U.S. patent application number 11/573709 was filed with the patent office on 2007-10-18 for stabilized kaolin slurry and methods for improving kaolin slurry stability.
Invention is credited to Michael J. Garska, Robert J. Pruett, Jun Yuan.
Application Number | 20070244243 11/573709 |
Document ID | / |
Family ID | 35429469 |
Filed Date | 2007-10-18 |
United States Patent
Application |
20070244243 |
Kind Code |
A1 |
Yuan; Jun ; et al. |
October 18, 2007 |
Stabilized Kaolin Slurry and Methods for Improving Kaolin Slurry
Stability
Abstract
Disclosed herein are stabilized kaolin slurries comprising a
kaolin comprising no more than about 80% by weight of particles
having an equivalent spherical diameter of less than 2 microns and
at least one stabilizer, wherein the stabilized kaolin slurry has a
28-day pour test result of at least about 80% poured. Also
disclosed are methods of making such stabilized kaolin
slurries.
Inventors: |
Yuan; Jun; (Kathleen,
GA) ; Garska; Michael J.; (Sandersville, GA) ;
Pruett; Robert J.; (Milledgeville, GA) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
35429469 |
Appl. No.: |
11/573709 |
Filed: |
August 16, 2005 |
PCT Filed: |
August 16, 2005 |
PCT NO: |
PCT/US05/29062 |
371 Date: |
February 14, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60601619 |
Aug 16, 2004 |
|
|
|
Current U.S.
Class: |
524/447 ;
501/141 |
Current CPC
Class: |
C01P 2004/54 20130101;
C04B 2235/5436 20130101; C01P 2006/80 20130101; C01P 2004/20
20130101; C04B 35/6264 20130101; C04B 35/63 20130101; C09C 1/42
20130101; C04B 35/632 20130101; C01P 2004/51 20130101; C04B 35/624
20130101; C04B 33/04 20130101; C01P 2004/61 20130101; C01P 2006/40
20130101; C04B 35/6263 20130101; C01P 2006/22 20130101 |
Class at
Publication: |
524/447 ;
501/141 |
International
Class: |
C09C 1/42 20060101
C09C001/42; C04B 33/00 20060101 C04B033/00 |
Claims
1. A stabilized kaolin slurry comprising: a kaolin comprising no
more than about 80% by weight of particles having an equivalent
spherical diameter (ESD) of less than 2 microns; wherein said
stabilized kaolin slurry has a solids content of at least about
40%, and a 28-day pour test result of at least about 80%
poured.
2. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry has a pH ranging from about 4.5 to about
7.5.
3-6. (canceled)
7. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry is substantially free of a dispersant.
8. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry comprises at least one dispersant.
9. (canceled)
10. The stabilized kaolin slurry according to claim 8, wherein the
at least one dispersant is present in an amount ranging from about
100 ppm to about 500 ppm on a dry basis relative to the total
weight of the slurry.
11. The stabilized kaolin slurry according to claim 8, wherein said
at least one dispersant is chosen from polyacrylates,
polyphosphates, and silicates.
12. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry has a 28-day pour test result of at least
about 85% poured.
13. The stabilized kaolin slurry according to claim 12, wherein
said stabilized kaolin slurry has a 28-day pour test result of at
least about 89% poured.
14. The stabilized kaolin slurry according to claim 1, wherein said
kaolin comprises no more than about 70% by weight of particles
having an ESD of less than 2 microns.
15. The stabilized kaolin slurry according to claim 14, wherein
said kaolin comprises no more than about 60% by weight of particles
having an ESD of less than 2 microns.
16. The stabilized kaolin slurry according to claim 15, wherein
said kaolin comprises no more than about 50% by weight of particles
having an ESD of less than 2 microns.
17. The stabilized kaolin slurry according to claim 16, wherein
said kaolin comprises no more than about 40% by weight of particles
having an ESD of less than 2 microns.
18-19. (canceled)
20. The stabilized kaolin slurry according to claim 14, wherein
said kaolin comprises from about 25% to about 45% by weight of
particles having an ESD of less than 2 microns.
21. The stabilized kaolin slurry according to claim 20, wherein
said kaolin comprises about 35% weight of particles having an ESD
of less than 2 microns.
22. The stabilized kaolin slurry according to claim 1, wherein said
kaolin has a shape factor of at least about 25.
23-24. (canceled)
25. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry has a solids content ranging from about
45% to about 60%.
26. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry has a Brookfield viscosity at 50% adjusted
solids ranging from about 300 cps to about 700 cps using a #2
spindle at 20 rpm.
27. (canceled)
28. The stabilized kaolin slurry according to claim 1, wherein said
stabilized kaolin slurry has a Hercules viscosity at 50% adjusted
solids of less than 10 dynes at 4400 rpm using an "A" bob.
29. The stabilized kaolin slurry according to claim 1, wherein said
stabilized slurry has a conductivity of no more than about 100
.mu.S.
30. The stabilized kaolin slurry according to claim 29, wherein
said stabilized slurry has a conductivity of no more than about 80
.mu.S.
31. (canceled)
32. The stabilized kaolin slurry according to claim 1, further
comprising at least one stabilizer.
33. The stabilized kaolin slurry according to claim 32, wherein
said stabilized slurry has a pH ranging from about 5.5 to about
9.5.
34. (canceled)
35. The stabilized kaolin slurry according to claim 32, wherein
said at least one stabilizer comprises at least one cellulosic
thickener.
36. The stabilized kaolin slurry according to claim 35, wherein
said at least one cellulosic thickener comprises
carboxymethylcellulose.
37. The stabilized kaolin slurry according to claim 35, wherein
said at least one cellulosic thickener is chosen from alkyl
celluloses, ethyl hydroxyethyl celluloses, hydroxymethyl
celluloses, hydroxyethyl celluloses, and hydroxypropyl
celluloses.
38. The stabilized kaolin slurry according to claim 32, wherein
said at least one stabilizer is chosen from montmorillonite,
smectite clays, hydrophobically modified ethoxylated urethanes,
polyacrylates, polyvinyl pyrrolidone, sodium alginate, xanthan gum,
silica thickeners, sodium magnesium silicate, acrylic acid
copolymers, and nonionic hydrophobically modified polyethers.
39. The stabilized kaolin slurry according to claim 32, wherein
said at least one stabilizer is present in an amount ranging from
about 0.01% to about 4% by weight, relative to the total weight of
the slurry.
40. (canceled)
41. A method of making a stabilized kaolin slurry, comprising:
filtering and rinsing a kaolin slurry to remove salt residue
therefrom until said resulting kaolin has a conductivity of no more
than about 100 .mu.S; resolubilizing said resulting kaolin to form
a resolubilized slurry; and adding at least one stabilizer to the
resolubilized slurry.
42. The method according to claim 41, wherein said stabilized
kaolin slurry has a 28-day pour test result of at least 80%
poured.
43. The method according to claim 42, wherein said stabilized
kaolin slurry has a 28-day pour test result of at least 85%
poured.
44. The method according to claim 43, wherein said stabilized
kaolin slurry has a 28-day pour test result of at least 89%
poured.
45. The method according to claim 41, wherein said resulting kaolin
has a conductivity of no more than about 80 .mu.S.
46. The method according to claim 41, wherein said slurry comprises
kaolin having no more than about 80% by weight of particles having
an equivalent spherical diameter (ESD) of less than 2 microns.
47. The method according to claim 46, wherein said slurry comprises
kaolin having about 25% to about 70% by weight particles having an
ESD of less than 2 microns.
48. The method according to claim 46, wherein said slurry comprises
kaolin having about 20% to about 65% by weight particles having an
ESD of less than 2 microns.
49. (canceled)
50. The method according to claim 48, wherein said slurry comprises
kaolin having about 25% to about 45% by weight particles having an
ESD of less than 2 microns.
51. (canceled)
52. The method according to claim 50, wherein said slurry comprises
kaolin having about 35% by weight particles having an ESD of less
than 2 microns.
53. The method according to claim 41, wherein said slurry comprises
kaolin having a shape factor of at least 25.
54. The method according to claim 41, wherein said at least one
stabilizer comprises carboxymethylcellulose.
55. The method according to claim 41, wherein said at least one
stabilizer comprises at least one cellulosic thickener chosen from
alkyl celluloses, ethyl hydroxyethyl celluloses, hydroxymethyl
celluloses, hydroxyethyl celluloses, and hydroxypropyl
celluloses.
56. The method according to claim 41, wherein said at least one
stabilizer is chosen from montmorillonite, smectite clays,
hydrophobically modified ethoxylated urethanes, polyacrylates,
polyvinyl pyrrolidone, sodium alginate, xanthan gum, silica
thickeners, sodium magnesium silicate, acrylic acid copolymers, and
nonionic hydrophobically modified polyethers.
