This naturally occurring silicate finds myriad applications ranging f r o m filter aids and thickening agents t o catalysts. The versatility derives from i t s unique three-dimensional s t r u c t u r e and needle-shaped particle form.
clay, commonly called attapulgite after Attapulgus the principal mineral it contains, is a crystalline hydrated magnesium aluminum silicate with a unique chain structure that gives it unusual colloidal and sorptive properties. I t is the principal member of a group of sorptive clays known collectively as fuller’s earth. Attapulgite has a wide variety of industrial applications. Colloidal grades are well known thickening, gelling, stabilizing, and thixotropic agents in products as diverse as paints and drilling muds. Sorptive grades find use as decolorizing and clarifying agents, filter aids, floor adsorbents, animal litter, pesticide carriers, components of no-carbon copy papers, and catalysts and refining aids. I n comparison with other clays used in the chemical process industries, attapulgite is characterized by high surface area, sorptivity, and decolorizing power. Its slips or slurries are viscous and thixotropic. However, unlike bentonite, attapulgite is not flocculated by electrolytes. Table I compares the general properties of attapulgite with those of the other principal clays used in the process industries, the bentonites and kaolin. Attapulgite is found in economic quantities only in the Georgia-Florida area of the United States, in India, and in the Soviet Union. U.S. production is estimated a t 300,000 to 400,000 tons a year. The mineralogy, properties, and uses of attapulgite have been reviewed by Buie (16), Grim (39, 40), Haden (47),Oulton (74, and Ovcharenko (75).
BASIC PROPERTIES Composition
As mined, Attapulgus clay contains 70 to 80% attapulgite; 10 to 15% montmorillonite, sepiolite, and other clays; 4 to 8% quartz; and 1 to 5y0 calcite or
dolomite. Nonclay fractions are removed during processing so that commercial products can contain u p to 85 to 90% attapulgite. Structure
The structure of attapulgite worked out by Bradley in 1940 is now generally accepted (14). I t consists of a double chain of tetrahedrons of silicon and oxygen (Si4011)running parallel to the long axis. Upper and lower parts of each double chain are linked by a layer of magnesium atoms in sixfold coordination. The chains form a network of strips which are joined together only along the edges. The over-all structure resembles a channeled wall where every second brick is missing. The structure of the unit cell of attapulgite is shown in Figure 1, a and 6 . T h e composition of the ideal cell is (OHz)4(0H)~Mg~Si~4 OH z oz ~0 ( 14). (However, actual composition varies because of partial replacement of magnesium by aluminum, iron, and other elements.) The crystal structure of the water-free clay is essentially the same as that of the hydrated clay, except for the tilted lattice and change in the a and 6 dimensions of cells. Each crystal unit normally contains eight water molecules. Four molecules are coordinated to the extreme magnesium ion as crystal water and the other four, often called zeolitic water, are held in loosely bound vagabond fashion in open channels. When the zeolitic water is removed, each channel has a n estimated free cross-section about 3.7 by 6.0 A. parallel to the long axis. Attapulgite was named for Attapulgus, Ga., the source of the first samples studied in 1935 by de Lapparent. Clays of similar structure had been found in the Palygorsk Range of the Urals in 1861 and named palygorskite. The structural identity of the two clays was recently confirmed by Huggins and coworkers (48). VOL. 5 9
NO. 9
SEPTEMBER 1967
59
.
. , ,
,
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:
. .
5
i
,,:
,
.. :~..
..
.
.
.
.
to as low as about 125 m.'/g. fot the thermally activated sorptive grades (Table 11). The decrease of surface area is the result of thermal treatment over 200' C., in which the open channels of the colloidal, crystalline attapulgite gradually collapse. In the anhydride thus formed, the internal areas are either too small or not availabae for adsorption. An abrupt decrease in surface area from 192 m.'/g. to 128 m.'/g. is reported even at temperaturesbetween 95" C. and 115O C. (70). There is much discussion and no egreement on the role of the internal or intracrystalliie channels in the adsorption of gases, water, alcohols, and other molecules. Haden (47) finds only "rare instances" when these channels are used, but some other workers suggest that the inner surfaces way take part in the mechanism of sorption (70, 78, 54, 58). Polar molecules, c h i d y water and ammonia, and, to a lesser extent, methyl and ethyl alcohols can enter the intracrystalliie channels in attapulgite, while aitmgen, Oxygen, and other nonpolar gasen cannot (IO). In many instances, chemisorption may account for the increased adsorption values reported for polar molecules. Differences in the nature of sorption can result in different surface data. For example, when attapulgite is calcined, nitrogen adsorption records no change in surface area between 200' and 650' C. However, water adsorption reaches a maximum a t 200" to 370" C. and decreases above that temperature (58). Similarly, the water adsorption of extruded attapulgite, which has 10% more surface area for nitrogen, is the same as that of the unextruded product (58). Adsorpiion
Attapulgite is highly sorptive in its natural form. I t This value is surpassed only by that of montmorillonite and sepiolite (704). Mad ofthis water is loosely held by Van dm Waals forces. takes up water rapidly to 200% of its own weight.
Fr& V-
TABLE II. T Y P l g L PHYSICAL PROPERTIES OF COMMERCIAL AHAPULGUS CLAYS mkdal G r d soqmi4 Gl& High &ih Rl+ Wl&e h luwila vary lopu *iI# rumn rumn rumn nsll)r 10-17 3-1 % h a t 2 2 0 ' F. 0 0 m;ttcr, % h at IXMO F. 10 1 2-5 1-3
Ignition hm, % at 1832' F. sesisc SRntY wllt density, tpmpcd, h/k' a=% BET. m.=/g. A w w parIick ire, miclolu, quivaImtrpbdealdiPmcter
oil -9
%bu
wt. *OfwmUm. L D n 3 l r .
22-5 2.3-2.4 1945 210 0.12-0.14*
...
