A method for producing an Attapulgite clay (Fuller's Earth) that
significantly removes other types of clays and minerals, resulting
in improved performance. A unique dispersant is used that will fully
disperse the individual Attapulgite particles in water such that
the particles remain in suspension, and allow the non-Attapulgite
clay particles to be liberated, which then can be easily separated
through various techniques. The Attapulgite clay may be recovered
from the dispersion and dried in such a manner to produce a finely
sized powder from ore, without the need for any grinding or milling
operation. The dried Attapulgite clay has a free moisture content
of 2-3%. The dried Attapulgite clay with adsorbed dispersant is
redispersed in water and retains thixotropic properties.
What is claimed is:
1. A wet method of processing naturally occurring clay ore to separate
Attapulgite clay from other materials comprising the steps of: crushing
the clay ore, adding a dispersant to water, preparing a slurry of
the clay ore with the aqueous dispersant to disperse the Attapulgite
clay in the water, separating the dispersed Attapulgite clay from
un-dispersed materials, and drying the dispersed Attapulgite clay
to a free-moisture content of approximately 2-3%.
2. The wet method of claim 1 further comprising the steps of adding
the dried clay to water and re-dispersing the clay using a low shear
mixer forming a dispersion containing up to approximately 35% by
weight of clay.
3. The wet method of claim 1 wherein the dispersant is sodium
polyacrylate having a molecular weight between 4000 and 5000.
4. The wet method of claim 1 wherein the dispersant is tetrasodium
5. The wet method of claim 1 wherein the separated Attapulgite
clay is in the form of elongated rods substantially free of grit
and non-Attapulgite clay.
6. The wet method of claim 1 wherein the dispersed Attapulgite
clay is dried using an air swept turbulent drier.
7. The wet method of claim 6 wherein the air in the drier is between
85.degree. C. and 210.degree. C.
8. A purified dry attapulgite clay having loosely bound, non-agglomerated
elongated rods, free of grit and non-attapulgite clay prepared in
accordance with the method of claim 1.
9. A wet method for separating and dispersing Attapulgite clay
comprising the steps of: crushing naturally occurring clay, adding
a dispersant to water, preparing a slurry of the naturally occurring
clay with the aqueous dispersant wherein the clay is dispersed in
the water, separating non-Attapulgite materials from the aqueous
slurry of Attapulgite clay, drying the dispersed Attapulgite clay,
adding the dry Attapulgite clay to water, and redispersing the clay
in the water using a low shear mixer without the addition of further
dispersant or a surfactant forming a dispersion containing up to
approximately 35% by weight of Attapulgite clay.
10. The wet method of claim 9 wherein the dispersant is sodium
polyacrylate having a molecular weight between 4000 and 5000.
11. The wet method of claim 9 wherein the dispersant is tetrasodium
12. The wet method of claim 9 wherein the non-Attapulgite material
is quartz, dolomite, limestone, feldspar, diatomaceous, earth, mica,
titania, aluminum montmorillonite, sepiolite, bentonite and kaolin.
13. An aqueous dispersion of attapulgite clay, free of grit and
non-attapulgite clay, avoiding additional dispersants or surfactants,
prepared in accordance with the method of claim 9.
14. A purified attapulgite clay comprising: a dispersant adsorbed
to the surface of the clay, elongated rods substantially free of
grit and non-Attapulgite clay, dried at atmospheric pressure in
turbulent air at a temperature of 85.degree. C.-210.degree. C. avoiding
stabilizers and grinding, and the attapulgite clay having a free-moisture
content of approximately 0.1%-9%.
15. The attapulgite clay of claim 14 wherein the dispersant is
sodium polyacrylate having a molecular weight between 4000 and
16. An aqueous dispersion of the attapulgite clay of claim 14
the dispersion containing up to approximately 35% by weight of attapulgite
FIELD OF INVENTION
This invention relates to the ability to treat naturally occurring
clay deposits and more particularly, to selectively disperse discrete,
individual particles of Attapulgite while liberating other non-Attapulgite
minerals such as Montmorillonite, Sepiolite, Bentonite, Calcium
Carbonate, Silica and Kaolin, from in between the Attapulgite Bundles.
