Method of improving water-swellable clay properties by re-drying, compositions and articles

A method of treating a water-swellable clay, initially having a Fe.sup.+3 /Fe.sup.+2 ratio of at least 1.0, preferably at least 3.0, and most preferably in the range of about 5.0 to about 15.0, after the clay has been mined and dried. After the common initial drying of the clay to a moisture content of 12% or less, the clay is re-wetted to a moisture content of more than 12% by weight, preferably at least about 15% or more, based on the dry weight of the clay, then re-dried to a moisture content of 12% by weight or less, based on the dry weight of the clay. This re-wetting and re-drying processing of a dried clay unexpectedly improves the water absorbency, and viscosity properties; increases the effectiveness of the clays as binders in sand molds and iron ore pelletizing; unexpectedly increases the rheology properties of the clays for oilwell drilling fluids, and lost circulation fluids, and as a suspending agent in the cosmetics and pharmaceutical industries; improves the binding characteristics of the clays to act as a binder for iron ores, such as taconite, and sand molding (foundry industry); and provides unexpectedly increased water absorption in forming water-swellable clay-based water barriers.

FIELD OF THE INVENTION 
The present invention is directed to a method of improving many of the 
properties of a non-blue, water-swellable clay, particularly bentonite, 
that initially has acceptable colloidal properties, e.g., has a Fe.sup.+3 
/Fe.sup.+2 ratio above 1.0, and preferably above 3.0, including the steps 
of drying the mined clay, re-wetting the clay, and re-drying the clay to 
improve its water-absorption ability; the dispersion of the clay in water; 
viscosity; fluid loss properties; ability to bind finely pulverized ores; 
and to improve its foundry properties as a binder for sand in the metal 
casting industry. The processed, re-wetted and re-dried water-swellable 
clay is unexpectedly better for use in oil well drilling fluids; lost 
circulation fluids; as a flocculent, for example in waste water treatment 
and wine clarification; as a suspending agent in the cosmetics and 
pharmaceutical industries; as a water-absorbable material to form a water 
barrier mixed with soil, in panels, and in flexible, multi-layer articles; 
for use in water-absorbent articles, such as diapers, tampons, absorbent 
pouches and the like; for pelletizing iron ore, particularly taconite; and 
for any other purpose wherein a water-swellable clay is used for its water 
absorption properties, dispersion properties, viscosity properties, and/or 
its ability to act as a binder. 
BACKGROUND OF THE INVENTION AND PRIOR ART 
Water-swellable clays that have acceptable water-swellability and colloidal 
properties, e.g., the non-blue bentonites having a Fe.sup.+3 /Fe.sup.+2 
ratio above 1.0, and preferably above 3.0, have a great number of 
industrial uses that rely upon the ability of the clay to absorb many 
times its weight in water, to provide a gel structur of sufficient 
strength to hold solids in suspension, and the ability of the 
water-swellable clays to act as a binder in forming sand molds in the 
metal casting industry and in pelletizing finely divided ores, e.g., iron 
ores, such as taconite. Some bentonite clays, such as the blue bentonites 
disclosed in Clem U.S. Pat. No. 2,672,442, require the uptake of calcium 
ions to provide acceptable water swellability and colloidal properties for 
industrial acceptance. The water-swellable clays useful as starting 
materials in accordance with the present invention are non-blue bentonites 
(green to greenish yellow to yellow to cream colored) that have 
industrially acceptable water swellability and colloidal properties and 
have a Fe.sup.+3 /Fe.sup.+2 ratio greater than 1.0, preferably at least 
3.0, and most preferably in the range of about 5.0 to about 15.0. Some of 
the industrial uses for these non-blue bentonites are generally described 
below. 
1. Drilling Muds 
In drilling wells by rotary methods it is a common practice to circulate, 
continuously, a drilling mud or fluid into and out of the borehole during 
the drilling operation. The drilling mud is pumped into the drill pipe 
from a mud pit and the mud passes down to the bottom of the borehole. The 
drilling mud then flows upwardly through the annular space between the 
borehole wall and the drill pipe, and finally flows from the borehole 
through a mud ditch back to the mud pit, wherein the mud is mechanically 
or chemically treated before recirculation through the borehole. 