12-1 6
6-10
4-6
2.3-2.5 28-36 125-135
2.3-2.5 28-36 125-135
2.3-2.5 28-36 125-135
L
L
b
80-135
lX440
140-090
V O L 5 9 NO. 9 S E P T E M B C R 1 9 6 7
61
During calcination the haystack structure o f , the colloidal clay becomes highly porous. Pore volume about 0.6 ml./g., and pore diameter about 200 A. (58). The development of this porous structure is believed. to play a mom important role in sorption than the h q h surface area. The change in sorptive p r o p t i e s at various temperatures is shown in Figure 3. The optimum sorption of yater and other small polar molecules occurs between 200" and 400' C. The increase in mrptivity may arise from enhanced chemisorption or from the liberation of zeolitic water from the channels (75). Howeyer, these inner channels, as pointed out above, re not available equally to all molecules. Seletive adsorption by :attapulgite has been mukh studied (70, 77, 50, 75). The order of sorptivity is suggested a: water > alcohols > acids > aldehydes > ketones > n-olefins > neutral esters > aromatics > cycloparaffins> paraffins (50). . Straight-chain hyd&&bons are more readily sorbed than those with branched chains (77, 75). The selectivity disappears when attapulgite is calcined above 8E0 C. (7.7). Products activated above 400° C. show an increased decolorizing activity caused by many factors. Among t h are ~ the increase in oxidation power of the surface (62) and changes in porosity and equivalent pore diameter.. The selectivity in adsorption plays an important d e in the decolorization of oils. It may also k o m e of commercial importance in other separation p&sses, such as the refining of crude petroleum oils by selective adsorption of light fractions. Rheologlca1 Propmt&
Attapulgite is one of the most important gel-forming clays. It gives stable suspensions of high viscosity a t relatively low concentrations compared to other clays. During dispersion the bundles of its needle-shaped crystals disassociate to form a random lattice that entraps liquid to increase the viscosity of the system. Attapulgite can thicken a large variety of liquids, includ~ingfresh and salt water, aliphatic and aromatic solvents, 62
INDUSTRIA 1' AND EN 0 I N E ERIN 0 C HE MI S T R Y
vegetable oils, wa&, glycols, ketones and some alcohols. The rheological pkperti& of athpulgite h&e been thoroughly studied kently.(31-33,36, ,37, 75, 76, ?Os). Attapulgite suspensions, like t h o k of ,other a n i t & p i c mat&&, are thFotmpic and non-Neytoni& a t all. amcentrations. They exhibit a rapid increase in..fluidi& hs the shear streso increases. Shear appears to sepai.ate the individual needles, which are held t e t h e r in bundles by electrostatic forces. Without sufficient she& force, attapulgite does not disperse well. Colloid mills and other high shear mixers are usually n e d e d io achieve optimum dispersion. The viscosities of aqueous d i s p i o n s Or attapdgite run as high as 40,000 cp. and over (Figure 4). Such dispersions have average equivalent spherical. ppticle sizes of 0.1 to 0.2 miicron. The high rate of develop merit of viscosity is shown in Figure 5. The ultima& viscosity does not depend on particle size alone. Coarser grades, such as Attagel 30 and 150, may be as efficient as the finer grades$ such as Attagel 20 and 40. Products of larger particle E& actualty may give a viscosity six times higher than the finer products at the same concentration (75). The vi&osity of attapulgite suspensions can be modified by additives, dispersants, and surfactants or by extrusion. Additives claimed to increase Viscosity in aqueous systems include 1 to 5% (by weight of clay) of fhe oxides of barium, calcium, or magnesium (75, 66, 9 4 , 0.5% of ai^ ethylene-maleic anhydride .copolymer (46),and 0.2 to 1 .O% of a coplymer of vinyl acetate with maleic anhydride (99). Magnesium oxide is claimed to increase Viosity by as much as five times (75). Attapulgtis clays modified with 5 to 10% of a glycol; such aS ethylene or diethylene glycol, i r e dective thickeners for water and such polar solventi as alcohols and ketones. The addition of glycol is said to double the viscosity over that of the untreated d a y (44). Extrusion of attapulgite incroaks the viscosity of water dispekions by as much as 50%. Howeve; the effect is lower in water containing sodium chloride (6). In general, the viscosity of aqueous suspensions of attapulgite is influenced only slightly by sodium chloride, other '
electrolytes, and conventional clay flocculating agents. This topic and the influence of dispersants and surfactants are discussed under chemical properties below. Plastic Properties
The plastic and water sorption properties of attapulgite and other clays have been extensively studied to determine the engineering and mechanical properties of clays and soils (103, 104). In general, the plastic and liquid limits and plasticity index of attapulgite are higher than those of other clays, with the exception of montmorillonite. The plasticity of clays is closely related to their ability to hold water, Attapulgite becomes plastic (plastic limit) at a water content of around 100% of its own weight. I t stays plastic (liquid limit) at the level of full saturation (about 200%). Thus, the range of plasticity (plasticity index) is about 100. However, this range may vary from 57 to 123, depending on variations in composition. All other clays except montmorillonite have a much narrower range of plasticity. Ion Exchange
The cation exchange capacity of natural attapulgite is rather low, generally about 20 to 30 meq. per 100 g. of clay. Capacity is nearly always below 50, but the high value of 65 meq./100 g. of clay is reported for sodium attapulgite (55). The values for attapulgite are somewhat higher than those for kaolinite and about one half to one third those for montmorillonite and vermiculite (40, p. 129). Capacity increases slightly when the particle size of the clay decreases (77).
Such acids as hydrochloric, phosphoric, oxalic, nitric, and acetic do not readily attack attapulgite. Acids in high concentrations are recommended for bleaching attapulgite (47). Hydrochloric acid may also be used to enhance its sorptive properties (12).
PROCESSING O F COMMERCIAL ATTAPULGITE PRODUCTS Commercial attapulgites fall into two major groups, colloidal grades and sorptive grades. U.S. producers offer over 100 different grades in all, each with distinctive properties tailored to intended end uses. The physical properties of typical commercial products are given in Table 11. Heat Treatment
In the commercial production of attapulgite, heat treatment is the crucial step that separates the colloidal and sorptive grades. As discussed under dehydration, thermal treatment of attapulgite results in the loss of its contained water and, eventually, in the formation of new phases. The properties of heat-treated clay depend on temperature, loss of water, and phase change, as illustrated in Figure 3. In practice, attapulgite, after crushing and removal of nonclay impurities, is dried or calcined in rotary dryers at the desired temperature. The method of drying may influence the properties of the clay. For example, bulk density is said to depend on the drying rate and drum temperatures ( 3 ) . Rapid drying with hot air (about 400' C.) and simultaneous disintegration into coarse particles improve considerably the properties of clay used in petroleum drilling mud (59).
Chemical Properties
One of the most valuable properties of attapulgite is its high chemical inertness. Colloidal attapulgite suspensions are generally unaffected by salt. For example, the viscosity of a suspension of 50 g. of attapulgite in 100 ml. of water is not substantially influenced by sodium chloride in saturation concentration (35 g./lOO ml. of water) (57). However, the viscosity of suspensions with lower attapulgite concentrations may be decreased in the presence of salt (6, 76, 86). (The decrease in yield of drilling mud averages 10 to 200/,.) Such other electrolytes as ammonia, sodium hydroxide, potassium chloride, and inorganic phosphates also have little effect, as demonstrated by the effective use of attapulgite to thicken and stabilize liquid fertilizers, latex paints, drilling muds, and other systems with high concentrations of electrolytes. I n a few isolated cases adverse effects have also been reported. Small concentrations (below 1%) of commercial dispersants can decrease considerably the viscosity of water-base paints thickened with attapulgite (22). A suspension of o.5yO attapulgite in water deflocculated in the presence of as little as 0.001N sodium oxalate, silicate, citrate, or sodium or lithium carbonates (17). Adverse effects of some inorganic salts on the yield of drilling mud have also been found (86).
