A process for upgrading a crude bentonite ore such that it can
be used advantageously to prepare unusually high aqueous solution
viscosities. This sequence comprises initially subjecting the crude
ore to a working or shearing stage, followed by a drying step to
about a 5% moisture level. Na.sub.2 CO.sub.3 is then dry-blended
with the material, and the sequence is completed by subjecting the
mix to a pulverizing step.
What is claimed is:
1. A process for enhancing the aqueous viscosity building characteristics
of a bentonite clay; which comprises in sequence the steps of:
(i) subjecting the crude bentonite ore to a shearing step as an
aqueous workable 20 to 50% water slurry by subjecting said workable
slurry to at least one pass through a pug mill;
(ii) drying the product then obtained to a moisture content of
(iii) adding between 1-10% of a bentonite-activating metal salt
or hydroxide, based on solids as a dry-blend; and
(iv) pulverizing the resultant blend into a powder.
2. The process of claim 1 wherein the bentonite-activating metal
salt is selected from one or more members of the group comprising
the water soluble carbonates and sulfates of Group IA and Group
IIA periodic table cations.
3. The process of claim 1, wherein the product in step (ii) is
dried to about 5 to 6% moisture.
4. The process of claim 1, wherein the salt employed is within
the 3 to 5% range based on bentonite solids.
5. The process of claim 4, wherein the salt comprises sodium carbonate.
6. The process of claim 5, wherein the sodium carbonate level is
7. The process of claim 6, wherein the sodium carbonate level is
8. The process of claim 1, wherein the bentonite activator is an
alkali metal hydroxide.
9. The process of claim 8, wherein the hydroxide is sodium hydroxide.
10. The process of claim 1, wherein the bentonite crude ore is
predominantly a calcium bentonite.
11. The process of claim 1, wherein the moisture content upon drying
is about 5% in step (ii).
12. The process of claim 1, wherein a chemical dispersant is present
in the wet slurry during the shearing step.
13. The process of claim 12, wherein the dispersant is tetrasodium
14. The process of claim 12, wherein the TSPP is employed at a
1-5% level based on bentonite solids.
15. The process of claim 12, wherein about 3% of said sodium carbonate
and about 2% of said dispersant are added.
BACKGROUND OF THE INVENTION
This invention relates to a process for preparing bentonite clays,
which when dispersed in water produce unexpectedly high solution
viscosities. Such characteristics are highly desirable in numerous
Bentonites are naturally occurring ores which are mined in various
regions of the world. Since these materials are highly colloidal
and readily swell in water to form thixotropic gels, they are well-known
for use as viscosity builders. This result obtains because bentonites
are platey-type clays having a micaceous sheet structure. Such clays
therefore are self-suspending, swelling and gelatinizing when mixed
with water. Because of these viscosity building characteristics,
bentonites find major utility as viscosity enhancers or builders
in such areas as drilling muds and fluids, concrete and mortar additives,
foundry and molding sands, compacting agents for gravel and sand
as well as cosmetics.
Most natural bentonites are found in nature to exist in the sodium
and/or the calcium form. The performance of a calcium bentonite
as a viscosity builder can often be enhanced by its conversion to
the sodium form.
The prior art details attempts to enhance the viscosity building
characteristics of bentonite clays by several approaches. For the
most part these involve working (or shearing) of the crude bentonite
ore. The sequence generally calls for a (1) working, e.g. milling;
(2) drying; and/or (3) pulverization sequence.
In some instances the use of an alkali pre-treatment is described
to "activate" the clays, prior to the milling or working
Hentz, U.S. Pat. No. 4,371,626 thus discloses that alkali "activation"
is only required for high calcium bentonite clays. It is suggested
that there is an ion exchange mechanism involved where the sodium
ion from either NaOH or Na.sub.2 CO.sub.3 replaces the calcium ion.
Hentz teaches that crude sodium bentonite can be upgraded with respect
to its viscosity building characteristics, without alkali treatment,
simply by (i) shearing the crude clay; (ii) drying the clay; and
(iii) grinding/pulverizing the dried clay.
Alther, U.S. Pat. No. 4,242,140 describes a process for upgrading
crude clays of the bentonite type by (i) adding 1-10% by weight
of NaOH or Na.sub.2 CO.sub.3 to the crude clay, or adding it during
compacting step; (ii) compacting the activator treated material;
and (iii) grinding.
No drying is required by the Alther process, the compacted clay
requires no further drying, and is ground and screened to the desired
Alther subsequently reviewed the state-of-the-art with respect
to bentonite activation in a review article. He summarizes it as
follows in "Improvement in Drill Mud Proper of Low Grade Bentonite
by Simultaneous Chemical Activation and Compacting", INTERCERAM,
Vol. NR 5, 1982, p. 503:
"State of the Art
Activation methods that are presently used are the following: 1.
Sodium carbonate is spread in dry or dissolved form (dissolved in
water) over the previously ripped bentonite bed and worked into
the clay with a disc or roto-tiller. The bed is then frequently
reworked over a period of several months to improve homogeneity.
