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DEMYSTIFYING THE METHYLENE BLUE INDEX

Authors:

Abstract

Clays & clay minerals have long been recognized as having a significant impact on oil sands tailings behavior, with increased clay content being associated with slower settling, higher required flocculant dosages and longer consolidation times. The Methylene blue index (MBI) is a simple index test that provides an indication of clay activity. This test has been in use in the oil sands for over 30 years and is routinely employed in test programs. This paper explains the Methylene blue test, the common sources of error in the method, the different way the results are reported and how to convert between them and the ranges of MBI reported in different tailings streams. The paper will also review how MBI is used to predict process or geotechnical behavior.
DEMYSTIFYING THE METHYLENE BLUE INDEX
Heather Kaminsky
Suncor Energy Inc. Calgary Alberta
ABSTRACT
Clays & clay minerals have long been recognized
as having a significant impact on oil sands tailings
behavior, with increased clay content being
associated with slower settling, higher required
flocculant dosages and longer consolidation
times. The Methylene blue index (MBI) is a simple
index test that provides an indication of clay
activity. This test has been in use in the oil sands
for over 30 years and is routinely employed in test
programs. This paper explains the Methylene blue
test, the common sources of error in the method,
the different way the results are reported and how
to convert between them and the ranges of MBI
reported in different tailings streams. The paper
will also review how MBI is used to predict process
or geotechnical behavior.
INTRODUCTION
The methylene blue index is a number used to
describe the clay content and activity of a sample.
The methylene blue test measures how much
methylene blue dye can be absorbed by a sample
as determined by a titration test. Methylene blue
absorbs to clay surfaces both external surfaces
and internal surfaces through ion exchange.
Methylene blue has a very strong affinity to clay
surfaces and so will displace any other ion present
on the surface. For this reason the methylene blue
test is sometimes described as testing the cation
exchange capacity of a material, however it is
actually more useful to think of the methylene blue
test as a measure of surface area as the
methylene blue effectively covers the clay surface.
Hang and Brindley described the surface area of
methylene blue as 130Å2. Therefore one can
calculate the surface area of the sample by
assuming that each titrated molecule covers 130Å2
of surface area.
Thus:  =  
  ×× ×
Where SA is the surface area of the sample in
m2/g, C is the concentration of MB in mol/mL, NA
is Avogadro’s number (6.022X1023 molecules/mol)
and A is the surface area of the MB molecule in
m2.
METHOD
The methylene blue index test most commonly
used in oil sands was developed by Amar Sethi at
MRRT labs (Sethi,1995) as a modification from
the ASTM test method. The test method has since
been refined by various groups, most particularly
CANMET energy (Omotoso & Morin, 2008) and
more recently the Clay Focus Group.
The key steps in the test are:
1) Dispersion of the sample to be tested -
the sample is dispersed using stirring,
boiling sonication and sodium bicarbonate
as a dispersing aid. Dispersion is
achieved when the sample has a
homogenous appearance with no clay
lumps or floating pieces on the surface.
The sample will also have an opalescent
appearance when swirled. For a video
showing a well dispersed sample see:
http://youtu.be/BTMk4hyiSpI .
2) Acidifying the sample just prior to titration
this removes the effects of ion oxide-
hydroxides from the titration.
3) Titrating the sample with methylene blue in
0.5-1 mL increments.
4) Determining the end point (usually using
the “halo method” where a drop of
slurried sample containing methylene blue
is placed on Whatman filter paper and
examined for the presence of a blue halo
which indicates an excess of methylene
blue).
5) Calculating the methylene blue index.
ASTM vs Oil Sands Method Comparison
The key differences from the ASTM method are:
the use of 0.006N methylene blue solution
instead of 0.01 N methylene blue solution.
The use of sodium bicarbonate as
opposed to distilled water for sample
dispersion.
The use of sodium hydroxide to assist with
dispersion;.
The use of sonication and heating with
mixing in dispersion as opposed to mixing
only.
