Pumpable and flowable bentonite clay slurries having a bentonite
solids content of about 50% or greater have been prepared for the
first time through the use of a non-aqueous fluidizing agent, characterized
by being a highly-saturated hydrocarbon oil with low affinity for
reactivity with bentonite or other hydrophilic swelling agents such
as starches, guars and xanthans. The slurries are useful in the
economical transport of bentonite without impairing its swellability
in aqueous media in applications such as mining, papermaking and
What is claimed is:
1. A high-solids, pumpable bentonite slurry, comprising a mixture
(a) a fluidizing agent consisting essentially of one or more hydrocarbon
oils exhibiting a degree of saturation of 95% or greater; and
(b) a bentonite clay wherein a level of solid bentonite in the
slurry makes up from 15 to 65% by weight of the total.
2. A bentonite slurry according to claim 1, wherein said fluidizing
agent is a liquid hydrocarbon containing from 18 to 23 carbons.
3. A bentonite slurry according to claim 2, wherein said liquid
hydrocarbon is a mixture of hydrocarbons containing 15 to 30 carbon
atoms and exhibiting a degree of saturation of at least about 95%.
4. A method for preparing a high-solids pumpable bentonite slurry,
comprising stirring particulate bentonite clay into a non-aqueous
fluidizing agent consisting essentially of hydrocarbon oils of from
15 to 50 carbon atoms per molecule exhibiting degree of saturation
of at least about 95%, so that the final bentonite solids content
in the slurry is greater than about 50% by weight.
5. A method according to claim 4, wherein said hydrocarbon oils
are a mixture of hydrocarbons containing 15 to 30 carbon atoms.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the use of non-aqueous fluidizing agents
for the preparation of stable, pumpable bentonite clay slurries
containing more than 15% to upwards of 50% solids by weight. In
slurries made according to the present invention, there is no significant
diminution of commercially valuable properties of the bentonite,
particularly its application as a thickener in aqueous media.
2. Description of the Prior Art
Bentonite is a generic term of a number of aluminum silicate clay
minerals which in native form appear as flakes or sheets, not unlike
mica. Structurally, bentonites consist essentially of flat plates
of aluminum-oxygen-silicon molecules laminated together like the
pages of a book. In contact with water, bentonite swells as it "unleafs".
It is believed that a strong electrostatic force between the layers
of the mineral draws in the polar liquid water and the sheet-like
structure swells up to eight times its original size as water forces
itself between the "pages".
Because of their very great water absorbency, bentonites result
in a thickening of aqueous media to which they are added, affording
a wide number of applications in the fields of paper-making, oil
recovery, mining and tunnel formation, agriculture, and drilling
muds to name only some major applications.
However, their very property of swelling in water upon which useful
applications of bentonites are based, leads to serious problems
in the handling, delivery and transportation of bentonite clays.
Pumpable aqueous slurries of bentonites do not commonly exhibit
a solids content of more than about 7%, above which settling or
caking occurs which impairs or destroys the pumpability of the slurry.
Not only is the maximum solids content of a pumpable aqueous bentonite
slurry only about 7%, but stock aqueous slurries of bentonite must
be kept agitated to prevent settling and caking which is very difficult
By way of example, in current paper-making operations carried out
at paper mill sites, bentonite clay is added to the head box after
dilution from a concentration of about 7% solids to about 0.5% solids.
This procedure requires significant expertise and care in order
to maintain uniform swelling response properties on the paper line.
Too, the operation naturally requires a large volume of make-up
water. On-site make-up involves considerable space and costly equipment
and servicing; a typical fabrication unit in a paper plant costs
more than $150,000.
Another illustration of the limitations inherent in the use of
aqueous bentonite slurries is afforded by the use of such slurries
in field applications, such as tunnel stabilization. Bentonite must
be pumped at the site at solids contents of only 1-5%. This has
the desired effect of placing the bentonite into selected locations,
but "uses up" a significant portion of the total water
absorbency of the bentonite clay.
