Note: Descriptions are shown in the official language in which they were submitted.
~ 3
- PATENT 3259A
CATIONIC PROCESSING OF MINERAL ORES
Related Applications
This application is related to USSN (Case 3259B),
filed concurrently.
Field of the Invention
This invention relates to the art of upgrading mineral
ores by processing which includes treating an aqueous
suspension of the ore with a dispersant before carrying out
steps to produce refined mineral products. In particular, the
invention relates to processing aqueous suspensions of ores to
provide refined products using cationic dispersants throughout
the processing.
Background of the Invention
Minerals almost invariably occur in nature in ores which
contain a variety of materials in addition to the particular
mineral constituent that is to be marketed. The nondesired
mineral ma~ter may be, for example, an impurity or a particle
size fraction of-the desired mineral that is too coarse (or too
fine) for an intended use. Especially where the desired
mineral material is very finely divided, for example, a
material having an appreciable content of particles finer than
050489 - 1 - 3259A
o~
2 micrometers, it is conventional to disperse the ore in water
to form an aqueous pulp before attempting to upgrade
(beneficiate) the ore. Dispersion (deflocculation) is
practiced to fluidize mineral pulps and it enhances the
separation of individual mineral particles from others by
increasing the electrical charge on the individual particles.
Anionic dispersants such as condensed phosphates and
sodium silicate are frequently used to fluidize ore pulps
containing negatively charged mineral particles at near neutral
to mildly alkaline pH values (e.g., pH 6-9) without the need to
consider the effect of using such dispersants on subsequent
processing. An exception is the case of finely mineralized
ores such as kaolin clay crudes in which chemical treatment
after dispersion is frequently essential and the presence of
the particular dispersant used to upgrade the ore may result in
undesirable interaction between dispersant and subsequently or
previously added reagents. See, for example, U.S. 3,594,203
(Sawyer et al).
Naturally-occurring sources of kaolin, generally known as
kaolin crudes, such as those mined in Georgia, U.S.A. and
Cornwall in England, are processed to recover upgraded kaolin
products. Many Georgia crudes contain well-crystallized finely
divided particles of kaolin having a median particle size of
about 1.5 micrometers in association with silica and silicate
impurities as well as colored ferruginous and titaniferous
impurities. Other commercially important Georgia crudes
contain less well-crystallized kaolin which are finer in
particle size, e.g., median size below 1 micrometer. The
Cornwall crudes typically contain only about 10% to 15% kaolin
which is coarser than the kaolin in the Georgia deposits. Vast
tonnages of such kaolin crudes are mined for the ultimate
050489 - 2 - 3259A
recovery of purified grades of kao~in having a higher
brightness and different particle size distribution than that
of the kaolin in the crude. The processing, frequently
referred to as "wet processing", almost invariably involves
crushing the kaolin crude, pulping the crushed crude in water,
removing coarse impurities (so-called grit), fractionating the
degritted crude to recover one or more fractions of desired
particle size distribution, bleaching to brighten one or more
of the fractions of kaolin, filtration and washing. In some
cases, additional upgrading to remove colored impurities by
flo.ation, selective flocculation and/or magnetic purification
is practiced and usually takes place before filtration. Such
additional upgrading also takes place when the clay is in the
form of a dispersed pulp.
When kaolin crudes are mixed in water without addition of
dispersant the resulting pulps are usually mildly acidic,
typically having a pH of 4-6 and the kaolin particles are
negatively charged. To the best of our knowledge, one or more
anionic dispersants are invariably added to a pulp of the crude
to create near neutral or mildly alkaline systems before
degritting and fractionation. ~hen these steps are followed by
bleaching with a reducing bleach, usually a hydrosulfite
(dithionite) salt, the previously dispersed alkaline pulp of
clay is first flocculated by adding an acid or alum to pH 3-5
because such bleaches are generally more effective at acidic pH
values and flocculation aids subsequent filtration. However,
the added acid or alum interacts with the dispersant to form
salts which are frequently deleterious to performance
properties of the kaolin product. After flocculation, the
bleached clay, in the form of a filter cake, must usually be
washed to reduce salt content. Filtration and washing add
considerably to the cost of processing. Subsequent processing
050489 - 3 - 3259A
depends on the form in which the puriEied kaolin is to be
supplied. So-called "predispersed grades" are usually
manufactured by adding a dispersant to the previously
flocculated clay to form a high solids slurry (e.g., 65-70%)
which is spray dried to provide a dry product containing a
dispersant. The production of slurried grades also entails the
addition of dispersant(s). Dispersant(s) added to previously
dispersed and flocculated clay are generally termed "secondary"
dispersants to distinguish them from dispersants used to
prepare ~ulps for degritting, fractionation, etc., which are
generally referred to as "primary" dispersants. Acid grades of
wet processed kaolins are produced without secondary dispersion
of acid-flocculated filtered clay.
The history of using alkali or negatively charged material
as primary dispersants for negatively charged clay dates at
least back to 1912 (U.S. Reissue Patent 14,583, Scherwin).
