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Freezing potentials in wet clays. II. Specific systems
Cold Regions Science and Technology, 3 (1980) 169--175 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
FREEZING POTENTIALS IN WET CLAYS.
II.
169
SPECIFIC SYSTEMS
S. Ramachandra Rao Department of Physics, University of Regina, Regina, Canada $4S 0A2 Thos. O'D. Hanley, S.J. Campion College, University of Regina, Regina, Canada $4S 0A2
dissolved electrolytes, and ionic compoABSTRACT
sition of clay minerals present in natural
With several variables controlled, elec-
soil systems we must obtain data with homo-
trical potentials were studied during the
ionic clays and investigate the effect of
freezing of a sludge of Regina clay, which
different variables on pure clays or natural
consists mainly of bentonite with some
clays thoroughly washed with distilled water.
illite and quartz.
The present
An initial potential V.
paper describes the results
of 28.5 mV at 20°C wa~ observed in natural
obtained with a natural clay (Regina clay)
Regina clay.
during studies of (i) the effect of soil pH,
Vi was slightly greater when
the clay was homoionic, containing K+, Ca++,
(2) the effect of ionic content,
or Fe+++ ions. Changes of Vi with pH con-
effect of water content, ~(4) the effect of
firmed that V. was electrokinetic in nature.
aging, and (5) moisture migration during
Freezing potentials were slightly higher in
freezing.
(3) the
the homoionic soils than in untreated soil, but were not significantly affected by mois-
EXPERIMENTAL DETAILS
ture content within the range tested. Aging The cell used for these experiments h a s
of the sludge had a pronounced effect on
been described in Part I of this paper.
the freezing potential, especially for the Regina clay, described in Part I, was
homoionic samples.
The amount of moisture washed several times with doubly distilled
migration toward the freezing front depended water.
A slurry containing about i00 g of
on the ionic content, being greater for K + clay and 800 ml of water was thoroughly
and Fe+++; an explanation for this effect stirred and allowed to settle, and the
is offered. discussed.
Plans for future study are supernatant water was decanted out.
The
washing procedure was repeated eight times after which the rate of settling of the INTRODUCTION clay was found to be extremely slow, which In part I of the present paper the sig-
was an indication that the dissolved elec-
nificance of the freezing potential and its
trolytes were all removed by the wash water.
possible importance in wet soil systems has
The slurry was centrifuged, the supernatant
It was pointed out that in
water was decanted out and tested to ensure
been described.
order to understand
the effect of a number
of physico-chemical variables such as pH,
that it was free of electrolytes
(test for
chloride ions with AgNO3) , and the clay was
170
dried at room temperature.
A known weight
of dry clay was mixed with amount of water
the required
to obtain a sample
desired moisture
of the
above w a s mixed with
solution
desired metal
ions
stirred
for one hour.
natant
liquid was decanted
was washed with double until
the washings
The residual temperature reached
sludge until
record
procedure
the v a r i a t i o n
tial as a function the cold plate In order moisture
the clay was as usual.
Since
to poten-
saw blade portion
cycles
the cell
the m o i s t u r e
In order of electrical measurements
a hackA
again to
suspended
in soil a set of
steel,
vertically
causes
for the than for
in Part I.
in place
for the changes
with
of the
to investigate
possible
in p o t e n t i a l
served on p r o g r e s s i v e l y
cooling
ob-
the clay
sludge.
RESULTS
with a both of in the clay
potentials
electrode
stainless
found w i t h an
in conjunction
steel electrode
base are recorded
slurry
in Table
(at pH 7.10)
on the cold plate Fig.
i.
experiments
as the clay
water
is shown
obtained
and frozen in
of potentials alone
in Fig.
(in place 2.
with the freezing
on Regina
different
electrolytes
Table
The values
2.