Extrusion
Extrusion or wet processing can be carried out before heat treatment. I t increases the viscosity, decolorizing, and filter aid properties of attapulgite products. However, it does not seem to alter the values for water adsorption. Extrusion breaks up and tears apart the bundles of attapulgite needles and increases the pore volume and surface area. Extrusion also prevents the cleaved fragments from falling back into the closely packed arrangement of the untreated mineral. I n plant operation the crushed and purified attapulgite is mixed with water to a volatile matter content of %yo or higher and then passed through an extruder. Extrusion at low moisture content and high pressure enhances decolorizing capacity up to 35y0 (6). A sudden increase in decolorizing efficiency occurs at die pressures of about 100 p.s.i. Above that level the increase is slow. The ratio of water to clay is important, and small variations in composition cause considerable changes in efficiency. The surface area of extruded attapulgite is about 10% higher (about 135 m.2/g.) than that of the natural clay (about 120 m.2/g.) when activated under the same conditions (58). However, the extruded product does not have higher water or gas sorption values. The viscosity of attapulgite suspensions is also inVOL. 5 9
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creased after the clay is extruded. The increase can be as high as 54% in pure water and 33y0in a solution containing 3y0 sodium chloride (6). Recent patents on attapulgite products for drilling muds indicate that extrusion has a beneficial effect on viscosity at all salt concentrations. The filter aid properties of attapulgite are also enhanced by extrusion. Clarification index increases by 507, and flow rate index by 2007, (25). Compaction of attapulgite with a volatile matter content of 10 to 40Y0 at pressures of 10 to 30 tons per square inch is also claimed to impart good decolorizing properties (702). Grinding
Corrugated roll mills are generally used to produce the coarse, granular grades of attapulgite. Products for oil decolorization, soil treatment, herbicides or insecticides, and floor adsorbents require coarser granular clays, while fertilizer and chemical conditioning agents, agricultural dust carriers, and pharmaceutical products need finer particle sizes. Finer sorptive grades are made in Raymond roll mills. Fluid energy mills produce colloidal and other specialty grades of fine particle size. Classification coupled with grinding also removes such contaminants as quartz, grit, dolomite, and calcite. Grinding sometimes influences properties adversely. For example, the viscosity of a fine particle attapulgite from a fluid-energy mill may be lower than that of a coarser grade made in a roll mill (75). Similarly, coarser grades of clay are reported to give higher API yields of petroleum drilling mud than finer grades (59). Dispersants and Surfactants
Colloidal attapulgite disperses readily in water when there is adequate shear to separate the bundles of needles. However, dispersion can be improved by using dispersants in aqueous systems and surfactants in nonaqueous media. Dispersants are used both in the wet processing of crude attapulgite products and as aids in the application of finished products to end-use systems. The most commonly employed dispersants are tetrasodium pyrophosphate (3, 4, 25, 92, 94); lignin and lignite derivatives, chiefly lignosulfonates of calcium and other metals (23, 45); sodium hydroxide; sodium silicate; tetrapotassium pyrophosphate; and sodium hexametaphosphate (87). They are generally used in concentration up to 1% by weight of the clay, depending on the system. Poor dispersion during processing can degrade the product. For example, in the preparation of attapulgite filter aids, dispersion of a slip with only l.5yc tetrasodium pyrophosphate gave a lower grade product than a slip with 2.4Yc (25). Dispersants sometimes reduce viscosity. Addition of 0.03y0 tetrasodium pyrophosphate to a dispersion of 10% attapulgite in water decreases the viscosity from 17,000 to 9200 cp. (66). In latex paint formulations, where 64
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
inorganic phosphates could decrease the viscosity, organic compounds are recommended as dispersants (63). Surfactants are used to improve dispersion in such hydrophobic systems as oils and aromatic hydrocarbon solvents. All three types of surfactant-cationic, anionic, and nonionic-are effective. Typical compounds are quaternary ammonium salts, fatty amine acetates, red oil, fatty sulfates, alkyl aryl sulfonates, and alkanol amides, amine oxides, and other fatty amine and amide derivatives. Other chemicals with similar effects include polymers and glycols. Use of surfactants often reduces the amount of colloidal attapulgite required for thickening. For example, when attapulgite is treated with diethylene glycol, its efficiency in gelling water and polar solvents is doubled, so that only half the amount of clay- is required to obtain the same viscosity (44). I n general, much higher concentrations of surfactants are required for nonaqueous systems than of dispersants for aqueous systems. The range of surfactant is between 1 5 and 50y0 based on the clay. I n practice, small amounts of water or hydrophilic compounds such as glycol are used with the surfactant during dispersion but can be eliminated afterward. Water may be supplied by the colloidal attapulgite itself, since it has a moisture content of over 10%. Table 111 lists organic dispersants reported in the recent patent literature. The surfactant is simply mixed into the clay in dry form, or agitated with it in water or a solvent. Alternatively, both attapulgite and surfactant are added directly to the medium to be thickened. Efficient agitation is usually required to obtain the desired dispersion. The mixture is occasionally reacted at elevated temperatures (98). Modified attapulgites often impart better properties than unmodified. For example, modified attapulgite fillers produce polyurethane foams in higher volume and with improved compression characteristics (29, 30). The amount and type of surfactant also influence the properties of the end product. Thus, the penetration value of a lubricating grease depends on the ratio of the nonionic and cationic surfactants used to disperse the attapulgite (42). Surfactants used during processing also influence filter aid properties (25). CO L LO I DA L APPLICATIONS The principal applications of colloidal grades of attapulgite generally involve thickening, gelling, stabilizing, or other modifications of rheological properties. Surface Coatings
Attapulgite is widely used in water-base and oleoresinous paints as a thickening, antisag, and leveling agent (63). In latex paints it is a particularly effective thickener, especially where highly thixotropic properties W . Lynwood Haden, Jr., is Associate Director of Research and I . Albert Schwint is Manager of adsorbents and catalyst sales w i t h the Minerals @ Chemicals Philipp Go@., Menlo Park, N . J .
AUTHORS
TABLE Ill.