The invention relates to a dry clay which is readily re-dispersed.
BACKGROUND OF THE INVENTION
Attapulgite Clay particles naturally occur as colloidal, high aspect
ratio, rod shaped particles that are tightly bundled together as
clusters. The rods tend to be all equal in particle length and diameter,
similar to a group of bound pipes or drinking straws. The individual
clusters are agglomerated randomly. The Attapulgite deposits located
in northern Florida and southeastern Georgia were formed in shallow,
magnesium rich bay waters, where other clay minerals were formed
simultaneously or were introduced through air and water movements.
Other minerals such as silica, calcium carbonate and magnesium carbonate
were also formed in place or were transported into the deposit during
its formation, resulting in a variety of non Attapulgite materials
being present in levels approaching 20 weight percent or more. In
order for the Attapulgite to be in a physical form acceptable for
commercial use, it needs to be processed into a powder. The Attapulgite
clay is historically processed by selectively mining the deposit,
classifying the ore according to its grit content and gelling properties,
drying, mechanically grinding or milling ore with minimal amounts
of contaminants, followed by particle size separation and drying
to a moisture content of approximately 10% to 6%. The non-Attapulgite
matter is also reduced in size and is partially removed during the
particle size classification process. The non-clay minerals can
be abrasive and must either be removed or reduced in size to lessen
their abrasive characteristics in order for the Attapulgite powder
to be useful in end use applications.
A dry grinding/milling operation will partially break up the bundle
clusters with the undesirable result of fracturing of individual
Attapulgite particles. This may be, in part, due to the presence
of grit and particles of non-clay matter which are present in the
clay ore and which break and damage the individual rods during the
dry grinding/milling operation. The individual Attapulgite particles
provide the absorptive, thixotropic, anti-settling, and/or binding
properties to a wide variety of end use applications. The crystal
structure of Attapulgite clay has positive and negatively charged
sites on the lateral surfaces of each particle and at the ends of
each individual particle. When the crystals were formed they joined
together in the straw clusters with random bundles orienting themselves
to neutralize the charges. When these individual particles are dispersed
by chemical or mechanical means the particles seek to satisfy the
negative and positive charges by randomly re-connecting particle
to particle instead of forming bundles and clusters. This unique
feature of attapulgite clay creates the thixotropic properties and
binding properties of Attapulgite. Particles with higher length
to width, or aspect ratios, typically are more efficient than particles
with lower aspect ratios in providing products with higher gel strength
and binding properties.
In end use applications, a chemical dispersant, predominantly tetrasodium
pyrophosphate (TSPP), will at best, separate a majority of the Attapulgite
bundles into individual particles in an aqueous medium under moderate-to-high
shear agitation. TSPP will also disperse other clay types present.
Individual clay particles of each clay species present, will remain
suspended in water. U.S. Pat. No. 3569760 has shown that non-clay
minerals will not remain suspended in the water and will settle
to the bottom due to gravitational forces if the clay-water slurry
is low enough in viscosity. The relatively large non-clay minerals,
which by their means of higher hardness, can resist size reduction
and thus can also be removed by screening, centrifuging, via sedimentation
tanks, hydrocyclone, or other physical separation means. The non-Attapulgite
clay minerals, such as Montmorillonite, Smectite, and Sepiolite,
will remain mixed in with the Attapulgite clay. The non-Attapulgite
clays do not have the same performance characteristics as Attapulgite
clay, some which are detrimental to performance in particular applications.
At the present time, the suppliers and users of Attapulgite are
dependent on the quality of natural deposits for the concentration
of non-Attapulgite clay content. The availability of high purity
Attapulgite clay relies on the economically inefficient selective
mining of the deposits.