The var-
is shown graphically
in d i s t i l l e d
Results
i.
was cooled
Similar v a r i a t i o n
of clay slurry)
with the
and with the cell
iation of these potentials
measured
the significance
in conjunction
strip of stainless
which were
then dried
was made using a standard
electrode
in when
were such
was conducted
water alone
in order
Ag-AgCI
content.
potentials
sludge,
longer
described
experiment
Electrical
at equal dis-
bottle,
to understand
described
conditions
drop to occur,
Another
frozen,
cylinder.
in an oven at 120°C and w e i g h e d
narrow
The
of each of the slices was w e i g h e d
determine
electrode
were followed
a longer time was required
distilled
of
the frozen portion.
weighing
in
and the
from each other using
in a stoppered
Ag-AgCl
I.
to one m o r e freezing
p a r t of w h i c h was
to slice
the changes
the Ag-AgCI
paragraph
the experiments
the clay to freeze
out of the p l a s t i c
(i cm)
between
the experimental
potential
of
in Part
the m i g r a t i o n
It was cut into three slices tances
and 8.62.
room,
from the cold plate
was pressed
7.10,
measured
the cell was cooled on the cold plate.
bottom plate of the cell was detached. wet clay mass,
successively
and
followed
six freeze-thaw
subjected
steel base of
the steel plate
that the cell was open to the air of the
At the end of 15 minutes
was removed
the preceding
content
has been described
after
and between
by weighing.
of electrical
to follow
and the stainless
and the two steel electrodes
ions.
of the temperature
upon subjecting
thaw cycles,
water
and
the Ag-AgCI
the cell,
the potentials
Poten-
electrode
between
In the next experiment,
was dried at room
the moisture
the Ag-AgCI
when the pH was 6.12,
out and the clay
free of C1
50% as d e t e r m i n e d
The general
the steel base of the cell.
the cell base were
thor-
the cell d e
electrode
The super-
distilled
were
as
of the
The slurry was
oughly
as container
this steel plate,
250 ml of a
of the chloride
ion.
in Part I, at equal distances
tials between specific
(K+ ' Ca ++ , or Fe +++ ) 40 g of clay w a s h e d
1 molar
using
scribed above
content.
To get clay sludge with
described
slurry,
clay treated with are surm~axized shown
in
in the table are
171
mean values from three runs.
The results
with greater water content
(50% solid).
show significant effects when the clay is
The values
treated with the chosen ions.
mean values of 3 or 4 runs.
A few experiments with a concentrated
results
were conducted
clay sludge containing
75% solid and 25% water.
content,
results are compared with those obtained
////s
o
/// I
•
\
t'
I
I
r,.E .,.
values are in moisture
the drop in potential upon
/ / •
'S''~ 0
These
show that while the initial
electrical potential lowered with decrease
In Table 3 the
•
shown in Table 3 are
""'-
4
~
8
I
~rz
-I0
-20
°i
t6 TIME
I
20 mln
I 24
E
.J p..-40
eo :
~\
--I00
Fig. 1. Potential differences between pairs of electrodes in a slurry of Regina clay. Dashed line, Ag-AgCl electrode vs base of the cell;-.-, Ag-AgCl electrode vs stainless steel plate; solid line, stainless steel plate vs base of the cell. The cell was placed on the cold plate at time t = 0, and f r e e z i n g b e g a n after approximately i0 min.
!
/
/
/ -60
/ --TQ
P'~.
/ I I I
°
-SG
Fig. 2. Potential differences between pairs of electrodes in distilled water. Dashed line, Ag-AgCI electrode vs base of the cell; --.-, Ag-AgCl electrode vs stainless steel plate; solid line, stainless steel plate vs base of the cell. The cell was placed on the cold plate at time t = 0, and freezing began after approximately i0 min.
172
TABLE Potential differences between the c l a y s l u d g e . Temperature Electrode
standard Ag-AgCI electrode and stainless steel electrodes 20°C. P o t e n t i a l s are s h o w n in m i l l i v o l t s .
combination
Ag-AgCI
vs u p p e r
Ag-AgCI
vs base of cell
Upper steel plate b a s e of c e l l
1
pH
pH 6.12
steel plate
+
7.10
in
pH 8.62
4
- 43
- 108
- 33
- 39
-
62
+ 37
-
-
46
vs
TABLE F r e e z i n g p o t e n t i a l s o b t a i n e d w i t h R e g i n a clay, 50%. P o t e n t i a l s in m i l l i v o l t s . Untreated Initial V 28.6
4
2
both
natural +
and homoionic. +
Moisture
content
+++
++
H 28.1
K 38.9
Ca 34.1
Fe 36.2
30.2
34.8
43.2
35.7
40.8
19.8
24.0
28.0
20.3
26.8
10.4
10.8
15.2
15.4
14.0
1
Maximum
V
Minimum
V
V
max . mln
- V max
mln
TABLE E f f e c t of m o i s t u r e o n the f r e e z i n g m e a n v a l u e s of 3 or 4 runs.
potentials
Natural 50% w a t e r content V.
