a
ions
shown the
there
under from
Another
decrease
but
this
susceptibility
of
ions
of
other
case
is
of
that
line
broadening
i t
was
Y-zeolites
a
this of
of
to
between
has also
of
spectrum
ion.
By
ESR s p e c t r a
of
occurred
is
been
dipolar the
these
ions pairs
and,
from
Cu(II)
exchanged
and S o r i a
was
to a reduction
a
similar
of
Cu(II)
in
interpreted
in trigonal
temperatures by
(48) 100°C,
show no c h a n g e
The e f f e c t
Cu(II)
upon double
i n t e n s i t y minimum a t
at
indeed,
dependent
performing
Conesa
measurements
accompanied
and corresponded
to
are the last
an ESR spectrum
conditions.
i n intensity
slow
different
coupling
the presence
a n ESR s p e c t r a l
t h e same
ions
but
a
in
i n the
the Cu(II)
exhibit
dehydration,
susceptibility
found
ions
ESR parameters,
Dipolar
were
temperature
were
allows
with
parameters
lattice.
to produce
degrees
varies
Cu(II)
a 4.2 Â separation
produce
of
ions
the
magnitude
reveal
the zeolite
Na-Y
evacuation
The
the 1st d e r i v a t i v e
magnetic
arising
with
a t ambient
Cu(II)
leaves
exchanged
(47).
calculation
of
varying
that
paramagnetism
hydrated
distinctive
Cu/Ce
the a b i l i t y
of
Cu(II)
temperature.
environment
with
and
adsorption
zeolites
experiments
cavities
integrations Y-zeolite
with
to
though,
When
of
latter
a l l paramagnetic
chemical
cases,
investigated
literature. (46),
spectra
permits
the
of
other
of
These
oxygen-broadening
many
than
ESR s p e c t r a
parameters. i n
with
in
both
in addition
and a range
they
ions
Not
from
orientation
experiments
where
Cu(II)
the large
the
cages,
high
interaction
exists
obtained
c a n be
the Cu(II)
prolonged
at
i n
of
exhibit by
reduction of
which
use samples
In these
of
to
to the
the mineral,
dehydration
they
the
of
times
followed
identified
is
concerned
reports
that
metal
have
as
sensitively
ions
is
to
provided
more
trace
a question
on is
components.
work
of
measurements
techniques
information
concentrations
Rapid
where
into
ESR
study
investigated
paramagnetic
the nature
the
in
mineral
oxidation
considerable
to
always
surfaces
trace
hydration
and
as
4 and
ions.
reported
distinctive
of
there
with
supercages
the
Information
clay
of
published
exchanged
while
in a
the l a t t e r
because
is
environments
number
of
dehydration
being
phases.
on
the study
degree
have
the
whilst
ESR and r e l a t e d
solid
zeolites
been
sample
and c h e m i c a l
metal
With
in
ions
t h e same
reveal
of
in
there
state
although
transition
and
with
similar
However,
vacuum,
chemical
the
Cu(II),
pairs
the
below
photoelectron-
fluoride,
applications
conditions.
species
undergo
and
6.
Is
being
(39).
and that
pH v a l u e s
between m e t a l
states
former
surfaces.
high
and
adsorbed
migrate
above
Mg
electronic
general
of
under
have
ion at
Pb(II) 2
kaolinite
as C r ( I I I )
montmorillonite
magnesium
mineral
relationship
the
on c h l o r i t e ,
on the s u r f a c e the
the
as
under
probing
pH v a l u e s
distinguish
as
oxide.
XPS species
at
Mg
the
(45),
aqua
remains
on/3- and δ-Μη0
Cr remains
Cr(III)
of
in
skeletal
occurs
Cr(III)
the
example,
electron-spectra
of
adsorbed
349
montmorillonite
the to
Minerals
Pb(IV)
that
hydroxide
is
on
to
adsorption
species
XPS
Pb(II)
oxidation
from
i l l i t e
on Aluminosilicate
symmetry.
above
300°C,
decrease to
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
Cu(I).