Gantt et. al. in U.S. Pat. No. 5358120 have shown that other
types of previously commercially available dispersants such as sodium
polyacrylates can be used with clay. However, sodium polyacrylates
with molecular weights less than 4300 while effective on kaolins
and bentonites, are typically not as effective with Attapulgite
when compared to TSPP, and thus are not generally used.
Attapulgite clay provides thixotropic and binding properties through
the process of re-flocculating after being typically dispersed at
less than 5% solids in an aqueous system, whereby a gel structure
is generated. Various salts, at additive levels, can act as re-flocculating
Historically, Attapulgite clay is dried to a free moisture content
of approximately, 10-16%, with an 8 or 9% minimum. At lower moisture
contents, the Attapulgite begins to lose its thixotropic properties
and does not readily re-disperse in water. Brooks, in U.S. Pat.
No. 4966871 has shown that it is possible to vacuum dry Attapulgite
down to less than 2% free moisture and still retain its thixotropic
properties, the importance being that the attapulgite is dried under
Attapulgite clay is frequently used as an additive product, often
comprising only 1 to 3 weight percent of the final composition.
Attapulgite clay does not disperse completely in a liquid medium
at these low concentrations. The believed cause is the lack of clay
to clay collisions needed to break up the agglomerates and bundles.
A technique used to overcome this behavior is one in which a 20
to 25% slurry is made, and when completely dispersed, it is diluted
with water down to the desired ultimate concentration.
There is a need to be able to efficiently and economically separate
Attapulgite clay from other clay types, from non-clay minerals while
not destroying the high aspect ratio of the particles with mechanical
grinding force. There is a need to reduce the moisture content of
attapulgite while maintaining gel properties to enhance it economic
benefit through concentration of the product for its end use application.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an economical and efficient
method to separate Attapulgite clay from other clay components and
minerals in clay ore.
It is an object of the invention to use the method to allow for
the mining of lower grade deposits which have historically not been
useable due to high concentrations of non-clay minerals.
It is an objective of the invention to use the method for the blending
of attapulgite ores in slurry form to efficiently produce products
with uniform physical and chemical properties.
It is a further object of the invention to provide a purified Attapulgite
It is yet another object of the invention to provide dry Attapulgite
clay particles which are readily dispersed in water without addition
of dispersant or surfactant.
It is a further object of the present invention to provide a dry
particulate Attapulgite clay which has less than 0.5% free moisture
content and retains thixotropic properties without using vacuum
In accordance with the teachings of the present invention, there
is disclosed a method of processing naturally occurring clay ore
to separate Attapulgite clay from other materials. This includes
the steps of crushing the clay ore, adding sodium polyacrylate to
water, the sodium polyacrylate having a molecular weight between
4000 and 5000 preparing a slurry of the clay ore with the aqueous
sodium polyacrylate to disperse the Attapulgite clay in the water,
dispersing the Attapulgite without fully dispersing the non-Attapulgite
Minerals, separating the non-Attapulgite minerals from the Attapulgite
and drying the dispersed, purified Attapulgite clay.
Additionally, there is disclosed a wet method of processing naturally
occurring clay ore to separate Attapulgite clay from other materials.
The method has the steps of crushing the clay ore and adding a dispersant
to water. A slurry of the clay ore is prepared with the aqueous
dispersant to disperse the Attapulgite clay in the water. The dispersed
Attapulgite clay is separated from the non-Attapulgite materials,
and the dispersed clay is dried to a free moisture content of approximately
There is further disclosed a wet method for separating and dispersing
Attapulgite clay. Naturally occurring clay is crushed. A dispersant
is added to water. A slurry of the naturally occurring clay is prepared
with the aqueous dispersant wherein the clay is dispersed in the
water. Non-Attapulgite materials are separated from the aqueous
slurry of Attapulgite clay. The dispersed Attapulgite clay is dried.
Up to approximately 35% by weight of the dry Attapulgite clay is
added to water. The Attapulgite clay is re-dispersed in the water
using a low shear mixer without the addition of further dispersant
or a surfactant.