3
of R e g i n a
Potentials
clay.
Clay
clay 25% w a t e r content
(in m i l l i v o l t s )
are
treated with K+ ions
50% water content
25% w a t e r content
28.6
20.0
38.9
25.8
30.2
24.4
43.2
28.3
19.8
13.2
28.0
13.1
10.4
11.2
15.2
15.2
1
V V
max . mln
V
-V max
. mln
TABLE F r e e z i n g p o t e n t i a l s in f r e s h a n d a g e d l e a s t four e x p e r i m e n t s .
sludges
Potentials V. l Clay
treatment
Untreated + K ++ Ca +++ Fe
Fresh
Fresh
clay.
Values
are averages
for a t
in m i l l i v o l t s V
-- Aged
4
of R e g i n a
V
max Aged
Fresh
V
min Aged
max
Fresh
- V
mln Aged
28.6
7.4
30.2
8.6
19.8
0.4
i0.4
8.2
38.9
i0.4
43.2
16.0
28.0
-i0.4
15.2
26.4
34.1
7.4
35.7
10.4
20.3
2.4
15.4
8.0
36.2
26.6
40.8
72.2
26.8
37.8
14.0
34.4
173
freezing
is not significantly
by the moisture
V, the electrode potential
affected
content of the sample.
A set of experiments
was conducted with
in the clay slurry
amounts to -0.265 V.
Similarly
Regina clay treated as before and allowed
electrode potential
to stand as a sludge for 3-4 weeks.
cell amounts
was considered
adequate
This
for obtaining
a
of the stainless
steel plate suspended
to -0.261 V.
When the stain-
less steel plate is positive
and the cell
sludge which is close to the wet soil in
base is negative,
the field.
between the two would be -0.265
The results
which also includes
are given in Table 4,
values
for sludge
which is -4 mY.
the potential
was noted experimentally.
comparison.
observed
The results
of moisture migration
studies
in Table 5.
as follows.
From the weight loss observed
on drying,
These are obtained
the weight of water per gram of
dry clay was calculated
in each of the slices.
Since the original water content freezing)
was known
(before
( ig water per ig dry
clay in most cases),
the amount of water
which migrated during
potentials
of
in clay slurries have a
negative sign. Further evidence
for the electrokinetic
nature of the potentials the variation with pH.
is obtained from
of each of the potentials
As seen from Table 1 each of the
electrode potentials
becomes
less negative
as the pH is lowered.
the freezing process
was determined.
- (-0.261)V,
It is thus
that the electrical
both electrodes
difference
This is the value which
which had not been aged for the purpose of
are recorded
the
of the base of the
The data presented
in Fig.
1 show that
on cooling from 20°C to 0°C the cell base becomes more negative until the freezing
DISCUSSION
stage.
As discussed zero potential systems appears electrical interface.
The sharp drop in potential
in Part I, the initial non-
observed with all clay mineral to originate
between the upper stainless
the base of the cell, a drop which corres-
from the
double layer at the clay-water From the data given in Table 1
ponds to the onset of freezing, result of
(i) the potential
it is found that with the Ag-AgCI electrode
plate becoming more negative
negative
and the stainless
potential
positive
the resultant
-43 mV.
Taking the standard electrode
potential
steel plate
cell potential
of the Ag-AgCI electrode,
difference
steel plate and
is
and
(ii) the
of the cell base becoming markedly
further observed
-0.2224
of the upper
less negative or more positive.
tinues,
is the net
It is
that as the cooling con-
the potential
of the cell base
TABLE 5 Moisture migration
observed
Ionic content of the clay Untreated K ++ Ca+++ Fe
in Regina clay treated with different Freezin 9 potential Vmax - Vm l.n (mY) 8.2 26.4 8.0 34.4
ions.
Weight of water per unit weight of dry clay Top slice Middle slice Bottom slice (frozen) 0.96 0.91 0.95 0.79
0.98 0.95 0.98 0.72
1.05 1.14 1.06 1.44
174
steadily becomes more positive the upper electrode The experiments
the slow variations
Fig.
of
atively greater positive follow the following
ites consist of layers of complex alumin-
an explanation
in potential
cooling.
for
with
It is observed
osilicates.