The option of using a larger mass (5+ g)
for sandy samples vs. the use of a fixed
sample mass (2g).
The type of filter paper used (Whatman 42
ashless vs Baroid 987).
In general the changes were made to achieve
more repeatable MBI data for oil sands samples.
The change in the solution strength was made as
the higher concentration is more prone to the
formation of dimers or other orientations of
methylene blue that cause an overestimate in
surface area. In addition, lower concentrations
produce more sensitive end points as you need
more mLs of the methylene blue solution to
achieve the same absorption. The use of sodium
bicarbonate and sodium hydroxide are both to
promote dispersion and to convert the clays to the
sodium exchanged form, which provides the
highest measure of MBI. The increase in sample
size allows for lower MBI samples to be assessed
accurately. Finally, the Whatman type of filter
paper was found to produce a more distinct halo
which improves the accuracy of end point
detection.
In general, a significant portion of the oil sands test
method is focused on ensuring that the sample is
dispersed. It is CRITICAL that the dispersion of a
sample be assessed by the physical appearance
of the sample rather than by assuming the sample
is dispersed because the dispersion steps have
been followed. This is because different samples
take a different amount of time to disperse.
Samples that have been subjected to Dean Stark
treatment, and in particular samples of froth solids,
froth treatment tailings or flocculated samples, are
extremely difficult to disperse.
When undertaking the testing of a set of samples
for the first time, a best practice is to use a series
of tests on the same sample at different dispersion
times to determine whether the MBI is consistent
between tests or if it is increasing as a function of
dispersion time. If the MBI is changing, the sample
was not sufficiently dispersed at the start of the
test.
INTERPRETING MBI
The fundamental MB test measures the number of
milliliters of MB solution absorbed a given mass of
sample. Usually the mass of sample used is small
so the end point of the titration is often less than 20
mLs. The standard titration step size is often 1mL
and so the relative uncertainty of the end point is
usually in the order of 5%.
One factor which complicates the understanding of
MBI in the industry is that different units are used
to present the MB index.
These are:
MB index (MBI) this is the
milliequivalents of MB per 100 g of
sample. It is calculated by multiplying the
MB# by the molarity of MB used (0.006 N).
For ores this number is usually between
0.25-2. For MFT this number is usually
between 5 and 15. This number is the
reporting units specified in ASTM and is in
SI units. It requires no additional
information in order to convert to other
units.
Methylene Blue # (MB#)- this is the
number of mLs MB used to titrate 100 g of
sample. This number assumes that the
reader knows the concentration of the MB
used (presumably 0.006N for oil sands)
but can be ambiguous in the case that the
ASTM procedure was used instead For
oil sands ores this number is usually
around 100. For MFT this number is
typically around 1500.
MB weight (MBW) this is the Weight of
MB used to titrate 100g of sample. This
requires knowledge of the molecular
weight of MB used to convert. Molecular
weight of Methylene Blue trihydrate
(reagent specified in CANMET procedure)
is 373.9 g/mol. The molecular weight of
pure methylene blue is then 319.84g/mol.
% Clay as determined by MB - this
generally takes the measured MBI and
applies an empirically derived conversion
between the MBI and the % clay mineral
as measured by Sethi by XRD&PSD on a
few samples of oil sands clay:
%  =
 
100+ 0.04
0.14
Surface area as determined by MB this
is a conversion based on the assumption
of a monolayer of methylene blue
absorbed on all available surfaces and that
the surface area of the methylene blue is
as described by Hang & Brindley.
One important point to note is that the magnitudes
of the numbers reported are VERY different
depending on the method of reporting used
(illustrated in Table 1 and Table 2). This can lead
to a false sense of precision in the test and
therefore a sense that the test is unreliable
because a 200 point scatter between similar tests
appears inaccurate.
It should be noted that if the activity is low and the
same mass of sample is used the uncertainties will
be quite high because the end point sensitivity is
usually ~1 mL. This is why it is important to re-test
low activity samples with more material to achieve
larger titration volumes/or reduce the titration step
size.