The drilling mud serves several purposes that influence such factors as the 
drilling rate, cost, efficiency and safety of the operation. The drilling 
mud lubricates and cools the drill bit, acts as a vehicle to carry the 
cuttings from the borehole, and provides sufficient equalizing hydrostatic 
pressure against the formation wall to prevent the borehole wall from 
cave-in during drilling. By using proper mud formulations, the borehole 
entry of gases and fluids encountered in the formations pierced by the 
drill is inhibited, thereby preventing possible collapse or blowouts 
resulting from uncontrolled influxes of these formation fluids. The 
drilling mud also exerts a "wall-building" effect whereby it often forms a 
thin filter cake on a borehole wall, thus sealing off the borehole and 
reducing water loss to the penetrated formations. 
An acceptable mud must have body, yet be free-flowing with relatively low 
viscosity in order to facilitate pumping. The mud must also have an 
acceptable gel strength in order to suspend solid material, if circulation 
is interrupted, and to prevent accumulation of solids at the drill bit to 
avoid mechanical jamming. Acceptable drilling muds may be either oil-based 
or water-based, and they are normally treated to provide the rheological 
properties that make them particularly desirable and useful for drilling 
wells. For example, drilling muds may be treated with barium sulfate 
(barite) or lead sulfide (galena) to increase their density. 
The efficiency of the drilling process is related to the velocity of the 
mud flowing up the annular space between the borehole wall and the drill 
pipe. This velocity is in turn related to the viscosity, density and flow 
properties of the mud. In addition, the drilling mud viscosity is known to 
depend upon the quality, concentration and state of dispersion of the 
colloidal solids of the mud. As the drilling operation proceeds, the 
rheological properties of the mud may be adversely affected by such 
factors as the nature of the drilled strata, loss or gain of water to the 
mud, chemically-active contaminants that may flocculate the mud, mud pH, 
and most importantly, the increasing temperatures and pressures 
encountered at deeper drilling depths. In order to maintain workable 
viscosities, the muds must be formulated to respond to varying 
circumstances and conditions encountered during use. Since improvements in 
efficiency are realized as the viscosity and density of a mud are 
increased, it is desirable to optimize drilling mud formulations to 
possess the highest viscosity and density workably feasible for a given 
formation at a given depth. 
Whenever possible, usually for reasons of economy, water-based drilling 
muds are used throughout the drilling operation. The suspending solids in 
water-based drilling muds are typically clays from the kaolinite, 
montmorillonite or ilite groups. These clays impart desirable thixotropic 
properties to the drilling mud and also coat the walls of the well with a 
relatively impermeable sheath, commonly called a "filter cake", that 
retards fluid loss from the well into the formations penetrated by the 
well. 
An exemplary montmorillonite clay that can be used in a water-based 
drilling mud is non-blue bentonite. The bentonite is dispersed within the 
water-based liquid as colloidal particles and imparts various degrees of 
thixotropy to the drilling mud. Non-blue, e.g., sodium bentonite, water 
swellable clays, that are re-wetted and re.dried, in accordance with the 
present invention are initially non-blue clays, e.g., are initially 
industrially acceptable for this purpose, having good water swellability 
and colloidal properties and having a sufficient ratio of Fe.sup.+3 
/Fe.sup.+2, at least above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and, after processing, 
have excellent rheological properties for use in preparing aqueous 
drilling muds. 
2. Lost Circulation Fluid 
One difficulty often encountered in rotary drilling operations involves the 
loss of unacceptably large amounts of the drilling mud into a porous or 
cracked formation penetrated by the drill. The loss of drilling mud is 
termed "lost circulation", and the formation is termed a "lost circulation 
zone" or a "thief formation". 
Lost circulation occurs when the well encounters a formation either having 
unusually high permeability or having naturally occurring fractures, 
fissures, porous sand formations, cracked or cavernous formations and 
other types of strata characterized by crevices, channels or similar types 
of openings conducive to drilling fluid loss. In addition, it is also 
possible for a formation to be fractured by the hydrostatic pressure of 
the drilling mud, particularly when a changeover is made to a relatively 
heavy mud in order to control high internal formation pressures. 
When lost circulation occurs, the drilling mud pumped into the well through 
the drill string enters the cracks in a cracked formation or the 
interstices of a porous formation and escapes from the wellbore, therefore 
precluding return of the drilling mud to the surface. In the most severe 
situation, the lost circulation zone takes the drilling mud as fast as it 
is pumped into the wellbore, and, in less severe situations, circulation 
of the drilling mud can be greatly reduced, and eventually result in a 
shutdown of drilling operations. Normally, the maximum amount of drilling 
mud loss that is tolerated before changing programs is approximately one 
barrel per hour. If a greater amount of drilling mud is lost, corrective 
measures are needed. Drilling generally is not resumed until the thief 
formation is closed off and circulation of the drilling mud reestablished. 
