Note: Descriptions are shown in the official language in which they were submitted.
21 791 1 6
- A process for the production of Paper
The present invention relates to a process for the
production of paper and more particularly to a process in
which a freshly prepared mixture of an aluminium compound and
anionic inorganic particles are added to a papermaking stock
in order to improve drainage and retention.
It is well-known in the papermaking art to use additive
systems of drainage and retention aids consisting of two or
more components which are added to the stock in order to
facilitate drainage and to increase adsorption of fine
particles onto the cellulose fibres so that they are retained
with the fibres. Systems comprising aluminium compounds and
anionic inorganic particles are well-known and usually these
components are used in conjunction with organic polymers, in
particular cationic polymers. Examples of anionic inorganic
particles widely used as for drainage and retention purposes
include silica-based particles and smectite clays, which have
proved to be very efficient.
The components of drainage and retention aid systems are
normally added separately to the stock. It is further known to
use drainage and retention aids comprising reaction products
of aluminium compounds and anionic inorganic particles. U.S.
Pat. Nos. 4,927,498 and 5,368,833 disclose aluminium-modified
silica particles obtained by reaction of silica particles with
aluminates. The latter patent discloses that the effect of
drainage and retention aids comprising cationic polymer and
aluminium-modified silica particles is enhanced when there is
also added to the stock an additional aluminium compound, e.g.
any of those conventionally used in papermaking.
According to the present invention it has been found
that it is possible to improve drainage and/or retention in
papermaking by mixing an aluminium compound with anionic
inorganic particles just prior to the addition to the stock.
More specifically, the present invention relates to a process
for the production of paper from an aqueous suspension of
cellulose-containing fibres, and optional fillers, which
comprises adding an aluminium compound and anionic inorganic
particles to the suspension, forming and draining the suspen-
sion on a wire, wherein the aluminium compound and anionic
2 1 791 1 6
.
inorganic particles are mixed immediately prior to the
addition to the suspension.
Thus in accordance with the invention there is
provided a process for the production of paper from a
suspension of cellulose containing fibres, wherein an
aluminium compound and anionic inorganic particles are
added to the suspension and the suspension is formed and
drained on a wire, characterised in that the aluminium
compound and anionic inorganic particles are mixed
immediately prior to addition to the suspension and in that
said anionic inorganic particles are selected from
colloidal silica, polysilicic acid, colloidal aluminium-
modified silica having a specific surface area up to 1000
m2/g, colloidal aluminium silicate having a specific
surface area up to 1000 m2/g, clays of the smectite type,
or mixtures thereof.
The process according to the present invention
results in improved drainage and/or retention in
papermaking as compared to processes in which the
components are separately added to the stock as well as
processes in which the components are reacted or mixed some
time before the addition. Thus, by applying the present
process the speed of. the paper machine can be increased and
lower dosage of the components can be used to give a
corresponding effect, thereby leading to economic benefits
and an improved papermaking process.
- 2 1 79 1 1 6
The process of the present invention comprises pre-
mixing the aluminium compound and anionic inorganic particles
immediately prior to the addition to the stock. Hereby is
meant that the contact time, i.e. the time from mixing these
components to adding the mixture formed to the stock, should
be as short as possible. Suitably, this period of time is less
than 4 minutes and preferably less than 2 minutes. This can be
effected by rapidly mixing an aqueous phase of aluminium
compound with an aqueous phase of anionic inorganic particles
and then incorporating the resulting aqueous mixture into the
stock.