It has been a generally recognized desideratum to provide a suspension
medium for bentonite slurries which itself is of high fluidity (therefore
permitting enhanced bentonite solids content) but which does not
interfere with the desired end-use subsequent swelling of bentonite
by water. As noted above, as a carrier any aqueous medium causes
swelling and uses up some of the absorbency.
A number of approaches are known which seek to resolve this problem
through the addition of any of a wide variety of additives or processing
stages. While some of these approaches have resulted in the preparation
of higher solids slurries--up to about 15% bentonite solids--they
generally increase costs considerably and usually harm subsequent
use of the bentonite as a thickener. Additionally, the control of
the swelling process is often not reproducible from batch to batch
and problems of settling and caking are still present.
Attempts have been made to use non-aqueous fluids as carriers of
the mineral, but these often brought their own problems such as
flammability, toxicity, or interference with the commercial process
in which bentonite serves as the thickener, e.g. paper-making. Some
likely candidates as carriers proved useless because of almost instantaneous
interaction with the bentonite to cause gelling or solidification
of the mixture.
SUMMARY AND OBJECTS OF THE INVENTION
In our efforts to find a useful non-aqueous fluidizer which would
allow the preparation of high solids, pumpable bentonite slurries,
we concluded that, at the minimum, the following conditions should
(i) the fluidizing agent should be "inert" in the sense
of minimal physical-chemical interactions between the fluid and
(ii) the fluidizing agent should not interfere with the normal
and intended operation of the bentonite (retention, formation, pitch
removal, viscosity increase, lubrication, etc);
(iii) the fluidizing agent should not be toxic or otherwise hazardous
for use in the intended application of the mineral, e.g. in paper
(iv) the fluidizing agent should allow slurries of significantly
more than 15% bentonite solids to be prepared; and
(v) the fluidizing agent should be readily available at relatively
low cost to permit its widespread use.
A particularly preferred fluid is highly saturated lubricating
oil that has been subjected to repeated hydrogenation steps to produce
an oil having a degree of saturation of about 95% or greater. An
example of such an oil is M-65, CAS [chemical abstract services]
No. 72623-86-0, which is a mixture of hydrotreated hydrocarbons
containing 15 to 30 carbon atoms, CAS No. 72623-95-9, which is a
mixture of hydrotreated hydrocarbons containing 20 to 50 carbon
atoms, and CAS No. 72623-87-1, which is a mixture of hydrotreated
hydrocarbons containing 20 to 50 carbon atoms.
The lubricating oil having CAS No. 72634-86-0 is obtained by treating
light vacuum gas oil and heavy vacuum gas oil with hydrogen in the
presence of a catalyst in a two stage process with dewaxing being
carried out between the two stages. It consists essentially of hydrocarbons
containing 15 to 30 carbon atoms. The lubricating oils having CAS
No. 72623-85-0 and 72623-87-1 are obtained by treating light vacuum
gas oil, heavy vacuum gas oil and deasphalted residual oil with
hydrogen in the presence of a catalyst in a two stage process with
dewaxing being carried out between the two stages. It consists essentially
of hydrocarbons containing 20 to 50 carbon atoms.
With a view to achieving the objects and overcoming the problems
aforementioned, the present invention provides according to one
aspect thereof a high-solids, pumpable bentonite slurry which comprises
a fluidizing agent consisting essentially of one or more hydrocarbon
oils exhibiting a high degree of saturation, mixed with from about
15 to upwards of 50% by weight of bentonite clay.