in
350
GEOCHEMICAL PROCESSES AT MINERAL SURFACES Small
ESR
amounts
spectra
hexaaquacopper(II) oriented
with
the
mineral
the
amount
as
a
1
formation
of
copper
formation
of
this
unit
lower
lowering
IR
indicated
and
could
be
surface
where
at
A1-0H and A1(0H)
when
a
Cu(II)
layer
has
silicates from
axial and i s
spectra
in
from
films
of
terms
aligned
at
approximately
results
i t
is
not
relative
smectites,
where
water
molecules,
again
adopted
perpendicular With
In can
dipolar
Mn
ions
which
It
was
hexaaquaraanganese(II) than
are
found
approximately molecules air,
for 30%
(52).
thus
decreased
when
positions
in
crystalline
hectorite
(53). was
The
of
that
was
with
Cu(II)
i n t o Mg of
that
three
Cu once
principal
line
present
with
axis
amounts
widths
of
somewhat were
between
broader
consistent
significantly of
exchanged conditions
collisions
to
(52). effects
t h e Mg
hydrated
mobility
structure
of
preferred
Fe, dipolar
fully
ions
such
type
F e a n d Mn a n d b e t w e e n
anisotropic
limited
was being
(51).
structural
Mn
with
no
significant
between
the
i n the
Cu
this
is
its
o f Mn i n t o
is
in
result
However,
between Doping
i.e.
with
two w a t e r
and a spectrum
an
water
on d r y i n g
the i o n i s
t o move
lines
with
in
greatly
molecules.
into
hexagonal
typical
o f Mn i n
observed.
varying
quantities
i n hydrolysis product having
partially
and t h i s
amounts
the
water
there
to
layer
tetrahedral
orientation
under
the
of
the adsorbed
sheets
that,
adsorbed
charge,
demonstrated
and which
(50)
an i n t e r l a y e r
having
increased
that
caused
hydrolyzed
and
of
retain
time
interlayer
resulted as
in
widths
the s i l i c a t e
interpreted
aqueous
increase
the faces
perpendicular
of
with
structure.
alignment
were
that
space,
or
layers
the s i l i c a t e
solutions
shown
the layer
observed,
smectites,
ions
200°C
Exchange Mg
clay
small
the
hydroxide
by a range
the s i l i c a t e .
l i t t l e
Line
matrices
of
axis
samples
that
Because
on the (001)
axis
distinguish
i n large
fluid
the
at
were
result
demonstrating
Dehydration
two
contains
found
from
copper
between
copper
hectorite
interactions
be m i n i m i z e d by d o p i n g
form.
the
was p r o p o s e d
exhibited
ESR s p e c t r a of
on the gibbsite
the metal.
steps
changes
to
preferential
iron,
hectorite,
is in
to
the
produced
a
i t
and t h e s i t u a t i o n where to
promote
of
t h e symmetry
With
the a i r - d r i e d
on
precipitation
i t has been
the o r i g i n
45°
to the plane
neighbouring
of
polymers
phase
the interlayer
the p r i n c i p a l
Mn(II)-exchanged
structural
with
behaviour
possible
alignment
in
intensity
present.
the clays
of
of
interaction
crystal
appreciable
in
orientation
are
saponite. no
interpreted
preferential
of
substitutions
space,
no
microscopy,
occupies
independent
octahedral
interlayer
water Such
was
structures,
symmetry
layers.
substitutions
groups
of
plane
a n d no s e p a r a t e - p h a s e
the edges 2
of
surfaces
solubility
there
silicate
monolayer
silicate
apparent
that
by e l e c t r o n
occurs
With
the
the
t h e commencement
free Cu(II)
i n an increase
hydroxide
hydroxide
the g i b b s i t e
hydroxyls
detected
adsorption
than
that
of
monomeric
i n t h e ESR s i g n a l
the
and i n d i c a t e s
l o w pH g a v e
to the (001)
5 resulted
The
hydrolysis, copper
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but a decrease
at
presence
from
perpendicular
Cu adsorbed of
the
component
t h e pH a b o v e
of
results
axis
on g i b b s i t e
with
rigid-limit
its principal
pH
solution
adsorbed
consistent
and a
surface.
occurs
Cu(II)
were
(49)« Raising
result
mineral
of
that
a
that
the oxovanadium(IV)
V at
low l e v e l s
was a d s o r b e d
ligand
hydroxide
of
of
environment
i n
nature.
of
on the c l a y that With
i o n on
adsorption
was
surface
partially
increasing
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
V
GOODMAN
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16.