SELECTED RECENT PATENTS O N ORGANIC DISPERSANTS FOR SYSTEMS T H I C K E N E D BY A T T A P U L G I T E Amount of Treated Reference Application of Treated Clay Modijier and Amount@ Clay, %b
A N I O N I C SURFACTANTS
35% Sodium lauryl sulfate 25% Sodium alkyl aryl sulfonate 20% Formaldehyde condensate of naphthalene-2sulfonic acid
14-1 5 17 0.6
Gelling kerosine, oil to grease Gelling oil to grease rhickening and stabilization of fertilizer
43 43 21
C A T I O N I C SURFACTANTS
:elling oil to grease or drilling mud ; thickening gasoline; capryl alcohol; soybean; kerosine; carbon tetrachloride Gelling oil to grease roint sealing composition made from alkyd resin, chlorinated rubber, linseed oil, vinyl chloride, or ester gum Filler for polyurethane foam
40% Tallow fatty dialkyl dimethylammonium chloride 40-70% Fatty dialkylamine acetate 30% Imidazoline condensate of fatty acid and aminoethyl ethanolamine 14. SOj, N-dimethyl ethanolamine
13-1 5
43
15-1 8 13-15
43 35 30
9
N O N I O N I C SURFACTANTS
20% Diethanolamine 20-25y0 Sorbitan polyoxyethylene trioleate or polyoxyethylene thioether 20-30y0 Mono- or diethanol fatty amide 50% Stearamide or methylene bis-stearamide 15-50y0 Mono diethanol fatty amide
12yoFatty amide
Thickener for wax coating composition Gelling kerosine Joint sealing composition based on mineral oil Binder of foundry sand containing 2% oil Gelling lubricating oils, methyl alcohol, ethyl alcohol, Cellosolve acetate Thickening wax based adhesive composition
12 14
87 43
11-16 4 To 20
83 20 84
15
82
5
67
SURFACTANT M I X T U R E S
1695; Polyoxyethylene stearylamine 10% Laurylammonium salt of laurylamine phosphate l0-15yO Fatty ammonium salt of fatty amine phosphate 2 0 - 4 0 ~ oPolyoxyethylene fatty amine
i
Binder for water-free foundry sand used with 2% lube oil
42
Thickening lube oil to grease
POLYMERS
5 yo Polyvinyl pyrrolidone or polyacrylamide 33 % Dimethyldichlorosilane 17y0Di-tert-butoxy diamino silane
10
Structural filler for polyurethane foams Thickening oils to grease, fillers for elastomers Thickening oils to grease, fillers for elastomers
... ...
29 98 98
5-1 0 15-20
44 28
MISCELLANEOUS
To 30% ethylene glycol, or diethylene glycol 15-25y0 2,4-Tolylene diisocyanate a
By weight of nttapulgite.
b
Thickening of water, alcohol, ketones Thickening and imparting thixotropy to polyester solutions in mineral spirits used as paint or ink
By weight of 'j?nfinrl composition.
are advantageous, as in exterior masonry and roof paints, texture paints, and specialty gelled paints. The attapulgite is generally incorporated at 5 to 10 lb./100 gal. of paint, but in gelled paints may be as much as 30 lb./100 gal. Such paints have excellent film build on sharp edges, and heavy films can be obtained if desired. Specially processed attapulgite products, such as Attagel 40, are fast-gelling thickeners for polyvinyl chloride, styrene-butadiene and acrylic latexes. They are used in concentrations up to 40 lb./100 gal. of paint. These formulations show improved hiding at all pig-
ment-volume concentrations, good gloss, freedom from polishing, good stain removal and scrub resistance, improved sag resistance, satisfactory freeze-thaw stability (in combination with organic thickeners), and good heat stability. In oleoresinous paints, such as white gloss enamels, attapulgite at around 10 lb./100 gal. of paint together with a surfactant gives thixotropic properties, good antisag values, and good leveling at low cost (22). Gelled flat soya-alkyd paints with excellent brushability after storage are obtained with about 2% attapulgite (28). VOL. 5 9
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65
Adhesives, Sealants, and Putties
Attapulgite is a particularly useful thickener for starch-base corrugating adhesives at 7 to 9 lb./100 gal. (68). Without a suitable thickener, the loss of viscosity during the application of starch adhesives often requires frequent adjustment of glue-roll clearances. Other applications include microcrystalline wax (82) and joint-sealing compounds based on alkyd resins, chlorinated rubber, and oils or other vehicles (34, 35, 83). The attapulgite content ranges from 8 to 207,. Such joint-sealing materials have excellent thermal stability and shelf life. They are excellent nonsagging sealers for automobiles when used alone or in combination with a bituminous material. I n putties and glazing compounds, attapulgite effectively prevents bleeding. One to 5 lb. of clay/lOO-lb. batch are usually employed (66).
water and 204 in salt water. Finer clays similarly processed have yields of 21 1 in fresh water and 183 in salt water. These yield values are as high as those obtained with bentonite in fresh water and considerably higher than those obtained in salt water. Treatment with such additives as 5% magnesium oxide increases the yield of a bentonite clay from 112 to 290 in fresh water, but does not affect it in salt water, where it may be as low as 36 (86). The water-retaining properties of attapulgite can be considerably improved by the addition of dextran (23), starch, karaya or tragacanth gums, or cellulose derivatives such as hydroxyethylcellulose or carboxymethylcellulose (57). Concentrations range from 0.5 to 10 lb./bbl. Addition of about 10 volume yo of diesel oil is also claimed to keep water loss low (23).