57. The method according to claim 41, wherein said at least one
stabilizer is present in an amount ranging from about 0.01% to
about 4% by weight, relative to the total weight of the slurry.
58. The method according to claim 41, wherein substantially no
dispersant is added to said slurry.
59. The method according to claim 41, further comprising adding at
least one dispersant.
60. The method according to claim 59, wherein the at least one
dispersant is chosen from polyacrylates, polyphosphates, and
silicates.
61. (canceled)
62. The method according to claim 59, wherein the at least one
dispersant is present in an amount ranging from about 100 ppm to
about 500 ppm on a dry basis relative to the total weight of the
slurry.
63. The method according to claim 41, further comprising
flocculating said kaolin slurry prior to said filtering and
rinsing.
64. The method according to claim 63, wherein said flocculation
comprises lowering the pH of said kaolin slurry to a value of about
5 or less.
65. The method according to claim 41, further comprising spray
drying said kaolin slurry prior to said filtering and rinsing.
66-68. (canceled)
69. A method for improving the stability of a kaolin slurry
comprising: filtering and rinsing a kaolin slurry with water to
remove salt residue therefrom, wherein said kaolin slurry comprises
kaolin having no more than about 80% by weight particles having an
ESD of less than 2 microns; and adding an effective amount of at
least one stabilizer, wherein the stabilized kaolin slurry has a
28-day pour test result of at least 80% poured.
70-76. (canceled)
77. The method according to claim 94, further comprising adding at
least one dispersant to said slurry.
78. (canceled)
79. The method according to claim 77, wherein the at least one
dispersant is present in an amount ranging from about 100 ppm to
about 500 ppm on a dry basis relative to the total weight of the
slurry.
80. The method according to claim 77, wherein said at least one
dispersant is chosen from polyacrylates, polyphosphates, and
silicates.
81. The method according to claim 94, wherein said stabilized
kaolin slurry has a Brookfield viscosity at 50% adjusted solids
ranging from about 300 cps to about 700 cps using a #2 spindle at
20 rpm.
82. (canceled)
83. The method according to claim 94, wherein said stabilized
kaolin slurry has a Hercules viscosity at 50% adjusted solids of
less than about 10 dynes at 4400 rpm using an "A" bob.
84. The method according to claim 94, wherein said slurry comprises
kaolin having about 25% to about 70% by weight particles having an
ESD of less than 2 microns.
85-86. (canceled)
87. The method according to claim 84, wherein said slurry comprises
kaolin having about 25% to about 45% by weight particles having an
ESD of less than 2 microns.
88. (canceled)
89. The method according to claim 87, wherein said slurry comprises
kaolin having about 35% by weight particles having an ESD of less
than 2 microns
90. (canceled)
91. The method according to claim 94, wherein said stabilized
kaolin slurry has a 28-day pour test result of at least about 85%
poured.
92. The method according to claim 91, wherein said stabilized
kaolin slurry has a 28-day pour test result of at least about 89%
poured.
Description
[0001] This application claims priority to U.S. Provisional Patent
Application No. 60/601,619, filed Aug. 16, 2004.
[0002] Disclosed herein are stabilized kaolin slurries and methods
of making such stabilized kaolin slurries.
[0003] Kaolin clay has many known applications in industry,
including, for example, use as a filler in papermaking, a coating
for paper, and a pigment in paint. Kaolin products are often
shipped in a high solid slurry form. Slurries of coarse platy clays
tend to settle quickly, making them difficult to transport. To
stabilize kaolin slurries, i.e., to prevent kaolin clay from
settling to the bottom of containers as hard sediments during
shipping, thickening agents, such as carboxymethylcellulose (CMC),
have been used and mixed into the kaolin products in the final
slurry makedown. However, such a stabilizing method worked for
finer and less platy clays, but has not worked effectively in the
past for coarser and/or more platy kaolin clay slurries.
[0004] Therefore, there remains a need for developing a method to
stabilize coarser and/or more platy kaolin clay slurries. The
present inventors have developed methods for stabilizing coarse
kaolin slurries.
[0005] In one aspect, the present disclosure relates to a
stabilized kaolin slurry comprising: [0006] a kaolin comprising no
more than about 80% by weight of particles having an equivalent
spherical diameter (ESD) of less than 2 microns;
[0007] wherein the stabilized kaolin slurry has a solids content of
at least about 40%, and a 28-day pour test result of at least about
80% poured, such as at least 85% and further such as at least 89%
poured. Such stabilized kaolin slurries are generally sufficiently
stable to permit normal shipping and handling.