Adsorption
on Aluminosilicate
Minerals
351
adsorption on w e t t e d h e c t o r i t e the p a r t i a l l y h y d r o l y z e d p r o d u c t was obscured by a spectrum from the s o l v a t e d oxovanadium(IV) i o n which had a linewidth greater than i n aqueous s o l u t i o n as a r e s u l t o f restricted m o b i l i t y . Under strongly dehydrating conditions the adsorbed V was observed to align with the principal V=0 a x i s p e r p e n d i c u l a r to the plane of the c l a y p l a t e l e t s . ESR has a l s o been used i n the c h a r a c t e r i z a t i o n o f s p e c i e s adsorbed on pillared clays, i . e . smectites with hydroxy-aluminium interlayers. Adsorption of Cu(II) on hydroxy-aluminium h e c t o r i t e produced mobile hexaaquacopper(II) and Cu(II) cheraisorbed to discrete s i t e s of the 0H-A1 interlayerÇ54)· The r a t i o o f c h e m i s o r b e d to m o b i l e Cu i n c r e a s e d w i t h i n c r e a s i n g pH, but even a t p H > 7 , when the solubility product of copper(II) hydroxide was exceeded, cheraisorbed Cu(II) remained the dominant species. This is in complete contrast to the results with g i b b s i t e (49), where precipitation of copper hydroxide was observed a t p H > 5 . S p e c t r a from air-dried f i l m s showed t h a t the C u ( I I ) had a x i a l symmetry w i t h principal axis perpendicular to the O H - A l - h e c t o r i t e ab p l a n e . At higher pH, a spectrum similar t o t h a t o f Cu(OH)^~ on a l u m i n a was observed, suggesting a l i g a n d exchange mechanism for Cu(II) adsorption on the complex. W i t h h y d r o x y - a l u m i n i u m m o n t m o r i l l o n i t e there was an i n c r e a s i n g c a p a c i t y f o r Na a d s o r p t i o n w i t h i n c r e a s i n g pH (55) and Na was not d i s p l a c e d by a d s o r p t i o n o f low l e v e l s o f Cu, indicating the existence of C u - s p e c i f i c s i t e s . I n c o n t r a s t t o the hectorite system, there was evidence of a hydroxy or hydroxy carbonate precipitate analogous to the situation with g i b b s i t e , although there was no g i b b s i t e d e t e c t e d i n t h i s system. ESR s p e c t r a showed the existence of a cheraisorbed species as well as electrostatically bound h e x a a q u a c o p p e r ( I I ) , but r a t h e r u n e x p e c t e d l y the Cu c o u l d be s o l u b i l i z e d w i t h ammonia o n l y a f t e r e x t r a c t i o n w i t h barium c h l o r i d e . The specific a d s o r p t i o n o f C u ( I I ) and C o ( I I ) by i m o g o l i t e , an a l u m i n o s i l i c a t e m i n e r a l w i t h t u b u l a r morphology o f c o m p o s i t i o n Al Si0 (OH) , was found t o be lower than f o r a l l o p h a n e s , which a r e related amorphous a l u m i n o s i l i c a t e m a t e r i a l s covering a range o f Al:Si ratios. Cu a d s o r p t i o n on s y n t h e t i c a l l o p h a n e s was dependent on the Si:Al ratio (increasing with i n c r e a s i n g A l ) (56) but no consistent effect was found with n a t u r a l a l l o p h a n i c c l a y s or f o r Co(II) adsorption. ESR s p e c t r a were i n t e r p r e t e d as i n d i c a t i n g t h a t adsorption of monomeric C u ( I I ) o c c u r r e d on an a l u m i n a - l i k e s u r f a c e , where OH was c o o r d i n a t e d to a s i n g l e A l i o n and a t a second type of site, which was thought t o be a s i n g l e SIOH o r A10H group, w i t h the distribuion o f C u ( I I ) between the s i t e s b e i n g dependent on the S i : A l ratio, pH and a d s o r b a t e c o n c e n t r a t i o n s , e x p o s u r e o f the a d s o r b e d Cu to ammonia resulted in l i g a n d exchange and the formation of Cu(II)-NH -surface complexes. W i t h imogolite some C u ( I I ) was desorbed from the surfaces as tetraamminecopper(II) ions and desorption of both Cu(II) and C o ( I I ) i o n s was r e a d i l y e f f e c t e d by c o m p l e x a t i o n w i t h EDTA o r by c o m p e t i t i o n w i t h P b ( I I ) o r p r o t o n s . 2