Oil Well Drilling Mud
Stabilization of Suspensions and Emulsions
Drilling mud contains 65 to 98Yc water, 2 to 30y0clay, barytes, hematite, and other weighting or miscellaneous materials up to 357& and rock cuttings and gas up to 10%. Other additives include buffers or stabilizers such as magnesium oxide or carbonate; water retainers such as dextran; glycols; and viscosity modifiers, chiefly sodium phosphates, tannins, and humic acids. Attapulgite is extensively employed where salt formations must be drilled, so that the mud becomes nearly saturated with salt. Bentonite, hectorite, and other montmorillonite clays fail to maintain their viscosity in the presence of sodium chloride, calcium sulfate, magnesium sulfate, or other electrolytes. As discussed above, suspensions of attapulgite are practically unaffected by such salts and also by degelling agents for clays. Attapulgite muds show good viscosity and gel and shear strength under drilling conditions. The mud yield and water-retaining properties of earlier attapulgite products were reported to be inferior to those of Wyoming bentonite and California hectorite (57). However, the mud yield (number of barrels of drilling mud of 15-cp. viscosity produced from 1 ton of clay) of attapulgite can be substantially increased by such additives as magnesium oxide (up to 4% based on clay) alone or with about 170 lime (86),1% magnesium oxide plus 2 to 3y0 guar gum (85),or 0.5y0 of a water-soluble copolymer of maleic anhydride with ethylene ( 4 6 ) . These additives increase the mud yield from 100 to 125 to as high as 260 in fresh water and 220 in salt water ( 8 6 ) . The synergistic effect of magnesium oxide and guar gum is claimed to give a salt water yield of 250 to 300 (85). Additives also increase the inertness of attapulgite to soluble salts (86). The additives are preferably included in the clay before extrusion. The mud yield is also influenced by the particle size of the attapulgite. Yield is increased when attapulgite is rapidly dried during processing and simultaneously disintegrated to obtain relatively coarse particles (59). Such products are claimed to have a yield of 239 in fresh 66
INDUSTRIAL A N D ENGINEERING CHEMISTRY
The high viscosity of attapulgite suspensions prevents sedimentation of solids in many otherwise unstable systems. For example, attapulgite a t 0.5 to 3% effectively stabilizes liquid fertilizer suspensions (27, 89, 90, 95). A typical high analysis formulation is: water, 453 lb.; Attagel 30 pregel (15yo),267 lb. ; wet process phosphoric acid, 442 lb. ; anhydrous ammonia, 98 lb. ; urea, 356 lb. ; potassiuni chloride, 384 Ib. (66). Stable slurries can also be made by suspending up to 75% ground phosphate rock in aqueous ammonia with 0.5-1 .Oyo attapulgite (90). Attapulgite is particularly useful with fertilizers produced with wet process acid containing several percent of iron and aluminum phosphates as contaminants. Attapulgite shows good suspending and pourability characteristics in such compositions. The suspensions are easily redispersed if necessary after storage. Unlike bentonite, which must be pregelled in water, attapulgite can be added dry to the phosphoric acid (95). Attapulgite can also be employed in mixtures with bentonite to prevent settling and the formation of large crystals in fertilizer suspensions with solids content over 307, (73). The preferred ratio of attapulgite and bentonite is 0.5 to 2:1, and the mixture is used in concentrations of 0.5 to 6.0Yc. Other examples of the suspending action of attapulgite are in pesticide dispersions and emulsions (45, 66),resin dispersions, oil-in-water emulsions and graphite dispersions (66),and cosmetic preparations (67). Because of its high water absorption, 1 to 2% attapulgite in portland cement slurries for cementing oil wells reduces the density of the slurry to the required level while setting time remains low (77). Thickening and Gelling Liquids
Attapulgite is a n efficient thickener for aqueous and organic liquids. I t is particularly suited for high temperature uses because of its insolubility. An important commercial application is the thickening of lubricating oils to grease with 6 to 157, attapulgite (42, 43, 84, 98).
These greases have good penetration values, although penetration depends partly on the ratio of cationic to nonionic surfactant used to treat the clay (42). 0ther liquids successfully thickened with attapulgite isopropyl alcohol (44),capryl include ethyl alcohol (84), alcohol (43),ketones, ethers, and esters ( 4 4 ,chlorinated aliphatic hydrocarbons (44, 84),linseed oil (44),soybean oil (43), wax compositions (Sir), and liquid polyesters (28). Stable gels are made from aqueous solutions containing 5 to 3oy0ammonia by treatment with 2 to 10% attapulgite. Addition of 2 to 570 lime increases stability and viscosity. These gels can be used as vehicles in paint, ink, and cleansing compositions (94). Some fire-retardant compositions contain 7 2 to 90% attapulgite, 5 to 15y0 bentonite, up to 1% surfactant, and up to 2% carboxymethylcellulose. The composition is used as a 10 to 15y0 suspension in water (78). Binding
Attapulgite has considerable binding power, which finds application in oil-bonded foundry sands (20, 39, 67), bauxite granules for sugar refining ( 2 ) , molecular sieves (69, 79),and such cosmetic preparations as rouge and bath powders. Filling
Modified attapulgite at concentrations of 9 to 10% is recommended as a filler for elastomers (98) and polyurethane foams (29, 30). In the foams, it improves the compression characteristics and increases foam volume.
SORPTIVE USES Decolorization
One of the oldest applications of attapulgite is the purification of liquids by adsorption of impurities. I n the contact process the liquid at temperatures up to 600" F. is treated with 0.5 to 3oy0attapulgite, which is later removed by filtration. I n the percolation process the liquid is passed continuously through a bed of attapulgite, often at somewhat elevated temperatures. Decolorizing grades of attapulgite have high surface area, good selectivity, and excellent mechanical and thermal stability. These grades are made by first extruding and then calcining at 300' to 800" C. Because of their relatively large pores, they are particularly strong adsorbents for compounds of high molecular weight, such as resins, asphaltous impurities, sulfonates, and coloring materials. Unlike some foreign attapulgites (72), domestic attapulgites are not activated by acid treatment. Attapulgite is used to purify a great variety of liquids, including oils, fats, waxes, resins, vitamins, brewery products, water, industrial wastes, and sewage. I t is also successfully used in reclaiming rubber, oils, and solvents by contact or cartridge processes. After use, the attapulgite can be regenerated by burning off the adsorbed organic matter at 550' to 600' C. (64).