[0008] In another aspect, the present disclosure relates to a
method for making a stabilized kaolin slurry by reducing the levels
of residual salts in a kaolin slurry, prior to addition of a
conventional thickener or stabilizer such as carboxymethylcellulose
(CMC) or the like. In the past, such stabilizers have typically
been found not to work effectively in coarser and/or platier kaolin
clay slurries. Without being bound by any theory, the present
inventors hypothesize that residual salts (electrolytes), such as
aluminum and calcium, are released over a short period of time
after slurry makedown. These residual salts are weakly absorbed by
large kaolin particles because of their relatively large proportion
of surface areas. Once released, the residual salts react with the
stabilizer to reduce its efficacy and preventing effective slurry
stabilization.
[0009] Accordingly, one aspect of the present disclosure relates to
a method of making a stabilized kaolin slurry, comprising:
[0010] filtering and rinsing a kaolin slurry to remove salt residue
therefrom until the resulting kaolin has a conductivity of no more
than about 100 .mu.S;
[0011] resolubilizing the resulting kaolin; and
[0012] adding at least one stabilizer to the resolubilized kaolin
slurry.
[0013] The conductivity of the kaolin after filtering and rinsing
can be, for example, no more than about 100 .mu.S, such as no more
than about 80 .mu.S, and even such as no more than about 60
.mu.S.
[0014] Another aspect of the present disclosure provides a method
of stabilizing a kaolin slurry comprising: [0015] filtering and
rinsing the kaolin slurry; [0016] resolubilizing the kaolin slurry;
and [0017] adding at least one stabilizer; wherein the stabilized
kaolin slurry has a 28-day pour test result of at least 80% poured,
such as at least 85% and further such as at least 89% poured.
[0018] Another aspect of the present disclosure provides a method
of stabilizing a kaolin slurry comprising:
[0019] providing a kaolin slurry having a solids content of greater
than 40% and comprising no more than about 80% by weight of
particles having an equivalent spherical diameter (ESD) of less
than 2 microns; and
[0020] adjusting the pH of the kaolin slurry to a value ranging
from about 4.5 to about 6.5 to effect partial flocculation of the
slurry.
[0021] For example, the pH can be adjusted to a value ranging from
about 5.0 to about 6.0, or even from about 5.5 to about 6.0. In
some aspects, slurries falling into these pH ranges can often be
stabilized without addition of any stabilizer. It may, however, be
necessary in some cases to add a small amount of a dispersant to
adjust the viscosity of the partially stabilized slurry into a
range suitable for pumping.
[0022] As disclosed herein, the term "equivalent spherical
diameter" (ESD) is a particle size of a given particle, and can be
determined by a standard test procedure employing Stokes' Law of
Sedimentation. For example, ESD can be determined by measuring the
sedimentation of the particulate product in a fully dispersed
condition in a standard aqueous medium, such as water, using a
SEDIGRAPH.TM. instrument, e.g., SEDIGRAPH 5100, obtained from
Micromeritics Corporation, USA.
[0023] As disclosed herein, a coarse and platy kaolin clay refers
to, for example, a kaolin comprising no more than about 80% by
weight of particles having an ESD of less than 2 microns, such as
no more than about 70% by weight of particles having an ESD of less
than 2 microns, further such as no more than about 60% by weight of
particles having an ESD of less than 2 microns, even further such
as no more than about 50% by weight of particles having an ESD of
less than 2 microns, and even further such as no more than about
40% by weight of particles having an ESD of less than 2 microns.
For example, the coarse and platy kaolin clay refers to a kaolin
comprising no more than about 50%, such as no more than about 40%,
by weight of particles having an ESD of less than 2 microns.
Further for example, the coarse and platy kaolin clay refers to a
kaolin comprising from about 20% to about 65% by weight, such as
from about 25% to about 60% by weight, further such as from about
25% to about 45% by weight, and even further such as 35% by weight
of particles having an ESD of less than 2 microns.
[0024] In addition, the kaolin disclosed herein can have a shape
factor of, for example, at least about 25, such as at least about
30 and further such as at least about 45. "Shape factor" as used
herein is a measure of an average value (on a weight average basis)
of the ratio of mean particle diameter to particle thickness for a
population of particles of varying size and shape as measured using
the electrical conductivity method and apparatus described in
GB-A-2240398/U.S. Pat. No. 5,128,606/EP-A-0528078, which are
incorporated herein by reference in their entirety, and using the
equations derived in these patent specifications.