3
4
3
In the ESR spectra of adsorbed oxovanadium(IV) i o n s on minerals, information on the nature of the a d s o r b e d s p e c i e s Is obtained from the g - v a l u e s and V h y p e r f i n e c o u p l i n g c o n s t a n t s , but ligand hyperfine s t r u c t u r e i s seldom, i f e v e r , o b s e r v e d . W i t h ENDOR much s m a l l e r h y p e r f i n e s p l i t t i n g s can be observed than w i t h ESR and it i s p o s s i b l e t o measure h y p e r f i n e c o u p l i n g from n u c l e a r s p i n s i n
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
GEOCHEMICAL PROCESSES AT MINERAL SURFACES
352
the
neighbourhood
splittings
for
oxovanadium(IV) those
from
matrix
ion
ENDOR
and
on
in
peak,
with
paramagnetic Y-zeolite
solution,
indicating
protons
outside
was
no
close
not
be
i n the centre
one
more
significant
lost
its
spectrum axial
(57)·
water
structure, occur
change
proton
sample.
This
and
and
there
although
showed binds
species
spectra
bulk
exhibited
illustrating
adsorbed
structure
result
molecule
ENDOR
and
are is
the more
great
(58),
a
did not
in
by
cause
spectrum N a ENDOR
V loses
of
chemical result
the
surrounded
complex
oxygens
sensitive value
molecules,
on dehydration of
as
from
sphere(57),
t h e ENDOR
more
four
type
simply
water
to
was no
shielded
evacuation a
that
to
was
there
the supercage
the ESR spectrum
signal,
thus
in
in
of
of
with
t o be s i m i l a r
1st coordination
approach Also,
V
proton
associated
found
the
its
there
layers.
were
that of
could
solvent
F o r example,
water
but i n the z e o l i t e
Because or
cation.
equatorial
complex a
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the axial
adsorbed
the
interaction
of
both
the
change
its
zeolite that
can
of dehydrating
the
than ESR t o changes performing
both
in
types
of
measurement. The small
ESEM t e c h n i q u e
hyperfine
information
on
interaction
in
provides
interactions the
number
addition
an a l t e r n a t i v e
and of
to
has
spins
distinguishing
to the hyperfine
coupling
of
domain
can
the
time papers
adsorption shown
of
that
with
have
results been
cations
Cu(II)
ammonia
or
water,
coordination
spheres.
into
is
silica
gel,
where ESR
of
and
mixed
The
triaqua
or
present
with
influence Cu(II)
the
the
interaction migrations ESR
of
have
same
as bulk
because
from
is
is
(61).
freezable
unfreezable, of
the surface
silica
of
alkali
metal
the
in
Influence
Cu(II)
(60).
t o form
the formation
that
a of
both
species
are
both
cations
can
geometry
of
C u ( I I ) . The
Tl-rich
NaTl-X and
ethanol
a n d DMSO
adsorbates
with
was
CsTl-X
interpreted
his with
with
with
of
observing
Measurements shown but at
that
zeolites. in
This
terms
of
paramagnetic
surfaces.
of
a resonance Cu(II)
temperatures
two t y p e s
of
from
Mn(II) at
behaves i t
room
i n the
experiences
water
are
found;
c r y s t a l l i z a t i o n and the
the ice structure
and
although
on s i l i c a
water
ions
Cu(II)
investigation,
adsorbed
lower
On f r e e z i n g which
adsorbed
mineral
type
and undergoes in
onto
of
observed
be used
i n
water,
their
the/S-cages.
