American MineralogistVol. 57, pp. 75r-764 <1972)

AN ASPECT OF THE WATER IN CLAY MINERALS:AN APPLICATION OT' NUCLEAR MAGNETIC RESONANCE

SPECTROMETRY TO CLAY MINERALOGY

Yasuo Krracewa, Department of Soils aniJ Fertilizers, NatinnalInstitute of Agriculttaal Sciences, Nishigahara Kita-ku, Tolqo

11/1, Japan

Asstnecr

is a broad band with maximum near 8400 cm-'.The absorption line width of wideJine NMR with water in allophane, is 0.12

gauss 3ll-"r, and expands to 0.8 gauss on drying at 110"C. The infrared absorp-tion spectrum of allophane shows a broad atrsorption band near 8480 or B4go cm-rassociated with o-rr stretching vibration. Protons in allophane are almost com-pletely exchanged by deuterons, and a large number of the hydroryl groups arereleased from allophane by fluoride. These results suggest for the properiies of thewater in allophane: comparatively unstable hydroxyl group, wea.k adsorption ofwater, continuous exchange of proton between adsorbed water and structuralhydroxyl groups, and difference from so-called ,,zeolite water."

Exchangeable proton content is determined by high-resolution NMR spee-trometry.

IxrnonucrroN

The properties of adsorbed water and structural hydroxyl groupsin clay minerals are very interesting, and their surface and atomicstructures are important. Many scientists have studied their propertiesby differential thermal analysis, thermogravimetry, infrared absorption

751

752 YASUO KITAGAWA

spectrometry, proton exchange reaction by deuterons, substitution of

hydroxyl group by various anions such as fluoride and phosphate, and

Karl-Fischer analysis. Moreover, thermodynamic studies on clay-

water systems have also been made by many scientists (Grim, 1968).

Recently, nuclear magnetic resonance (NMR) spectrometry has

been widely applied to various fields of chemistry. several researchers

introduced NMR to the study of water adsorbed on powder specimens.

montmorillonite by pulsed NMR. W'oessner, Snowden, Jr', and Meyer(1970) d.iscussed the application of pulsed NMR to the clay-water

system. Anderson (1970) studied the water a,t phase boundaries in

frozen soils by wide-line NMR spectrometry. Prebble and currie(1970) measured. the free water in soils by a wideline NMR technique.

In this paper, the properties of water in several clay minerals is dis-

cussed. The results obtained with wide-line NMR for protons are

compared with the data obtained from infrared absorption spectra.

Further, protons in clay minerals were exchanged by deuterons, and

the exchangeable protons were detected by high-resolution NMR spec-

trometry. Paulsen and Cooke (1964a, b) proposed a method for quan-

titative determination of active hydrogen based on the exchange reac-

tion of the group with heavy water and the determination of the

exchanging protons by NMR spectrometry. Kula, Rabenstein, and

Reed (1965) determined the water of crystallization in ethylenedini-trilotetraacetates with heavy water by NMR spectrometry. Fluoride

ion was substituted for the hydroxyl group in clay minerals to examine

the stabitity of their structural hydroxyl group.

SauPr,Ps

One sample each of kaolinite, halloysite, montrnorillonite, molecular sieve, and

two of allophane were used.Kaolinite was frorn Kaolin Dry Branch, Georgia, obt'eined from Ward's Natu-

ral science Establishment, rnc., Rochester, N.Y. The X-ray diffraction pattern

indicated the ,clay fraction of the kaolin contained a srnall amount of mica

minerals and 14 A minerals as impurities. The halloysite was found in a clav bed

altered from volcaniclastic material distributed near Numanoi, Tochigi, Japan'

The results of examination by X-ray diffraction analysis, differential thermal

analysis, and chemical analysis showed its clay fraction consisted of halloysite

and accessory iron oxide. Montmorillonite used was volclay Bentonite sPV,

obtained from American colloid company, skokie, Illinois. X-ray difrraetion

analysis revealed the clay fraction contained a small amount of qtrartz in addi-

NMR OF CLAY MINERALS 7t3

tion to montmorillonite. Allophane samples were collected Jrom two wealheredpumice beds: one is the so-called Kanumatsuchi in Kanuma, Tochigi, Japan; andthe other is Misokuchi in lijima, Nagano, Japan. The results of X-ray diffractionanalysis and chemical analysis indicated in both samples small amounts of ironoxide. The molecular sieve, type 4A was produced. by Linde Company. The frac-tion minus 100 mesh was used.