Still further, there is disclosed a purified dried, particulate
Attapulgite clay comprising Attapulgite clay separated from non-clay
matter, the Attapulgite clay having a free moisture content of approximately
These and other objects of the present invention will become apparent
from a reading of the following specification, taken in conjunction
with the enclosed drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged view of dispersed Attapulgite crystals.
FIG. 2 is an enlarged view of a smectite/ Attapulgite cluster.
FIG. 3 is an enlarged view of clusters of Attapulgite with other
clay and grit obtained by the dry separation process of the prior
FIG. 4 is an enlarged view of isolated Attapulgite rods obtained
by the wet separation process of the present invention.
FIG. 5 is a diagram of the purification of Attapulgite clay.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
We have made the unexpected discovery that the efficiency of a
particular sodium polyacrylate, which preferably has a molecular
weight of approximately 4700 allows for higher concentrations
of Attapulgite clay in a water slurry at a lower viscosity than
is attainable when using TSPP or other sodium polyacrylate dispersants
having lower molecular weights. The practical upper limit for processing
the Attapulgite concentration when using TSPP as the dispersant
is approximately 30%, above which the slurry becomes highly dilatent
and the viscosity becomes too high for handling. Other sodium polyacrylates
with lower molecular weights will not efficiently disperse the Attapulgite.
The approximate 4700 MW sodium polyacrylate imparts the ability
to prepare at least 35% concentration Attapulgite slurry and still
have acceptable handling characteristics. This property offers the
economic advantage of more efficient manufacture of formulations
that begin with a 35% slurry that is diluted down to a lower concentration
(typically 1-3% used in suspension fertilizers) as fewer slurry
batches need to be prepared to yield the same amount of final product.
When further studied, we have made an additional unexpected discovery
that by using said higher molecular weight sodium polyacrylate,
the Attapulgite particles will rapidly disperse with significantly
improved efficiency in water under moderate-to-high shear conditions,
(see FIG. 1.). The result is that more of the non-attapulgite clays
present will remain as relatively large, liberated particles, along
with the non-clay matter present. The non-Attapulgite clays can
be easily removed by physical means such as screening or centrifuging
along with the non-clay matter. The result is an increased purity
form of Attapulgite that is essentially grit free. The 4700 molecular
weight sodium polyacrylate does not rapidly disperse smectite, montmorillonite,
kaolin or other clay minerals due to its high molecular weight.
The relatively lower molecular weight sodium polyacrylates tested
will not disperse the Attapulgite particles as efficiently, thus
achieving less separation of and non-clay particles. See FIG. 2
where the molecular weight of the sodium polyacrylate used is 2600.
We have further discovered that even using TSPP, with wet processing
and drying in a spray drier or air swept tubular dryer, the resulting
product can be re-dispersed with low shear mixing. Previously product
dried by conventional drying techniques such as rotary dryers and
flash dryers produced a product that would not re-disperse. It is
possible to achieve separation of Attapulgite clay from the non-Attapulgite
minerals and purification of Attapulgite clay can be achieved with
the wet process when using TSPP as the dispersant. The purified
Attapulgite can be re-dispersed with low shear up to 35% concentration
of slurry solids can be obtained. Re-dispersion of dry clay using
TSPP separation has previously been obtainable only with HIGH shear
equipment and, even under these conditions, only 10-15% solids were
obtainable. In the present invention, there is no need for additional
TSPP or a surfactant. The purity Attapulgite clay obtained with
TSPP dispersant is not as high as the purity obtained with the high
molecular weight sodium polyacrylate. The TSPP is not able to retard
the hydration of Smectite minerals found as contaminants in the
attapulgite. The non-clay minerals can be removed by screening and
centrifuging the slurry. However, the use of TSPP is more economical
and for those end uses of Attapulgite clay such as Agricultural
grades, where high purity is not essential, an efficient and relatively
low cost method is disclosed herein.