According to a preferred embodiment of the invention, an
aqueous stream of aluminium compound is brought into contact
with an aqueous stream of anionic inorganic particles, where-
upon the resulting aqueous stream is introduced into the sus-
pension. This can be effected by directing separate streams of
the components to be mixed towards each other, allowing them
to impinge on each other and introducing the mixture so formed
into the stock. Suitably mixing is carried out under turbulent
flow conditions which promotes more intensive and rapid mixing
of the streams. The streams can be mixed by means of any
mixing device having at least two inlets into which separate
streams of the components to be mixed are supplied and having
at least one outlet through which the resulting mixture is
passed and subsequently introduced into the stock. By applying
the stream mixing process, in particular when using a mixing
device of the above-mentioned type, the components of the
21 791 1 6
resultant stream can be brought into intimately contact for a
period of time less than one minute prior to the incorporation
into the stock, which has been found to be very effective,
especially contact times of less than about 30 seconds and
suitable less than about 15 seconds. The stream mixing
embodiment is further advantageous from a practical point of
view and confers operational benefits. Mixing devices that can
be used to carry out the present process are known in the art,
even though intended for other types of components and for
other purposes. For example, use can be made of mixing pipes
that are essentially Y or T shaped, whereby the discrete
streams of the components can be passed in essentially oppo-
site directions in order to impinge on each other, whereupon
the resultant mixture is passed into the stock. Differently
shaped mixing pipes as well as static mixers can also be used.
Anionic inorganic particles that can be used according
to the invention include silica-based particles, clays of the
smectite type, and mixtures thereof. It is preferred that the
particles are in the colloidal range of particle size. Silica-
based particles, i.e. particles based on SiO2, includingcolloidal silica, different types of polysilicic acid,
colloidal aluminium-modified silica, colloidal aluminium
silicate, and mixtures thereof, are preferably used, either
alone or in combination with other types of anionic inorganic
particles. Suitable silica-based particles and methods for
their preparation are disclosed in U.S. Pat. Nos. 4,388,150;
4,954,220; 4,961,825; 4,980,025; 5,127,994; 5,368,833; and
5,447,604 as well as International Patent Publications WO
94/05596 and WO 95/23021.
Silica-based particles suitably have a particle size
below about 50 nm, preferably below about 20 nm and more
preferably in the range of from about 1 to about 10 nm. The
specific surface area of the silica-based particles is suit-
ably above 50 m2/g and preferably above 100 m2/g. Generally,the silica-based particles can have a specific surface area up
to 1700 m2/g. The colloidal silica suitably has a specific
surface area up to 1000 m2/g and preferably up to 950 m2/g.
Suitably the colloidal aluminium-modified silica and colloidal
21 791 1 6
aluminium silicate also have a specific surface area up to
1000 m2/g and preferably up to 950 m2/g. The specific surface
area can be measured by means of titration with NaOH according
to the method described by Sears in Analytical Chemistry
28(1956):12, 1981-1983.
According to a preferred embodiment of the invention,
the anionic inorganic particles are thus silica-based
particles having a specific surface area within the range of
from 50 to 1000 m2/g and preferably from 100 to 950 m2/g.
Suitable silica-based particles of this type are generally
supplied in the form of aqueous sols, for example as disclosed
in U.S. Pat. Nos. 4,388,150 and 4,980,025. The latter patent
discloses sols comprising particles having at least a surface
layer of aluminium silicate or aluminium-modified silicic acid
containing silicon atoms and aluminium atoms in a ratio of
from 9.5:0.5 to 7.5:2.5.
According to another preferred embodiment of the present
invention, use is made of a silica sol having an S-value in
the range of from 8 to 45~, preferably from 10 to 30~,
containing silica particles having a specific surface area in
the range of from 750 to 1000 m2/g, preferably from 800 to 950
m2/g, which are surface-modified with aluminium to a degree of
from 2 to 25~ substitution of silicon atoms, as disclosed in
U.S. Pat. No. 5,368,833. The S-value can be measured and
calculated as described by Iler ~ Dalton in J. Phys. Chem.
60(1956), 955-957. The S-value indicates the degree of aggre-
gate or microgel formation and a lower S-value is indicative
of a higher degree of aggregation.