For the clay mineral samples, except for the molecular sieve, the fractionless than 2 pm @lay fraction) was prepared by sedimentation; the fractionsuspended in alkaline or acidic water was syphoned off at the required time .ac-cording to Stokes' law. Kaolinite, halloysite, and montmorillonite were dispersedin NaOH-alkaline solution at pH 8.5; and allophane in HCI-acid solution atpII 35. Iron oxide in halloysite and allophanes was, then, removed by adithionate-citrate system buffered with sodium bicarbonate after Mehra andJackson (1959). After the above procedures, the samples saturated with hydroniumion were prepared; i.e. the clay fraction wag washed with 0.02N HCl, water,ethanol, and acetone, air-dried, and pulverized.

Expunrunmel

The water in the samples was determined by gravimetric analysis; namely,the loss in weight after heating at 110 and 1000'C was meazured.

Before the measurement by wideJine NMR, two kinds of specimen wereprepared; one air-dried at room temperature, and the other dried at 110"C for72 hours in an oven. The wideJine NMR spectrum was obtained at 20'C usinga Varian System WL-12, under the following condition: iadio frequency,7978MHz; external magnetic field, 1862 gauss; modulation width, 0O79 gauss; sweep-ing rate,0.25-05 gauss/min; and response time, l sec. The specimen was packedto about a 3 cm depth in a pyrex glass tube having a 15 mm outside diameter.From the chart,6If-"r at 20"C was determined.

The infrared absorption spectrum was measured in the range of the absorp-tion band associated with stretching and defornation vibrations of the hydroxylgroup from 1200 to 4000 cm-l by using a Hitachi Model EPI-G2 infrared spectrom-eter. The tablet for measurement was prepared by pressing at 200 kg/cm" amixture o{ 1 mg of specimen with 200 mg of KBr.

Protons of the water or hydroxyl group in clays were exchanged with deuteronsby the following method; 0.2 g of the specimen was suspended in a coveredcentrifuge tube containinC 5 ml of heavy water with dissolved 0.146 g of NaCIat room temperature, and the specimen was allowed to stand for 20, 50, 230, or1430 minutes and then centrifuged for 10 minutes at 200 rprn. Ileavy waterused in this experiment had a 99.75 percent purity and was made by MerckCompany. Proton amount removed into the supernatant liquid was determinedby high-resolution NMR spectrometry. To prepare the standard for the calibra-tion curve, aliquots of water were mixed with the heavy water containing thedissolved 0.146 g NaCl; less than 9 mol of water was added to a liter qf theheavy water; 9 mol of water is equivalent to 18 mol of proton. The high-resolu-tion NMR spectrum was obtained at a radio frequency of 6O MTTz; sweepingrate, I Hz/sec; temperature during the measurement was 25'C; by using a VarianSystem T-60, and DSS (2,2-dimethyl-2-silapentane-5-sulfonate) was employed asa standard zubstance. A pyrex glass tube with 4 mm outside diameter was fiIledto a depth of 3 cm with the supernatant liquid to make the absorption measure-

YASAO KII'AGAWA

ment. The intensity of the absorption line was determined from the value of thtrintegral curve of the absorption spectrum drawn on the strip chart.

The amount of hydroxyl group in clays removed by fluoride was determinedby the following method: 0.5 g of specimen saturated with ammonium ion waszuspended in'a centrifuge tube wiih 80 mI of 0.5, 1.0, or 2.0 N ammoniumfluoride solution, kept in a thermostat at 30"C for 24 hours, and centrifuged at2000 rpm for l0 minutes. Supernatant liquid (20 ml each) was titrated with0.1 N H$SO" using bromthymolblue indicator, and the amount of hydroxyl groupreleased from the specimen was calculated.