[0025] The stabilized kaolin slurry disclosed herein can have a
solids content ranging from about 40% to about 60% by weight
relative to the total weight of the slurry, such as from about 45%
to about 55%, and further such as from about 50% to about 60% by
weight relative to the total weight of the slurry. In other
embodiments, the stabilized kaolin slurry has a solids content of
at least 40%, such as at least 45%, and further such as at least
50% by weight relative to the total weight of the slurry.
[0026] Viscosity is a measure of a clay's resistance to changes in
flow. Those having ordinary skill in the art are familiar with
typical ways of measuring viscosity, which include, for example,
Brookfield viscosity and Hercules viscosity.
[0027] Brookfield viscometers provide a measure of a clay slurry's
low shear viscosity, expressed in units of centipoise (cp). One
centipoise is equal to one centimeter-gram-second unit. (One
centipoise is one hundredth (10.sup.-2) of a poise.) Thus, all
other things being equal, a 100 centipoise sample has a lower
viscosity than a 500 centipoise sample.
[0028] Hercules viscometers provide a measure of a clay slurry's
high shear viscosity. Hercules viscosity is typically measured by
placing a cylinder (bob) of appropriate diameter and length
(typically the A-bob) into a sample clay slurry. Hercules
viscosities of various samples can be compared by holding constant
the percent solids concentration of the sample, the bob size, and
the applied force. The Hercules viscometer applies a force to the
bob which causes it to spin at a controlled accelerating rate. As
the viscometer increases the bob spin rate, the viscous drag on the
cup increases. Clay slurries with poor high shear rheology will
exert the maximum measurable force on the cup at a lower bob rpm
than clay slurries with "good" high shear rheology. Hercules
viscosity is therefore typically expressed in terms of bob spin
rates, or revolutions per minute (rpm) as a function of the
relative applied force (dynes). A "dyne endpoint" is an indication
of very low Hercules viscosity. A dyne endpoint is reached when the
bob reaches its maximum rpm before the maximum measurable force is
exerted on the cup.
[0029] In one aspect, the stabilized kaolin slurry disclosed herein
can have a Brookfield viscosity at 50% adjusted solids ranging, for
example, from about 300 cps to about 700 cps as determined by a
Brookfield model DV.1 digital viscometer using a #2 spindle at 20
rpm. The stabilized kaolin slurry can also have a Brookfield
viscosity at 50% adjusted solids of, for example, at least about
400 cps as determined by a Brookfield model DV.1 digital viscometer
using a #2 spindle at 20 rpm.
[0030] In one embodiment, the stabilized kaolin slurry has a
Hercules viscosity at 50% adjusted solids of less than 10 dynes at
4400 rpm using an "A" bob.
[0031] When a stabilizer such as carboxymethylcellulose is used,
the stabilized kaolin slurry can have a pH ranging, for example,
from about 5.5 to about 9.5, and further, for example, from about
6.5 to about 7.5. However, when no stabilizer is used, the pH can
typically range from about 4.5 to about 7.5, such as from about 5.0
to about 6.5, further such as from about 5.0 to about 6.0, even
further such as from about 5.5 to about 6.0, and even further such
as from about 5.7 to about 5.8.
[0032] The pour test can be used as an indicator of the long term
stability of the kaolin slurries. In the pour test, a number of
samples of the slurry are placed into beakers and weighed. At the
selected time intervals, one of the beakers is upended and the
sample is allowed to pour out for a period of 1 minute. The beaker
is then re-weighed and the percentage of sample that successfully
poured from the beaker is determined as a percentage of the total
initial sample weight. Generally, the higher the pour-test
percentage, the more stable the slurry against settling.
[0033] The at least one stabilizer disclosed herein comprises, for
example, at least one cellulosic thickener, such as CMC. The at
least one cellulosic thickener can be chosen, for example, from
alkyl celluloses, ethylhydroxyethyl celluloses, hydroxymethyl
celluloses, hydroxyethyl celluloses, and hydroxypropyl celluloses.
In addition, the at least one stabilizer disclosed herein can be
chosen, for example, from montmorillonite, smectite clays,
hydrophobically modified ethoxylated urethanes, high molecular
weight polyacrylates, polyvinyl pyrrolidone, sodium alginate,
xanthan gum, silica thickeners, sodium magnesium silicate, acrylic
acid copolymers, and nonionic hydrophobically modified
polyethers.
[0034] The at least one stabilizer disclosed herein can be present
in an amount ranging from about 0.01% to about 4% by weight, such
as from about 0.01% to about 2% by weight, relative to the total
weight of the slurry.