This patent teaches using "electrolytes containing ions of an
electric character which is the same as the character of the
part of the composite mass which it is desired shall remain in
suspension in sol-condition". This concept is pursued in
Scherwin's subsequent patent (U.S. 1,233,713), which discloses
fractional sedimentation of kaolin in a dispersed system. An
advance is reflected in U.S. 1,324,958 (Feldenheimer) in which
an acidic material is used to neutralize the alkaline
deflocculating agent and to floc the clay in order to settle
materials not ordinarily settled in a deflocculated
condition. Subsequent patents disclose particle size
fractionation of kaolin in dispersed state in centrifuges,
usually followed by flocculation by acid addition, filtration
and washing of the filter cake. A major advance in the
development of the kaolin industry was reflected in the
050489 - 4 - 3259A
establishment of a 2 micrometers particle size cut-off point
when fractionating kaolins to prepare paper coating clay and
the use of centrifuges to carry out t:he desired fractionation
of the crude clay. Crudes having a median particle size of 1.5
micrometers are conventionally classified in centrifuges to
recover premier coating grades (at least 90% by weight finer
than 2 micrometers) and coarse filler kaolin having a median
size of 4-6 micrometers. A major present use of kaolin crudes
is as a source of bleached minus 2 micrometers fractions of
kaolin clay supplied principally for the paper coating
industry.
The growth of the kaolin industries in the U.S. and abroad
has also generated many other innovations including the use of
a variety of primary dispersants, all anionic, and including
sodium silicates, silicate hydrosols, condensed phosphate
salts, polyacrylate salts, and "auxiliary" dispersants such as
sulfonates.
Similarly, the art of producing carbonate pigments and
fillers from naturally-occurring dolomitic and calcitic ores by
processes utilizing wet milling and wet particle size
classification has used anionic dispersants, exemplified by
sodium polyacrylates, added, for example, during grinding,
followed in some instances by flocculation. See, for example,
- U.S. 3,980,240 (Nott), U.S. 3,990,642 (Nott), and U.S.
4,165,840 (Lewis et al).
,., ~
The concept of using a negatively charged dispersant
(sodium silicate, mixtures thereof with sodium carbonate, or
hydrosols derived from sodium silicate) in the froth flotation
of kaolin has been extended to other finely mineralized
negatively charged mineral oxide and silicate ores, for
example, talc ores, tin (cassiterite) ores, (U.S. 3,915,391,
050489 - 5 - 3259A
6 ~ . ~
Mercade), fluorspar ores (U.S. 3,8~3,915, Mercade) and
scheelite (tungsten) ores, (U.S. 3,915,391, Mercade).
Cationic surfactants have been clisclosed as a means to
disperse various clays in organic liquids. See, for example,
U.S. 2,797,196, Dunn et al.
In accordance with U.S. 3,804,656, Kaliski, et al, a
negatively charged filler or pigment such as kaolin is
dispersed with a combination of nonionic and cationic surface
active agents at a strongly alkaline pH. The cationic material
is not added as a primary dispersant nor is it present during
wet processing. ! ' ~
U.S. 4,738,726, Pratt et al, discloses high bulking
pigments obtained by adding a cationic polyelectrolyte to
previously degritted and fractionated kaolin clay to partially
flocculate the clay. Anionic primary and secondary dispersants
are used and the cationic material is used to partially
flocculate, not to disperse the clay.
U.S. 4,210,488 (Reus et al) discloses addition of a
cationic polymer (polypiperidine halide) "absorbed" on a fine
particle carrier such as kaolin to improve the dry strength of
paper or to improve the effect of optical brighteners. The
absorbed polymer is said to create a positive charge on the
kaolin particles. The cationic material is not added during
wet processing of the carrier.
Numerous publications make reference to the addition of
cationic polyelectrolytes to paper coating composition
containing mineral pigments such as clay or calcium carbonate
to improve the coating structure by imparting a bulked
structure. See, for example, Coco, C.E., Soy Protein Latex
Interpolymers - Properties and Function, Preprints TAPPI
Coating Conference 1987.
050489 - 6 - 3259A
r-
EPA 281,134 (Weige) relates ta cationic pigment
dispersion, especially for producing paper coating
compositions, containing a pigment component, a cationised
polymer, which encloses the pigment particles as a protective
colloid, and optionally a cationic polymer and/or ammonium
compound as dispersant for the coated pigment particles. The
cationic polymer PVA increases the zeta potential of the
dispersion to the isoelectric point or into the cationic
region. The pigment can be ground or precipitated calcium
carbonate, (calcined) kaolin, TiO2, ZnO, satin white, aluminum
hydrosilicates or their mixtures.
In commonly assigned copending application USSN
filed concurrently herewith, cationically processed kaolin
crude of the type described in U.S. 3,586,523 (Fanselow et al)
is calcined to provide an improved high brightness, low
abrasion kaolin opacifying pigment useful for coating or
filling paper or an ingredient of paints or plastics. Our
copending patent application, USSN 07/309456 filed February 10,
1989, describes the use of cationic polymers and the like as
secondary dispersants for slurrying calcined kaolin pigments.
To the best of our knowledge, the prior art does not
disclose or suggest the use of cationics as primary dispersants
for kaolin or other ores.
Summary of the Invention
The present invention comprises a process for upgrading a
naturally-occurring ore containing negatively charged mineral
particles which features the use of a water-soluble organic
cationic primary dispersant and involves adding a sufficient
quantity of cationic dispersant, preferably a cationic
050489 - 7 - 3259A
polyelectrolyte, to an aqueous ore pu:Lp to impart a positive
electrical charge to the normally negative charged mineral
particles. The cationically dispersed pulp is then upgraded to
recover mineral particles or a desired portion thereof.
In the presently preferred embodiments, the invention is
directed to a novel method for upgrading kaolin clay crudes
wherein the crude is upgraded by wet processing in the presence
of a primary dispersant which is a cationic material used in
dispersant effective quantity, preferably at an acidic pH.