According to another aspect of the invention, there is provided
a method for preparing a high-solids pumpable and flowable bentonite
slurry by stirring particulate bentonite clay into a non-aqueous
fluidizing agent to a content of greater than about 50% bentonite
solids, where the fluidizing agent consists essentially of highly
saturated hydrocarbon oils of from 15 to 50 carbon atoms per molecule.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments and applications of the invention will hereinafter
be described with reference made to the drawings, in which:
Drawing 1 is a schematic illustration of use of high-solids bentonite
slurries according to the invention to isolate an area in which
pit mining operations are carried out, controlling seepage of ground
water into the pit;
Drawing 2 is a schematic representation of the use of bentonite
slurries according to the present invention in the recovery of petroleum
from a subterranean pool of oil;
Drawings 3a and 3b schematically illustrate the use of slurries
according to the present invention to provide bentonite solids for
the stabilization of soil in tunneling applications, such as subway
Drawing 4 schematically illustrates the use of pumpable bentonite
slurries according to the present invention to assist in the recovery
of oil in a drilling operation, comprising the drilling mud.
BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT
A number of potential candidates among non-aqueous organic fluids
were tested for ability to carry high levels of bentonite clays
in stable dispersion. We found that even some of the nominally "inert"
or "saturated" oils which were available exhibited high
interaction with bentonite that precluded their use for the desired
One particular commercially available oil was found to yield remarkably
superior results, namely the saturated oil referred to as M-65 in
the experimental examples given below, as well as mixtures of this
oil with a minor proportion of oil M-FTS-365 as additive.
We concluded that good results were obtainable, where a hydrocarbon
oil was saturated to the highest degree possible through a series
of hydrogenation steps to achieve a degree of saturation of 95%
or greater. This degree of hydrogen saturation may be measured by
monitoring of physical properties or by chemical measurement of
the "Iodine Number", long used to determine the level
of residual unsaturation in hydrocarbons.
What we have found to be of critical importance, however, is that
the "saturation" not be achieved by the addition to hydrocarbon
double bonds of functional groups or constituents other than hydrogen
itself; such added functionalities typically exhibit a strong surface
reactivity on bentonite clays and do not yield "bentonite inert"
The material that has shown the best effect upon fluidizing bentonites
is a "severely" saturated lubricating oil via severe sequential
hydrogenation steps having a degree of saturation of about 95%,
or greater. It is recognized under CAS number 72623-86-0, being
primarily composed of hydrocarbons containing 18-23 carbons. The
viscosity of the oil is quite low at 8.9 cst (at 40.degree. C.)
and 2.5 cst (at 100.degree. C.). This is marketed by Merlyn Coatings
& Chemicals under the name M65.
Use of Various Fluids as Bentonite Fluidizers FLUID BENTONITE MAXIMUM
BENTONITE % mineral seal oil sodium bentonite O* 7 dibutyl phthalate
plasticizer " 10 motor oil " 10-12 mineral spirits solvent
" settles mineral oil B " 13 water " 5 water containing
salt " 7 aqueous zinc salt solution (M-X-1)** " 7-8 cosmetic
grade mineral seal oil " 13 proprietary saturated oil (M-65)**
" flowable at 55% proprietary saturated oil (M-65)** sodium
bentonite 2DH* flowable at 50% *available from Ciba Specialty Chemicals
**available from Merlyn Coatings & Chemicals
Fluidity of High Solids, Non-Aqueous Slurries After Freezing RESULTS
OF FLUIDIZER BENTONITE FREEZING water 7% sodium bentonite irreversible
caking proprietary saturated oil (M-65)** 15% sodium bentonite no
settling or caking proprietary saturated oil (M-65)** 50% sodium
bentonite slight settling, but easily re-dispersible proprietary
oil (M-65) + 0.5% M-FTS-365** 50% sodium bentonite slight settling
*available from Ciba Specialty Chemicals **available from Merlyn
Coatings and Chemicals
The mixtures of bentonites with M65 with or without M-FTS-365 added
does not require any special stirring apparatus or agitation procedure.
A simple mechanical agitation effects the slurrying of the bentonite
in the fluidizing agent.