can
have
in
exchanged
the«-cage
zeolite,
dehydration
associated
above
mobility
which
was
encountered
manner which
adsorbed
result
with
have
present.]
indicating
adsorbates
used
decreased
one
that
into
NaTl-X
(59)
molecules
the Cu(II)
coordination
after
environments. and
Κ
to interact
polar
liquid
are
distorted
temperature a
was a b l e
been
and In
and
the copper
the
et a l
to demonstrate
Cu(II)
intensity,
interaction
difficulties in
Na
of
species.
same
spectroscopy
study
Mn(II)
whereas
observed
with
difficulties,
g e l and i n t e r a c t i n g
i n a series
able
dipolar analysis
o f ESEM t o t h e
that
is
Cu(II)
were
forces
location
such
of
Ichikawa ligand
to
species
and
on the c o o r d i n a t i o n and l o c a t i o n o f
Tl(l)
raonoaqua
zeolites no
to
zeolites
species
KT1-X but
studies
Tl-X
species,
two
providing particular
Although
present
silica
be noted
different
ESEM
of
into
only
should
completely
co-cations
presence
hexaaqua
have
[It
the hexaaquacopper(II)
ion-exchanged
solids.
exchanged
measuring
of
for a
on the a p p l i c a t i o n
on i n o r g a n i c
ions
for
isotropic
constants.
sometimes
published
method
advantage
responsible
contributions several
the
cannot
be
i n t e r a c t i o n . NMR, I R a n d d i f f e r e n t i a l
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
other formed
thermal
16.
GOODMAN
Adsorption
analysis
(DTA)
strucure
of
mineral field
also
adsorbed
propertes, gradient
influenced
by
Adsorption
and
The
have
on Aluminosilicate
by
around
the
Al,
degree
of
of
Downloaded by COLUMBIA UNIV on October 6, 2014 | http://pubs.acs.org Publication Date: November 13, 1987 | doi: 10.1021/bk-1987-0323.ch016
i l l i t e
and
occurred,
leading
similar
manner,
and hence
in
ZSM-5
of
complex
metal Thus
the
XPS
showed
formation
dehydration
of
of
conveniently
followed
Demetallation
of
and
(69)·
luminescence
Sn(IV) after
cation
destruction
possibility
as
well
of
as
pH
mono-
or
as
4-9.
a
kaolinite
and
polymeric
hydroxy
In
contrast,
an
ion
competing of 6
for
showed
resembling two
the on
association
of
imogolite ESR
adsorbing
the
ESEM a
range
were
able
for in
N-
and
number.
all
the
of
the
in
the
on
that
one
the
two
metal
to
Na the
another
ion
to
and
have
shown
surface
the
O-coordinated
a
gives photon
investigate that
complexes
the
in
determine
copper
involve on
the
whether
the
from
to
ESR
being
proceed
measurements
different
involve
the
organic
to
that
matter
for
a to
was
pH one the
complex, physical
surface,
which
at
species,
Cu humate
mineral
via
species
imogolite
adsorbed
of
(30,31).
solution
(32).
on
formation
clays
appeared
to
the
complexes
the
charged
large
appeared
whereas
produce
an
obtained
by
(71).
to size and
ligands
of
that the
or
two
a
form
these
seem
difference
Cu(II)
adsorbate
depending
Differences
but
not
silica-exchanged
one
Cu
(72).
ligands,
symmetry
other
with
Interaction
and
to
novel
the
IETS
mineral
with
showed
coordinate
in
a and
IR-allowed
used
sites
different
identical
the
is
spectra
Raman- and/or
however,
positively
on
the
N-coordinated
the the
UV-visible
indicating to
a
and to
as
using
on m o n t m o r i l l o n i t e and
humate
polarity
coordination
in
particular
Cu was
on
In
(68),
occur,
close
different
complex,
adsorbates to
interaction,
at
of
uncomplexed
results of
led
absorbance
forbidden
have
shown
montmorillonite
that
(67).
porphyrin adsorbed
on a l u m i n a
Furthermore,
the
IR
observed
are
are
of
sites
solution
extracted
spectrum
that (70)
been
adsorbed
(71).