Table 1: Example of different MBI values on high activity MFT
mLs of
MB
titrated
Mass of
Sample
(g)
Normality
of MB
meq/mol
MW of
MB
g/mol
MBI
meq/
100g
g/100g
MB #
(mLs
0.006N/100g)
% Clay
Measured
20
1
0.006
319.84
12
2000
86
Typical
Uncertainty
1
0.001
0.00001
0
0.6
100
4
Relative
uncertainty
5%
0.1%
0.2%
0.0%
5%
5%
5%
Table 2: Example of different MBI values on low activity MFT
mls of
MB
titrated
Mass of
Sample
(g)
Normality
of MB
meq/mol
MBI
g/mol
MBI
meq/
100g
MBW
g/100g
MB #
(mLs
0.006N/100g)
% Clay
Measured
3
1
0.006
319.84
1.8
576
300
13
Typical
Uncertainty
1
0.001
0.00001
0
0.6
192
100
4
Relative
uncertainty
33%
0.1%
0.2%
0.0%
33%
33%
33%
33%
The other source of confusion around MBI is that
the % clay determined by MBI can be greater than
100% and doesn’t always correlate with the % clay
measured by other methods. This is because the
% clay assumes an “average” oil sands clay.
It is easiest to explain this in terms of surface area
the typical surface areas of the common clay
minerals which occur in oil sands are listed in
Table 3 along with the MBI and “% clay” one would
expect to see for a sample containing only that
mineral with that surface area. As you can see, a
sample containing 100% kaolinite would have an
MBI of only 3 but would show up as 100% clay
mineral by XRD and would probably show up as
close to 100% less than 2 micron (clay size) by
sieve hydrometer. On the other hand a sample
containing only 2.5% smectite and 97.5% sand
would still give an MBI of 3 but would show up as
only 2.5% clay mineral by XRD (if it was even
detected) and would probably show up as only
2.5% less than 2 micron by sieve hydrometer.
Table 3: Typical Surface area, MBI and % Clay
for pure clay samples
Mineral
Typical
Surface
Area
(m2/g)
Expected
MBI for
pure
sample
(meq/100g)
Expected
% Clay
using Sethi
correlation
Kaolinite
20
3
19%
Illite
100
13
92%
Smectite
800
102
730%
“Oil
Sands
Clay”
110
14
100%
Oil sands typically contain several clays in various
proportions but generally end up with surface
areas between 100-120 m2/g of clay so the
correlation between MBI and particle size and by
clay mineral determined by XRD calculated by
Sethi works relatively well as a comparison
between clay particle size and MBI (it is empirically
derived but works out to an average surface area
of 110 m2/g). The problem with the conversion is
when a very active clay (i.e. high in smectite) or a
very inactive clay (i.e. high in kaolinite) comes
around and throws off the correlation. Ideally one
would use both particle size and MBI to get
information about the particle size distribution as
well as the likely activity of the particles.
USES OF MBI
The MBI is very useful in predicting the total
surface area of a sample which in turn can help
predict a variety of properties such as:
Amount of water trapped as bound water
given a variety of double layer strengths.
Surface area available for chemical
reactions.
Exchangeable cation sites available for
chemical reactions.
These fundamental properties can in turn be used
to help predict the outcomes of the various
processes in oil sands.
Bitumen Recovery
One of the early correlations noted is the
relationship between the MBI of an ore and the
expected bitumen recovery. Namely, as the MBI
increases the likelihood of poor recovery also
increases. This is because as the particle surface
area increases there is an increased hindrance to
the flow of water and hence an increase in
viscosity of the fluid.
Ores that process well usually have an MBI of 0.6
meq/100g or less (<5 m2/g, <100 mls 0.006N
MB/100g). Ores with an MBI greater than ~1.3
meq/100g (>10m2/g) usually process poorly unless
significantly more water is used in the process.