2 that with distilled water only the
swelling.
of the cell base becomes
more positive with the development
electrode
The potential
remains almost constant.
leads to the conclusion in potential
the water molecules
When the wet clay is frozen,
steadily
interlaminar frozen zone.
water migrates
the
toward the
As it migrates
with it the ions present
This
Montmorillon-
between the layers and cause
of the
of the upper
course.
When these layers come in
contact with water, penetrate
ice front.
This may
becomes more negative.
from
potential
charge.
performed with distilled
water alone may provide
progressive
and that
it carries
in it.
This effect is more marked with clay
that the variations
observed on progressively
sludges aged for 3 to 4 weeks
(Table 4).
During the aging of clays in water,
poly-
cooling the clay sludge are the result of
silicic acids are formed which could
the effect of temperature
affect
the migration
quently
the freezing potential. It was + +++ ions and Fe ions en-
kinetic potential
on the electro-
at the clay-water
inter-
face.
of ions and conse-
found that while K
It is interesting
to consider why there
is a non-zero potential
for both the upper
hance the freezing potential with aged ++ sludges, Ca ions do not show appreciable
steel plate and the cell base when distilled
change,
water is used.
sludge they too raise the freezing potential
An electrochemical
potential
is to be expected between the Ag-AgCl electrode and the steel.
There appears
to be a small electrochemical at room temperature electrodes, different
between
alloys.
forming calcium polysilicates
potential
the two steel
The nearly
This could be due to the combination of ++ ions with polysilicic acid species
Ca
also
which may be made of slightly
crease of this potential
although with freshly prepared
the p o t a s s i ~
linear in-
as a function of
which are
only very sparingly soluble (Velde, 1977). + K ions raise the freezing potential because
precipitated
silicate out.
species are not
In the case of Fe +++,
freezing point agrees with the temperature
since these are tripositively charged, +++ only a fraction of the Fe ions are
dependence
lost by combination
time while
the base was cooling to the
of an electrochemical
potential
The results
for small changes in temperature. The results recorded
moisture
in Table 2 show
that H + ions have no significant on the freezing potential.
with polysilicic
from the determination
content upon freezing
show that water migrates
effect
There is, how-
regions of clay. the observations
toward the frozen
This is in accord with of Korkina
(1965), who
has attributed moisture migration
value of freezing potential
voltages
to
of
(Table 5)
ever, a marked effect in the presence of + ++ +++ K , Ca , and Fe Ions. Since a large corresponds
acid.
originating according
to the
in the solutions
the frozen region becoming more positive,
the ground;
the presence of these ions in the clay
produce
causes the frozen soil to acquire rel-
the near layer to the freezing
in
to her, the voltages
a movement of the moisture
from
front,
175
thereby creating in the adjacent layer a
some stage studies of freezing potentials
scarcity of moisture which is replenished
in the field be undertaken as well.
by a flow of moisture from the lower layers under the effect of the moisture gradient. Similar observations have been recorded by Hoekstra and Chamberlain (1966), and Penner
(1964), Hoekstra
(1971).
investigators
of the
referred to above.
toward the frozen regions
is related to the freezing potential which is recorded by the sharp drop in voltage when freezing sets in. At the present stage of the project it is difficult to know just what direction of effort will be most useful.
As a rea-
sonable next step we are presently
studying
the migration of ions during freezing, and freezing potentials silica and clays.
the
and of the National
Research Council of Canada. REFERENCES
The
present work further indicates that moisture migration
The authors gratefully acknowledge
support of the National Science Foundation (Grant No. DPP76-80072),
The results thus far obtained are consistent with the observations
ACKNOWLEDGMENT
in mixtures of standard It is important that at
Hoekstra, P. (1966), Moisture movement in soils under temperature gradients with the cold side temperature below freezing, Water Resources Research, 2: 241-250. Hoekstra, P. and Chamberlain, E. (1964), Electro-osmosis in frozen soil, Nature 203: 1406-1407. Korkina, R.I. (1965), Electrical potentials in freezing solutions and their effect on migration, CRREL Draft translation 490. Penner, E. (1971), Soil moisture distribution by ice lensing in freezing soils, Proc. 17th Annual Meeting, Can. Soc. Soil Sci., 44-62. Velde, B. (1977), Clays and Clay Minerals in Natural and Synthetic Systems, Elsevier, Amsterdam.