Attapulgite is also an excellent adsorbent for radioactive wastes. When sintered, it prevents leaching of the radioactive materials (53, 55). I t is also recommended for the purification of organic coolants in atomic reactors (24). Paper Reclaiming
In a similar application, attapulgite is recommended to reclaim the fiber from scrap waxed paper (5, 26). The shredded paper is mixed with two to 20 times its weight of attapulgite and heated to about 120" C. The clay adsorbs wax and polyethylene so that the paper can be repulped. The clay is regenerated by heating to about 550" C. For example, the wax content of a frozen food overwrap broke may be reduced from 25 to 0.52y0 by loading as low as two parts clay to one part of broke. Removal of wax-polyethylene mixtures is equally effective. The operating cost is estimated at less than $9 per ton ( 5 ) . Conditioning
Because of its excellent adherence characteristics, controlled particle size, nontoxicity, high oil adsorption, and low bulk density, attapulgite is an ideal conditioning agent to prevent caking, sticking, and gumming of such products as fertilizers (65, 97-93), chemicals, and resins (65)* For these applications attapulgite is calcined at 250" to 450' C. and ground to fine particle size. For coating, the granules or prills of fertilizer or other product are tumbled with 0.5 to 3.0% attapulgite in a rotary vessel. Alternately, the prills may be sprayed with a colloidal dispersion of attapulgite (92). Attapulgite conditioning is used both on nitrogen fertilizers such as sodium nitrate, ammonium nitrate, or urea (97-93) and on high analysis mixtures (65). The loss of ammonia in ammonium nitrate products can be effectively prevented by pretreating the clay with sulfur dioxide, sulfuric acid, or aluminum sulfate (93). Attapulgite coatings are also used on ammonium nitrate prills for explosives. Conditioning urea with attapulgite a t 5 to 50% by weight of urea is reported to increase the utilization of urea in feed compositions (73). Pesticide Carriers
Granular or fine attapulgite is the most widely used solid carrier for insecticides, herbicides, and soil fumigants. I t was also patented recently as a carrier for snake-repellent compositions (49). The clay is impregnated with aldrin, dieldrin, malathion, or other pesticide to produce free-flowing granules or dusts, which are easily applied under controllable conditions. Filter Aid
A relatively new application for attapulgite, now under development, is as a filter aid for sugar refining, water treatment, and other industrial processes (3, 4, 25). For VOL. 5 9
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this use, extruded attapulgite is calcined at 800" to 1000" C . to give an amorphous product of low bulk density. Since commercial attapulgite deposits are nearer major U.S. markets than other filter-aid materials, attapulgite could offer substantial savings in both freight and treatment costs. Pharmaceutical Uses
Because of its high adsorption and lack of toxicity, attapulgite finds application in pharmaceuticals, particularly intestinal preparations, where it is far superior to other clays in the adsorption of diphtheria toxin, bacteria, and alkaloids (8, 9 ) . The recommended concentration of attapulgite is about 10% (67). In antacid preparations attapulgite also helps control the neutralization rate. I n veterinary application attapulgite is primarily used in boluses for the treatment of dysentery in large animals and in tablets (67). I t is superior to other clays in the extraction of gonadotropic hormones (701). Cleansing Products
The high sorptivity of attapulgite has led to its wide use as an adsorbent for the removal of water, grease, oil, dirt, dust, and odors from floors or other surfaces in factories, farms, canning plants, butcher shops, tanneries, garages, grocery stores, greenhouses, power plants, and warehouses. Similar grades are also used for litter and bedding for laboratory animals, poultry, and pets. I n a related application, attapulgite is used in drypowder rug and upholstery cleaners. These products consist of a carrier such as wood flour, a solvent such as deodorized kerosine, attapulgite, and a surfactant. Dirt and grease are removed by the solvent and surfactant and adsorbed on the clay. Other Uses
Attapulgite has a variety of other sorptive applications. A special dry-powder fire extinguisher for lithium and other light metals is formulated with graphite and 5 to 157, attapulgite as anticaking agent (700). Addition of 5 to 1070,attapulgite to tobacco is claimed to reduce the inhaled tar content by as much as 4Oy0 ( 1 ) . Magnetic compositions are obtained by impregnating attapulgite with an iron salt, and reducing to produce elemental iron (87). Attapulgite may also be used in thin coatings as a dielectric capacitor that performs well a t high temperatures because of its high heat stability (47).
CATALYTIC APPLICATIONS Attapulgite has long been used in various catalytic applications, particularly in the oil industry. However, its largest present catalytic application is in specialty copy papers. NCR Paper
NCR (no carbon required) papers make multiple copies without carbon paper. The upper or receiving surface of the copy sheet is coated with attapulgite. The 68
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
lower or transfer surface is coated with starch containing minute encapsulated droplets of colorless dyestuff intermediates, such as di- or triphenyl methane derivatives with a lactone structure (38). (In some cases both coatings are applied together on the copy sheet.) Writing or typewriting breaks the dyestuff globules so that they penetrate the attapulgite, which catalyzes their conversion into the colored product. For this application the attapulgite may be treated with acids or salt solution of such bivalent metals as nickel, copper, iron, zinc, barium, or cadmium (38). This treatment is claimed to decrease the high surface activity of attapulgite so as to minimize the attraction of atmospheric impurities that would reduce the colorforming capacity of the clay (72). The clay coating, containing 20 to 257, attapulgite, is usually 0.005 in. thick (38). Binders are starch (38), dextrin (71) or mixtures of etherified starch and butyl rubber (72). Petroleum Refining
Attapulgite can be used for the selective removal of gum-forming diolefins and acetylenes from petroleum stocks by polyinerization without removing the high octane monoolefins (51). The reaction is carried out in the vapor phase at 300" to 500" F., pressures up to 75 p.s.i., and liquid hourly space velocities of one to two. Attapulgite catalyzes the decomposition of mercaptans and organic sulfide to hydrogen sulfide and olefins. This reaction can be used for the desulfurization of gasoline (7). Typical operating conditions are 700' to 800" F., low pressures, and a liquid hourly space velocity of one. The process cannot be applied to feedstocks containing unsaturates because of undue polymerization. Attapulgite can also be used as a carrier for the copper catalyst in the sweetening of petroleum stocks by oxidation of mercaptans to disulfide (52, 97). Chemical Processing
The ability of attapulgite to catalyze the polymerization of styrene has recently been demonstrated (96). The reaction is carried out in the liquid phase, in benzene or carbon tetrachloride, in the presence of 2 g. of catalyst/100 g. of styrene. Both attapulgite and kaolinite gave 10070 conversion, but the best over-all yield of 63Y0 was obtained over attapulgite in boiling benzene. Isobutylene is often polymerized with acid into solid dimers and trimers that can be shipped conveniently to the users. The depolymerization of the polymer can be carried out over attapulgite, supported phosphoric acid, or other catalysts. Attapulgite is an excellent catalyst that produces high purity monomer in good yield (19). The reaction is carried out at about 400" C. and a liquid hourly space velocity of one. The once-through conversion is over 80%. The high efficiency of attapulgite in retaining radioactive ions has lead to its development as a carrier in the radiation synthesis of chemicals (55, 88).