Although the ability to prepare pumpable bentonite slurries of
such a high solids content is new and surprising, one of ordinary
skill in the art could well contemplate a number of practical applications
for slurries made according to the present invention. Some of these
will now be described, but it must not be inferred that the list
of applications below is all inclusive:
It is current practice to use a bentonite barrier to surround a
mining operation where there is a concern about groundwater seepage
into the pit. As an example, if it were desired to mine the center
of an area in which groundwater was an issue, a trench would be
constructed about the circumference of the proposed area and bentonite
would be placed in the trench. Subsequent contact with the groundwater
promotes swelling and the trench acts as a water barrier. A benefit
of this approach is that the trench could be left after use without
requiring dismantling or removal (as would be the case with "non-dirt"
related materials such as cements or other dam materials). This
is indicated in FIG. 1. The placement of bentonite in the trench
is difficult (as the dry mineral is very light and easily windblown,
and the aqueous slurry of greater than 5% solids cumbersome).
(ii) Oil Recovery
In oil recovery applications it is desirable that water be pumped
down a bore-hole permitting the oil to rise to the surface. This
is schematically represented in FIG. 2. Most oil recovery is associated
with porous substrata and it is necessary to seal these pores of
the bore-hole to direct the bulk of the water stream to the oil
level rather than having the water pressure diluted by having water
channeled off in various other directions. Bentonite, in a fluidizing
form is very suitable in this application as it can be readily directed
into the bore-hole, flow along the walls of the porous substrata,
and upon subsequent wetting with the stream of pressurized water
it will gel in the pores and offer a slick, non-absorbent surface
to the bore-hole. This actually saves not only considerable water
losses into the substrata, but also reduces the subterranean water
pressure. Upon recovery of the necessary oil, this bentonite layer,
unlike artificial materials, need not be removed from the bore-hole
and the hole may be sealed without further action.
In subway and other tunnel applications, bentonite materials are
often used as a soil stabilizer to reduce erosion and soil wash-out
potential. A slurry of about 5% bentonite solids is directed into
the cavity, or around underground conduits and upon subsequent wetting
with water this layer swells and gels and restricts erosion and
in some cases leakage from crack and conduits. Two major benefits
of using the fluidized bentonite are (a) the water holding capacity
of the fluidized bentonite is not impaired (as it is by the presence
of the 95% water added with the 5% bentonite in aqueous slurry form),
and (b) the higher degree of fluidity of the bentonite used with
the fluidizer permits the conduit to be more completely coated as
the fluidized bentonite can adhere to the conduit surface and is
slick enough to flow around the circumference. This is indicated
in FIG. 3.
(iv) Oil Drilling
Because bentonite is slimy when wet it is used to lubricate drill
bits during mining and oil recovery. Use of a fluidized bentonite
which can activate "at a distance" from the entry port
of the drilling cavity permits the lubrication of the bits to be
carried out at the drilling interface, as is illustrated substantially
in FIG. 4. This has the potential to save energy and materials during
the drilling phase.
Bentonite slurries have the ability to aid in paper-making in a
number of ways. It aids in first-pass retention, drainage, removal
of "stickies", and significantly improves formation and
therefore printing uniformity. Most commonly it is used in conjunction
with polymers. In the headbox bentonite is commonly employed at
about 0.5% but initial make-up equipment is necessary to make a
bentonite concentrate at about 7-10%. The slurries must be constantly
agitated to maintain their suspension and the process is both costly
and occupies a high space factor. Water uses are tremendous in the
preparation of the final 0.5% slurry. Use of the fluidized bentonites
should reduce the make-up efforts considerably, will reduce the
amount of make-up water used, and will aid in handling of the bentonite
in winter situations. Potentially it may also assist in the pre-preparation
off-site of the bentonite slurry.
The fluidizing agent used in preparing high-solids bentonite slurries
is effective for the purpose by reason of its physicochemical inertness
relative to the hydrophilic and reactive surface of the bentonite
clays. For that reason, the fluidizing agent is also suitable for
a number of materials other than bentonite commonly used as swelling
agents in aqueous media such as xanthan gums, polyacrylamides and
The examples given in the present application are not to be taken
as exhaustive or limiting, the scope of the invention being defind
by the claims appended hereto.