We have further discovered that when Attapulgite slurry is prepared
with sodium polyacrylate or TSPP, and then dried in a spray drier,
an air swept tubular dryer or other low temperature, high turbulence
methods of drying, the sodium polyacrylate or the TSPP remain adsorbed
on the Attapulgite particles. The dried Attapulgite will readily
re-disperse into water without the need for a dispersant or surfactant
to be pre-mixed into the water. This does not occur with dry ground
Attapulgite dispersed with TSPP and dried by conventional means
such as a rotary dryer or a flash dryer. In addition, with the removal
of non-clay minerals, higher performance is observed in the ability
to provide thixotropy, binding, and suspension behavior.
Another unexpected discovery was the ability of the adsorbed sodium
polyacrylate or TSPP to allow the Attapulgite to retain its thixotropic
properties when dried to less than 0.5% moisture at atmospheric
pressure with high air turbulence, without the need for vacuum drying
and/or without the need for a silicone or silane type stabilizer.
Commercially, a dryness of approximately 2-3% moisture is practical.
Another unexpected discovery was the wet processing method of attapulgite
production results in a higher percentage of high aspect ratio attapulgite
crystals being liberated from the individual clusters when compared
to attapulgite which is processed by grinding dried attapulgite
ore. The removal of the crystalline silica and calcium carbonate
by using the wet process eliminates the abrasive grinding experienced
in conventional mechanical grinding processes. See FIG. 1 and FIG.
In the present invention, Attapulgite clay ore is mined and crushed
into pieces small enough so that they can be blunged into a slurry.
The sodium polyacrylate dispersant, having a molecular weight range
of between 4000 and 5000 is pre-mixed with water. The sodium polyacrylate
concentration preferably is between 1 and 4 weight % of the clay
content. The Attapulgite clay is gradually added under moderate-to-high
shear to the water--sodium polyacrylate solution, until fully dispersed.
The Attapulgite bundles and clusters become separated into colloidal
particles allowing for the liberation of other non-Attapulgite particles
from the dispersed Attapulgite bundles. The non-clay particles are
removed along with the non-clay matter including grit, via physical
means. The substantially de-gritted Attapulgite clay is then de-watered
or dried in dryer that uses, heated turbulent air at atmospheric
pressure until the desired residual moisture content is achieved.
Preferably, the drying process is at atmospheric pressure at a temperature
between 85.degree. C. and 210.degree. C. During the drying process,
the particles `self-coalesce` into loosely bound elongated rods.
They do not re-flocculate into tightly bound bundles and agglomerates.
The final form may include a filter cake or a dried powder. The
filter cake and/or the dried powder can be easily re-dispersed into
water without the use of additional dispersant. One effective drying
method which may be employed is spray drying. Spray drying offers
the ability to produce uniformly sized granules whose size can be
controlled by adjusting the process conditions in the spray dryer.
Other air swept drying methods have also been proven to work efficiently
where heated turbulent air is used between 85.degree. C. and 210.degree.
C. with similar results. Thus, finely sized Attapulgite granules
can be made without a grinding or milling procedure that would fracture
the Attapulgite crystals, thereby reducing performance.
EXAMPLES 1 THROUGH 9
Samples of various quality clay were slurried, using between 1.0
and 1.8 weight percent, on a dry clay basis, of sodium polyacrylate
with a molecular weight between 4000 and 5000. The slurries consisted
of approximately 25 weight % clay in de-ionized or distilled water.
The sodium polyacrylate was mixed with the water until a homogeneous
solution was achieved, then the clay was gradually added under moderate-to-high
shear, until completely wetted. The slurries were filtered with
a 325 mesh screen and then dried into a free flowing powder. X-ray
and Atomic Absorption analysis methods were used to compare the
compositional quality of the raw material and the finished material.
The following species were identified: Attapulgite, smectite clay
(i.e., montmorillonite, sepiolite), quartz, calcite, dolomite, apatite,
illite, mica, kaolinite, as well as other trace minerals. The results
are listed below in Table 1.
