Binary mixtures of polyacrylates and sodium silicates are used as deflocculating agents for kaolin slurries to ensure pumpability and pourability of the slurry. An example of a binary mixture is a mixture of 67% by weight sodium polyacrylate having a weight average molecular weight of 4,200 and 33% by weight of sodium silicate on a dry solids basis.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to binary deflocculating mixtures useful in reducing 
viscosity of kaolin slurries. 
2. Description of the Prior Art 
Kaolin, a clay which is essentially a hydrated aluminum silicate, is a well 
known article of commerce having varied uses. For example, kaolin is used 
as a filler in the body of paper and as a component of paper coatings. For 
such and other uses, kaolin is generally shipped as a 70% by weight 
aqueous slurry in tank cars and tank wagons. It is important to ensure 
that the slurry is a liquid, freely pumpable and pourable slurry so that 
it can be handled with no difficulty throughout slurry formation, shipping 
and use. One problem which arises when kaolin slurries are shipped in this 
manner, especially during summer months, is that slurry temperatures rise 
considerably thus increasing viscosity to undesirable levels which 
interfere with handling. In attempts to control viscosity, dispersants or 
deflocculating agents have been employed such as sodium polyacrylate, 
sodium metasilicate, tetrasodium pyrophosphate and other complex 
polyphosphates. Sodium polyacrylate is the deflocculant of choice; 
however, it is the most expensive. The silicates, although less expensive 
than sodium polyacrylate are less effective on a weight basis. With 
respect to both, kaolin slurry viscosities tend to rise over a period of 
time, especially in the presence of elevated temperatures. 
SUMMARY OF THE INVENTION 
Binary mixtures of soidum polyacrylate and sodium silicates have been found 
to be excellent deflocculating agents or dispersants for aqueous kaolin 
slurries. Kaoline slurries containing these mixtures are characterized by 
their pumpability and pourability as well as their ability to withstand 
viscosity increase during transportation and storage at elevated 
temperatures. Further, although silicates generally are less effective 
than polyacrylates on a weight basis, it has been found that binary 
mixtures which contain both polyacrylates and silicates as described 
herein are superior to the use of polyacrylates or silicates alone. That 
is, synergy with respect to (1) viscosity control and (2) viscosity 
stability with time at ambient and elevated temperatures have been 
achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Binary mixtures containing sodium polyacrylate plus one or more sodium 
silicates are present in kaolin slurries in amounts sufficient to ensure 
pumpability and pourability of the slurry and to withstand viscosity 
increases at elevated temperatures (e.g., 120 deg. F.). Generally, from 
about 0.40% by weight to about 1.00% by weight of the binary mixture on a 
dry solids basis based on the weight of the kaolin in the slurry can be 
used. Preferably, about 0.5% by weight of the binary mixture on a dry 
solids basis is used based upon the weight of the kaolin in the slurry. 
The relative amounts of the two components in the binary mixture with 
respect to each other are from greater than about 50% by weight to about 
80% by weight of sodium polyacrylate and from less than about 50% by 
weight to about 20% by weight of silicate, on a dry solids basis. The 
slurries contain from about 50% by weight to about 75% by weight, 
preferably about 70% by weight solids, the remainder being water. 
The binary mixture or deflocculant can be introduced into the slurry as 
such or each of its components can be introduced separately. This is 
followed by mixing. The binary mixture itself can be prepared by simple 
mixing of its components. The components can be in the form of solids or 
aqueous solutions so that the mixture can be a solid or an aqueous 
solution. When in solution form, generally there can be from about 30% by 
weight to about 50% by weight of solids and from about 70% by weight to 
about 50% by weight of water. Aqueous solutions of these mixtures upon 
standing do not separate. 
The polyacrylate is generally sodium polyacrylate although other salts such 
as the ammonium and potassium salts may be used. The polyacrylate is 
essentially neutralized and has a weight average molecular weight of from 
about 2,000 to about 10,000. These polyacrylates are well known articles 
of commerce and their preparation from acrylic acid is likewise well 
known. 
Regarding sodium silicates, also known as soluble silicates, they are a 
family of chemicals composed of different proportions of sodium oxide 
(NA.sub.2 O), silica (SiO.sub.2) and usually but not always water (H.sub.2 
O). Examples of commercial sodium silicates are Na.sub.2 O:2SiO.sub.2, 
sodium orthosilicate (2SiO.sub.2 :SiO) and sodium metasilicate. The sodium 
silicates are supplied in both liquid, i.e., aqueous solutions and solid 
form. Useful commercial products are set forth below. 
Grade designations are taken from literature of Diamond Shamrock Chemicals 
Company. 
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GRADE 50 
Specific Gravity at 20 deg. C. 
1.526 (50.0 deg. Baume) 
Viscosity at 20 deg. C. 
335 Centipoises 
Weight Ratio Na.sub.2 O:2.00 SiO.sub.2 
Weight Per Gallon 12.71 Pounds 
Solids Content 44.1% 
GRADE 52 
Specific Gravity at 20 deg. C. 
1.559 (52.0 deg. Baume) 
Viscosity at 20 deg. C. 
1760 Centipoises 
Weight Ratio Na.sub.2 O:2.40 SiO.sub.2 
Weight Per Gallon 12.98 Pounds 
Solids Content 47.3% 
GRADE 42 
Specific Gravity at 20 deg. C. 