Pursuant to one aspect of the invention, the crude kaolin
clay is subjected to processing including degritting,
fractionation and bleaching with a hydrosulfite salt, all of
these steps being carried out while a pulp of the clay is
cationically dispersed at an acidic pH which, as mentioned, is
desirable for effective bleaching. Most preferably, anionic
dispersants or added basic materials are not present during any
of these steps. The processing takes advantage of the fact
that the cationically dispersed slurry of degritted
fractionated kaolin is already acidic when the clay is in a
condition suitable for bleaching. In conventional kaolin
processing, the anionically dispersed clay is flocculated with
acid before bleaching and the added acid interacts with the
primary anionic dispersant(s) to form salts. Since, in the
present invention, the kaolin is already at an acid pH, no
separate acid addition is required. Thus, the process of the
present invention would be expected to result in a bleached
kaolin slurry with a lower quantity of deleterious soluble
salts. Further, in practice of our invention the clay is
dispersed and therefore bleaching can be carried out at solids
higher than those that can be effectively employed when
bleaching flocculated slurries.
050489 - 8 - 3259A
The pulp of fractionated (or fractionated and bleached)
clay may then be spray dried to produce a dry kaolin product
which, when added to water, results in a cationically dispersed
clay product. A small amount of additional cationic dispersant
may be required before spray drying.
When carried out at high solids, such processing avoids
the need to employ filtration and washing steps which add
significantly to the cost of the conventional wet processing of
kaolin crudes.
In another embodiment, slurries of the cationically
dispersed acidic slip of bleached fine clay, wet processed in
accordance with this invention at lower solids, is flocculated
by adding an anionic material which neutralizes the cationic
dispersant. The flocced clay system is filtered to produce a
filter cake which is washed and then fluidized by adding a
secondary dispersant which may be either cationic (to produce
an acidic cationically dispersed high solids slurry of
beneficiated clay intended for shipment in that form) or
anionic (to produce an anionically dispersed high solids slurry
of anionically dispersed clay intended for shipment in that
form.)
The accompanying figure illustrates embodiments for
upgrading kaolin crude, all utilizing a cationic material for
primary dispersion. One embodiment results in cationically
predispersed dry clay (A); another results in a high solids
slurry of cationically dispersed clay (~); a third results in a
high solids slurry of anionically predispersed dry clay (C);
and a fourth results in a high solids slurry of anionically
dispersed clay (D). The term "predispersed" is used herein in
the conventional sense, i.e., a dry product which when mixed
with water results in a slurry in which the kaolin particles
are in a dispersed condition without further addition of
dispersant.
050489 - 9 - 3259A
Detailed DescriDtion of P~efe!rred Embodiments
This invention is described in connection with its utility
in upgrading kaolin crudes. The figure illustrates the
processing steps used to produce various cationically processed
kaolin pigments that result in cationic as well as anionic
pigments.
The process of the present invention is conveniently
carried out by adding a dispersant effective amount of one or
more cationic materials to the required amount of water for the
desired solids in a vessel equipped with a stirrer. Once the
cationic dispersant has dissolved, the crushed kaolin crude is
added slowly with sufficient agitation to give a well dispersed
fluid suspension. If necessary, the slurry may be passed
through a sieve or other conventional degritting apparatus such
as a "sandbox" to remove undispersed aggregates or coarse
impurities.
A crude kaolin cationically dispersed and degritted at a
high solids level of 55% to 65% may be further upgraded at high
solids by subsequent centrifugation steps to classify the
kaolin into more desirable particle size fractions. Since the
cationically dispersed kaolin slurries are at an acidic pH
ranging from 3.0 to 5.0, reducing bleaches such as sodium
dithionite may be added directly, using the same quantities
used in conventional anionic processing systems which normally
range from 4 lb. to 15 lb./ton active bleach (based on the
weight of the dried kaolin in the slurry.) Bleaching improves
the color properties of kaolin pigments. The kaolin slurry is
then spray dried directly after bleaching thereby eliminating a
costly filtration step necessary in low solids processing. The
spray dried material is a cationically predispersed hydrous dry
kaolin (PRODUCT A in the figure) product. When Product A is
050489 - 10 - 3259A
added to a bleached slurry of cati~nically processed clay to
increase the solids con_ent, the resu:Lt is a high solids (above
50%) cationically dispersed hydrous kaolin slurry product with
a pH ranging from 3.0 to 5.0 (PRODUCT B in the figure).
As shown in the accompanying figure, pigments similar to
those processed at high solids to produce A and B, may also be
produced by a low solids process, ranging from 20% to 30%
slurry solids; however, a slurry filtration step is necessary
to increase the solids content prior to spray drying or to
produce a high solids cationically dispersed hydrous kaolin
slurry.
Anionic pigments can be produced from cationically
processed kaolin by adding anionic dispersing agents after the
bleaching step. To prepare such pigments, appropriate anionic
dispersing agents such as alkali silicates tsodium silicate),
sodium polyacrylates, tetrasodium pyrophosphate, etc. may be
added to the cationic slurries individually or in various
combinations in amounts adequate to render a charge reversal of
the pigment to negative. The addition of anionic materials to
effect charge reversal may be carried out using either low or
high solids slurries. When added to high solids slurry a
costly filtration step is eliminated and the slurry is sent
directly to the spray drier which produces a dry anionically
predispersed hydrous kaolin product (PRODUCT C in the
figure). In low solids processing, sufficient anionic
dispersant is added to flocculate the slurry which is then
filtered with subsequent water washing of the filtercake. The
filtercake is redispersed with a secondary dispersant (anionic)
to produce a high solids anionically dispersed slurry of
hydrous kaolin (PRODUCT D in the figure).