According to another preferred embodiment of the present
invention, use is made of a polysilicic acid having a high
specific surface area, suitably above about 1000 m2/g. In the
art, polysilicic acid is also referred to as polymeric silicic
acid, polysilicic acid microgel and polysilicate microgel,
which are all encompassed by the term polysilicic acid.
Suitably the polysilicic acid have a specific surface area
within the range of from 1000 to 1700 m2/g and preferably from
1050 to 1600 m2/g. Polysilicic acids that can be used
according to the present invention include those disclosed in
U.S. Pat. Nos. 4,388,150; 4,954,220; and 5,127,994.
21 791 1 6
The polysilicic acid can be prepared by acidifying a
dilute aqueous solution of alkali metal silicate, such as
potassium or sodium water glass, preferably sodium water
glass, which suitably contains about 0.1 to 6 % by weight of
SiO2. Acidification can be carried out in many ways, for
example by using acid ion exchange resins, mineral acids, e.g.
sulphuric acid, hydrochloric acid and phosphoric acid, acid
salts or acid gases, suitably ion-~ch~ngers or mineral acids
or a combination thereof. Where more stable polysilicic acids
are desired, it is preferred to use acid ion-exchangers. The
acidification is suitably carried out to a pH within the range
of from l to 11 and preferably to a pH within the acid range
of from 2 to 4. According to another preferred aspect of the
invention, partial acidification is carried out to a pH of
from about 7 to 10, thereby forming a polysilicic acid which
is usually termed activated silica. In comparison with sols
comprising silica-based particles of lower specific surface
area, aqueous polysilicic acids are usually considerably less
stable. Due to this, polysilicic acids should not be stored
for too long times but a certain aging, e.g. for a day or a
couple of days at a concentration of not more than about 4 to
5% by weight, can result in an improved effect. In accordance
with another preferred embodiment of the invention, the
aqueous polysilicic acid to be used is produced at the
location of intended use. This mode of operation can be
applied in the whole acidified pH range of 1 to 11, even when
using less stable polysilicic acids in the pH range of 4 to 7
which usually gel rapidly.
Clays of the smectite type that can be used in the
process of the present invention are known in the art and
include naturally occurring, synthetic and chemically treated
materials. Examples of suitable smectite clays include
montmorillonite/bentonite, hectorite, beidelite, nontronite
and saponite, preferably bentonite and especially such which
after swelling preferably has a surface area of from 400 to
800 m2/g. Suitable bentonites and hectorites are disclosed in
U.S. Pat. Nos. 4,753,710 and 5,071,512, respectively.
21 791 1 6
~_ 7
Suitable mixtures of silica-based particles and smectite clays,
preferably natural bentonites, are disclosed in International
Patent Publication WO 94/05595 where the weight ratio of
silica-based particles to clay particles can be within the
range of from 20:1 to 1:10, preferably from 6:1 to 1:3.
Aluminium compounds that can be used in the process of
the invention are known in the art and include alum, alumina-
tes, aluminium chloride, aluminium nitrate and polyaluminium
compounds, such as polyaluminium chlorides, polyaluminium
sulphates, polyaluminium compounds containing both chloride
and sulphate ions, polyaluminium silicate-sulphates, and
mixtures thereof. The polyaluminium compounds may also contain
other anions, for example anions from phosphoric acid, organic
acids such as citric acid and oxalic acid. Suitable aluminium
compounds are disclosed in U.S. Pat. No. 5,127,994. According
to a preferred embodiment of the invention, the aluminium
compound is an aluminate, e.g. sodium or potassium aluminate,
preferably sodium aluminate. According to another preferred
embodiment of the invention, use is made of an acid aluminium
compound which thus can be selected from alum, aluminium chlo-
ride, polyaluminium compounds and mixtures thereof.
The pre-mix used in the present process can be formed by
admixing the anionic inorganic particles with aluminium
compound in a weight ratio within the range of from 100:1 to
1:1. Suitably the weight ratio anionic inorganic particles to
aluminium compound is within the range from 50:1 to 1.5:1 and
preferably from 20:1 to 2:1.