Rpswrs AND DrscussroN

Water Content

The content of water in specimens determined from loss in weighton heating at 110 and 1000"C is shown in Table 1. Weight loss wasonly 1.2 percent in the kaolinite on drying at 110oC, but about 7 per-cent was lost in the halloysite, despite the fact it belongs to the samemineral group as kaolin. Both minerals lost about 13 weight percenton heating to 1000oC. Two thirds of the total water in montmorillonitewas lost at 1'10'C. Montmorillonite lost an additional 5 percent of itsweight after heating to 1000'C, the value is lower than that for kaolinminerals. The water content of these layer silicates agrees well withthe values obtained by other analysts (Grim, 1968). The molecularsieve, type 4A had a comparatively high content of water, and about70 percent of the total water was lost while drying at 110'C. Thisresult suggests that considerable amount of the water in the molecularsieve remains in an adsorbed form, for no hydroxyl group is found inthe structural lattice of this mineral according to Reed and Breck

TasLn 1. Loss or Wnrcnr oN Hperrnc er 110 ewo 1,000'C, ai.ru Pnomrv CoNrur.rrCer,culerno nnolr Wprcrrr Loss

tross of v€i€*rt (percat) ircton cort@.t (reI-/g)

r-:-ooc l,ooooc rotar trooc ].rooooc rotal-

Eaour1t6

laUdyslta

iloLscul.al steyg, 4l

llJ.otrrbee, NaluDa

llLopbue, UlEotsuchl.

],2.9 14.1

1r.o N.L

4.6 14.9

5.8 2O. '

L2.6 ".7lz.t 16.2

:r4., 15.6

14.4 22.1

5.L 1,6.5

6.4 22.4

14.O 17.4

t7.+ 40.2

7.L

].o.t

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24.L

7 . 9

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* loos of rclght oor:oslnnils to mter contmt.

NMR OF CLAY MINERALS 755

(1956). Both specimens of allophane have a great deal of water, ands of the total water in the specimens was lost on drying at 1l0oc. Thiswill be discussed later.

Wide-Line NMR and Inlrared Absorptinn

Fra. 1. Derivatives of the wide-line NMR absorption line: montmorilloniteairdried (Mwo); halloysite air-dried (HNo); kaolinite air-dried (KGo); andkaolinite dried at tl0'C (KGh).

6Hmst= 0.l3gouss

= 0.3,4.5 gouss

756 YASUO KITAGAW'A

Frc. 2. Derivatives of the wide-line NMR dbsorption line of molecular sieve,

type 4A: air-dried (L4Ao); and dried at 110'C (L4Ah)'

Frc. 3. Derivatives of the wide-line NMR absorption line of allophanes: Misot-

suchi air-dried (AMo); Misotsuchi dried at 110'C (AMh) ; Kanuma air-dried(AKo); and Kanuma dried at 110'C (AKh).

= 0.16 gouss

SHmst

6Hmst S H m s t=0 Egouss

NMN OF CLAY MINERALS 757

the magnetic field between maximum and minimum is the maximumslope line width, Df/-.1.

Figure 1 shows the curves for the layer silicates, kaolinite, halloysiteand montmorillonite. The absorption line in kaolinite is the double lineconsisting of 0.3 gauss and 4.5 gauss lines for 011-u1. The intensity ofthe wider absorption line may be far stronger than the narrower one,because the intensity is the value obtained from twice the integrationof the derivative curye. Only the narrower line has disappeared ondrying at 1l0oC. This result suggests that the narrower line is asso-ciated with the adsorbed water, and the wider one corresponds.to thestructural hydroxyl group. From the viewpoint of NMR, protons inkaolinite, air-dried at room temperature, may be separated into twoindependent systems, and protons in different sysrems may not bemutually exchanged. The absorption line for halloysite was 0.18 gaussand narrower than that for kaolinite. The absorption line disappearedon drying at 110'C. This seemed to be associated with the release ofthe adsorbed water on halloysite, but the adsorption energy of thewater may be lower than in the case of kaolinite. The signal due to thehydroxyl group in the halloysite lattice was not observed in themeasurement. This may be due to a strong absorption line from theadsorption water compared with that of the structural hydroxyl group.The adsorption line of wide-line NMR for water in montmoriflonitewas 0.13 gauss in 81/ps1, &nd also disappeared after drying at 1l0oC.The water adsorbed on montmorillonite seems to be more like a liquidthan the water in halloysite, because montmorillonite has a doublelayer sheet of water in the space between the structural layers, whilehalloysite has a monolayer sheet of water in its interlayer sp'ace. Thewide-line NMR absorption also suggests this difference in the struc-ture. ' ,