TABLE 1 Material Identification % Attapulgite % Smectite % Quartz
% Calcite #1 85 2 7 <1 #2 85 2 4 ND* #3 90 1 3 ND #4 85 1 6 ND
#5 90 1 3 ND #6 85 1 6 ND #7 90 <1 3 ND #8 60 30 3 ND #9 60 25
4 <1 *ND not detected
Specimen #1 the reference specimen, is a relatively high quality
grade with 85% Attapulgite content, with a low 2% smectite content,
without any processing. Specimen #2 the control specimen, which
is specimen #1 that was processed according to the preceding paragraph,
except that TSPP was used as the dispersant in place of sodium polyacrylate.
Specimen #2 did not exhibit any purification other than some grit
removal during the screening. The Attapulgite and smectite contents
remained the same. Specimen #3 was also processed from Specimen
#1 according to the preceding paragraph, this time using the above-identified
sodium polyacrylate dispersant. Specimen #3 tested with an increase
in Attapulgite content from 85 to 90%. The smectite content decreased
1%. The remaining 4% is comprised of an additional 1% reduction
of quartz plus reduced amounts of apatite, illite and mica. This
can be attributed to the increased dispersion of the Attapulgite
bundles, freeing up more entrapped contaminant particles via physical
separation. Specimens #4 and #6 are two other grades of Attapulgite
clay, a low and high gelling grade, respectively which have been
processed with TSPP but without the sodium polyacrylate dispersant.
Specimens #5 and #7 are the corresponding specimens treated with
the sodium polyacrylate dispersant. In both cases, the Attapulgite
content increased from 85 to 90%. Specimen #8 is a relatively impure
Attapulgite, with a high smectite content of 30%. Upon processing
with the sodium polyacrylate dispersant, (Specimen #9) the smectite
content is reduced from 30 to 25%, along with a drop in illite/mica
content from 6% to 1%.
A specimen of Attapulgite clay, with a moisture content of between
8 and 13 weight %, was dispersed in tap water at 35% solids, using
said sodium polyacrylate dispersant. The viscosity was measured
at 300 cps using a Brookfield RVT viscometer. The slurry was then
de-gritted with a 325 mesh screen and dried at 105.degree. C. at
atmospheric pressure to a powder to approximately the original moisture
content. The de-gritted Attapulgite was then re-slurried into water
at 35% solids without the use of any additional dispersant. The
viscosity was then measured at 340 cps. The slight increase is proportional
to the amount of grit removed and the results can be considered
similar and within experimental reproducibility.
A specimen of Attapulgite clay was dispersed using said sodium
polyacrylate dispersant in tap water at 35% solids. The slurry was
de-gritted and spray dried to yield a dry, powdered Attapulgite.
The free moisture content was determined and the viscosity was measured
at an industry standard quality control test level of 7% solids
in water. The Attapulgite powder was then dried further at approximately
105.degree. C. to produce various free moisture content specimens.
These specimens were subsequently tested for their respective viscosities
and ability to re-flocculate into a gel structure that provides
TABLE 2 Free Moisture Viscosity @ 7% Content (%) solids in deionized
water (cps) 9 10 5 8 1 8 1 6 0.5 6 <0.1 6
The specimen dried to 0.5% free moisture was re-slurried in tap
water at 7% solids. The viscosity was approximately 6 cps. Upon
the addition of 0.7% (total weight basis) potash, the resulting
viscosity obtained was 3100 cps; indicating the ability to re-flocculate
and generate a gel structure.
A specimen of Attapulgite was slurried into water at 35% solids
using various grades of sodium polyacrylate dispersants. The amount
of dispersant used was varied between 1 and 2.5% in order to determine
the most effective level, using the minimum viscosity obtained as
the criteria (an indication of degree of dispersion). The results
were recorded as viscosity vs % dispersant added (Table 3). Note:
non-crosslinked sodium polyacrylates with molecular weights greater
than approximately 4700 are not known to exist. It can be expected
that, if available, they would exhibit similar or improved performance.