FREEZING POTENTIALS IN WET CLAYS.
II.
169
SPECIFIC SYSTEMS
S. Ramachandra Rao Department of Physics, University of Regina, Regina, Canada $4S 0A2 Thos. O'D. Hanley, S.J. Campion College, University of Regina, Regina, Canada $4S 0A2
dissolved electrolytes, and ionic compoABSTRACT
sition of clay minerals present in natural
With several variables controlled, elec-
soil systems we must obtain data with homo-
trical potentials were studied during the
ionic clays and investigate the effect of
freezing of a sludge of Regina clay, which
different variables on pure clays or natural
consists mainly of bentonite with some
clays thoroughly washed with distilled water.
illite and quartz.
The present
An initial potential V.
paper describes the results
of 28.5 mV at 20°C wa~ observed in natural
obtained with a natural clay (Regina clay)
Regina clay.
during studies of (i) the effect of soil pH,
Vi was slightly greater when
the clay was homoionic, containing K+, Ca++,
(2) the effect of ionic content,
or Fe+++ ions. Changes of Vi with pH con-
effect of water content, ~(4) the effect of
firmed that V. was electrokinetic in nature.
aging, and (5) moisture migration during
Freezing potentials were slightly higher in
freezing.
(3) the
the homoionic soils than in untreated soil, but were not significantly affected by mois-
EXPERIMENTAL DETAILS
ture content within the range tested. Aging The cell used for these experiments h a s
of the sludge had a pronounced effect on
been described in Part I of this paper.
the freezing potential, especially for the Regina clay, described in Part I, was
homoionic samples.
The amount of moisture washed several times with doubly distilled
migration toward the freezing front depended water.
A slurry containing about i00 g of
on the ionic content, being greater for K + clay and 800 ml of water was thoroughly
and Fe+++; an explanation for this effect stirred and allowed to settle, and the
is offered. discussed.
Plans for future study are supernatant water was decanted out.
The
washing procedure was repeated eight times after which the rate of settling of the INTRODUCTION clay was found to be extremely slow, which In part I of the present paper the sig-
was an indication that the dissolved elec-
nificance of the freezing potential and its
trolytes were all removed by the wash water.
possible importance in wet soil systems has
The slurry was centrifuged, the supernatant
It was pointed out that in
water was decanted out and tested to ensure
been described.
order to understand
the effect of a number
of physico-chemical variables such as pH,
that it was free of electrolytes
(test for
chloride ions with AgNO3) , and the clay was
170
dried at room temperature.
A known weight
of dry clay was mixed with amount of water
the required
to obtain a sample
desired moisture
of the
above w a s mixed with
solution
desired metal
ions
stirred
for one hour.
natant
liquid was decanted
was washed with double until
the washings
The residual temperature reached
sludge until
record
procedure
the v a r i a t i o n
tial as a function the cold plate In order moisture
the clay was as usual.
Since
to poten-
saw blade portion
cycles
the cell
the m o i s t u r e
In order of electrical measurements
a hackA
again to
suspended
in soil a set of
steel,
vertically
causes
for the than for
in Part I.
in place
for the changes
with
of the
to investigate
possible
in p o t e n t i a l
served on p r o g r e s s i v e l y
cooling
ob-
the clay
sludge.
RESULTS
with a both of in the clay
potentials
electrode
stainless
found w i t h an
in conjunction
steel electrode
base are recorded
slurry
in Table
(at pH 7.10)
on the cold plate Fig.
i.
experiments
as the clay
water
is shown
obtained
and frozen in
of potentials alone
in Fig.
(in place 2.
with the freezing
on Regina
different
electrolytes
Table
The values
2.