These results are contrasted wiih the infrared absolption sfiectrashown in the left side bf Figure 4. Kaolinite had absorption bands withfour distinct peaks at 3700, 3670, 36b0, and 8620 cm-l assolciatefl withO-H stretching vibrations'of the structural group, but'a ile# dignalsfrom adsorbed water were found. Halloysite has an infrared absorftionband at 1640 cm-l associated with the deformation vibration of ad-sorbed water, besides absorption bands with double peaks at 8700 and3600 cm-l associated with stretching vibrations of the structuralhydroxyl group. The absorption band between 8600 cm-1 uod 3ZOOcm-1 may be associated with stretching vibrations of adsorbed waterin halloysite. Montmorillonite also had two kinds of infrared absorp-tion bands due to adsorbed water and the structural hydroxyl group;3630 cm-l due to the stretching vibration from the structural hydroxyl

758 YASAO KITAGAWA

goup; 3430 and 1630 cm-r due to the stretching vibration and defor-mation vibration, respectively, of adsorbed water. The absorptibn bandassociated with the stretching vibration of adsorbed water in mont-morillonite was shifted to a lower wave number than the absorptionband in halloysite. This result may be related to the state of adsorbedwater in both minerals as mentioned in the discussion of wide-lineNMR. The infrared absorption band associated with the O-H stretch--ing vibration of the structural hydroxyl group in layer silicates hasalready been studied in detail by many researchers in relation to theposition and.direction of the hydroxyl group (Serratosa and Bradley,1958; Lyon and Tuddenham, 1960; and Hidalgo and Vinas, 1962).

The wide-line NMR spectrum of protons in the molecular sieve, type4A, showed very sharp absorption with 8I1-"r 0.07 gauss at room tem-perature. The absorption line expanded on drying at 110oC, and 8I/-"rincreased to 0.16 gauss. This suggested that, the water in the molecularsieve was closer to free liquid, and a considerable amount of water wasalso adsorbed on the mineral even after 72 hours of heating at 110"C.The drying resulted in the expansion of the line width, possibly be-

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Fro.4. The infrared absorption spectra of kaolinite (KG), halloysiie (EN),montmorillonite (MW), molecular sieve, type 4A (L4A), allophane, Kanuma(AK), and allophane, Misotsuchi (AM).

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lt

cause bindins rorces ::"::::" *"",-*d the surrac. "r;:molecular sieve became stronger with a decrease of absorbed water.

In the infrared absorption spectrum for the molecular sieve, type 4A,shown in the right side of Figure 4, a broad absorption band wasfound at 3400 cm-1 associated with O-H stretching vibrations, andanother band was clearly found at 1660 cm-1 due to the O-H defor-mation vibration. This suggested that the absorbed water of the molec-ular sieve is at several energy levels.

The shape of the wide-line NMR curves was almost the same forthe two specimens of allophane (Fig. 3). The specimens, air-dried atroom temperature, had 0.12 gauss 8I1^"y. The line width in allophaneswas wider than for the type 4A molecular sieve, but narrower than inmontmorillonite. The absorption line in allophanes expanded to 0.8gauss 811-.1 on drying at 110oC. The infrared absorption spectra ofallophanes showed the absorption bands associated with the O-IIstretching vibrations at 3490 and 3480 cm-1 in Kanuma allophane andMisotsuchi allophane, respectively, and the other band due to O-IIdeformation vibrations at 1630 cm-1 in both specimens (Fig. 4). Theabsorption band associated with the stretching vibration of adsorbedwater was located at the higher side of the wave number than thebands for the molecular sieve and montmorillonite, despite the resultof wide-line NMR. This suggests that the water molecules are ad-sorbed more strongly on allophane than they are on the molecular sieve.The water remaining in allophane after drying at 110'C was more likea liquid, rather than a structural hydroxyl group in kaolinite, based onthe fact that 8F/-"r in the former was less than I gauss. Many havestudied the dehydration of allophane by means of thermogravimetrysince Ross and Kerr (1934), and found that allophane releases waterslowly in the temperature between 200 to 1000"C.