The amount of anionic inorganic particles added to the
suspension may vary within wide limits depending on, for
example, the type of particles used. The amount is usually at
least 0.01 kg/ton, often at least 0.05 kg/ton, calculated as
dry particles on dry fibres and optional fillers. The upper
limit can be 10 and suitably is 5 kg/ton. When using silica-
based particles, the amount suitably is within the range of
from 0.05 to 5 kg/ton, calculated as SiO2 on dry stock system,
preferably within the range of from 0.1 to 2 kg/ton.
The amount of aluminium compound added to the suspension
may depend on the type of aluminium compound used and on other
effects desired from it. It is for instance well-known in the
21 791 1 6
art to utilize aluminium compounds as precipitants for rosin-
based sizes. The amount of aluminium compound mixed with the
anionic organic particles to form the pre-mix and subsequently
added to the stock should suitably be at least 0.001 kg/ton,
calculated as Al203 on dry fibres and optional fillers.
Suitably the amount is within the range of from 0.01 to 1
kg/ton and preferably within the range from 0.05 to 0.5
kg/ton. If required, additional aluminium compounds can be
added to the stock at any position prior to draining. Examples
of suitable additional aluminium compounds include those
defined above.
The concentrations of the aqueous phases of aluminium
compound and anionic inorganic particles to be mixed according
to the invention can be varied over a broad range and may
depend on the type of components used. Solutions of aluminium
compound can have a concentration of at least 0.01% by weight,
calculated as Al203, and the upper limit is usually about 25%
by weight. Suitably the concentration is within the range of
from 0.1 to 10 and preferably from 0.2 to 5% by weight.
Aqueous phases of anionic inorganic particles to be used for
mixing can have a concentration of at least 0.01% by weight,
and the upper limit is usually about 20% by weight. Suitably
the amount is within the range of from 0.1 to 15 and prefer-
ably from 0.5 to 10% by weight. The freshly prepared mixture,
the pre-mix, can have a dry content of at least 0.01~ by
weight, and the upper limit is usually about 20% by weight.
Suitably the dry content is within the range of from 0.05 to
10 and preferably from 0.1 to 5% by weight.
The freshly prepared mixture of aluminium compound and
anionic inorganic particles according to the invention is
preferably used in conjunction with at least one organic
polymer acting as a drainage and/or retention aid which can be
selected from anionic, amphoteric, nonionic and cationic
polymers and mixtures thereof. The use of such polymers as
drainage and/or retention aids is well-known in the art.
Suitably at least one cationic or amphoteric polymer is used,
preferably cationic polymer. The polymers can be derived from
natural or synthetic sources, and they can be linear or
branched. Examples of suitable polymers include anionic,
21 791 1 6
`_
amphoteric and cationic starches, guar gums and acrylamide-
based polymers, as well as poly(diallyldimethyl ammonium
chloride), polyethylene imines, polyamines, polyamidoamines,
melamine-formaldehyde and urea-formaldehyde resins. Cationic
starch and cationic polyacrylamide are particularly preferred
polymers. When using the pre-mix of the present process in
combination with an organic polymer as mentioned above, it is
further preferred to use at least one anionic trash catcher
(ATC) . ATC' s are known in the art as neutralizing agents for
detrimental anionic substances present in the stock. Hereby
ATC'S can enhance the efficiency of the components used in the
present process. Thus, further suitable combinations of
polymers that can be co-used with the pre-mix of the present
invention include ATC in combination with high molecular
weight polymer, e.g. cationic starch and/or cationic poly-
acrylamide, anionic polyacrylamide as well as cationic starch
and/or cationic polyacrylamide in combination with anionic
polyacrylamide. Suitable ATC's include cationic polyelectro-
lytes, especially low molecular weight highly charged cationic
organic polymers such as polyamines, polyethyleneimines, homo-
and copolymers based on diallyldimethyl ammonium chloride,
(meth)acrylamides and (meth)acrylates. Even if arbitrary order
of addition can be used, it is preferred to add the polymer or
polymers to the stock before the mixture of aluminium compound
and anionic inorganic particles. Normally, ATC's are added to
the stock prior to other polymers.