[0035] In one embodiment, the stabilized kaolin slurry disclosed
herein is substantially free of any dispersant (i.e., comprising
less than 100 ppm by weight of dispersant on a dry basis). In
another embodiment, the stabilized kaolin slurry disclosed herein
further comprises at least one dispersant. In the case where a
dispersant exists in the stabilized kaolin slurry disclosed herein,
the at least one dispersant is present in an amount of, for
example, less than about 250 ppm on a dry basis, such as ranging
from about 100 ppm to about 200 ppm by weight on a dry basis
relative to the total weight of the slurry. In another embodiment,
the at least one dispersant is present in an amount from about 100
ppm to about 500 ppm by weight on a dry basis, relative to the
total weight of the slurry.
[0036] The at least one dispersant disclosed herein can comprise,
for example, at least one polyelectrolyte chosen, for example, from
polyacrylates and copolymers comprising at least one polyacrylate,
polyphosphates, and silicates such as sodium silicate, lithium
silicate, and ammonium silicate.
[0037] According to the method of making a stabilized kaolin slurry
disclosed herein, the filtering and rinsing operation of a kaolin
slurry by water to remove salt residue can be conducted by any
conventional process known in the field. For example, a lab ceramic
filter funnel attached with a flask can be used for the filtering
and rinsing operation, which simulates the filtering/dewatering
action by a typical rotary vacuum filter. The top of the funnel has
a shape of a large cup with a flat and porous bottom. Filter paper
is placed on the porous bottom of the funnel cup. Slurry is poured
into the cup. The flask attached below the funnel is connected to a
vacuum pump that pulls the water through filter paper into the
flask. After filtering out the water, a moisten cake of the kaolin
forms in the cup. Additional water may then be poured into the cup
one or more times to effect the rinsing operation. Other
conventional dewatering methods that may be used in accordance with
the present invention further include clarification, settling,
centrifugal washing, rotary vacuum filtration and pressure
filtration.
[0038] In measuring the conductivity of the resulting kaolin after
filtering and rinsing, 10 g of clay slurry or filter cake of the
kaolin on a dry basis diluted to 10% solids with de-ionized water
is used. The conductivity is measured using a conductivity probe of
a conductivity meter by conventional methods known in the field,
such as through the use Orion Model 120 Conductivity Meter, in the
unit of mS or .mu.S.
[0039] In one embodiment, a kaolin slurry is stabilized using the
method disclosed herein and has a 28-day pour test result of at
least 80% poured, such as at least 85% poured, and further such as
at least 89% poured.
[0040] In some embodiments, substantially no dispersant is added to
the kaolin slurry in the method disclosed herein. But in other
embodiments, the method of making a stabilized kaolin slurry
disclosed herein further comprises adding at least one dispersant.
The at least one dispersant can be the same as described as above.
It can be present in an amount ranging, for example, from about 100
ppm to about 200 ppm by weight, relative to the total weight of the
slurry on a dry basis.
[0041] The method of making a stabilized kaolin slurry disclosed
herein can further comprise flocculating a kaolin slurry prior to
the filtering and rinsing operation. The flocculation can be
accomplished by any conventional process known in the field. For
example, the flocculation can be accomplished by lowering the pH of
the kaolin slurry to a value of about 5 or less.
[0042] In addition, the method of making a stabilized kaolin slurry
can further comprise spray drying a kaolin slurry prior to the
filtering and rinsing operation.
[0043] Also disclosed herein is a method for improving the
stability of a kaolin slurry comprising:
[0044] filtering and rinsing the kaolin slurry by water to remove
salt residue therefrom, wherein the kaolin slurry comprises kaolin
having no more than about 80% by weight particles having an ESD of
less than 2 microns; and
[0045] adding an effective amount of at least one stabilizer, so
that the stability of the resulting kaolin slurry is improved as
measured by a 28-day pour test.
[0046] The term "improve" means that the stability as measured by a
28-day pour test of a kaolin slurry subject to the method disclosed
herein is higher, i.e., a higher percentage of the treated kaolin
slurry is poured than the originally untreated kaolin slurry.
[0047] All percentages and amounts expressed herein are by weight.
All amounts, percentages, and ranges expressed herein are
approximate.