The interruption of normal circulation prevents the entrainment of cuttings 
and other materials from the borehole, leads to reduced hydrostatic 
pressure, possibly followed by the influx into the wellbore of high 
pressure formation fluids, and can result in the flooding of oil.producing 
zones with mud or the like, and may eventually cause the drill string to 
become stuck in the borehole. Even in situations where circulation is not 
completely lost and some drilling mud can return to the surface, the 
drilling mud flowing into the lost circulation zone must be replaced 
continuously. If the drilling mud loss is sufficiently high, the cost of 
continued drilling or well operation may become prohibitive. Therefore, 
the lost circulation of drilling mud is a condition that must be prevented 
or be corrected as quickly as possible. 
The best method of controlling lost circulation is to conduct a drilling 
program such that mud loss will not occur. However, situations exist 
wherein even correct drilling techniques cannot avoid lost circulation. 
Therefore, many methods have been used in attempts to plug the cracks or 
interstices of lost circulation zones to prevent the escape of drilling 
muds. As a result, a wide variety of materials have been pumped into the 
well with the drilling mud in an effort to bridge or fill the cracks or 
interstices of thief formations. It has been found that some materials are 
successful under certain drilling conditions, yet the same material is 
unsuccessful under other drilling conditions. 
One common method is to increase the viscosity of the drilling mud or to 
increase the resistance of the drilling mud to flow into the formation. 
Another technique involves the addition of a bulk material, such as 
cottonseed hulls, cork, sawdust, perlite, ground walnut shells, hay, wood 
shavings, granular plastic, vermiculite, rock, mica flakes, leather 
strips, beans, peas, rice, sponges, feathers, manure, fish scales, corn 
cobs, glass fiber, asphalt, ground tires, burlap or other fabrics to the 
drilling mud. By adding these fibrous, flaky or granular solids to the 
drilling mud and pumping the resulting mixture into the borehole, a bridge 
or mat forms over the cracks or interstices responsible for drilling mud 
escape. 
Although lost circulation zones frequently are plugged by such bulk 
materials, successful plugging of the thief formation is not assured. Even 
if large volumes of a solids.containing drilling mud are pumped into the 
borehole, a bridge or mat may never form over the cracks or interstices of 
the thief formation. Moreover, the introduction of large quantities of a 
drilling mud containing a relatively high percentage of bulky solids can 
produce pressure surges that cause further fracturing and therefore result 
in additional fissures for even greater drilling mud losses. Bulk 
materials further proved unsuccessful in sealing off porous formations 
because they have a tendency to deteriorate under the high drilling 
pressures, and therefore decrease in volume and become slimy so as to 
"worm" into the formation openings without forming an effective seal. 
The water-swellable clays processed in accordance with the present 
invention are processed by starting with an industrially acceptable, e.g., 
non-blue bentonite clay, that is initially industrially acceptable for 
this purpose, having good water swellability and colloidal properties and 
having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at 
least 3.0 and most preferably in the range of about 5.0 to about 15.0. The 
non-blue bentonite clay is re-wetted and re-dried, as described in more 
detail hereinafter and, after processing, have the ability to continue to 
swell and increase viscosity upon entering the interstices of a thief 
formation for effective plugging. 
3. Foundry Industry Binders 
Green sand molding is the production of molded metal objects from tempered 
molding sand and is the most diversified molding process used to cast 
ferrous as well as non.ferrous metal castings. Green sand molding is 
favored by foundry men because it is economical and permits both quality 
and quantity production. Green sand is defined as a water tempered molding 
sand mixture with plasticity. A green sand mold used for casting steel 
usually consists of silica sand, a clay binder, and/or an organic additive 
mulled together with temper water. 
One or more binders mixed with the silica sand are essential to maintain 
the sand in a predetermined mold configuration. One of the most commonly 
employed green sand binders is clay, such as a water-swellable sodium 
bentonite clay or a low-swellable calcium bentonite clay. The amount of 
the clay binder that is used together with the sand generally depends upon 
the particular type of sand used in the mixture and the temperature of 
firing. Silica sand grains expand upon heating. When the grains are too 
close, the molding sand moves and expands causing the castings to show 
defects such as "buckles" (a deformity in the casting resulting from 
excessive sand expansion), "rat tails" (a rough, irregular depression that 
appears on the surface of a casting, or a minor buckle), and "scabs" (a 
breaking away of a portion of the molding sand when hot metal enters the 
mold). To overcome this harmful expansion, more clay is added to the sand 
mixture since the clay contracts upon firing thereby compensating for the 
expansion of the silica sand grains. In green sand molding, the 
reproducibility of the dimensions obtained on the casting are the result 
of such factors as shrinkage, changes in dimensions of mold cavity, 
hardness of mold, stability of molding sand, mechanical alignment of flask 
and maintaining a fixed temperature. 