FUTURE PROSPECTS The commercial availability of attapulgite in large tonnages a t relatively low cost has already made it an important raw material in a variety of industries. Although originally developed for petroleum refining, attapulgite today finds its largest uses in unrelated applications. As producers and consumers expand their research efforts in attapulgite, this unique silicate will undoubtedly play an even mvre diversified role in technical products of the future. REFERENCES (1) Allegrini, A. P. (to Minerals & Chemicals Philipp Corp.), U.S. Patent 3,049,449 (.A m- . 14. 1962). (2) Ibid., 3,098,045 (July 16, 1963). (3) Allegrini, A. P., Cecil, T. A. (to Minerals & Chemicals Philipp Corp.), Ibid., 3,050,863 (Aug. 28, 1962). (4) Zbid., 3,174,826 (March 23, 1965). (5) Allegrini, A. P., Claxton, A. W., Tuppi 43, 164A-65A (April 1960). (6) Amero, R. C., Cappell, R. G., Petrol. Rejner 22, 82 (January 1943). (7) Amero, R. C., Wood, W. H., Oil Gas J.46,82 (May 24,1947). ( 8 ) Barr, M., J.Am. Phnrm. Asroc., Sci. Ed. 46, 490 (1957). (9) Barr, M., Arnista, E. S., Zbid., pp. 486, 493. (10) Barrer, R . M., Mackenzie, N., J.Phys. Chem. 58, 560 (1954). (1 1) Barrer, R. M., Mackenzie, N., MacLeod, D. M., Ibid.,p. 568. (12) Beaufour, A. H., Beaufour, G. H., French Patent 1,349,897 (Jan. 24, 1964). (13) Belasco I. J. (to E. I . du Pont de Nemours & Co.), U. S. Patent 2,965,488 (Dec. 20, i960). (14) Bradley, W. F., Am. Mineralofist 25, 405-410 (1940). (15) Buffett, J. B. (to Minerals & Chemicals Philipp Corp.), U.S. Patent 3,205,082 (Sept. 7, 1965). (16) Buie, B. F., Gremillion, L. R., Georgia Mineral Newsletter 16 (1-2), 20 (1963). (17) Caldwell, 0. G., Marshall, C. E., “A Study of S?me Chemical and Physical Properties of the Clay Minerals Nontronite, Attapulgite, and Saponite,” Missouri Univ. Agr. Exp. Sta. Research Bull. 354 (1942). (18) Chessick, J. J., Zettlemoyer,A. C . , J . Phys. Ckem. 60, 1181 (1956). ( 1 9 ) Ciapetta, F. G., Macuga, S. J., Leum, L. N., IND. END. CHEM.40, 2091 (1 948). (20) Clem, A. G. (to American Colloid Co.), U.S. Patent 2,971,922 (Feb. 14, 1961). (21) Dawson, F. Martin D. L. (to Imperial Chemical Industries and Scottish Agricultural Iddustries,’Ltd.), British Patent 984,920 (March 3, 1965). (22) Dobkowski, T. P., unpublished data, Minerals & Chemicals Philipp Corp., Menlo Park, N. J. (23) Dodd, C. G. (to Pure Oil Co.), U.S. Patent 3,046,221 (July 24, 1962). (24) Duerksen, J. H., Charlesworth, D. H., Atomic Energy Canada, Ltd., AECL 1683 (1963). (25) Duke, J. B., Greene, E. W. (to Minerals & Chemicals Philipp Corp.), U.S. Patent 3,080,214 (March 5, 1963). (26) Elias, R . F. (to Minerals & Chemicals Philipp Corp.), Ibid., 3,055,791 (Sept. 25, 1962). (27) Esteoule, J., Compt. Rend. 260, 1686 (1965). (28) Ferrigno, T. H . (to Minerals & Chemicals Philipp Corp.), U.S. Patent 2,975,071 (March 14, 1961). (29) Ibid., 3,024,209 (March 6, 1962). (30) Ibid., 3,150,109 (Sept. 22, 1964). (31) Gabrysh, A. F., Eyring, H., Cutler, I., J . Am. Ceram. Soc. 45,334 (1962). (32) Gabrysh, A . F., Eyring, H., Shimizu, M., Asay, J., J . Appl. Phys. 34, 261 (1963). (33) Gabrysh, A. F., Ree, T., Eyring, H., McKee, N., Cutler, I . , Tranr. SOC.Rheol. 5 , 67-84 (1961). (34) Goodwin, M . E., Sawyer, E. W., Smith, H. A. (to Minerals & Chemicals Philipp Corp.), U S . Patent 2,894,848 (July 14, 1959). (35) Zbid., 2,969,337 (Jan. 24, 1961). (36) Granquist, W. T., Hollingsworth, C. A., J . ColloidSci. 18,538 (1963). 59,2192 (1963). (37) Granquist, W. T., Hollingsworth, C. A., Trans. Faraday SOC. (38) Green, B. K., Sandberg, R. W. (to National Cash Register Co.), U.S. Patent 2,550,469 (April 24, 1951). (39) Grim, R. E., “Applied Clay Mineralogy,” McGraw-Hill, New York, 1962. (40) Grim, R . E., “Clay Mineralogy,” McGraw-Hill, New York, 1953. (41) Haden, W. L., “Attapulgite: Properties and Uses” in “Proceedings of the 10th National Conference on Clays and Clay Minerals,’’ E. Ingerson, Ed., p. 284, Pergamon Press, New York, 1963. (42) Haden, W. L., Martin, C. 0. (to Minerals & Chemicals Corp. of America), U.S.Patent2,819,210 (Jan.7, 1958). (43) Ibid., 2,885,360 (May 5, 1959). (44) Haden W. L Polon J. A. (to Minerals & Chemicals Philipp Corp.), Zbid., 3,227,657’(Jan. 1966).’ (45) Harrison T. S. Littler C. A . (to E . I . du Pont de Nemours & Co.), Ibid., 3,157,486 (&Io”. li, 1964):’ (46) Harryman, P. H., Oakes, D. y. (to Monsanto Co.), Zbid., 3,222,278 (Dec. 7, 1965). (47) Hogue, L. J. (to General Electric Co.), Ibid., 3,185,906 (May 25, 1965). (48) Huggins, C. W., Denny, M. V., Shell, H . R., U.S. Bur. Mines, Rep. Inuest. No. 6071 (1962). (49) Jenkins, J. H., U S . Patent 3,069,314 (Dec. 18, 1962). (50) Johnston, W. A . , “Adsorption and Catal sis” unpublished data, Minerals & Chemicals Philipp Corp., Menlo Park, N.J., 795;. (51) Kalichevsp V. A., Stagner, B. A., “Chemical Refining of Petroleum,” ACS Monograph 0.63, p. 292, Reinhold, New York, 1942. I
4:
(52) Kerr, J., Burgess, J. (to Peter Spence & Sons, Ltd.), British Patent 976,381 (Nov. 2 5 , 1964). (53) Kerr, J, M., Bull. Am. Ceram. Soc. 38, 374 (1959). (54) Kinter, E. B., Diamond, S., in “Proceedings of the 7th National Conference on Clays and Clay Minerals,” E . Ingerson, Ed., p. 125, Pergamon Press, Kcw York, 1960. (55) Klett, R. J., Sicilio, F.,Horton, N. H., Bull. Georgia h a d . Sci.20,23 (September 1962). (56) Kulbicki, G.,Am. Mineralogist 44, 752-64 (1959). (57) Larsen, D. H., in “Proceedings of the 1st National Conference on Clays and Clay Minerals,” J. A. Pask and M. D . Turner, Eds., p. 269, California Div. Mines, Bull. 169, San Francisco, 1955. (58) McCarter, W. S. W., Krieger, K. A., Heinemann, H . , IND.END.CHEM.42, 529 (1950). (59) Malone, T. S., Allegrini, A. P. (to Minerals & Chemicals Philipp Corp.), U.S.Patent3,079,333 (Feb.26,1963). (60) Martin-Vivaldi, J. L., Cano-Ruiz, J., in “Proceedings of the 4 t h National Conference on Clays and Clay Minerals,” A. Swineford, Ed., pp. 173, 177, National Academy of Sciences, National Research Council, Washington, D.C., 1956. (61) Miericke, K. A . (to National Lead Co.), U.S. Patent 3,027,265 (March 27, 1962). (62) Miller, J. G., Haden, W. L., Oulton, T. D., “Oxidizing Power of the Surface of Attapulgite Clay,” in “Proceedings of the 12th National Conference on Clays and Clay Minerals,” W. F. Bradley, Ed., p. 381, Pergamon Press, New York, 1964. (63) Minerals & Chemicals Philipp Corp., “Paint Technical Manual,” Menlo Park, N.J. (64) Minerals & Chemicals Philipp Corp., Tech. Data Sheets T. I . 452 and 956, Menlo Park, N.J. (65) Ibid., 653B, 1963. (66) Ibid., 1025C, 1963. (67) Minerals & Chemicals Philipp Corp., Tech. Information No. MDX-101, January 1965. 1681 Ibid.. 311. “Adhesive Technical Manual.” , Mav, 1965. (69) Mitchell, W. J., Moore, W. F. (to Union Carbide Corp.), German Patent 1,055,515 (April 23,1959). (7Q) Mumpton, F. A . , Roy, R., in “Proceedings of the 5th National Conference on Clays and Clay Minerals,” A. Swineford, Ed., p. 136, National Academy of Sciences-National Research Council, Washington, D.C., 1958. (71) National Cash Register Co., German Patent 1,152,429 (Aug. 8, 1963). (72) National Cash Register Co., Netherlands Patent Application 6,505,671 (Nov. 8, 1965). (73) Newsom, W. S. (to International Minerals & Chemical Corp.), U.S. Patent 3,096,170 (July 2, 1963). (74) Oulton,T. D., Georgia Mineral Newsielter16 (1-2), 26 (1963). (75) Ovcharenko, F. D., Ed., “The Colloid Chemistry of Palygorskite,” English trans]., Daniel Davey & Co., New York, 1964. (76) Packter, A,, Rheol. Acta 2, 44-50 (1962). (77) Patchen, F. D. (to Socony Mobil Oil Co.), U.S. Patcnt 3,197,317 (July 27, .
I
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(1965).
(78) Petertyl, S. V., Davis, D. W. (to Johns-Manville Corp.), Ibid., 3,080,316 (March 5, 1963). (79) Pollitzer, E. L., Kvetinskas, B. (to Universal Oil Products Co.), Ibid., 3,158,579 (Nov. 24, 1964). (80) Preisinger, A., “Sepiolite and Related Compounds: Its Stability and Application,” in “Proceedings of the 10th National Conference on Clays and Clay Minerals,” E. Ingerson, Ed., p. 365, Pergamon Press, New York, 1963. ( 5 1 ) Rumberger, G. C. (to Petrolite Corp.), Belgian Patent 620,817 (Nov. 14, 1962). (82) Ibtd., 620,819 (Nov. 14, 1962). (83) Sawyer, E. W. (to Minerals & Chemicals Philipp Corp.), U.S. Patent 9,048,494 (Aug. 7, 1962). (84) Ibid., 3,049,498 (Aug. 14, 1962). (85) Zbid., 3,220,947 (Nov. 30, 1965). (86) Sawyer, E. W., Haden, W. L. (to Minerals & Chemicals Philipp Corp.), Ibid., 3,185,642 (May 25, 1965). (87) Schuele, W. J. (to Franklin Institute of the State of Pennsylvania), Ibid., 3,042,543 (July 3, 1962). ( 8 8 ) Sicilio, F., Klett, R. J., Knight, J. A . , Intern. J . Appl. Radiation Isotopes 12, 141 (1961). (89) Slack, A . V., Hatfield, J. D., Walters, H. K. (to Tennessee Valley Authority), U.S. Patent 3,109,729 (Nov. 5, 1963). (90) Smalter, D. J. (to International Minerals & Chemical Corp.), Ibid., 3,206,298 (Sept. 14, 1965). (91) Smith, H. A. (to Minerals & Chemicals Philipp Corp.), Ibzd,, 3,041,159 (June 26, 1962). (92) Zbid., 3,143,410 (Aug. 4, 1964). (93) Smith, H. A . , Sawyer, E. W. (to Minerals & Chemicals Philipp Corp.), Ibid., 3,125,434 (March 17, 1964). (94) Ibid., 3,148,970 (Sept. 15, 1964). (95) Ibid., 3,160,495 (Dec. 8, 1964). (96) Solomon, D . H., Rosser, M. J., J.Appl. Polymer Sci. 9, 1261 (1 965). (97) Sorg, L. V. (to Standard Oil Co. of Indiana), German Patent 1,102,950 (March 23, 1961). ( 9 8 ) Tatlock, W. S . (to E. I . du Pont de Nemours & Co.), U.S. Patent 2,784,110 (March 5, 1967). (99) Van der Watt, H. V. H., Bodman, G. B., in “Proceedings of the 9th National Conference on Clays and Clay Minerals,” E. Ingerson, Ed., p. 568, Pergamon Press, New York, 1962. (100) Warnock, W. R. (to Ansul Chemical Co.), U S . Patent 3,090,749 (May 21, 1963). (101) Watson, W. B., Knouse, R. W., Clin. Chem. 11 (5), 575 (1965). (102) Weier, J. V. (to Minerals & Chemicals Philipp Corp.), U.S. Patent 2,968,633 (Jan. 17,1961). (103) White, W. A., (a) Am. Mineralogist 34, 508 (1949); (b) Ph.D. thesis, University of Illinois, 1955. (104) White, W. A., Pichler, E., Illinois State Geol. Survey, Czr. 266 (1959). (105) Wood W. H. Granquist W. T. Krieger I. M in “Proceedings of the 4th National konfereke on Cla;s and h a y Miderals,’;’A. Swineford Ed., p. 240 National Academy of Sciences-National Research Council, Washkgton, D.C.: 1956.
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