The var-
is shown graphically
in d i s t i l l e d
Results
i.
was cooled
Similar v a r i a t i o n
of clay slurry)
with the
and with the cell
iation of these potentials
measured
the significance
in conjunction
strip of stainless
which were
then dried
was made using a standard
electrode
in when
were such
was conducted
water alone
in order
Ag-AgCI
content.
potentials
sludge,
longer
described
experiment
Electrical
at equal dis-
bottle,
to understand
described
conditions
drop to occur,
Another
frozen,
cylinder.
in an oven at 120°C and w e i g h e d
narrow
The
of each of the slices was w e i g h e d
determine
electrode
were followed
a longer time was required
distilled
of
the frozen portion.
weighing
in
and the
from each other using
in a stoppered
Ag-AgCl
I.
to one m o r e freezing
p a r t of w h i c h was
to slice
the changes
the Ag-AgCI
paragraph
the experiments
the clay to freeze
out of the p l a s t i c
(i cm)
between
the experimental
potential
of
in Part
the m i g r a t i o n
It was cut into three slices tances
and 8.62.
room,
from the cold plate
was pressed
7.10,
measured
the cell was cooled on the cold plate.
bottom plate of the cell was detached. wet clay mass,
successively
and
followed
six freeze-thaw
subjected
steel base of
the steel plate
that the cell was open to the air of the
At the end of 15 minutes
was removed
the preceding
content
has been described
after
and between
by weighing.
of electrical
to follow
and the stainless
and the two steel electrodes
ions.
of the temperature
upon subjecting
thaw cycles,
water
and
the Ag-AgCI
the cell,
the potentials
Poten-
electrode
between
In the next experiment,
was dried at room
the moisture
the Ag-AgCI
when the pH was 6.12,
out and the clay
free of C1
50% as d e t e r m i n e d
The general
the steel base of the cell.
the cell base were
thor-
the cell d e
electrode
The super-
distilled
were
as
of the
The slurry was
oughly
as container
this steel plate,
250 ml of a
of the chloride
ion.
in Part I, at equal distances
tials between specific
(K+ ' Ca ++ , or Fe +++ ) 40 g of clay w a s h e d
1 molar
using
scribed above
content.
To get clay sludge with
described
slurry,
clay treated with are surm~axized shown
in
in the table are
171
mean values from three runs.
The results
with greater water content
(50% solid).
show significant effects when the clay is
The values
treated with the chosen ions.
mean values of 3 or 4 runs.
A few experiments with a concentrated
results
were conducted
clay sludge containing
75% solid and 25% water.
content,
results are compared with those obtained
////s
o
/// I
•
\
t'
I
I
r,.E .,.
values are in moisture
the drop in potential upon
/ / •
'S''~ 0
These
show that while the initial
electrical potential lowered with decrease
In Table 3 the
•
shown in Table 3 are
""'-
4
~
8
I
~rz
-I0
-20
°i
t6 TIME
I
20 mln
I 24
E
.J p..-40
eo :
~\
--I00
Fig. 1. Potential differences between pairs of electrodes in a slurry of Regina clay. Dashed line, Ag-AgCl electrode vs base of the cell;-.-, Ag-AgCl electrode vs stainless steel plate; solid line, stainless steel plate vs base of the cell. The cell was placed on the cold plate at time t = 0, and f r e e z i n g b e g a n after approximately i0 min.
!
/
/
/ -60
/ --TQ
P'~.
/ I I I
°
-SG
Fig. 2. Potential differences between pairs of electrodes in distilled water. Dashed line, Ag-AgCI electrode vs base of the cell; --.-, Ag-AgCl electrode vs stainless steel plate; solid line, stainless steel plate vs base of the cell. The cell was placed on the cold plate at time t = 0, and freezing began after approximately i0 min.
172
TABLE Potential differences between the c l a y s l u d g e . Temperature Electrode
standard Ag-AgCI electrode and stainless steel electrodes 20°C. P o t e n t i a l s are s h o w n in m i l l i v o l t s .
combination
Ag-AgCI
vs u p p e r
Ag-AgCI
vs base of cell
Upper steel plate b a s e of c e l l
1
pH
pH 6.12
steel plate
+
7.10
in
pH 8.62
4
- 43
- 108
- 33
- 39
-
62
+ 37
-
-
46
vs
TABLE F r e e z i n g p o t e n t i a l s o b t a i n e d w i t h R e g i n a clay, 50%. P o t e n t i a l s in m i l l i v o l t s . Untreated Initial V 28.6
4
2
both
natural +
and homoionic. +
Moisture
content
+++
++
H 28.1
K 38.9
Ca 34.1
Fe 36.2
30.2
34.8
43.2
35.7
40.8
19.8
24.0
28.0
20.3
26.8
10.4
10.8
15.2
15.4
14.0
1
Maximum
V
Minimum
V
V
max . mln
- V max
mln
TABLE E f f e c t of m o i s t u r e o n the f r e e z i n g m e a n v a l u e s of 3 or 4 runs.
potentials
Natural 50% w a t e r content V.