Clays have been blended in the past in an attempt to achieve acceptable 
combinations of premeabilities, green compression strengths and dry 
compression strengths in the molding sand mixture or composition. Toward 
this end, it is known to mix a sodium bentonite with a calcium bentonite 
or a kaolinite clay in an attempt to achieve the high dry compression 
strength of the sodium bentonite clay together with the high green 
compression strengths of the calcium bentonite clay and the low 
permeability of the kaolinite clay. See Foundry Sand Practice by Clyde A. 
Sanders, 6th Edition, 1973, pp. 585-590. As set forth in a co.pending 
application, Ser. No. 336,095 filed Apr. 11, 1989, hereby incorporated by 
reference, a mixture of sodium bentonites as a binder in the preparation 
of a foundry sand provides synergistic results with respect to green 
compressive strength; hot compressive strength; dry compressive strength; 
flowability; surface finish; activation speed; and/or shake-out. One or 
more of these properties are better in the blend than each of the sodium 
bentonites, prior to blending. 
It has been found that by processing water. swellable, e.g., bentonite, 
clays by re-wetting and re-drying, in accordance with the present 
invention, by starting with non-blue, e.g., initially industrially 
acceptable water-swellable clays having good water swellability and 
colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 
above 1 0, preferably at least 3.0 and most preferably in the range of 
about 5.0 to about 15.0, after processing, by re-wetting and re-drying, 
such clays have improved foundry properties for use as binders in the 
foundry industry, when used alone or in combination with other 
water-swellable clays. 
4. Iron Ore Pelletizing 
Taconite is a high.grade iron ore that consists chiefly of fine.grained 
silica mixed with magnetite and hematite. As the richer iron ores approach 
exhaustion in the United States, taconite becomes more important as a 
source or iron. To recover the ore mineral in a usable form for the 
production of iron, taconite must be finely ground, and the magnetite or 
hematite is concentrated by a magnetic or other process. The concentrate 
must be agglomerated into chunks of size and strength suitable for the 
blast furnace. 
Industrially acceptable, non-blue, water-swellable clays, particularly 
sodium bentonites, have been used as binders for iron ores, such as 
taconite ores, in the formation of pellets having sufficient strength for 
subsequent processing of the iron ore pellets. Some of the important 
characteristics for the iron ore pellets bound with water-swellable clay 
are: ballability, the balling characteristics (kinetics) of the 
ore-water.clay mixture; wet compression strength of the pellet; resistance 
to fracture by impact (drop test); deformation under load; resistance to 
over-wetting of the pellet surface by recondensation of moisture onto the 
green balls in colder layers during drying; resistance to decrepitation 
(shock temperature), i.e. sudden pellet-spalling occurring when pellets 
are heated too rapidly; and dry compression strength. 
Green ball agglomerates are normally produced by rolling fine ore in drums, 
discs or cones. Through the rolling action in the drum, the ore particles 
are rearranged and come into contact, with each other. At the point of 
contact, the liquid layers around the particles coalesce, causing a 
reduction of the external surface of the water film. A decrease in the 
free surface energy of the agglomerate is the driving force for the 
formation of the nuclei. During the subsequent growth, these aggregates 
are compacted. The porosity decreases and the pore-water is forced to the 
surface. In this so-called transition region, the rate of growth is 
maximal. Investigations into the mechanism of pellet formation have 
demonstrated that the kinetics of green pellet formation are extremely 
dependent on the free moisture content of the system. 
Each system, dependent on ore and the water-swellable clay, has critical 
moisture limits within which strong green pellets are formed. At low 
moisture contents, the rate of pellet growth is slow and the pellets are 
brittle. The rate of pellet growth increases as the amount of moisture 
increases. Beyond this moisture limit, the rate of growth becomes 
excessive, and the pellets produced are irregular, weak and too plastic. 
Therefore, there exists a narrow range in which optimum pelletization 
results are achieved. 
Since it is virtually impossible to extract water from the system, it is 
imperative that the binding additive must have moisture binding ability in 
order to control the effect of moisture in the feed. Bentonite, the most 
common additive, makes less water available to participate in the 
pelletizing process, due to an intracrystalline absorption. 
The starting water-swellable clays that are processed in accordance with 
the present invention, by re-wetting and re-drying, are non-blue, e.g., 
are initially industrially acceptable for this purpose, having good water 
swellability and colloidal properties and having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and, after processing, 
have new and unexpected properties in pelletizing iron ores, particularly 
taconite. 