TABLE 3 Viscosity vs. Wt. % Dispersant [Molecular Weight] 
   Wt % cps cps cps cps 1 1360 4925 4900
6050 1.25 300 860 1900 3850 1.5 730 1160 1555 2700 1.75 1200
855 1755 2800 2 2050 2625 3525 2.25 2750 2125 2.5 3225
The observable trend is that higher molecular weight sodium polyacrylates
are more efficient dispersants.
The effectiveness of dispersant with respect to the viscosity was
tested using dionized water and saturated salt water. Brookfield
viscosity values (in cps) were obtained with: 1. 30% crude clay
with 3.2% sodium polyacrylate (mw 4700) 2. 30% crude clay with
2% TSPP 3. 30% crude clay with 2% TSPP which had been dried and
The above results are unexpected compared to Attapulgite clay prepared
by methods used prior to this invention. In deionized water without
salt, the Attapulgite clay readily disperses and the viscosity is
not changed. This is because there is no excess ionic contamination
in the Deionized Water, the clay readily disperses but forms no
gel structure because there are not enough ions present to flocculate
it. However, the relatively high viscosity obtained with 40% solids
is most unexpected and is an indication of the ability of the effectiveness
of the dispersants in the wet procedure. In previously known dry
procedures, TSPP has not demonstrated the ability to disperse the
clay in deionized water. The drying and rehydrating of TSPP treated
clay has not been known previously.
Salt in water causes the clay to set and gel. Saturated salt water
is most effective in producing gelling. Using prior art, it is generally
possible to obtain a maximum viscosity in the range of 20000-25000
cps. The clay plus dispersant of the present invention produced
a viscosity of 32000 to 35000 with 20% solids. Viscosities as
high as 88000 cps have been obtained in saturated salt water.
In summary, clay ore is purified and separated from non-Attapulgite
material by dispersing the ore in an aqueous solution of sodium
polyacrylate having a molecular weight of approximately 4000-5000.
Non-Attapulgite materials are efficiently liberated from in between
the Attapulgite Bundles in this sodium polyacrylate solution. Non-clay
material ("grit") is liberated as well. In this manner,
the Attapulgite clay can be separated from non-Attapulgite material.
The slurry is dried to provide a powder of Attapulgite clay. There
is residual sodium polyacrylate in the dried Attapulgite clay such
that upon addition of water, the Attapulgite redisperses without
the addition of further dispersant. The redispersed Attapulgite
clay retains thixotropic properties. Thus, a purified form of Attapulgite
clay is provided which is more economical to use. Also, poorer quality
clay ore can be processed economically to provide more purified
The method blunging the crude Attapulgite was as follows:
Three 55 gallon drums of crude Attapulgite were dispersed with
TSPP. The slurry was made to 30% solids using 2% TSPP based on the
weight of the clay. The blunged slurry was screened over a 200 mesh
screen and the -200 mesh fraction passing through the screen was
retained for use. The +200 mesh fraction retained by the screen
Three 55 gallon drums of crude Attapulgite were dispersed with
sodium polyacrylate. The slurry was made to 30% solids using 3.2%
sodium polyacrylate based on the weight of the clay. The blunged
slurry was screened over a 200 mesh screen and the -200 mesh fraction
passing through the screen was retained for use. The +200 mesh fraction
retained by the screen was discarded.
The slurry of Example 14 and Example 15 were each dried to a free
moisture content of between 2-3%. Each of the dried Attapulgite
clays were redispersed in water using a low shear apparatus.
Although many means may be used to mix the crude clay and aqueous
dispersant, a preferred method is to use a high shear mixer. The
high shear mixer more efficiently produces the desired mix of the
clay with aqueous dispersant to separate the clay from the non-materials
present in the clay.
Thus, it has been shown that by using the wet process method with
either TSPP or sodium polyacrylate, that Attapulgite clay can be
separated from grit and non-clay and can be dried to a free moisture
content of approximately 2-3% which can be easily redispersed in
water with low shear.
Obviously, many modifications may be made without departing from
the basic spirit of the present invention. Accordingly, it will
be appreciated by those skilled in the art that within the scope
of the appended claims, the invention may be practiced other than
has been specifically described herein.