The amount of organic polymer can be varied over a broad
range depending on, among other things, the type of polymer or
polymers used and other effects desired from it. Usually, use
is made of at least 0.005 kg of polymer per ton of dry fibres
and optional fillers. For synthetic cationic polymers, such as
for example cationic polyacrylamide, amounts of at least 0.005
kg/ton are usually used, calculated as dry on dry fibres and
optional fillers, suitably from 0.01 to 3 and preferably from
0.03 to 2 kg/ton. For cationic polymers based on carbohydra-
tes, such as cationic starch and cationic guar gum, amounts of
at least 0.05 kg/ton, calculated as dry on dry fibres and
optional fillers, are usually used. For these polymers the
amounts are suitably from 0.1 to 30 kg/ton and preferably from
2179116
-
1 to 15 kg/ton.
The improved retention and dewatering effect with the
system of the invention can be obtained over a broad stock pH
range. The pH can be within the range from about 3 to about
10. The pH is suitably above 3.5 and preferably within the
range of from 4 to 9.
The process according to the invention can be used for
producing cellulose fibre containing products in sheet or web
form such as for example pulp sheets and paper. It is prefer-
red that the present process is used for the production of
paper. The term "paper" as used herein of course include not
only paper and the production thereof, but also other sheet or
web-like products, such as for example board and paperboard,
and the production thereof.
The process according to the invention can be used in
the production of sheet or web-like products from different
types of suspensions containing cellulosic fibres and the
suspensions should suitably contain at least 50% by weight of
such fibres, based on dry substance. The suspensions can be
based on fibres from chemical pulp, such as sulphate and
sulphite pulp, thermomechanical pulp, chemo-thermomechanical
pulp, refiner pulp or groundwood pulp from both hardwood and
softwood, and can also be used for suspensions based on
recycled fibres. The suspension can also contain mineral
fillers of conventional types, such as for example kaolin,
titanium dioxide, gypsum, talc and both natural and synthetic
calcium carbonates. The stock can of course also contain
papermaking additives of conventional types, such as wet-
strength agents, stock sizes based on rosin, ketene dimers or
alkenyl succinic anhydrides, and the like. The present
invention makes it possible to improve the retention of such
additives, which means that further benefits can be obtained,
for example improved sizing and wet strength of the paper.
The invention is further illustrated in the following
Examples which, however, are not intended to limit same. Parts
and ~ relate to parts by weight and ~ by weight, respectively,
unless otherwise stated.
21 791 1 6
11
Example 1
In the following tests the dewatering effect was
evaluated by means of a Canadian Standard Freeness (CSF)
Tester, which is the conventional method for characterizing
dewatering or drainage capability according to SCAN-C 21:65.
The stock used was based on 60:40 bleached birch/pine
sulphate to which 0.3 g/l of Na2SO4 10H2O was added. Stock
consictency was 0.3% and pH 7Ø Additions of chemicals were
made to a baffled Britt Dynamic Drainage Jar with a blocked
outlet at a stirring speed of 1000 rpm. Without addition of
chemicals the stock showed a freeness of 280 ml. In the tests,
use was made of a cationic polymer, Raisamyl 142*, which is a
conventional medium-high cationized starch having a degree of
substitution of 0.042, hereafter designated CS, which was
added to the stock in an amount of 10 kg/ton, calculated as
dry on dry stock system. When adding solely CS to the stock a
freeness of 280 ml was obtained. The aluminium compound used
was sodium aluminate, hereafter designated NaAl, which was
added to the stock in amounts defined below, calculated as
Al2O3 per ton of dry stock system. The anionic organic
material used was a silica sol of the type disclosed in U.S.