5. Water Absorbency and Swellability 
The water-swellable clays re-wetted and re.dried in accordance with the 
principals of the present invention are capable of new and unexpected 
water-absorbency and swellability making them very useful for a number of 
industrial products and processes. The water-swellable clays re-wetted and 
re-dried in accordance with the principles of the present invention 
provide unexpected water absorbency and swellability making the clays very 
suitable for use in moisture impervious panels; for preventing water 
contaminated with industrial waste from seeping through soil containing 
one or more of the treated water-swellable clays; for water.proofing 
compositions in non-viscous sprayable forms, or paste or putty-like forms, 
capable of being applied by spray methods, caulking gun, or trowel; for 
use together with elastomers and/or plasticisers for preventing the 
seepage of water through the compositions; together with other additives 
such as xanthan gum and/or other gums for maintaining stability in 
salt.contaminated water; together with other components to manufacture a 
flexible grout composition; for use as a water-swellable material in a 
layered water.sealing article of manufacture; for use in filtering 
contaminants from oils; for use in clarifying aqueous solutions, such as 
in the wine industry, and to flocculate contaminants from waste water; and 
for use in carbonless copy paper when acid treated. 
Examples of these technologies and uses for water-swellable clays are 
disclosed in the following U.S. Patents, all of which are hereby 
incorporated by reference: Clem U.S. Pat. No. 3,186,896; Clem U.S. Pat. 
No. 4,048,373; Clem U.S. Pat. No. 4,021,402; Clem U.S. Pat. No. 4,084,382; 
Clem U.S. Pat. No. 4,087,365; Clem U.S. Pat. No. 4,279,547; McGroarty U.S. 
Pat. No. 4,316,833; Piepho U.S. Pat. No. 4,332,693; Harriett U.S. Pat. No. 
4,534,925; Harriett U.S. Pat. No. 4,534,926; Alexander U.S. Pat. No. 
4,634,538; Harriett U.S. Pat. No. 4,668,724; Harriett U.S. Pat. No. 
4,696,698; Harriett U.S. Pat. No. 4,696,699; Alexander U.S. Pat. No. 
4,886,550; Harriett U.S. Pat. No. 4,733,989; Alexander U.S. Pat. No. 
4,832,793; Harriett U.S. Pat. No. 4,810,573; and Alexander U.S. Pat. No. 
4,847,226. 
Excellent gel strength is achieved when industrially acceptable, water 
swellable, non-blue starting clays are processed in accordance with the 
present invention. The water-swellable clays processed in accordance with 
the present invention are non-blue, e.g., are initially industrially 
acceptable for gel strength, having good water swellability and colloidal 
properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 above 
1.0, preferably at least 3.0 and most preferably in the range of about 5.0 
to about 15.0, and after processing by re-wetting and re-drying, the clays 
are excellent suspending agents for use in the cosmetics and 
pharmaceutical industries in amounts well known in the art. 
SUMMARY OF THE INVENTION 
In brief, the present invention is directed to a method of treating 
industrially acceptable, non-blue, water-swellable clays that are 
initially industrially acceptable, having good water swellability and 
colloidal properties and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2 
above 1.0, preferably at least 3.0 and most preferably in the range of 
about 5.0 to about 15.0, and, after the clay has been mined and dried, 
re-wetting and re-drying the clay for unexpected improvement of clay 
properties. After the common initial drying of the water-swellable clay to 
a moisture content of 12% or less, the clay is re-wetted to a moisture 
content of more than 12% by weight, preferably at least about 15% or more, 
based on the dry weight of the clay, and then re.dried to a moisture 
content of 12% by weight or less, based on the dry weight of the clay. 
This re-wetting and re-drying processing of a dried, non-blue, 
industrially acceptable clay having a Fe.sup.+3 /Fe.sup.+2 ratio above 1.0 
unexpectedly improves the water absorbency, and viscosity properties; 
increases the effectiveness of the clays as binders in sand molds and iron 
ore pelletizing; unexpectedly increases the rheology properties of the 
clays for oilwell drilling fluids, and lost circulation fluids, and as a 
suspending agent in the cosmetics and pharmaceutical industries; improves 
the binding characteristics of the clays to act as a binder for iron ores, 
such as taconite, and sand molding (foundry industry); and provides 
unexpectedly increased water absorption in forming water-swellable 
clay-based water barriers. 