Presently preferred primary cationic dispersants (or
secondary cationic dispersants, when used) are water soluble
050489 ~ 3259A
~ J
cationic polyelectrolytes. See, f3r example, U.S. 4,174,279.
Cationic polyelectrolytes are characterized by a high density
of positive charge. Positive charge density is calculated by
dividing the total number of positive charges per molecule by
the molecular weight. Generally the high charge density of
polyelectrolytes exceeds lX10-3 and such materials do not
contain negative groups such as carboxyl or carbonyl groups.
In addition to the alkyl diallyl quaternary ammonium salts,
other quaternary ammonium cationic polyelectrolytes are
obtained by copolymerizing aliphatic secondary amines with
epichlorohydrin. See U.S. Pat. No. 4,174,279. Still other
water-soluble cationic polyelectrolytes are poly(quaternary
ammonium) polyester salts that contain quaternary nitrogen in a
polymeric backbone and are chain extended by the groups. They
are prepared from water-soluble poly(quaternary ammonium salts)
containing pendant hydroxyl groups and bifunctionally reactive
chain extending agents; such polyelectrolytes are prepared by
treating an N, N, N(l), N(l) tetraalkylhydroxyalkylenediamine
and an organic dihalide such as a dihydroalkane or a
dihaloether with an epoxy haloalkane. Such polyelectrolytes
and their use in flocculating clay are disclosed in U.S. Pat.
No. 3,663,461. Other water soluble cationic polyelectrolytes
are polyamines. Polyamines are usually supplied commercially
under trade designations; chemical structure and molecular
weight are not provided by the suppliers.
The aforementioned cationic dispersants are known when
used at appropriate dosages to partially flocculate negatively
charged clays. See, for example, U.S. 4,738,726 (Pratt et.
al.), and references cited therein. It should be noted that as
incremental dosages of such cationic materials are added to
anionically charged particles, the initial effect is that of
flocculation. As dosages increase beyond the levels at which
050489 - 12 - 3259A
flocculation occurs, dispersion (de-flocculation) occurs and the
charge on the particles becomes positive. Charge may be
determined by the use of the Lazer Zee Meter, Model 501,
manufactured by PEN KEM, Inc; other zleta potential measuring
devices can be used.
Cationic dispersants used in practice of this invention
also include low molecular weight polyamines (e.g., ethylene
diamine or hexamethylene diamine), long carbon chain amines or
quaternary ammonium salts (e.g., "dimethylditallow" ammonium
chloride). Foaming may be a problem with surface active
quaternary ammonium compounds such as dimethylditallow ammonium
chloride.
The amount of cationic dispersant required depends on the
nature of the cationic dispersant as well as the nature of the
surface of the mineral particles. A lower molecular weight
diallyl polymer salt is less effective in conferring a cationic
charge than is the same polymer of higher molecular weight.
Quaternary ammonium polymers of high charge density are more
effective than those of lower charge density. Higher surface
area, fine particle minerals require more dispersant than do
coarser particles. The magnitude of the anionic charge before
treatment with the cationic dispersant also affects the amount
required. A mineral carrying a high anionic charge will
require a greater amount of cationic dispersant than will a
mineral which initially has a lower anionic charge.
A dimethyl diallyl quaternary ammonium chloride polymer
commercially available under the trademark designation Polymer
261LV from the Calgon Corporation has been found to be
particularly useful in the practice of the present invention.
The polymer is supplied as an aqueous solution containing
approximate~y 42% active polymer; the supplier estimates the
050489 - 13 - 3259A
molecular weight of the reagent to-be between 50,000 and
250,000. Generally, 0.2 to 0.75 percent active Calgon 261LV is
required to disperse crude kaolins in aqueous suspensions in
the range of 45% to 60% solids. The particle size distribution
and surface area of the kaolin dictate the amount of polymer
required to impart cationic dispersion in the slurries.
Cationically dispersed kaolin slurries are acidic and pH ranges
between 3.0 and 5.0 as measured on a pH meter. Kaolins that
have been previously treated with anionic agents require even
higher amounts of Calgon 261LV to disperse them cationically.
The following nonlimiting examples are given to illustrate
the best modes presently contemplated for practicing this
invention.
All particles sizes in these examples in the micrometer
size range were determined by a conventional sedimentation
technique using the Sedigraph~ 5000 analyzer. All pH values
were determined by an Orion Research pH meter (model 701A).
All charge values were obtained by use of the Lazer Zee Meter
(supra).
When sodium silicate was used in illustrative examples,
N0Brand sodium silicate was employed. N0Brand sodium silicate
is a solution containing about 8.9~ wt. Na2O, about 28.7% wt.
SiO2 and the ba~ance water.
Example 1
This example illustrates the use of cationic dispersion in
the wet processing of a Georgia kaolin crude (Washington
County, Georgia) of the type conventionally processed using
only anionic dispersants to produce a No. 1 grade of paper
coating kaolin. The crude kaolin used was a well crystallized
kaolin. Typical crude of this type contains about 1.76% wt.
050489 - 14 - 3259
2~
titania and about 0.34% wt. iron (as Fe2O3) as impurities.