Pat. No. 4,388,150. The sol was alkali-stabilized to a molar
ratio of SiO2:Na2O of about 40 and contained silica particles
with a specific surface area of about 500 m2/g, hereafter
designated P1. The anionic inorganic particles were added to
the stock in amounts defined below, calculated as dry per ton
of dry stock system.
The process according to the invention was carried out
by adding the cationic polymer to the stock followed by
stirring for 30 seconds, adding the pre-mix to the stock
followed by stirring for 15 seconds, and then trans~erring the
stock to the CSF Tester. The pre-mix used was prepared by
feeding an aqueous stream of the aluminium compound containing
0.5~ by weight of Al2O3 and an aqueous stream of anionic
inorganic particles containing 0.5~ by weight of particles to
a mixing device equipped with two inlets and one outlet. In
the mixing device the separate streams were intimately mixed
whereupon the resultant stream was introduced into the stock.
The streams of the pre-mix were brought into contact for less
*~rade-mark
2 1 79 1 1 6
12
than about 5 seconds prior to addition to the stock.
Comparisons tests were conducted by adding the first
component + second component + third/last component to the
stock during 45 seconds with stirring following each addition,
and with stirring for 15 seconds following the last addition,
and then the stock was transferred to the CSF Tester. The
components are defined in Table 1.
Table 1
Test Order of adding NaAl Pl CSF
10 No the comPonents kq/ton kq/ton ml
1 NaAl + CS + Pl 0.2 1.0 635
2 NaAl + CS + P1 0.3 1.0 635
3 CS + NaAl + P1 0.3 1.0 635
4 CS + P1 + NaAl 0.3 1.0 630
CS + Pre-mix 0.2 1.0 650
6 CS + Pre-mix 0.3 1.0 655
As is evident from Table 1, the process utilizing a pre-
mix of sodium aluminate and silica-based particles according
to the invention improved the dewatering over Tests 1 to 4 in
which the components were separately added to the stock.
Exam~le 2
In this Example, the procedure according to Example 1
was followed in order to test a sol of silica-based particles
of the type disclosed in U.S. Pat. No. 5,368,833. The sol had
an S-value of about 25~ and contained silica particles with a
specific surface area of about 900 m2/g which were surface-
modified with aluminium to a degree of 5%. This type of
particles is designated P2.
Table 2
30 Test Order of adding NaAl P2 CSF
No the comPonents kq/ton kq/ton ml
1 NaAl + CS + P2 0.1 1.0 670
2 NaAl + CS + P2 0.2 1.0 675
3 NaAl + CS + P2 0.3 1.0 67S
4 CS + Pre-mix 0.1 1.0 685
CS + Pre-mix 0.2 1.0 695
~ 6 CS + Pre-mix 0.3 1.0 695
As can be seen from Table 2, the dewatering effect was
improved when applying the pre-mix process of this invention.
21 791 1 6
ExamPle 3
In this Example, the procedure according to Example 1
was followed in order to test a suspension of the type
disclosed in International Patent Publication WO 94/05595. The
5 suspension contained silica-based particles of the type P2
according to Example 2 and natural bentonite in a weight ratio
of 2: 1. This type of particles is designated P3.
Table 3
Test Order of adding NaAl P3 CSF
10 No the components kq/ton kg/ton ml
1 NaAl + CS + P3 0. 2 1.0 590
2 NaAl + CS + P3 0.3 1.0 595
3 CS + NaAl + P3 0.3 1.0 585
4 CS + Pre-mix 0.2 1.0 615
CS + Pre-mix 0.3 1.0 620
The process according to the present invention showed
improved drainage over Tests 1 to 3 in which the components
were separately added to the stock.