[0048] The present invention is further illuminated by the
following non-limiting examples, which are intended to be purely
exemplary of the invention. In the examples shown below, the
following abbreviations are used: [0049] C211=sodium polyacrylate;
and [0050] #/t=number of pounds per ton. [0051]
CMC=carboxymethylcellulose
EXAMPLES
Example 1
[0052] In this example, a coarse platy kaolin clay having a
particle size distribution such that about 56% by weight of the
particles have an ESD of less than 2 microns and about 9% by weight
of the particles have an ESD of less than 0.25 microns. This coarse
platy kaolin clay was first spray-dried, and then subjected to one
of the six methods as shown below--control, A, B, C, D, and E:
##STR1##
[0053] The solid content, Brookfield viscosity, Hercules viscosity,
and stability using the pour test were measured for each resulting
kaolin slurry made from those six methods.
[0054] The T-bar method was used to measure the vertical viscosity
distribution of the samples, which changes as settling occurs over
time. Typically, the viscosity of the top portion of a sample will
decrease and that of the lower portion will increase as settling
occurs. T-bar measurements are made using a Brookfield viscometer
fitted with a Brookfield Helipath Stand and a special "T-bar" type
spindle. The Helipath stand slowly raises or lowers the Brookfield
viscometer so that the rotating shearing element of the T-bar
spindle describes a helical path through the test sample. By always
cutting into fresh material, the problems of channeling or
separating are minimized. In the current example, samples can be
considered fully settled when the upper T-bar viscosity approaches
"0" cps and the lower approaches 400,000 cps. In the current
example, monitoring of a given sample was terminated after a full
settling measurement.
[0055] The pour test method was also used to assess the long term
stability of the kaolin slurries. In the pour test, a number of
samples of the slurry were placed into beakers and weighed. At the
selected time intervals, one of the beakers was upended and the
sample was allowed to pour out for a period of 1 minute. The beaker
was then re-weighed and the percentage of sample that successfully
poured from the beaker was determined as a percentage of the total
initial sample weight.
[0056] The results are shown in the table below: TABLE-US-00001 CPS
#2, Solid @ 20 Dynes @ T-Bar Viscosity Poured % rpm 4400 rpm 0 day
7 day 14 day 21 day 28 day % A (Comparative) 58.3 320 580 rpm 0/0
0/400,000+ --/-- --/-- --/-- 18.5 B (Comparative) 49.8 300 8.7
dynes 1600/1600 2400/22400 0/180,000 0/400,000+ --/-- 26.7 C
(Comparative) 56.7 310 1240 rpm 1000/1000 2000/400,000+ --/-- --/--
--/-- 16.7 D (Inventive) 47.4 330 6.0 dynes 800/800 3000/12000
4000/17000 3000/26000 0/42,000 89 E (Comparative) 55.8 270 1820 rpm
0/0 0/400,000+ --/-- --/-- --/-- 20.0 Control 52.9 610 100 dynes
4000/4000 10,000/64,000 24,000/400,000+ --/-- --/-- --/--
[0057] As shown in the table, the kaolin slurry made under the
method D, which is in accordance with the present disclosure, is
stabilized, and has a 28-day pour test result of about 89%,
exhibiting significant improved long term stability.
Example 2
[0058] Samples of a spray dried hydrous kaolin having a particle
size of 33%<2 microns, a shape factor of about 20 and a GE
Brightness of about 87, were made down at about 58% solids. The
slurries were dosed with CMC PE-30 at various increments from 0.5
pounds per ton to 8 pounds per ton. Additionally, samples were
stabilized by partially flocculating the slurries with sulfuric
acid. The mixture was mixed and diluted with water to obtain a
final Brookfield viscosity ranging from 600 cps to 700 cps when
read with a #2 spindle at 20 rpm. The samples were then poured into
a pint jar for a 28 day stability test in accordance with the
procedures described below. The samples were tested for solids
concentration, Brookfield viscosity at 20 rpm, pH, and Hercules
viscosity before beginning the stability test.
[0059] The stability test includes monitoring the viscosity of the
slurry over a 28 day period using a T-bar spindle. Readings were
taken at 7 day intervals and were read at about 1/2 inch from the
top surface of the slurry for the upper reading and about 1/2 inch
from the bottom for the lower reading. After 28 days, the weight
percent of the slurry that poured out of the jar in 1 minute was
measured and was designated as the first pour. The sample was
returned to the jar and shaken for a few seconds and again poured
out for 1 minute to obtain the weight percent of the slurry for the
second pour. Brookfield viscosity and Hercules viscosity were then
measured on this material.