Median particle size of the degritted kaolin is about 1.6
micrometers (equivalent spherical diameter); about 92% by
weight of the particles is <10 micrometers, 80% <5 micrometers,
and 56% <2 micrometers. The crushed crude kaolin was received
at 78% solids (22% volatiles).
Deionized water (1540 9) was added to a beaker. Using
moderate speed stirring provided by a drill press mixer
equipped with a 2" uplift stainless steel propeller, 5128 g of
the crude kaolin was gradually added to the water with
alternate drop-by-drop additions of Calgon 261LV polymer (42%
active) until the crude appeared dispersed when examined
visually. The slurry was stirred for an additional 90 minutes
after combining all of the ingredients. The total amount of
cationic polymer added was 0.175~ (100% active weight basis)
based on the dried weight of the kaolin. Solids content in the
dispersed slurry was 60~ and the pH was 3.6.
The 60% solids slurry was then diluted to 42~ solids by
adding 2858 9 of deionized water while the slurry was
stirred. The slurry pH after dilution was 3.6.
The diluted acidic cationically dispersed slurry was
degritted by passing it over a vibrating 325 mesh sieve
(U.S.). The >325 mesh portion that collected on top of the
screen was set aside and the <325 mesh portion passing through
the screen was collected in a beaker. Solids content in the
<325 mesh slurry measured after mixing with a spatula was found
to be 34.9%, resulting in a 82% yield. The lower than normal
yield obtained for the <325 mesh portion may have been caused
by an inadequate amount of Calgon 261LV to disperse the crude
kaolin sufficiently prior to degritting. A +47mv zeta
potential value was obtained using the Lazer Zee Meter after a
050489 - 15 - 3259A
~ 3'~3~
portion of the <325 mesh fraction was diluted with supernatant
extracted from a separate portion of the same fraction.
The <325 mesh slurry was then fractionated to obtain the
<2 micrometers particles by using a conventional gravitational
sedimentation method. The slurry was divided equally into two-
gallon plastic beakers. The slurry height in each of the
beakers was adjusted to 22 cm by adding more deionized water
followed by stirring on the drill press. Solids content in
each slurry was 17.7%. After permitting the slurries to stand
undisturbed for 16 hours, no hard sediment had formed in either
beaker, indicating that the slurries were not adequately
dispersed. To improve dispersion, 0.05% Calgon 261LV polymer
(based on the weight of the dried kaolin) was added to one of
the slurries during stirring on the drill press mixer. After
permitting the slurry to stand undisturbed for 6 hours, a hard
sediment had formed indicating adequate dispersion. The same
amount of cationic polymer was then added to the other slurry
which resulted in a total of 0.225% (active) polymer addition
based on the weight of the dried kaolin in each slurry. Both
of these further dispersed slurries were recombined, stirred
manually, and redivided into three separate containers. The
slurry height in each of the containers was 8 cm. All three
slurries were permitted to stand undisturbed for 6 hours before
gently pouring out the supernatants. The three supernatants
were retained together in a single plastic bucket and the
remaining hard sediments at the bottom of each container were
diluted by adding approximately 1 liter of deionized water to
each one. The sediments were redispersed during stirring on
the drill press mixer. The three slurries formed from the
sediments were recombined and mixed.
A second gravitational sedimentation was carried out to
remove additional <2 micrometers material from the sediments
050489 - 16 - 3259A
formed by the previous fractionation-. The slurry (from
sediments) was diluted with enough deionized water to give 8 cm
slurry heights after dividing into the same three containers
used for the first gravitational sedimentation. The three
slurries were permitted to stand undisturbed for 6 hours before
gently pouring out the supernatants. The three supernatants
were retained in a separate container and the remaining
sediments formed in the three containers were transferred to a
single 2 gallon plastic beaker.
A third and final gravitational sedimentation was carried
out to recover more <2 micrometers material from the sediments
formed by the second fractionation. The previously combined
sediments were diluted with deionized water until the slurry
was 21 cm high in one beaker and after stirring on the drill
press mixer the slurry pH was 3.6. After permitting the slurry
to stand undisturbed for 16 hours, the supernatant was gently
poured out and collected in a separate beaker and the remaining
sediment was set aside.
All supernatants retained from the three gravitational
sedimentations were mixed together in a single container
resulting in a 5.38% solids slurry. The yield of <2
micrometers kaolin was determined to be 1556 9 or 47.5% based
on <325 mesh fraction.
The <2 micrometers fine fraction kaolin was bleached with
8 lb. of sodium dithionite reducing bleach per ton of dry
kaolin. This was performed by sifting 6.225 g of the bleach
powder into the slurry during low speed stirring on the drill
press mixer. After 5 minutes of mixing the slurry appeared
visually brighter. After static aging the slurry for 18 hours
its pH was 3.2 and specific conductivity was 0.586 micromhos.
A +17 mv zeta potential value was obtained using the Lazer Zee
050489 - 17 - 3259A
.V,~.e 3. ~ r-
meter after diluting a portion of t-he bleached slurry with
clear supernatant extracted by centrifuging another portion of
the main bleached slurry.
A preliminary filtration test was performed by extracting
three 100 g samples from the main bleached slurry after aging
and mixing. The first sample was filtered "as is" on a Buchner
funnel under vacuum using Whatman #5 filter paper. Aside from
a few cloudy drops of filtrate at the beginning of the
filtration the filtrate was clear. Sodium hydroxide solution
(2% active) was added to the second sample to increase pH to
7.0 and after permitting the sample to static age for a few
minutes clear supernatant formed at the top portion of the
slurry indicating good flocculation of the kaolin particles.