Proton Erchange Reactton and Substitution of HydroxEl Group

The proton content in heavy water was determined from the high-resolution NMR spectrum using DSS as a standard. Chemical shiftdue to the protons in water was 2.1 ppm of the I value. The calibrationcurve of the concentration of protons in heavy water versus the peakintensity obtained from the integral curve drawn in the charb is shownin Figure 5, with a good straight line within the concentration rangetested.

The amount of protons in the specimens exchanged by deuterons isshown in Table 2. The exchange reaction was complete within 30minutes in all specimens except in montmorillonite. The protons in,montmorillonite exehanged slowly. This may be due to the jelly-like

zffi YASUO KITAGAWA

consistency of the montmorillonite suspension in water so that thewater around the mineral is stagnant. The protons in kaolinite wasnot exchanged, but the protons in halloysite s/ere exchanged to agreater extent than the water lost on drying at 110'C. This suggeststhat the protons of the structural hydroxyl group in halloysite arepartially exchangeable. In the molecular sieve, type 4A, almost allprotons were changed by deuterons. The protons in allophane wereexchangeable in spite of the high water content. The protons seemto be continuously exchanged between adsorbed water and the struc-tural hydroxyl group in allophane. Wada (1966) found this phenom-enon by infrared absorption spectrometry of clay minerals.

The results of substitution by fluoride showed that a few hydroxylgroups in kaolinite and montmorillonite were released; 0.3 mmol/g inkaolinite and 0.6 mmol/g in montmorillonite were released with 2Nammonium fluoride treatment. From halloysite, 1.5 mmol/g of hydroxylgroup was released using 0.5N ammonium fluoride, and the amountof hydroxyl group released by fluoride increased as the concentrationof ammonium fluoride solution increased. Hofmann et ol. (1956) foundthat a marked increase of the hydroxyl group released from kaolin

J

8aoo.

- 061218

x l0-2odded Proton ( m mol / DzO ml )

Frc. 5. The calibration curve between the peak intensity of high-resolutionNMR associated with water-state proton versus the amount of proton addedto heavy water.

=oco.c

x l0-2

NMR OF CLAY MINERALS 761

Tril,s2. PnoroN Excnewcno ny DournnoN

PToton moI,/g

Reactlon tine

(hous)

Ilaol-lnl.te

Halloyslte

I4otrtnorll].onit e

MoLeculaT sleve, 4A

AJlopbaae, Kmuna

Allophane, Misotsuchi

t r , t r

9 . 4 9 . 4

5 .5 2 .4

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7 2 < 7 7 ?

40 .8 75 .o

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10.9 10.5

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2O.5 49.2

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minerals occurred as the concentration of the ammonium fluoride solu-tion exceeded lN. Most of the hydroxyl groups released by fluoridefrom kaolinite and montmorillonite seem to be from the edges of thestructural units.

On the other hand, abundant hydroxyl groups were released fromallophane with ammonium fluoride solutions: 7.0, L1.9, and 14.4mmol/g with 0.5, 1.0, and 2.0N solutions, respectively. The hydroxylgroups in allophane may be more reactive to fluoride ion even at com-paratively low concentration. The increase, in hydroxyl groups releasedfrom allophane, Ievels off in ammonium fluoride solutions of about 2Nconcentration, according to Egawa et aI. (lgBO). The stability of thestructural hydroxyl group in clay minerals to fluoride ion may beclosely related to the exchangeability of protons in the structural lattice.