1.408 (42.0 deg. Baume) 
Viscosity at 20 deg. C. 
63 Centipoises 
Weight Ratio Na.sub.2 O:2.54 SiO.sub.2 
Weight Per Gallon 11.73 Pounds 
Solids Content 37.5% 
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EVALUATION OF THE BINARY MIXTURES IN KAOLIN SLURRIES 
The efficacy of the deflocculants is determined by conducting heat aging 
tests of kaolin slurries containing same and observing viscosity changes 
of the slurry. The following procedure was used. 
Apparatus 
Electrically heated convection oven 
8 oz. glass jars, capped 
Brookfield viscometer, Model LVT 
Reagents 
Ultrawhite 90 (Georgia Kaolin Co.) clay slurry (58% by wt. clay, 42% by wt. 
water), no dispersant present 
Sodium polyacrylate/sodium silicate aqueous solution (1:0.5 wt. ratio of 
solids), 40% by wt. total solids in the solution 
Procedure 
A. Preparation of deflocculating agent 
Aqueous solutions of sodium polyacrylate having a weight average molecular 
weight of 4,200 and sodium silicate shown below were mixed together with 
additional water to form the following composition. 
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Sodium polyacrylate solution 
62.0% 
(43.0% by wt. solids) 
Sodium silicate solution 
30.2% 
Grade 50 (44.1% by wt. solids) 
Water 7.8% 
100.0% 
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The weight ratio of sodium polyacrylate/sodium silicate is 1:0.50. 
B. Preparation of slurry 
Ultrawhite 90 kaolin clay slurry (58% by wt. solids) obtained from Georgia 
Kaolin Co. and the deflocculant solution from Part A were stirred together 
using a mechanical mixer. 
C. Test method 
1. Slurry viscosity determination 
To different 340 gram portions of the kaolin slurry prepared according to 
Part B above were added small, weighed increments of deflocculating agent, 
each increment followed by mechanical mixing and a viscosity determination 
using a Brookfield Model LVT viscometer. Increments were added past the 
point where viscosity begins to increase. 
2. Heat Aging Test 
Initial slurry viscosities are determined. Samples are then placed in 
capped jars and put into an oven at 120 deg. F. for fourteen days. At end 
of this time, slurry viscosities are again determined. 
For a fuller understanding of the nature and advantages of this invention, 
reference may be made to the following examples. These examples are given 
merely to illustrate the invention and are not to be construed in a 
limiting sense. All quantities, proportions and percentages are by weight 
and all weights of the deflocculant and kaolin are of solids. 
The characteristics of the binary mixtures as well as their ability to 
function as deflocculating or dispersing agents for kaolin slurries are 
illustrated in Table I below. The binary mixtures and slurries containing 
same were prepared and viscosities measured at room temperature in 
accordance with the preparation and test procedure given above. 
TABLE I 
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Kaolin Slurry Viscosities at Room Temperature 
Na Poly- Na Polyacryate.sup.1 / 
% of Disper- 
acrylate.sup.1 
Na Silicate.sup.2 
Na Silicate 
sant Solids 
soln. - 43.0% 
Soln. Soln. (2:1 wt. 
Based on by wt. solids 
44.1% by wt. 
ratio) 40% by 
Kaolin Solids 
(cps) solids (cps) 
wt. solids (cps) 
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0.40 500 2750 60 
0.45 58 700 31 
0.50 30 155 20 
0.55 36 40 30 
0.60 48 32 46 
0.65 62 36 58 
0.70 80 44 78 
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.sup.1 Mol. wt. = 4,200 
.sup.2 Grade No. 50 
As the data in Table I indicate, use of the binary mixtures to reduce 
viscosity of kaolin slurries is in most instances far superior to the use 
of each component alone. 
The following Table II demonstrates a major advantage resulting from use of 
the present invention, viz., the efficacy of the binary compositions over 
a period of time and at elevated temperatures. 
TABLE II 
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VISCOSITY STABILITY OF 58% BY WEIGHT SOLIDS 
KAOLIN SLURRIES (OVEN TEMPERATURE = 120.degree. F.) 
% Dispersant 
% Solids in 
Brookfield 
Brookfield Visc. 
Solids on 
Dispersant 
Visc. Before 
After 14 Days Ag- 
Slurry Visc. 
Dispersant Clay Solids 
Soln. Aging (cps) 
ing at 120.degree. F. (cps) 
Change 
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Na polyacrylate.sup.1 
0.50 43.0 50 60 Increase 
Colloid 211.sup.2 
0.50 43.0 50 80 Increase 
(Na polyacrylate) 
Sodium silicate 
0.50 47.3 45 65 Increase 
No. 52 
Sodium silicate 
0.50 44.1 45 170 Increase 
No. 50 
Na polyacrylate.sup.1 / 
0.50 40.0 45 40 Decrease 
sodium silicate.sup.3 mixture 
1:0.50 wt. ratio 
__________________________________________________________________________ 
.sup.1 Mol. wt. 4200? 
.sup.2 Mol wt. 3180? 
.sup.3 Grade No. 50 
The above data demonstrate that the binary mixtures of this invention, in 
contrast to each component alone, result in viscosity stability of the 
kaolin slurry over a period of time and at elevated temperatures. 
While the invention has been described with reference to certain specific 
embodiments thereof, it is understood that it is not to be so limited 
since alterations and changes may be made therein which are within the 
full intended scope of the appended claims.