Sodium polyacrylate solution (2%) was added to the third slurry
to increase pH to 7.0 and after static aging the sample for
several minutes a cloudy supernatant formed at the top
indicating poorly flocculated kaolin.
The main portion of bleached slurry was divided into two
separate portions for filtration. One portion weighing 5700 g
was filtered "as is" on a 24 cm Buchner funnel with vacuum
(Whatm~n #5 paper), and a 1000 ml deionized water rinse
followed. The pH of the second portion of bleached slurry was
adjusted to 7.0 with sodium hydroxide solution (10% active)
with mixing. After l hour static aging the clear supernatant
that formed at the top of the slurry was gently poured off and
discarded and a zero mv zeta potential value was obtained from
the flocculated kaolin portion. The flocculated slurry was
then divided into three equal portions for filtration on three
24 cm Buchner funnels. Each filtercake was rinsed with 1000 ml
of deionized water.
050489 - 18 - 3259A
Exam~le-2
This example illustrates the use of cationic dispersion in
the wet processing of a 50%:50% blend of two Georgia kaolin
crudes from mines commonly referred to as Dixie and Califf.
The crude blend contains a large number of finely divided
kaolin particles and is of the type useful in producing low
abrasion calcined kaolin opacifying pigment. A control sample
to illustrate conventional anionic wet processing was also
prepared. The kaolins were received as crushed crudes. The
Dixie sample was at 80.2% solids (19.8% volatiles); and the
Califf sample was at 81.6% solids (18.4% volatiles).
Following is a description of the wet processing of the
crude blend using cationic primary dispersion.
Deionized water (4930 g) was weighed into a two gallon
beaker. Using low speed stirring (300 r.p.m.) provided by a
drill press mixer equipped with a 2" uplift stainless steel
propeller, 0.60% active Calgon 261LV (44.5% active aqueous
solution) based on the dried weight of the crude kaolin was
added to the deionized water. Slowly and simultaneously 2500 g
of each crude calculated on a dry weight basis (3117 9 Dixie
and 3064 9 Califf) was added to the diluted polymer solution
during continuous stirring at a moderate speed. To further
disperse the slurry, an additional O.lS% active Calgon 261LV
(44.S%) based on the dried weight of the kaolin was added to
the slurry and stirring continued for one hour at an increased
speed of 1000 r.p.m. The dispersion of the slurry was checked
by examining the sediment that formed after permitting the
slurry to settle-in the beaker overnight. The supernatant
portion was poured out and retained and the sediment that had
formed was hard and evenly stratified, indicating adequate
dispersion in the slurry for degritting and fractionation. The
OS0489 - 19 - 3259A
supernatant portion was recombined-with the sediment and
stirring at 1000 r.p.m. on the drill press followed. The
slurry pH was 4Ø
Degritting the acidic cationically dispersed kaolin slurry
was carried out by passing it over a 100 mesh (U.S.) sieve.
The >100 mesh residue was set aside and the <100 mesh slurry
that passed through the sieve was collected and immediately
passed over a 325 mesh sieve (U.S.). The >325 mesh residue
that collected on top of this sieve was combined with the
previously collected >100 mesh residue. This portion was set
aside. Yield of the <325 mesh portion was found to be 67% and
the slurry solids was 25.2%. A +50 mv zeta potential value on
the <325 mesh fraction was obtained with the aid of the Lazer
Zee Meter (model 501 Pen Kem Inc.) after diluting a portion of
the slurry with deionized water. During moderate stirring on
the drill press, the 25.2% solids slurry was diluted to 15%
solids with an addition of 8770 9 of deionized water and the
slurry was dispersed further by adding 0.05% active Calgon
261LV based on the dried weight of the kaolin.
The <325 mesh slurry was then fractionated to extract the
<1 micrometer particles (equivalent spherical diameter) by
using a conventional gravitational sedimentation method. The
slurry was divided equally into two five gallon plastic buckets
(having straight walls), and the resulting slurry height in
each of the buckets was 19 cm. After permitting the slurries
to static settle for 53 hours, the supernatant portions were
gently poured out and retained. The hard sediments that had
formed on the bottom of the buckets were diluted with deionized
water, mixed on the drill press, combined and remixed
vigorously on the drill press. The slurry formed from the
sediments was at 17.9% solids.
050489 - 20 - 3259A
r~ r~l
A second gravitational sedime~tation was carried out to
recover additional <1 micrometer material from the sediments
formed by the previous fractionation. The slurry (from
sediments) was diluted to 15% solids by adding deionized water
during stirring on the drill press. The height of the slurry
in the bucket was 21 cm. After permitting the slurry to settle
undisturbed for 40 hours, the top 13 cm of supernatant was
gently siphoned off and collected in a separate beaker. The
supernatants obtained from the first and second gravitational
sedimentations were combined and stirred. Yield of the <1
micrometer fraction was found to be 64.0% and the slurry solids
measured 7.6%.
The <1 micrometer fraction was upgraded further by passing
the slurry through a high intensity magnetic separator Model #
WHIMS 3X4L (Carpco Inc.) containing a steel wool matrix.
Slurry was passed through the magnet at 100 ml per minute flow
rate. The product collected was visually brighter and had a
6.1~ solids content and a pH of 4Ø
To improve the brightness of the <1 micrometer fraction of
acidic cationically dispersed magnetically purified kaolin
slurry, it was bleached with 6 lb. of sodium dithionite
reducing bleach based on one ton of dried kaolin. This was
performed by sifting bleach powder into the slurry during
manual stirring followed by 5 more minutes of stirring. The
slurry was then permitted to static age overnight in a covered
plastic bucket.