adsorption
the
by
reactions
ions
vibrational
possible,
with
presence
minerals
complexes
montmorillonite adsorption
availabile
the
of
formed.
has
process
bisglyclneCu(II)
adsorption
aqua
reversible
ligand
number
species
with
exchange
Mazor
not
a
i l l i t e
often
chromium(III)
spectroscopy(IETS)
bands
adsorbed
were
of
is
environment
hydrolysis
remained
that
and
was
diglycinates
Adsorption
minerals
can a l s o
was
produces
bidentate
It
was
tunneling that
observing
Hipps
be
complex.
glycinates
acts
range
the
by
that
by
which anion
transitions
spectroscopies. Co
of
technique
the
and
porphyrin
to
minerals
the
tetra(4-pyridyl)
reaction,
electron
spectroscopic
glycine
tin
on
ammonium
complexes
spectroscopy,
and
Inelastic
Ni
of
The
on
electric
shown
on m o n t m o r i l l o n i t e and
being
dehydration
the
hexaamminecobalt(III)
adsorbed
hydroxide
ions.
of
been
of
effect
the
coordination
in
reaction case
species
the
ammonium hectorite
has
complexes
change
kaolinite,
cobalt(II)
zeolites
an
(66)·
tris(ethylenediamine)
chloropentaaraminecobalt(III) formation
width,
ion.
to
Investigation
NMR l i n e
hydration
and
the
can have
which
metal
in
which
transition
reactions
hexaamminechroraium(III) chlorite,
the
employed
(62-65),
c h a r a c t e r i z a t i o n of
adsorption
followed
e.g.
around
the
been
water
353
Minerals
on
the
chemical
in
A^were
to
reflect
in
adsorbate
approximately
with
molecules
square
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
observed a
change ligand planar
GEOCHEMICAL PROCESSES AT MINERAL SURFACES
354 complexes
with
two
O-coordinated octahedral four
oxygens,
coordinated
Complexes affinity stability
Cu(II) for
indicated
of
Downloaded by COLUMBIA UNIV on October 6, 2014 | http://pubs.acs.org Publication Date: November 13, 1987 | doi: 10.1021/bk-1987-0323.ch016
smectite
large
clay fit
a
of
amounts
bis
complex
pH
these
the
on
spectroscopies
is
hectorite
interlamellar indicating
using
shown lost
the
surface
field
be
of with
explained
towards ions
the
are too
50% h u m i d i t y , a n d ,
the c l a y ,
the
square
d i e t h y l e n e t r i a m i n e and i s more
complicated,
i n s o l u t i o n as a and N i ( I I )
hectorite
function
complexes
surface
complexes
prefers water
a r e formed
Ni(II)
complexes
are
functions
as only
a very
of
absorption
Axially-coordinated
and planar
The planar
the c l a y
With
orbitals
increasing
E S R , IR a n d U V - v i s i b l e
that
on d - d
number
solvent Cu(II)
at
to
a
with
could
anionic
Cu(II)
complexes.
surface.
that
of
aqueous
and to decrease
results
the s i t u a t i o n
studies
in
based
stabilization
on
linearly
existing
high
crystal
field
adsorbed
(76).
complexes
readily
The
crystal
a r e added
a
overall
bis(ethylenediamine)
(74).
These
adsorbed complexes
have
are
for
the minerals
the complex
tetragonally-distorted molecules
the complexes
tris(ethylenediamine)
Adsorption
ligands
of
(75).
have
with
calculations
montmorillonite sheets
of
different
(77).
with
t h e G a n d i n - p l a n e IT
heterogeneous
that
between
large
several
involving
formed
minerals
to increase
density
as
shows
with
for
for
and
the c l a y
tetraethylenepentamine with
than
complexes
lODq,
of
acts
XRD
planar
ammines
orbital
values
adsorbed
charge
loading
to
when
ions clay
parameters
was o b s e r v e d
negative
the
distorted
complexes, were
bis(ethylenediamine)Cu(II)
increased complex.