3
of R e g i n a
Potentials
clay.
Clay
clay 25% w a t e r content
(in m i l l i v o l t s )
are
treated with K+ ions
50% water content
25% w a t e r content
28.6
20.0
38.9
25.8
30.2
24.4
43.2
28.3
19.8
13.2
28.0
13.1
10.4
11.2
15.2
15.2
1
V V
max . mln
V
-V max
. mln
TABLE F r e e z i n g p o t e n t i a l s in f r e s h a n d a g e d l e a s t four e x p e r i m e n t s .
sludges
Potentials V. l Clay
treatment
Untreated + K ++ Ca +++ Fe
Fresh
Fresh
clay.
Values
are averages
for a t
in m i l l i v o l t s V
-- Aged
4
of R e g i n a
V
max Aged
Fresh
V
min Aged
max
Fresh
- V
mln Aged
28.6
7.4
30.2
8.6
19.8
0.4
i0.4
8.2
38.9
i0.4
43.2
16.0
28.0
-i0.4
15.2
26.4
34.1
7.4
35.7
10.4
20.3
2.4
15.4
8.0
36.2
26.6
40.8
72.2
26.8
37.8
14.0
34.4
173
freezing
is not significantly
by the moisture
V, the electrode potential
affected
content of the sample.
A set of experiments
was conducted with
in the clay slurry
amounts to -0.265 V.
Similarly
Regina clay treated as before and allowed
electrode potential
to stand as a sludge for 3-4 weeks.
cell amounts
was considered
adequate
This
for obtaining
a
of the stainless
steel plate suspended
to -0.261 V.
When the stain-
less steel plate is positive
and the cell
sludge which is close to the wet soil in
base is negative,
the field.
between the two would be -0.265
The results
which also includes
are given in Table 4,
values
for sludge
which is -4 mY.
the potential
was noted experimentally.
comparison.
observed
The results
of moisture migration
studies
in Table 5.
as follows.
From the weight loss observed
on drying,
These are obtained
the weight of water per gram of
dry clay was calculated
in each of the slices.
Since the original water content freezing)
was known
(before
( ig water per ig dry
clay in most cases),
the amount of water
which migrated during
potentials
of
in clay slurries have a
negative sign. Further evidence
for the electrokinetic
nature of the potentials the variation with pH.
is obtained from
of each of the potentials
As seen from Table 1 each of the
electrode potentials
becomes
less negative
as the pH is lowered.
the freezing process
was determined.
- (-0.261)V,
It is thus
that the electrical
both electrodes
difference
This is the value which
which had not been aged for the purpose of
are recorded
the
of the base of the
The data presented
in Fig.
1 show that
on cooling from 20°C to 0°C the cell base becomes more negative until the freezing
DISCUSSION
stage.
As discussed zero potential systems appears electrical interface.
The sharp drop in potential
in Part I, the initial non-
observed with all clay mineral to originate
between the upper stainless
the base of the cell, a drop which corres-
from the
double layer at the clay-water From the data given in Table 1
ponds to the onset of freezing, result of
(i) the potential
it is found that with the Ag-AgCI electrode
plate becoming more negative
negative
and the stainless
potential
positive
the resultant
-43 mV.
Taking the standard electrode
potential
steel plate
cell potential
of the Ag-AgCI electrode,
difference
steel plate and
is
and
(ii) the
of the cell base becoming markedly
further observed
-0.2224
of the upper
less negative or more positive.
tinues,
is the net
It is
that as the cooling con-
the potential
of the cell base
TABLE 5 Moisture migration
observed
Ionic content of the clay Untreated K ++ Ca+++ Fe
in Regina clay treated with different Freezin 9 potential Vmax - Vm l.n (mY) 8.2 26.4 8.0 34.4
ions.
Weight of water per unit weight of dry clay Top slice Middle slice Bottom slice (frozen) 0.96 0.91 0.95 0.79
0.98 0.95 0.98 0.72
1.05 1.14 1.06 1.44
174
steadily becomes more positive the upper electrode The experiments
the slow variations
Fig.
of
atively greater positive follow the following
ites consist of layers of complex alumin-
an explanation
in potential
cooling.
for
with
It is observed
osilicates.