The final step in the cationic wet processing of this
sample was to remove excess liquid. Since the solids content
in the slurry was only 6.2~ and filtration by vacuum in Buchner
funnels would consume too much time, the slurry solids was
increased to 30.5~ before filtration by centrifugation. This
050489 - 21 - 3259A
was done by centrifuging several portions of the low solids
slurry in a SORVALL~ SS-3 centrifuge at 9500 r.p.m. until a
clear supernatant was obtained. The clear supernatants were
poured off and discarded and the sediments formed during
centrifugation were mixed into the bleached slurry. The 30.5%
solid slurry was then filtered under vacuum on several Buchner
funnels by placing 655 g of slurry in each funnel (200 g dry
kaolin). Each filter cake was rinsed twice with 200 ml of
deionized water.
The rinsed filter cakes were then removed from the funnels
and dried at 180F for 4 hours. The dried kaolin was then
pulverized twice in a MIKRO-SAMPLMILL using the 0.039" round
hole screen.
The particle size distribution of the cationically
processed hydrous kaolin product was: 92% <2 micrometers, 80%
<1 micrometer, 53% <0.5 micrometer, 0% <0.2 micrometer and
median size was 0.48 micrometer. Block brightness of the
pigment when measured on the Elrepho Reflectance Meter (Carl
Zeiss Corp.) was 87.9%.
Preparation of an anionically processed kaolin pigment was
carried out for purposes of comparison following the same wet
processing steps used to produce the cationic pigment. The
processing steps were slurry makedown with a primary
dispersant, degritting, fractionating, high intensity magnetic
separation, bleaching, filtration, and washing.
In the initial step of a slurry makedown with a primary
dispersant, N~Brand sodium silicate (37.7% active aqueous
solution) was added to the deionized water in the amount of
0.20% sodium silicate (dry basis) based on the dried weight of
the crude kaolin blend (2500 g of Dixie and 2500 g of
Califf). ~he crude kaolin was added to the diluted sodium
050489 - 22 - 3259A
silicate solution until the slurry-solids was 45%. The slurry
pH was 8.5. The yield of <325 mesh kaolin after degritting the
slurry was 65% and the slurry was 31.1.% solids (pH 8.5). Two
gravitational sedimentations to obtain the <1 micrometer size
kaolin particles were carried out after diluting the 31.1%
solids degritted portion to 15% solids with deionized water.
After the initial fractionation the sediment was diluted to 15%
solids again, however, 0.05% sodium silicate based on the dried
weight of the kaolin was added to the slurry to improve
dispersion. The slurry pH was 8.4 and the kaolin was
sedimented again to recover more of the <1 micrometer
particles. The yield of the <1 micrometer fraction was 69.0%
based on the <325 mesh portion and the slurry contained 9.0%
solids. High intensity magnetic separation followed producing
a brighter slurry. The slurry solids were 7.3%. The magneted
slurry was further upgraded by dithionite bleaching. Since the
slurry pH was 7.9 and dithionite bleaching is most effective in
acidic systems, the slurry pH was adjusted to 3.0 by adding
sufficient sulfuric acid (10% active solution) prior to the
addition of bleach. Bleaching with sodium dithionite in an
amount equivalent to 6 lb. per ton of dried kaolin was carried
out by adding the bleach to the slurry while stirring. The pH
of the bleached slurry after static aging overnight was 3.5.
To remove the liquid phase from the slurry, it was filtered
under vacuum on several Buchner funnels (2700 9 per funnel) and
the filter cakes were rinsed twice with 200 9 of deionized
water (2:1 rinse). The filter cakes were removed from the
funnels and dried at 180F for 4 hours. Pulverization of the
dried filter cakes followed by passing them twice through the
MIKRO-SAMPLMILL.
The particle size distribution of the anionically
processed hydrous kaolin product was: 98% <2 micrometers, 96%
050489 - 23 - 3259A
<1 micrometer, 82~ <0.5 micrometer~ 36% <0.2 micrometer, and
the median size was 0.25 micrometer. alock brightness of the
pigment when measured on the Elrepho Reflectance Meter was
87.2%.
Exam~le 3
This example illustrates the use of a cationic primary
dispersant in the wet processing of a Georgia kaolin crude from
a mine commonly referred to as Dixie. A control sample to
illustrate conventional anionic wet processing was also
prepared. As in Example 2, the crude used contains a large
number of finely divided kaolin particles and is of the type
useful in producing low abrasion calcined kaolin opacifying
pigments. The Dixie crude was received as a crushed crude
containing 80.2% solid materials (19.8% volatiles).
The use of a primary cationic dispersant in wet processing
is described first.
The crude kaolin was made down in a slurry form at 45%
solids as follows. Deionized water (4876 g) was weighed into a
two gallon plastic beaker. Using low speed stirring (300
r.p.m.) provided by a drill press mixer equipped with a 2"
uplift stainless steel propeller, 0.53~ active Calgon 261 LV
(44.5% solids) based on the weight of the dried kaolin was
added to deionized water. Slowly and continuously 6235 g of
Dixie crude (5000 9 dry) was added to the diluted polymer
solution during continuous stirring at a moderate speed (600
r.p.m.). After all of the crude was added, the stirring speed
was increased to and maintained at 1000 r.p.m. for one hour.