The sodium carbonate, if spread over the bed in dry form, will dissolve,
due to the bentonite's inherent moisture, rain, water and snow.
When activation is performed on the stockpile, a layer of 15 cm
to 20 cm of bentonite is deposited. Sodium carbonate is then spread
or sprinkled onto this layer, followed by discing. These steps are
then repeated until the desired stockpile size is achieved. 2. Where
bentonites are not field-dried, sodium carbonate may be added to
wet crude bentonite en route to an extruder or multiple extruder
stages, followed by drying. It is common to add water in addition
to sodium carbonate to facilitate extrusion. The shearing action
disorients the particles and increases the ion exchange. Here the
bentonite is not dried and moisture is reduced to approximately
20% after extrusion. 3. The bentonite is first passed through a
mechanical kneader, which works the sodium carbonate into the bentonite,
and then steam is passed through the clay. The steam, whose low
viscosity allows it to penetrate the clay aggregates, will split
them and thus allow penetration and ion exchange. In addition the
mobility of sodium ions is increased due to the action of the steam,
increasing the exchange rate. 4. A pug mill may also be used, whereby
the soda ash is sprinkled onto a field-dried bentonite during its
stay on the conveyor belt, with subsequent pugging. Most of the
above-listed methods have these parameters in common: they either
require time, a large amount of energy, and lots of water, or all
three parameters together. The author found that when a bentonite
is compacted, while sodium carbonate is simultaneously being added,
not only are time and energy saved, but the API properties (viscosity
and water loss) appear to improve much more than with the use of
Lang, U.S. Pat. No. 3,700,474 teaches that the crude bentonite
clays can be made more readily water dispersible by compacting the
clay which has been previously pulverized. However, no mention is
made in either the specification or claims with respect to the need
for any drying sequence or addition of alkali or salt.
Goodman et al, U.S. Pat. No. 4,483,934 describes a method of beneficiating
raw bentonite ore to improve its color. This involves the alkali
treatment of the ore, working, shearing by milling followed by drying
of the product.
It should be noted that in all the cases cited above, the prior
art employs the use of an alkali or salt treatment as an "activator",
either prior to or during the early milling or "working"
stage of the sequence. In no instance is the addition of alkali
considered or described as being added at the last step of the sequence,
such as at "dry-blend", prior to pulverization, and as
a matter of fact, such would be highly contrary to the prior art
SUMMARY OF THE INVENTION
It has now been unexpectedly found that by shifting the processing
sequence from that described in the prior art, we can obtain a significantly
enhanced sodium bentonite capable of unusually high solution viscosities.
The sequence that we have discovered unexpectedly represents a
total reversal of the state-of-the art procedures and theories.
This results in an unanticipated increase in the solution viscosity
of a solution prepared with this inverted bentonite treatment.
The present invention calls for the initial working by shearing
of a 20 to 50% water slurry of the crude ore, which has not had
any salt treatment. The resultant product is then subsequently dried
to about a 5 to 15% moisture level, preferably to about 5 to 10%,
and more preferably to about 5 to 6% moisture. To this dried bentonite
material is then added a "bentonite-activating" metal
salt or hydroxide, typical of which is Na.sub.2 CO.sub.3. The dry-blend
is then pulverized. The preferred Na.sub.2 CO.sub.3 salt is added
in the general range of from 3 to 5%, although With certain crudes
up to as much as 8% to 10% Na.sub.2 CO.sub.3 can be useful.
Although both calcium bentonite and mixtures of calcium bentonite
and sodium bentonite can benefit from the invention, it is preferred
to use a predominantly calcium bentonite as the starting crude.
In accordance with the foregoing, it may be regarded as an object
of the present invention, to provide a process modification which
significantly improves (increases) the viscosity characteristics
of aqueous bentonite solutions.
It is a further object of the invention to provide a method of
upgrading bentonites, particularly calcium bentonites, without the
need for any preliminary, lengthy aging/activation treatment.
DESCRIPTION OF THE PREFERRED EMBODIMENT
According to a preferred embodiment of this invention, the crude
bentonite is initially subjected to shearing in a pug mill. Three
or more passes through the milling process are often beneficial,
but may not be required for many bentonites, wherein but a single
pass confers most of the benefits of the invention. The pug mill
can, for example, be of the type described in U.S. Pat. No. 3,574,345.
The sheared product thus obtained is then dried to a moisture level
of about 5 to 6%; although higher levels o moisture can be used,
up to 10 to 15%.
The dried product obtained at this stage of the sequence is then
dry-blended or mixed with preferably about 3-5% Na.sub.2 CO.sub.3
(in some instances up to about 8-10% Na.sub.2 CO.sub.3 by weight
can be beneficial), and the resultant mixture is then pulverized.
This is distinguished from the prior art since the Na.sub.2 CO.sub.3
salt in this case is added, by simple dry-blending, at the end of
the process. The prior art teaches addition of salts such as Na.sub.2
CO.sub.3, either to the ore stage or during the initial milling
stage to activate the ore.