ESR
similar and
minerals
average
higher molecular
and
parameter,
energy
if
much
energies
splitting
whereas
in
molecule,
3d t r a n s i t i o n m e t a l
although
solution
oxygens
oxygens
5-coordinated
montraorillonite-type
(73),
transition
Distorted
lattice
lattice
and one a d s o r b a t e
constants
solution
two
four
ligands.
of
for
and
involve
complexes.
lattice
TT-bond
adsorbates
ligands
on the
diamagnetic, weak
axial
ligand. Cu(II) show
and
a high
the
case
with
complex. the
that
Fe(phen) as
3
2
twice the
of
a
(80). the
7VM(phen)
3
whereas
as F e ( p h e n )
2 +
,
to
a
to
resolve
having
3
+
of
in
(79;. This
property
of
3
2 +
of
exploited
a labile
metal
with A-Ru(phen)
3
2
"**
but not
t h e Co o r F e
presence
achiral
complexes
of A.-Ru(phen)
molecule,
spectrum of
- m o n t m o r i l l o n i t e complex enantiomers
3
2 +
*
such as the
* -montmorillonite resulted
i n the e l e c t r o n i c
o r one a r o m a t i c
2 +
in
(M=Ru,Fe,Ni),
2 +
either
the
an
3
3
adsorbed
2
mixture
chromatographically
two a r o m a t i c
Fe(phen)
is
3
+
were
enantiomeric
to produce
Fe(phen)
in
couple,
complexes of
racemic
of
2
the
as a b i s 3 +
3
the CEC has been
introduced
The ^ - N i ( p h e n )
Fe(phen)
when
A s was
an increase
to twice
mixtures
Adsorption
been
-
montmorillonite
antiraceraize
being
*
shown
racemic
c a t i o n by A ~ N i ( p h e n )
orange
2
Adsorption
A-M(phen)
of
adsorbate. molecules
seen
3
(phen)
(78).
exists
complex,
X"" i o n p a i r s
2 +
of
and racemic
activity
used
3
of
adduct
adsorption
-montmorillonite. acridine
was
surface.
racemic mixture An
observed
optical
solvent,
surface
Cu(II)
in a tris
the F e ( p h e n )
mineral
species,
1,10-phenanthrollne
(hectorite)
adsorbed
bound
of
antiracemization
accepted
with
on m o n t m o r i l l o n i t e has been
t h e amount
complex
were
the
the adsorbed
adsorption in
pure
with
"*"
Fe remains
potential
in
associated
complexes
for a smectite
ethylenediamine,
Although
oxidation
above
Fe(II)
affinity
has of
recently organic
and one a l i p h a t i c
(81).
In Geochemical Processes at Mineral Surfaces; Davis, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
in the
ring
16.
GOODMAN
Reactions The
Adsorption
involving
the
chemical
quality.
of
as
natural of
papers
molecules
have
with
condensation
of
warming
wetting
drying, observed
Levi
and
(82)
the was
incorporated
into
detected.
Less
dimer
greater
2
and
adsorption
over Two
the types
a
the
environmental
presented
in
the
2 of
(85,86).
ESR s p e c t r a
to
the
terms
of
electron
observed
(87),
anisole
of
the
Type
g-value from
Cu(I)
occur
and
with
and
although arene some
Na
monomer largest and
found
ATP
yields
of
in
the
peptide.
Mg-montraorillonite although was
the
not
divalent than
adsorbed
(84).
2'-,
for
the
peptide
metal
by
ions
Also
pyrimidine
between
be
decomposed
accelerated
small
only to
montmorillonite
Pure
was
or
alanine
ADP was
for
preference
related
reaction
be
is
an
2 complex
the
purine
nucleotides
3'-
and
5*-AMP
adsorption
this
the
organic
an
of
the
to
aromatic
to
the
aromaticity
of
can
radical
a
be
Type
complex
narrow
to
in
Cu(II),
cation.
Similar
However
with
1 complexes
were
were
to
peak
the
seen
montmorillonites on
Cu(II),
explained
molecules.
ethers
Cu its
of
only of
with
retains
bonded
molecule
organic
Cu(II)
benzene
absence
result
aromatic
types
of
benzene
consist
and
benzenes on
the
edge
there
other
both
molecules
on
species to
complex
donation of
1
alkyl-substituted
adsorption
the
Mg