[0060] In order to evaluate a slurry with no or very little
polyacrylate a second series of tests were run. For the second set
of experiments, a slip was flocculated with sulfuric acid to a pH 3
and bleached with 2 pounds per ton sodium hydrosulfite. This was
then filtered and the filter cake was used for the following
experiments. These samples were then prepared and tested as
described above.
[0061] When CMC PE-30 was used as the stabilizer, the slurries
required high dosages to maintain a stable slurry for the full 28
days of the test. See Table 2. Good results were not obtained until
a dose rate of 8.0 pounds per ton was used. TABLE-US-00002 TABLE 2
Tests Using CMC Brookfield % (cps) Hercules Days Pour Chemical #T
pH solids #2 @20 rpm (rpm) stable Result test % none 0.0 6.7 58.0
544 2230 28 settled CMC PE30 0.5 6.7 58.0 540 2170 14 settled CMC
PE30 1.0 6.7 58.0 600 1882 7 settled CMC PE30 2.0 6.7 58.0 620 1614
14 settled CMC PE30 4.0 6.7 58.0 724 1410 21 settled none 0.0 7.1
58.0 620 1458 21 settled CMC PE30 0.5 7.1 58.0 640 1540 7 settled
CMC PE30 1.0 7.0 58.0 480 1328 7 settled CMC PE30 2.0 6.9 58.0 606
1206 14 settled CMC PE30 4.0 6.9 57.9 670 1206 14 settled CMC PE30
2.0 6.8 57.9 540 1430 7 settled CMC PE30 8.0 7.1 50.0 480 28 stable
95.7 CMC PE30 8.0 7.1 52.5 620 28 stable 92.9 CMC PE30 8.0 7.1 50.0
412 28 stable 97.0 CMC PE30 8.0 7.1 52.5 644 28 stable 89.6
Example 3
[0062] The use of sulfuric acid to partially flocculate the slurry
while still allowing it to remain fluid enough to pump was also
tested as a mechanism for stabilizing the coarse slurries of
interest. These tests showed that the coarse filler slurry could be
stabilized most effectively by using sulfuric acid at a pH ranging
from about 5.5 to about 6.0. See Table 3. TABLE-US-00003 TABLE 3
Tests Using Sulfuric Acid Brookfield % (cps) Hercules Days Pour
Chemical #T pH solids #2 @20 rpm (dynes) stable Result test %
H.sub.2SO.sub.4 pH 6.0 6.0 58.0 700 28 stable 95.0 H.sub.2SO.sub.4
pH 6.5 6.5 58.0 600 21 settled CMC + H.sub.2SO.sub.4 1 + pH 6.5 6.5
58.0 620 7 settled H.sub.2SO.sub.4 pH 5.5 5.4 55.3 600 10.8 28
stable 97.2 H.sub.2SO.sub.4 pH 5.0 5.0 52.7 600 5.0 28 stable 95.5
H.sub.2SO.sub.4 pH 5.5 5.5 54.6 600 11.5 28 stable 97.8
H.sub.2SO.sub.4 pH 5.0 5.0 52.0 600 5.5 28 stable 96.2
[0063] These tests show that pH alone could be used to make a
stable slurry from the coarse hydrous kaolin slurry. For example,
the pH may range from about 5.5 to about 6.0. However, without the
addition of a small amount of polyacrylate the slurry solids should
be maintained lower than about 50% in order to be fluid enough to
pump easily. The addition of just 0.5 pounds per ton (i.e., about
0.25 kilograms per ton) could allow the solids loading of the
slurry to increase into the range of about 54% to about 58%. For
example, results could be achieved when the polyacrylate was added
after the soda ash or at the same time. Excessive shearing can also
have a detrimental effect on the slurry solids. For example, a test
that sheared the slurry for 30 minutes in a Waring blender reduced
the solids of the final slurry from 57% to 54%.
[0064] Unless otherwise indicated, all numbers expressing
quantities of ingredients, reaction conditions, and so forth used
in the specification and claims are to be understood as being
modified in all instances by the term "about." Accordingly, unless
indicated to the contrary, the numerical parameters set forth in
the following specification and attached claims are approximations
that may vary depending upon the desired properties sought to be
obtained by the present invention.
[0065] Other embodiments of the invention will be apparent to those
skilled in the art from consideration of the specification. Other
embodiments of the invention will be apparent to those skilled in
the art from consideration of the specification and practice of the
invention disclosed herein. It is intended that the specification
and examples be considered as exemplary only, with a true scope and
spirit of the invention being indicated by the following
claims.
* * * * *