Accordingly, one aspect of the present invention is to provide a new and 
improved method of beneficiating the chemical and/or physical properties 
of already industrially acceptable, non-blue, water-swellable clays, e.g., 
sodium bentonites that have good water swellability and good colloidal 
properties, and having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2, above 
1.0, preferably at least 3.0 and most preferably in the range of about 5.0 
to about 15.0, and, after processing, the re-wetting and re-drying 
improves the usefulness of the clay in one or more industries that 
water-swellable clays are used for their gel strength, suspending 
properties, binding properties, water-absorbing ability, or ability to 
increase the viscosity of aqueous liquids. 
Another aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, and have a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, by initially drying 
the clay to a moisture content of about 12% by weight or less, after 
mining, and thereafter by re-wetting the clay to a moisture content of 
more than 12% by weight, preferably at least about 15% by weight, and then 
re-drying the clay to a moisture content of about 12% by weight or less. 
Another aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, including initially 
drying the mined clay to a moisture content of about 12% by weight or 
less, if necessary; re-wetting the clay to a moisture content of more than 
12% by weight, preferably at least about 15% by weight; and then re-drying 
the clay to a moisture content of about 12% by weight or less. 
Another aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and, after the clay 
has been dried to a moisture content of about 12% by weight or less, the 
clay is processed by re-wetting the clay to a moisture content of more 
than 12% by weight, preferably at least about 15% by weight, and then re 
drying the clay to a moisture content of about 12% by weight or less, to 
improve the gel strength of the clay. 
Still another aspect of the present invention is to provide a new and 
improved method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2 above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and after the clay has 
been dried to a moisture content of about 12% by weight or less, the clay 
is processed by re-wetting the clay to a moisture content of more than 12% 
by weight, preferably at least about 15% by weight, and then re-drying the 
clay to a moisture content of about 12% by weight or less, to improve the 
capacity of the clay to suspend and/or flocculate solids or immiscible 
liquids in aqueous or organic dispersions. 
Another aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and after the clay has 
been dried to a moisture content of about 12% by weight or less, the clay 
is processed by re-wetting the clay to a moisture content of more than 12% 
by weight, preferably at least about 15% by weight, and then re drying the 
clay to a moisture content of about 12% by weight or less, to improve the 
water-absorbing capacity of the clay. 
Another aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and after the clay has 
been initially dried to a moisture content of about 12% by weight or less, 
the clay is processed by re-wetting the clay to a moisture content of more 
than 12% by weight, preferably at least about 15% by weight, and then 
re-drying the clay to a moisture content of about 12% by weight or less, 
to increase the capacity of the clay to increase the viscosity of aqueous 
liquids. 
A further aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and after the clay 
initially has been dried to a moisture content of about 12% by weight or 
less, the clay is processed by re-wetting the clay to a moisture content 
of more than 12% by weight, preferably at least about 15% by weight, and 
then re-drying the clay to a moisture content of about 12% by weight or 
less, to increase the capacity of the clay to bind adjacent particles 
together, such as in forming sand molds for the foundry industry, and in 
binding iron ore particles together in forming iron ore pellets. 
Another aspect of the present invention is to provide a new and improved 
method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and after the clay has 
been dried to a moisture content of about 12% by weight or less, the clay 
is processed by re-wetting the clay to a moisture content of more than 12% 
by weight, preferably at least about 15% by weight, and then re-drying the 
clay to a moisture content of about 12% by weight or less, to increase the 
gel strength of an aqueous drilling mud containing the treated clay. 
Still another aspect of the present invention is to provide a new and 
improved method of treating already industrially acceptable, non-blue, 
water-swellable clays, e.g., sodium bentonites, that have good water 
swellability and good colloidal properties, having a sufficient ratio of 
Fe.sup.+3 /Fe.sup.+2, above 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0, and after the clay has 
been dried to a moisture content of about 12% by weight or less, the clay 
is further processed by re-wetting the clay to a moisture content of more 
than 12% by weight, preferably at least about 15% by weight, and then 
re-drying the clay to a moisture content of about 12% by weight or less, 
to increase the capacity of the clay, in aqueous suspension, to plug 
cracks and interstices in a well to minimize loss of a drilling fluid. 
The above and other aspects and advantages of the present invention will 
become more apparent when considered together with the following detailed 
description of the preferred embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed to a method of treating already 
industrially acceptable, non-blue, water-swellable clays, e.g., sodium 
bentonites, that have good water swellability and good colloidal 
properties, having a sufficient ratio of Fe.sup.+3 /Fe.sup.+2, above 1.0, 
preferably at least 3.0 and most preferably in the range of about 5.0 to 
about 15.0, and after the mined clay is initially dried to a moisture 
content of about 12% by weight or less, the clay is processed by 
re-wetting and re-drying the initially dried industrially acceptable, 
water-swellable colloidal clay to very simply and unexpectedly improve 
many of the properties that make water-swellable clays desirable 
industrial additives. 