2 that with distilled water only the
swelling.
of the cell base becomes
more positive with the development
electrode
The potential
remains almost constant.
leads to the conclusion in potential
the water molecules
When the wet clay is frozen,
steadily
interlaminar frozen zone.
water migrates
the
toward the
As it migrates
with it the ions present
This
Montmorillon-
between the layers and cause
of the
of the upper
course.
When these layers come in
contact with water, penetrate
ice front.
This may
becomes more negative.
from
potential
charge.
performed with distilled
water alone may provide
progressive
and that
it carries
in it.
This effect is more marked with clay
that the variations
observed on progressively
sludges aged for 3 to 4 weeks
(Table 4).
During the aging of clays in water,
poly-
cooling the clay sludge are the result of
silicic acids are formed which could
the effect of temperature
affect
the migration
quently
the freezing potential. It was + +++ ions and Fe ions en-
kinetic potential
on the electro-
at the clay-water
inter-
face.
of ions and conse-
found that while K
It is interesting
to consider why there
is a non-zero potential
for both the upper
hance the freezing potential with aged ++ sludges, Ca ions do not show appreciable
steel plate and the cell base when distilled
change,
water is used.
sludge they too raise the freezing potential
An electrochemical
potential
is to be expected between the Ag-AgCl electrode and the steel.
There appears
to be a small electrochemical at room temperature electrodes, different
between
alloys.
forming calcium polysilicates
potential
the two steel
The nearly
This could be due to the combination of ++ ions with polysilicic acid species
Ca
also
which may be made of slightly
crease of this potential
although with freshly prepared
the p o t a s s i ~
linear in-
as a function of
which are
only very sparingly soluble (Velde, 1977). + K ions raise the freezing potential because
precipitated
silicate out.
species are not
In the case of Fe +++,
freezing point agrees with the temperature
since these are tripositively charged, +++ only a fraction of the Fe ions are
dependence
lost by combination
time while
the base was cooling to the
of an electrochemical
potential
The results
for small changes in temperature. The results recorded
moisture
in Table 2 show
that H + ions have no significant on the freezing potential.
with polysilicic
from the determination
content upon freezing
show that water migrates
effect
There is, how-
regions of clay. the observations
toward the frozen
This is in accord with of Korkina
(1965), who
has attributed moisture migration
value of freezing potential
voltages
to
of
(Table 5)
ever, a marked effect in the presence of + ++ +++ K , Ca , and Fe Ions. Since a large corresponds
acid.
originating according
to the
in the solutions
the frozen region becoming more positive,
the ground;
the presence of these ions in the clay
produce
causes the frozen soil to acquire rel-
the near layer to the freezing
in
to her, the voltages
a movement of the moisture
from
front,
175
thereby creating in the adjacent layer a
some stage studies of freezing potentials
scarcity of moisture which is replenished
in the field be undertaken as well.
by a flow of moisture from the lower layers under the effect of the moisture gradient. Similar observations have been recorded by Hoekstra and Chamberlain (1966), and Penner
(1964), Hoekstra
(1971).
investigators
of the
referred to above.
toward the frozen regions
is related to the freezing potential which is recorded by the sharp drop in voltage when freezing sets in. At the present stage of the project it is difficult to know just what direction of effort will be most useful.
As a rea-
sonable next step we are presently
studying
the migration of ions during freezing, and freezing potentials silica and clays.
the
and of the National
Research Council of Canada. REFERENCES
The
present work further indicates that moisture migration
The authors gratefully acknowledge
support of the National Science Foundation (Grant No. DPP76-80072),
The results thus far obtained are consistent with the observations
ACKNOWLEDGMENT
in mixtures of standard It is important that at
Hoekstra, P. (1966), Moisture movement in soils under temperature gradients with the cold side temperature below freezing, Water Resources Research, 2: 241-250. Hoekstra, P. and Chamberlain, E. (1964), Electro-osmosis in frozen soil, Nature 203: 1406-1407. Korkina, R.I. (1965), Electrical potentials in freezing solutions and their effect on migration, CRREL Draft translation 490. Penner, E. (1971), Soil moisture distribution by ice lensing in freezing soils, Proc. 17th Annual Meeting, Can. Soc. Soil Sci., 44-62. Velde, B. (1977), Clays and Clay Minerals in Natural and Synthetic Systems, Elsevier, Amsterdam.