Tlsl,o 3. Hyonoxrr, Gnoup Rnr,n.lsno rx AulrowrurrtrLuonror Sor,urrox

of nmJ./g

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NE*F (oomal-ity) 1 .O

traou!Lte

Eal loyslte

UoatDorlloDLt6

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o.2 0 .2 0 . ,

r. .5 1.9 2.8

o .4 0 .5 0 .5

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YASAO KITAGAWA

Cowcr,usroN

The energy levels of water are clearly distinguished between ad-sorbed water and structural hydroxyl groups in layer silicates suchas kaolinite, halloysite, and montmorillonite, but such differentiationof water in zeolite and allophane is very difficult. Especially in allo-phane, this is difficult because its atomic structure is as yet not, clearlyunderstood. The results of proton-exchange reactions and substitutionof hydroxyl groups by fluoride suggest that all hydroxyl groups inallophane are exposed on the surface.

Fransdorff and Kington (1958) found from the infrared absorptionspectrum of synthetic zeolite, type 4A, that the absorption band at1650-1660 cm-1, associated with the O-H deformation vibration, doesnot change but the peak of the absorption band associated with theO-H stretching vibration shifts from 3486 cm-1 to 3377 cm-a as wateris added to the zeolite, and it becomes more like liquid water, 3390cm-'. In the liquid H2O-DgO system, the absorption band associatedwith O-H stretching vibration is situated at 3388 cm-1, and OH-Odistance is 2.85 A, according to Van Eck, Mendel, and Fahrenfort(1958). Reed and Breck (1956) reported that molecular sieves, typeA series, have two kinds of cavities; large ones are 11.4 A in diameter,and small ones are 6.6 A. The adsorbed water in the molecular sieve,type 4A, may be kept in the cavities. On the other hand, Kitagawa(1971) proposed that allophane consists of close-packed "unit parti-cles" 55 A in diameter. On tha't basis, allophane has also two kinds ofcavities among the particles; large ones are about 23 A in diameterand small ones are about 12 A; larger than the cavities in themolecular sieve. A part of the adsorbed water in allophane is keptwithin the cavities but a great deal of adsorbed water surrounds theallophane particles. The proton in adsorbed water is continuouslyexchanged with proton in the structural hydroxyl group. Aceordingly,the absorption line of wide-line NMR and infrared absorption spec-trum in allophane may be different from those in molecular sieve,type 4A. The water adsorbed on allophane and the molecular sieveis slowly released at temperatures higher than 200oC, but the water inallophane may be essentially different from so-called "zeolite water."

The structural hydroxyl group of allophane is different from thatof kaolinite; protons in allophane are continuously exchanged betweenthe structural hydroxyl group and adsorbed water, but protons in thekaolinite structure are stable to the exchange reaction. This may berelated to the position and the direction of the hydroxyl group in thedifferent mineral structures.

NMN OF CLAY MINENALS 763

The properties of water in allophane present an interesting study,and it will be an important problem in the future.

Acrwowr,nnclrr:Nrs

I wish to thank Dr. Y. Watanabe, National In-.titute of Agricullural Sciences,and Dr. Y. Sugitani, Tokyo University of Education, for helpful advice. Themeasurements of wideJine NMR were carried out by Dr. S. Takahashi, Na-tional Research Institute for Metals, and thc measurements of high-redolutionNMR were done by Miss Y. Yamamoto, Application Laboratory, Nippon Elec-tric Varian, I,td.

RnrnnnNcns

Annnnson, D. M. (1920) phase boundary water in frozen soils. U.S. Arrng ColilRegions Res. Eng. Lab,, Res. Rep. z74.

Ecr, C., L. Var.r, P. Varv, ervn J. F,rnnnNronr (1958) A tentative interpretation ofthe results recent X-ray and infra-red studies of liquid water a.nd II-O + D"Omixtures. Proc. Roy. Soc. London A247,472.4.81.

Ecewl, T., A. Saro, aun T. Nrsnrlrune (1g60) Release of OH ion from clayminerals treated with various anions, with special reference to the structureand chemistry of allophane. Nendo Kagaku, no Shinpo (Adu. CIaA Sci.,Toltgo), 2,282-262. (In Japanese)

FnaNsnonrn, G. J. C., arvo G. L. KrrvcroN (1958) A note on the thernodynamicproperties and infra-red spectra of sorbed water. Proc. Rog. Soc. LondonA2+7,469472.