The above.defined, non-blue, water-swellable clay starting materials, such 
as non-blue sodium bentonite, are obtained for use in the aforementioned 
industries by mining the clay, in a wet condition, generally having about 
20% to about 25% by weight water, based on the dry weight of the clay, and 
then drying the clay to a suitable moisture content, e.g., 5-10% based on 
the dry weight of the clay so that the clay is suitable for grinding to a 
desired particle size distribution. Sometimes these clays are dried in the 
field to a desirable moisture content of about 10-15% water, based on the 
dry weight of the clay, so that the industrial drying step is unnecessary 
prior to grinding. In any event, the clay is always too wet, as mined, to 
effectively grind the clay to a desired particle size distribution so that 
drying is always necessary after mining and prior to grinding. 
Unexpectedly, and surprisingly, it has been found that if the 
above-defined, non-blue, water-swellable clays are mined and dried and the 
clay is re-wetted to a moisture content of more than 12% by weight, 
preferably at least about 15% by weight water, based on the dry weight of 
the clay, and preferably to about 18% to about 25% water, based on the dry 
weight of the clay, and then re-dried down to a moisture content of about 
12% by weight or less, preferably about 5% to about 8% or 10% water, based 
on the dry weight of the clay, the thus processed clay has improved 
properties of viscosity; water absorbency; capacity to disperse solids and 
water-insoluble materials in aqueous suspension; capacity to flocculate 
suspended solids from water; and binding ability both for the foundry 
industry as a sand binder, and as an ore binder, e.g., iron ore binder, 
particularly a taconite binder for pelletizing taconite. 
The water-swellable colloidal clays that are useful as starting materials 
in accordance with the present invention are non-blue bentonites (green to 
greenish yellow to yellow to cream colored) that have industrially 
acceptable water swellability and colloidal properties, having a Fe.sup.+3 
/Fe.sup.+2 ratio greater than 1.0, and preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0. Such clays, including 
any non-blue, water-swellable colloidal clay which will hydrate in the 
presence of water, i.e., will swell in the presence of water, are 
substantially improved in accordance with the method of the present 
invention. 
In accordance with one important embodiment of the present invention, the 
non-blue colloidal clay is bentonite. A preferred non-blue bentonite is 
sodium bentonite, which is basically a hydratable montmorillonite clay of 
the type generally found in the Black Hills region of South Dakota and 
Wyoming. This clay has sodium as a predominant exchange ion. However, the 
bentonite starting material utilized in accordance with this embodiment of 
the present invention may also contain other cations such as magnesium and 
iron, so long as the Fe.sup.+3 /Fe.sup.+2 ratio of the starting material 
(prior to re-wetting and re-drying) is at least 1.0, preferably at least 
3.0 and most preferably in the range of about 5.0 to about 15.0. 
There are cases wherein a montmorillonite predominant in calcium ions can 
be converted to a high swelling sodium variety through a well.known 
process called "peptizing". The colloidal clay starting material utilized 
in this invention may be one or more peptized bentonites so long as the 
Fe.sup.+3 /Fe.sup.+2 ratio of the starting material (prior to re-wetting 
and re-drying) is at least 1.0, preferably at least 3.0 and most 
preferably in the range of about 5.0 to about 15.0. The non-blue colloidal 
clay starting material may also be any member of the dioctahedral or 
trioctahedral smectite group or mixtures thereof so long as the Fe.sup.+3 
/Fe.sup.+2 ratio of the starting material (prior to re-wetting and 
re-drying) is at least 1.0, preferably at least 3.0 and most preferably in 
the range of about 5.0 to about 15.0. Examples are Beidellite, Nontronite, 
Hectorite, Sepiolite and Samonite. Attapulgite and Kaolin clay also are 
beneficiated when re-wetted and re-dried in accordance with the present 
invention. To achieve the full advantage of the present invention, the 
colloidal clay, i.e., bentonite, generally is finely divided or ground as 
known for use in water barrier panels and the like, i.e., 4 to 350 mesh, 
preferably 20 to 50 mesh, either prior to re-wetting the non-blue clay, or 
after re-wetting and drying the re-wetted initially non-blue clay. 