Ores with an MBI in between 0.6 -1.3 are typically
very sensitive to water chemistry effects.
Predicting Flocculent dosage
Another well documented correlation with MBI is
the flocculent dosage as the MBI of a sample
increases there is a trending increase in the
dosage required to obtain specific settling
objectives. This was documented by Kaminsky et
al. in the CONRAD water conference in 2012 for
settling tests on batch sample. Similarly, Suncor
uses an MBI clay based dosage to report
flocculent doses for TRO (Revington, 2014).
Correlation with Yield Stress
Suncor TRO has also found a direct correlation
between the yield stress of MFT and the clay to
water ratio of the slurry as determined by MBI MFT
(Omotoso et al., 2014). If the MFT is then optimally
flocculated, there is another direct correlation
between the yield stress of the flocculated MBI and
the MBI of the unflocculated MFT (Diep et al.,
2014). Of course, other factors such as previous
shear energy will also influence the yield stress of
a system so these correlations are site specific.
Yield strength, of course, can then be correlated
with other properties such as pump demand and
beach slope.
Correlation with MFT Volume
Since MBI can be used to estimate the amount of
water associated with the surfaces of the clay at
different double layer strengths, it can therefore
also be used to estimate the total volume of water
trapped by the clay at different double layer
strengths and hence the expected total volume of
MFT. Omotoso et al. have demonstrated an
empirical correlation between volume of MFT and
the MBI of the MFT. (Omotoso et al., 2014).
Correlation with Atterberg Limits
There are several published correlations between
Atterberg limits and MBI in the geotechnical
literature (Cerato, 2001). Unfortunately, none have
been published for oil sands. Published data where
Atterberg limits and MBI have both been measured
on oil sands fine tailings show a disappointing
correlation. Atterberg limit tests are also an index
test and as such the results are best compared
when the tests have been conducted in the same
mine. The 2013 presentation by Gidley highlighted
that the test method used for Atterberg limit testing
can have a significant impact on the results. As
such, the lack of correlation from literature is
unsurprising as there is a limited amount of data
where MBI and Atterberg limits were tested over a
significant range using consistent methods.
Identification of Unstable or Low Permeability
layers
MBI has been used outside the oil sands industry
to characterize the stratigraphy of soil foundations
and identify unstable layers (Chiappone et al,
2004). It has also been used within the industry to
identify low permeability regions within tailings
ponds (Lovbakke, 2014).
CONCLUSIONS
The MBI test is a useful index test with a wide
range of applications. As an index test, its power
lies in the fact that it is a relatively quick and
inexpensive test that can easily be applied to a
large number of samples. Having a large number
of data points means that more detailed
characterization tests can be more carefully
selected and therefore the highest value data
achieved.
As with most index tests it is important to
understand the principles behind the test and the
factors that can influence the outcome when
determining how to measure and use the index for
a given application. In the case of MBI, the degree
of dispersion is the single factor that most strongly
influences the test outcome and therefore should
be critically assessed when setting up a testing
program.
REFERENCES
ASTM Standard: C 837 99 (Re-approved 2003)
Cerato, A. (2001). Influence of Specific Surface
Area on Geotechnical Characteristics of Fine
Grained Soils (Unpublished graduate dissertation).
Department of Civil & Environmental Engineering,
University of Massachusetts.
Chiappone, A., Marello, S., Scavia, C., & Setti, M.
(2004). Clay mineral characterization through the
methylene blue test: comparison with other
experimental techniques and applications of the
method. Canadian Geotechnical Journal, 41 (6),
1168-1178.
Diep, J., Weiss, M., Revington, A., Moyls, B., &
Mittal, K. (2014). In-line mixing of mature fine
tailings and polymers. In Jewell, R., Fourie, A.,
Wells, P.S., van Zyl, D. (Eds.), Proceedings of the
17th International Seminar on Paste and Thickened
Tailings (pp. 111-126). Canada: InfoMine Inc.