Gnru, R. E. (1968) Clag Mineraloga, Znd ed., McGraw-IIill Book Company,New York.

HonnreNx, U., A. Wnrss, G. Kocu, A. Mnrrr,pn, ervo A. Scrror,z (1g56) Intra-crystalline swelling, cation exchange, and anion exchange of minerals ofthe montmorillonite group anC of kaolinite. Proc. Nat. Conl. Claas ClaUMi.neral.4,27A287.

Krrec,rwe, Y. (1971) The "unit particle" of allophane. Amer. Mineral. 56,46'5.475.

Kur.e, R. J., D. L. Rennxsrrrx, exn G. H. Rono (1g6b) Nuclear magnetic reso-nance technique for determining hydration numbers. Anal. Chem. 37, 1783-r7u.

LvoN, R. J. P., eno W. M. Trmnelruervr (1g60) fnfra-red determination of thekaolin group minerals. Natwe 185, 835-886.

Mnunn, O. P., eNo M. L. Lcr<sox (195g) Iron oxide removal from soils andclays by a dithionite-citrate system buffered with sodium bicarbonate. Proc.Nat. Conf . Cl,ws Claa Mi,neral. 7, glZ-A2Z .

Peur,snN, P. J., exl W. D. Cooro (1964a) Quantitative determinati,on of hy-drogen and fluorine in organic compounds by nuclear magnetic resonancespectrometry. Anal. Chem. 36, 1713-1721.

-, AND - (1964b) Determination of active hydrogen by nuclear mag-netic resonance spectrometry. ArcI. Chem. 36, 172l-1722.

Pnnrnr,o, R. E., er.ro J. A. Cunnrn (lg70) Soil water measurement by a low-resolution nuclear magnetic resonance technique. J. Soi.t Sci. 21,27&-?€f'.

Rsno, T. B., rNo D. W. Bnncr (19b6) Crystalline zeolites IL crystal stmctureof s1'nthetic zeolite, type A. J. Amer. Chem. Soc.78, W7Z-ffi27.

7M YASUO KITAGAWA

Rnsrxc, H. A. (1965) Apparent phase-transition effect in the NMR spin-spinrelaxation time caused by a distribution of correlation times' J- Chem. Phgs'

43, 66H78.eno J. K. TrrorupsoN (1969) NMR relexation of rvatcr plotons in zeo-

Iite; effect of paramagnetic impurities. Collog. Ampere, 75,237-2iL1.AND - (1970) NMR relaxation of water in zeolite l}X- ?nd Int'

ConJ. MoI. Sieue Zeol:ites, 770-775.,lNo J. J. Knnss (19&) Nuclear magnetic resonance relaxation

time of water adsorbed on charcoal J. PLtgs. Chem.68, 1621-1627'Ross, C. S., ervr P. F. Kpnn (1934) Hatloysite and allophane. U-S- GeoI. Suru'

Prof. Pap. 185G, 135-148.Snnterose, N. M., A. Hroar,co, eNo J. M. VrNes (1962) Orientation of OII bonds

in kaolinite. Nature 195, 486-487.eNr W. F. Bneor,nv (1958) Infra-red absorption of OH bonds in micas'

Nature 181, 111.TrroursoN, J. K..,rxr H. A. Rnsrxc (1967) Surface heterogeneity of zr charcoal:

Comparison of results of NMR and adsorption methods. J- Chem' Phys.47,

3685-3686.Wlne, K. (1966) Deuterium exchange of hydroxyl group in allophane' SoiI Sci'.

Plant Nutr. 12, 176-182.WonssNnn, D. E., eNo B. S. SNownpN, rn. (1969a) A study of the orientation

of adsorbed water molecules on montmorillonite clays by pulsed NMR'J. CoIIoid Interlace Sci. 30, 54-68.

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Manuscript receiued, June 18, 1971 ; accepted tor Wblication, September 7, 1971.