The dispersion of the slurry was checked by examining the
sediment that formed after permitting the slurry to settle in
050489 - 24 - 3259A
~ .5
the beaker overnight. The supernat-ant was poured out and
retained and the sediment that had formed was hard and
uniformly stratified, indicating adequate dispersion of the
slurry for degritting and fractionating. The supernatant was
recombined with the sediment and stirring at 1000 r.p.m.
followed. The slurry was pH was 4Ø
Degritting the acidic cationically dispersed kaolin slurry
was carried out by first passing it over a 100 mesh (U.S.)
sieve. The >100 mesh residue was set aside and the <100 mesh
slurry that passed through the sieve was collected and
immediately passed over a 325 mesh (U.S.) sieve. Deionized
water was used to rinse both of the sieves after which the two
residues were recombined and set aside. Yield of the <325 mesh
portion was found to be 86.9% and the slurry solids was 26.4%.
The degritted crude was then prepared for fractionating by
a conventionally used gravitational sedimentation method to
obtain only the finely divided particles measuring <1
micrometer (equivalent spherical diameter) in size. During
moderate speed stirring on the drill press, the 26.4% solids
cationically dispersed slurry was diluted to 15% solids with
deionized water. The slurry was then divided equally into two
straight walled five gallon plastic buckets which gave a 21 cm
slurry height in each. After static settling the slurries for
53 hours, the top 17.5 cm of supernatant was siphoned off and
retained. The hard sediments that had formed at the bottom of
each bucket were diluted with deionized water to 15% solids,
redispersed on the drill press mixer, recombined and then
remixed at 1000 r.p.m. by the drill press. The height of the
slurry in the bucket was 20 cm and pH was 4Ø To recover more
fine material, the slurry was permitted to settle for 40 hours
and the top 13 cm of supernatant was siphoned off and combined
050489 - 25 - 3259A
3~?A~
with the supernatant retained from-the previous sedimentation.
Yield of <1 micrometer material was found to be 63.8%.
The final step of cationically wet processing this sample
was to remove the excess liquid. Since the volume of the
slurry was large and the solids content low and filtration by
vacuum in Buchner funnels would take a long time, the slurry
solids was increased by centrifuging several portions of the
slurry in the SORVALL centrifuge at 9500 r.p.m. until clear
supernatants were obtained. The clear supernatants were poured
out and discarded and the sediments formed during
centrifugation were mixed into the original slurry, thereby
increasing its solids content. This higher solids slurry was
then filtered under vacuum on several Buchner funnels, in an
amount equal to 200 g of dried kaolin.
The filter cakes were removed from the funnels and dried
at 180F for 4 hours and double pulverization in a MIKRO-
SAMPLMILL using the 0.039" round hole screen followed.
The particle size distribution of the cationically
processed hydrous kaolin product was: 95% <2 micrometers, 81%
<1 micrometer, 50% <0.5 micrometer, 0% <0.2 micrometer, and the
median size was 0.50 micrometer. Block brightness of the
pigment was 85.4%.
For purposes of comparison, an anionically processed
pigment was prepared by following the same wet processing steps
used to produce the previously made cationic pigment, but using
an anionic primary dispersant. Processing steps included
slurry makedown with a primary dispersant, degritting,
fractionating, and filtering. Processing sequence, equipment,
addition rates, and mixing speeds to process the anionically
dispersed system were the same as those used for the previously
processed cationically dispersed system.
050489 - 26 - 3259A
~ 3~
In the initial step of slurry-maltedown with a primary
dispersant, sodium silicate (37.7~ ac~ive aqueous solution) was
added to the deionized water in the amount of 0.20% based on
the dried weight of the crude kaolin (5000 9). The crude
kaolin was added to the diluted sodium silicate solution which
resulted in 45% solids slurry and the slurry pH was 8.6. After
degritting, the <325 mesh yield was 83.2% and the slurry
contained 33.3% solids. Two gravitational sedimentations to
obtain the cl micrometer size kaolin particles were carried out
by diluting the degritted slurry to 15% solids with deionized
water. After the initial fractionation the sediment was
diluted to 15% solids and the slurry was settled again. Yield
of the combined fine fractions was 64.1~ and the pH of the
slurry was 8.3. The next step in processing was to remove the
excess liquid by filtration. To speed filtration, the fine
fraction slurry was flocculated by adding sulfuric acid (10~
active solution) in an amount sufficient to reduce the pH to
3.5. After permitting the flocculated slurry to stand
overnight, the kaolin flocs settled and the clear supernatant
was poured out and discarded. The concentrated slurry was then
filtered on several Buchner funnels (200 q dry kaolin each).
Each filtercake was rinsed twice with 200 ml of deionized water
after which they were dried at 180F for 4 hours and pulverized
with two passes through the MIKRO-SAMPLMILL using the 0.039"
round hole screen.
The particle size distribution of the anionically
processed hydrous kaolin product was: 98% <2 micrometers, 93%
<1 micrometer, 75% <0.5 micrometer, 33% <0.2 micrometer, and
the median size was 0.28 micrometer. ~lock brightness was
85.7%.
050489 - 27 - 3259A
q~
While this invention has been ~escribed with particular
emphasis on its application to upgracling kaolin ores, it will
be understood that principles of the invention can be applied
to upgrading other ores such as other silicate or aluminous
ores and carbonate ores. When processing carbonate ores such
as calcitic or dolomitic ores the p~ during primary dispersion
should be sufficiently high to avoid decomposition of the ore.
050489 - 28 - 3259A