Gildey, I., & Moore, T. (2013, February). Impact of
Test Methodolgy on the Atterberg Limits of Mature
Fine Tailings. Paper presented at the CONRAD
Oilsands Clay Conference, Edmonton AB.
Hang, P.T., & Brindley, G.W. (1970). Methylene
Blue absorption by clay minerals determination
of surface areas and cation exchange capacities.
Clays and Clay Minerals, 18, 203-212.
Kaminsky, H., Sedgwick, A., Clark, J., & Fan, A.
(2012). Importance of Clay & Water Chemistry in
Flocculation. Presented at the CONRAD Water
Conference, Edmonton AB.
Lovbakke, D. (2014). Methylene Blue Index
Applications to Tailings Issues. Presented to the
meeting of the COSIA Clay Focus Group.
Omotoso, O., & Melanson A. (2014). Influence of
clay minerals on the storage and treatment of oil
sands tailings. In Jewell, R., Fourie, A., Wells,
P.S., van Zyl, D. (Eds.), Proceedings of the 17th
International Seminar on Paste and Thickened
Tailings (pp. 269-280). Canada: InfoMine Inc.
Omotoso, O., & Morin, M. (2008). Methylene Blue
Procedure: Dean Stark Solids. CanmetENERGY:
Devon.
Sethi, A. (1995, January 23). Methylene Blue Test
for Clay Activity Determination in Fine Tails. MRRT
Procedures.
APPENDIX A CONRAD METHOD FOR
MBI DETERMINATION CONRAD
CLAY FOCUS GROUP DRAFT (2012)
MODIFIED FROM CANMET
PROCEDURE
1.OBJECTIVE AND SCOPE OF THE
PROCEDURE
The Methylene Blue Procedure is intended to
address dispersion of oil sands process solids prior
to methylene blue adsorption described in general
by the ASTM Standard Test Method for Methylene
Blue Clay (C 837-99 (Re-approved 2003). This
procedure is designed to be effective for all oil
sands process streams but it may not be optimal
for all streams. In this method all samples/sub
samples are assumed to be representative of the
process being stream being tested, recognizing
that care is required to ensure this is true.
A mature fine tailings (MFT) analog is used as a
calibration standard, to monitor the level of
dispersion provided by the dispersion equipment
used for sample preparation. The MFT analog is
comprised of sand, montmorillonite, de-ionized
water and bitumen. Bitumen and water are
removed using Dean Stark extraction, the same
procedure used for extracting bitumen and water
from test samples.
2. PURPOSE
This procedure was developed specifically for oil
sands process solids but could be used for oil-free
minerals as well.
3. APPARATUS
250ml beakers;
1L volumetric flasks;
analytical balance, accurate to 0.001g;
hotplate/magnetic stirrer and stir bars;
methylene blue powder;
mortar & pestle;
top-loading balance, accurate to 0.01 g;
disposable pipettes;
ultrasonic bath (Cole Parmer 1 ½ gallon with
40kHZ transducers & built in seep frequency);
room temperature water bath;
hand held pH meter;
burette stand;
50ml burette with teflon stopcock;
whatman 42 ashless filter paper;
watchglasses;
dean-stark extraction apparatus for
preparation of mft-analog calibration standard.
4. REAGENTS
Analytical grade reagents shall be used in all tests.
De-ionized water shall be used unless
otherwise indicated in the procedure.
Methylene Blue trihydrate (M.W. 373.9) (1 ml =
0.006 meq). Dissolve 2.2436 g of Methylene
blue powder in 1L de-ionized water (or 1.1218
g in 500 ml). Wrap volumetric flask in
aluminium foil to keep the solution from
degrading. A fresh batch should be used within
a day.
10% w/w NaOH (sodium hydroxide). Dissolve
10g of NaOH pellets in 90g of deionized water.
10% v/v H2SO4 (sulfuric acid). Add 10 ml of
concentrated H2SO4 to 90 ml de-ionized water.