Example 4
In this Example, a comparison was made in a manner
similar to Example 1 except that polyaluminium chloride,
designated PAC, was used as the aluminium compound and
polysilicic acid was used as the anionic inorganic particles.
The polysilicic acid was prepared by acidification of a sodium
silicate solution having a molar ratio of Si2O:Na2O of 3.5:1
and SiO2 content of 5.5~ by weight to a pH of about 2. 5 by
means of a cation exchange resin saturated with hydrogen ions.
The obtained polysilicic acid was aged for about 30 hours and
then diluted with deionized water to a concentration of 0.5
by weight of SiO2. The polysilicic acid so formed had a speci-
fic surface area of 1200 m2/g and is hereafter designated P4.
The stock used in this Example was prepared from the
stock according to Example 1 to which chalk was added in an
amount of 30~, based of dry fibres. The stock so obtained had
a pH of 7.5 and showed a freeness of 330 ml. The solution of
aluminium compound contained 0.25~ by weight of Al2O3 and the
amount of aluminium compound added to the stock was calculated
as Al2O3 per ton of dry stock system.
2t791i6
Table 4
Test Order of adding PAC P4 CSF
No the components kq/ton kg/ton ml
1 CS + P4 - 1.0 535
2 CS + PAC + P4 0.25 1.0 595
3 PAC + CS + P4 0.25 1.0 570
4 PAC + CS + P4 0.33 1.0 580
CS + Pre-mix 0.16 1.0 600
6 CS + Pre-mix 0.25 1.0 620
7 CS + Pre-mix 0.25 1.5 615
8 CS + Pre-mix 0.33 1.0 605
The pre-mix process according to the invention showed
improved effect over the process with separate additions.
Exam~le 5
In this Example, the procedure according to Example 4
was followed except that the aluminium compound used was alum.
Table 5
Test Order of adding Alum P4 CSF
No the components kq/ton kq/ton ml
1 Alum + CS + P4 0.33 1.0 600
2 CS + Alum + P4 0.33 1.0 590
3 CS + Pre-mix 0.23 1.0 610
4 CS + Pre-mix 0.29 1.0 615
CS + Pre-mix 0.35 1.0 620
As is evident from the Table, the pre-mix process
resulted in improved dewatering.
Example 6
In this Example, the procedure according to Example 4
was essentially followed except that the aluminium compound
used was sodium aluminate. The process of the invention was
further compared with a process disclosed in U.S. Pat. Nos.
4,927,498 and 5,176,891 using a polyaluminosilicate. The poly-
aluminosilicate was prepared by adding a sodium aluminate
solution containing 2.5% by weight of Al2O3 to 1~ by weight of
aqueous polysilicic acid, prepared and aged as described in
Example 4, to give a molar ratio of Al2O3 to SiO2 of 13:87,
whereupon the product was diluted to a concentration of 0.5~
by weight. This product is designated PAS. The time from
bringing the sodium aluminate solution and aqueous polysilicic
21 791 1 6
acid into contact followed by dilution to introducing the
product so formed into the stock was 10 minutes. In Table 6,
molar ratio refers to molar ratio of A12O3 to SiO2.
Table 6
Test Order of adding Molar PAS NaAl P4 CSF
No the components ratio kq/ton kq/ton kq/ton ml
1 NaAl + CS + P4 20:80 0.25 1.0 560
2 CS + NaAl + P4 20:80 0.25 1.0 580
3 CS + PAS 13:87 1.08 580
4 CS + Pre-mix 13:87 0.08 1.0 610
CS + Pre-mix 13:87 0.16 1.0 640
6 CS + Pre-mix 13:87 0.25 1.5 650
7 CS + Pre-mix 20:80 0.25 1.0 645
8 CS + Pre-mix 25:75 0.33 1.0 630
Pre-mixing sodium aluminate and polysilicic acid
according to the present process provided improved dewatering
in comparison with the process using separate additions as
well as the process using polyaluminosilicate.