According to a further aspect of this invention, the following
broad category of bentonite-activator salts and hydroxides will
be effective in meeting the objectives of the invention:
Group IA periodic table cations including Na.sup.+, Li.sup.+, K.sup.+
and Cs.sup.+ in soluble salts and hydroxides, including carbonates
and sulfates are considered useful. In Group IIA cations, Mg.sup.++
in soluble salt form is useful. The transitional metals, Ni.sup.++,
Zn.sup.++, Cu.sup.++ and possibly Co.sup.++ are considered useful.
The above cations will be available as carbonate and sulfate salts
or hydroxides. In specific instances, (NH.sub.4).sub.2 CO.sub.3,
Al.sub.2 (SO.sub.4).sub.3 and Fe.sub.2 (SO.sub.4).sub.3 may be useful
activators for certain clays.
The preferred treatment of this invention involves the use of Na.sub.2
CO.sub.3, which has been found to give the most beneficial results.
The level of salt addition which has been found to be most effective
is broadly between 1% and 10% based on the weight of bentonite;
a preferred range is from 3 to 5% by weight, with the optimum level
being about 5%.
Additionally, the embodiment of this invention may also include,
but is not limited to, the use of an optional dispersing agent during
the shearing step, such as tetrasodium pyrophosphate (TSPP) in amounts
between about 1-5% by weight of the dry bentonite.
The invention is further illustrated by the following Examples,
which are deemed to be illustrative, and not delimitive of the invention
otherwise set forth.
A sample of a crude predominantly calcium bentonite clay wet cake
containing 35% moisture and 2% tetrasodium pyrophosphate dispersant
was sheared by being subject to one pass through a conventional
pug mill, of the type aforementioned. The energy dissipated in the
pass through the pug mill was about 30 Hp-hr/ton of dry solids.
Upon completion of this working step, the material was dried in
a Blue M.RTM. oven until the moisture content was reduced to about
5%. The sample was then dry blended with 3% Na.sub.2 CO.sub.3 and
then pulverized. The sample was then added to water such that the
solution represented 5% solids level. Brookfield viscosity data
was measured at 30.degree. C. using a No. 3 spindle, as 1100 cps.
The processing conditions of Example 1 were repeated, except that
during the pugging step no TSPP was used. Instead, 2% TSPP, together
with 3% sodium carbonate, were dry blended with the sample from
the oven. The resulting Brookfield viscosity (No. 2 spindle) was
555 cps. (In all of Examples 1 to 7, the same crude was used.)
The conditions of Example 2 were repeated, except that no TSPP
was used and 5% sodium carbonate was dry blended with the oven dried
sample. The measured Brookfield viscosity (No. 3 spindle) was 1438
The procedure in this Example constituted a conventional processing
and was a control. Specifically in this instance, a sample of the
same crude bentonite clay, as in Example 1, was subjected to one
pass through the pug mill in the presence therein of 5% sodium carbonate.
The resulting product was dried as in Example 1 to the same moisture
level, and the sample was then added to water and its Brookfield
viscosity (spindle No. 1) evaluated as in Example 1 and found to
be 32 cps.
In this Example, a further control was provided. No pugging was
utilized. Instead, the sample at about 5 to 10% moisture was dry
blended with 5% sodium carbonate and otherwise tested as in Example
1, and found to yield a viscosity (No. 3 spindle) of 920 cps.
This constituted a further control. The procedure used was identical
to Example 4, except that three passes through the pug mill, each
dissipating the mentioned approximate 30 Hp-hr/ton of dry solids,
to a total of 90 Hp-hr/ton. The resulting product displayed a Brookfield
viscosity (No. 1 spindle) of 16 cps.
The procedure was amenable to Example 3, except for the use of
three passes through the pug mill. The measured viscosity (No. 3
spindle) was 1710 cps.
In this Example, (and in Example 9-11) a different bentonite crude
was used than in prior Examples, but still constituting a predominantly
calcium bentonite. The procedure used was the same as in Example
3, and was found to yield a viscosity (No. 1 of spindle) of 152
The procedure used was identical to that of control Example 4,
except the crude was that of Example 8. The resulting viscosity
(No. 1 spindle) was measured at 8 cps.
The procedure utilized in this Example was the same as in Example
8, except that 8% sodium carbonate was dry blended into the product
from the oven. The resulting viscosity was measured (No. 3 spindle)
at 600 cps.
The procedure utilized here was identical to that of Example 9,
except that 8% sodium carbonate was used. The measured viscosity
(No. 1 spindle) was 8 cps.
While the present invention has been particularly set forth in
terms of specific embodiments thereof, it will be understood in
view of the instant disclosure, that numerous variations upon the
invention are now enabled to those skilled in the art, which variations
yet reside within the scope of the present teaching. Accordingly,
the invention is to be broadly construed, and limited only by the
scope and spirit of the claims now appended hereto.