0.015M NaHCO3 (sodium bicarbonate). Add
1.26 g of dry NaHCO3 to 1 L de-ionized water.
pH 4,7 & 10 buffer solution (calibrating pH
meter).
Coarse Ottawa sand, retained on 200-mesh
sieve.
Na-montmorillonite, marketed as Bentonite by
Fisher Scientific.
Solids and toluene -free oil sands bitumen
produced from a dean stark extraction of oil
sand ore.
5. SAFETY PRECAUTIONS
Wear gloves and protective eyewear when
handling methylene blue, caustic and acidic
agents. It is particularly painful if it enters the eyes
and will stain skin a very dark blue. If you get
Methylene blue on your clothes or skin apply liquid
dish-soap immediately to the area (without water).
6. MFT-ANALOG STANDARD PREPARATION
a) Add Ottawa sand (35 g), water (55 g), bitumen
(5 g) and bentonite (5 g) into a clean glass jar.
b) Mix the 100-g mixture thoroughly.
c) Run the entire mixture through standard Dean
Stark extraction. Sub-sampling without
adequate homogenization may cause the
bentonite to preferentially pass through the
Dean-Stark thimble. Once bitumen and water
have been extracted, the dried solid serves as
a bulk standard sample containing 12.5-wt%
bentonite. The bitumen free standard is
referred to as an MFT-analog.
d) Gently shatter the MFT-analog using a mortar
and pestle to remove clumps of materials.
e) Store as bulk standard.
7. PREPARATION OF METHYLENE BLUE
SOLUTION
Prepare 500 ml of 0.006 N Methylene Blue
solution. Stir solution at 400 rpm for a minimum of
10 minutes to ensure that all the dye is dissolved.
Prepare this solution fresh daily.
8. DISPERSION OF SAMPLES
1) The MFT-analog must have gone through
the Dean Stark extraction process or
equivalent bitumen removal process. All
test solids are assumed to have gone
through the Dean Stark extraction process
or equivalent bitumen removal process.
Bentonite is used as received.
2) Measure out in a clean beaker,
approximately 1 g of MFT-analog on a top
loading balance and record the weight.
3) In a second clean beaker, measure
approximately 0. 2 g bentonite on a top
loading balance and record the weight.
4) For each test sample place a clean dry
beaker on the top-loading balance and
tare the weight. Before adding the sample
please take the following into
consideration:
5) Is the sample very sandy? If so, use 5 g of
sample.
6) Does the sample contain large proportions
of clay? If so, use 1-2 g of sample.
7) Add the sample to the beaker and record
the weight of the sample used.
8) Add 50 ml of 0.015 M NaHCO3 to each
sample. Add NaHCO3 carefully so that the
solids don’t get spread all over the inside
of the beaker. Use a disposable pipette to
rinse the sides of the beaker with some of
the NaHCO3 solution already in the
beaker.
9) Add 2 ml of 10% w/w NaOH solution to
each sample with a disposable pipette.
Place a clean dry stir bar in the mixture.
Cover the beaker with a watchglass to
keep the sample from evaporating. This
step is to try and improve the dispersion of
a sample the pH of the solution should
be measured, if the pH of the slurry
increases above 11.5 coagulation of the
clays is likely and the amount of NaOH
added just be lowered or eliminated
entirely.
10) Soak samples overnight (minium of 12
hours).
11) In the morning place samples on a
hotplate/stirrer set to 120° C (the sample
should not heat above 60° C with the
hotplate set at this temperature monitor
temperature as different hotplates heat at
different rates). Set the stirrer to a
minimum of 250 rpm. Adjust the mixing
speed as required. Make sure the sample
is mixing completely and that all solids are
in suspension and should move freely
around the beaker. Use a glass rod with a
rubber policeman to dispel any
agglomerations.
12) Heat and stir the sample for 20 minutes
then transfer to an ultrasonic bath
operating at a 42 kHz for an additional 20
minutes.