The crude, mined, non-blue, industrially acceptable clay that already 
possesses sufficient water swellability and good colloidal properties and 
has a Fe.sup.+3 /Fe.sup.+2 of at least 1.0, preferably at least 3.0 and 
most preferably in the range of about 5.0 to about 15.0, can be dried in 
any manner that is known in the art to achieve a clay in a condition 
capable of being ground to a desired particle size distribution. Grinding 
can be performed in accordance with the present invention prior to or 
after re-wetting and re-drying the clay, to achieve the same beneficial 
results. 
In accordance with the principles of the present invention, the mined and 
dried industrially acceptable clay should be re-wetted to a water content 
above about 12% by weight, preferably at least about 15%, based on the dry 
weight of the clay, and re.dried to a water content of about 12% or less, 
based on the dry weight of the clay, prior to or after grinding. The 
improvement in clay properties is achieved in accordance with the present 
invention regardless of the method used for wetting, drying, and grinding 
the clay so long as the dried water-swellable clay, having a moisture 
content of about 12% or less, is re-wetted to a water content of more than 
12% by weight, preferably at least about 15% by weight, based on the dry 
weight of the clay, and more preferably at least about 18% based on the 
dry weight of the clay, and thereafter re-dried to a water content of 
about 12% or less, based on the dry weight of the clay. 
To illustrate the substantial and unexpected increase in the properties of 
an industrially acceptable, water-swellable clay when re-wetted and 
re-dried in accordance with the present invention, a crude sodium 
bentonite clay having a Fe.sup.+3 /Fe.sup.+2 ratio of at least 1.0 was 
obtained from the Black Hills region of South Dakota, and the clay was 
dried after mining to a moisture content of 6.8% by weight water, based on 
the dry weight of the clay, and ground so that 80% by weight of the 
bentonite clay passed through a 200 mesh screen. Example 1 in the 
following Table I shows the properties of a first portion of the sodium 
bentonite clay that was not re-wetted and re.dried. Example 2 of Table I 
shows the same clay that had been further processed by re-wetting to a 
water content of 18% water, based on the dry weight of the clay, and then 
re.dried to a moisture content of 6.6%, based on the dry weight of the 
clay. Example 3, of Table I shows the properties of the same dried, ground 
clay mixed with 20 pounds per ton of soda ash and thereafter re-wetted to 
a moisture content of 18% water, based on the dry weight of the clay, and 
re.dried to a moisture content of 6.6% water, based on the dry weight of 
the clay. 
TABLE I 
______________________________________ 
EXAMPLE 1 2 3 
______________________________________ 
Moisture Content (% by wt) 
6.8 6.6 6.6 
Free Swell (cc/2g) 
30 34 34 
% WPA 839 909 950 
viscosity: 600 dynes/cm.sup.2 
18 41 56 
viscosity: 300 dynes/cm.sup.2 
10 25 35 
AV (cps) 9 20.5 28 
PV (cps) 8 16 21 
YP (lbs/100 sq ft) 
2 9 14 
Fluid Loss (mls) 15.7 12.0 11.8 
Immediate Viscosities at 
Varying Hydration Times 
2 minutes (600/300) 
16/10 22/13.5 -- 
4 minutes (600/300) 
16/10 23/14 -- 
6 minutes (600/300) 
16/10 24/15 -- 
10 minutes (600/300) 
16/10 25/15 -- 
15 minutes (600/300) 
16/10 26/16 -- 
20 minutes (600/300) 
16/10 26.5/16 -- 
______________________________________ 
As shown in Table 1, the viscosity of aqueous solutions containing 6% by 
weight clay processed in accordance with Examples 2 and 3were 
substantially and unexpectedly higher than the same aqueous solutions 
containing the same percentage of the clay of Example 1. Further, the free 
swell and water absorption capacity for the clays processed in accordance 
with Example 2 & 3 were substantially and unexpectedly higher than the 
clay of Example 1. 
A very unexpected property, making the clays processed in accordance with 
the present invention very useful in fluid loss compositions, is the 
ability of the clays processed in accordance with the present invention to 
increase the viscosity of aqueous compositions with time, as shown in the 
lower portion of Table I. As shown in Table I, an aqueous composition 
containing the clay of Example 1 had a constant viscosity in aqueous 
solution with time, whereas aqueous compositions containing the clays of 
Examples 2 and 3, processed in accordance with the present invention, 
showed unexpected increases in viscosity with time, enabling the clays to 
enter cracks and interstices in drill hole earthen formations while in the 
incompletely swollen state and later swell to clog the thief formation. 
It should be understood that the present disclosure has been made only by 
way of preferred embodiments and that numerous changes in details of 
construction, combination and arrangement of parts can be resorted to 
without departing from the spirit and scope of the invention as hereunder 
claimed.