13) The samples should now be dispersed.
Check that the samples show full
dispersion:
14) A fully dispersed sample will be free of
floating particles such as small balls of
clay that may have become impregnated
with air. These particles should be
captured using a glass rod and policeman
and pulverised while inside the sonification
vessel to ensure they are dispersed
properly.
15) Solids should be move freely from the
corners of the sonification vessel and not
adhere in clumps. These agglomerations
should be captured using a glass rod and
policeman and pulverised while inside the
sonification vessel to ensure they are
dispersed properly.
16) Look for signs of streaming birefringence
within the sample. Birefringence is the
effect produced by the individual clay
particles as they rotate violently by the
sonic sound waves within the bath. The
effect it produces is similar in appearance
to a tornado inside the mixed sample with
the clay particles turning in a cone-shaped
column appearing a dark and then light
brown in colour as they individually catch
the ambient light at different angles and
then reflect them outwards at two distinct
angles of refraction.
17) If the sample is not dispersed repeat step
14 until the sample is fully dispersed.
NOTE: DISPERSION IS THE MOST
IMPORTANT PART OF THIS METHOD. If
the sample is not dispersed completely the
titration results will be inaccurate.
18) The times and methods provided in this
method are from extensive testing at
CANMET. Equipment varies from lab to
lab and it wears out. By periodically
performing optimization testing on the
equipment with a known sample such as
bentonite, an MFT analog, or an in-house
standard, one can always know the
amount of mixing and sonication time
necessary to achieve an optimum
dispersion (i.e. a level at which methylene
blue index does not increase with
mixing/sonication time).
9. TITRATION OF SAMPLE
1) Place the beakers in a room temperature
water bath and let them cool for 3-5
minutes. The following steps are carried
out for the Bentonite first, followed by the
MFT-analog, then for the test samples.
Commentary samples which are too hot
will show diminished MBI’s. Room
temperature is optimal for this test.
2) Place the beaker on a stirring plate located
underneath the burette and start stirring
the sample (no heat).
3) Place the handheld pH meter in the
solution of the sample. Add 10% v/v
H2SO4 until the pH drops to 2.5-3.8..
Titrate the sample with 0.006 N Methylene
Blue while the sample is stirring.
4) Commentary: a pH of 2.5-3 has been
found to tighten the halo effect and make
end point detection easier. There is a
significant amount of buffering capacity in
most oil sands samples making a precise
pH difficult to achieve which is why the
2.5-3.8 is recommended.
5) Add the methylene blue solution in 1 ml
increments. Switch to 0.5 ml increments
when the sample is close to reaching the
endpoint. From prior experience with pure
bentonite, depending on the batch, the
endpoint can range between 28 and 34
mls. If the pure bentonite sample is not
within this range there may be an issue
with the methylene blue or with the
procedure and the test is not considered
valid.
6) With a transfer pipette, remove an aliquot
of the sample (after each titrant addition)
and place one droplet on a piece of
Whatman 42 ashless filter paper. Continue
placing drops of sample on the filter paper
after each addition of titrant until the
endpoint is reached. .The endpoint is
observed when there is excess of
methylene blue in the water phase of the
sample indicating. A blue halo will form
around the sample droplet on the filter
paper. A UV lamp may be used to
enhance the detection of the halo.
Continue 2-3 drops passed the end point
to allow for endpoint verification.
7) Record the ml’s of methylene blue
required to reach the end point. An MBI
test is only considered valid if it has a
precision of 5% or better for instance if the
end point of a test is 10mL of methylene
blue and step wise titration was done in
0.5mL increments this would lead to a
precision of 5%. A maximum of 50mL of
Methylene blue is recommend for a valid
test. For tests of multiple samples the
methylene blue test should be repeated on
approximately 5% of the samples to
ensure that the results are repeatable.
10. CALCULATIONS
METHYLENE BLUE INDEX (MBI)
 
100=   ×  
    ()
×100
METHYLENE BLUE NUMBER (MB#)
#  0.006
100
=  0.006 
    ()×100
11. OTHER CALCULATIONS
These calculations are often requested by oil
sands operators but should be treated as useful
correlations and not direct outputs of the
methylene blue test.
WEIGHT PERCENT CLAY
%  = + 0.04
0.14 100
Note this can lead to a wt% Clay greater than
100%
ACTIVE SURFACE AREA (BASED ON
REFERENCE 3)
  2
= ×130 × 0.06022
12. STANDARDIZATION
  ±0.25 
100
=  ×%   
100
The precision is taken from the ASTM Standard:
C837-99.
%   
=    
     +    
IF THE MFT-ANALOG MBI IS OUTSIDE THE
SPECIFIED RANGE, THE
DISPERSION EQUIPMENT SHOULD BE
CHECKED AND TEST SAMPLES REPEATED.
13. UNCERTAINTY ANALYSIS
Following the method for propagating uncertainties
outlined in “An Introduction to Error Analysis” by
John R. Taylor, the uncertainty in the methylene
blue index can be simplified as:
2
2
2
sampleMass sampleMass
mlsMB
mlsMB
Normality
Normality
MBI
MBI
δ
δδδ
++=
Since the values uncertainty in the concentration
and the uncertainty in the weight are very small
relative to the uncertainty in the volume, they can
be neglected from the equation leaving:
mlsMB
mlsMB
MBI
MBI
δδ
Similarly, since the methylene blue surface area is
given by Hang and Brindley 1970 as:
0602.0130××= MBISA
MB
, the relative
uncertainty in the surface area is also the relative
uncertainty in the volume.
MBI should therefore be reported to no more
decimals than the uncertainty in the measurement
For instance assuming 5mL of MB was used to
titrate 2g of solids and the uncertainty in the end
point was 0.5mL the result would be:
5mL * 0.006/2*100 = 1.5
With an uncertainty of
0.5*0.006/5*100=0.15
Therefore it is appropriate to report the result as
1.5±0.2 or 1.5 (i.e. to two significant figures)
Or for MB#
=5/2*100 = 250 with an uncertainty of 0.5/2*100 =
25
Therefore it is appropriate to report the result as
250±25 or 2.5×102
15. ACKNOWLEDGMENTS
The CONRAD Clay focus group would like to
acknowledge the efforts of Amar Sethi, Michelle
Morin and Oladipo Omotoso in their efforts to
improve the application of methylene blue analysis
in the oil sands industry.
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Cerato, A. (2001). Influence of Specific Surface Area on Geotechnical Characteristics of Fine Grained Soils (Unpublished graduate dissertation). Department of Civil & Environmental Engineering, University of Massachusetts.
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  • M Weiss
  • A Revington
  • B Moyls
  • K Mittal
Diep, J., Weiss, M., Revington, A., Moyls, B., & Mittal, K. (2014). In-line mixing of mature fine tailings and polymers. In Jewell, R., Fourie, A., Wells, P.S., van Zyl, D. (Eds.), Proceedings of the 17 th International Seminar on Paste and Thickened Tailings (pp. 111-126). Canada: InfoMine Inc.
Impact of Test Methodolgy on the Atterberg Limits of Mature Fine Tailings. Paper presented at the CONRAD Oilsands Clay Conference
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Gildey, I., & Moore, T. (2013, February). Impact of Test Methodolgy on the Atterberg Limits of Mature Fine Tailings. Paper presented at the CONRAD Oilsands Clay Conference, Edmonton AB.
Importance of Clay & Water Chemistry in Flocculation. Presented at the CONRAD Water Conference
  • H Kaminsky
  • A Sedgwick
  • J Clark
  • A Fan
Kaminsky, H., Sedgwick, A., Clark, J., & Fan, A. (2012). Importance of Clay & Water Chemistry in Flocculation. Presented at the CONRAD Water Conference, Edmonton AB.