450
NOTES AND NEWS
Fic. 3. Resolution of low level thermorumr.r".."n..]n
Nacl by fast heating.
RarBnu.lcns
AuunNronr, w. F. (1957), Thermoluminescenceof Anhydrite: Master's thesis
held bv the
Library, University of Wisconsin.
Asnnv, G. E. eNn Kar.r.acnrn, R. c. (195g), An apparatus for the study of thermoluminescencefrom minerals: Am. Mineral,.,43, p. 695-706.
Hourrnue.Ns, E. G., JAcnn, E., Scndw, M., aNo Sreurlnn, H. (1957), Messungen
der
Thermolumineszenz als Mittel zur untersuchung der thermischen und der strahlungs_
geschichte von natiirlichen Mineralien und Gesteinen: Annalen der phys.ih,20,
2g3292.
Lnwrs, D. R., Wurr.unn, T. N., .ruo Cn,lrlr,lN, C. W. (1g5g), Thermoluminescence
of
rocks and minerals. Part I. An apparatus for quantitative measurement: Am.
Mi,neral..
44, |21-11n.
Sruuonns, D. F' (1953), Thermoluminescence and surface correlation of limeston
es: BuII.
Amer. Assoe. Petrol. Geol,.,37, ll4-124.
THE AMERICAN
MINERALOGIST,
VOL 46, MARCH_APRIL,
1961
ADSORPTION OF ETHYLENB GLYCOL AND GLYCEROL
BY MONTMORILLONITE*
(Clay-OrganicStudies,Part Vi)
Rnrwul,nn
W. HollmaNN AND G. W. BnrNoLly, Depa.rtn enf of
C eramic T echnology, T he p enns^vla
ania S tate LIniaer sity,
U niver sity p arh, p enn,sylvania.
The swelling of montmorillonite
immersed in ethylene grycor or in
glycerol has been used for many years to identify montmoiillonite
in
* contribution No. 60-32
from the coilege of Mineral rndustries, The pennsyivania
State University, University park, pennsylvania.
t Part IV. SeeHofimannand Brindley (1961).
NorES AND NEWS
451
mixtures of clay minerals. It is sometimes believed that montmorillonite has an 'affinity' for these compounds such that they are strongly
absorbedfrom aqueoussolutions. The present note describesmeasurements which show that they are not preferentially absorbedfrom aqueous
solutionsto any appreciableextent.
In previous work (Brindley and Rustom, 1958,and more particularly,
Hofimann and Brindley, 1960) isotherms for the adsorption of a variety
of non-ionic organic compounds of Ca-montmorillonite from aqueous
solutions have been determined to study the features of the organic
molecule which affect the adsorption. Two factors were found to afiect
the adsorption equilibria in solution: chainJength and CH-activity' For
molecules with small CH-activity, a minimum chain-length of about 6
carbon atoms is required for preferential adsorption and on this basis
neither ethylenegiycolnor glycerolwouldbe expectedto showpreferential
adsorption.
Experiments have been made to determine the adsorption isotherms
of ethylene glycol and glycerol on Mg-montmorillonite from aqueous
solutions.The Mg-saturated clay was used becauseit was immediately
availableand other studies (Brindley, Hoffmann and Bender, 1960)had
shown that for several substancesthe exchangeableinorganic cation has
no significant influence on the organic adsorption, at least for the ions
Na+, Ca2+,and Mgz+.
Suspensionscontaining 15 mg. clay per ml. and ethylene glycol or
glycerol in concentrationsvarying from 2.5X10-2 to 50X10-2 molar
were equilibratedfor 20 hr. After centrifugingfor 2 hr., the organic content of the supernatantliquid was determinedby dichromate oxidation.
For neither compound could any depletion in concentrationbe detected
except for small variations within the accuracy of the analytical determinations (Xt77. Therefore these compoundsdo not show any preferential adsorption from aqueous solutions on montmorillonite.
Part of the clay paste remaining in the centrifuge tubes was taken
with a minimum of adherent liquid and allowed to dry on glass slides.
The clay-organic films were then examined in a stream of dry air by
r-ray difiraction using a Phillips Norelco diffractometer with filtered
CuKa radiation. The results showed that complexeswere formed containing one layer of water, one layer of organic material, two layers of
organic material, or mixtures thereof according to the organic concentration of the adherent solution in the initial clay paste.
The spacings for the one- and two-layer organic complexes are 13.90
+ 0 . 1 A a n d 1 6 . 8 r * 0 . t A f o r e t h y l e n eg l y c o l , 1 3 . 9 5 + 0 . 1i t a n d 1 7 . 7 r
+0.1 A for glycerol respectively,and 11.9s*0.06 A for a single water
Iayer.
452
NOTES AND NEWS
It has been pointed out already (Hoffmann and Brindley, 1960) that
the type of complex formed after drying a clay-water-organicmixture
doesnot dependso much on the adsorptionequilibria existingin aqueous
solution as on the relation of the volatility of the organic compound to
that of water. Among the substancesinvestigated, two extremeshave
been found:
(i) Substanceswith high volatility may be adsorbed strongly from
aqueoussolutionsunder equilibrium conditions,but may not form complexeson drying as both the water and the organicsubstanceevaporate.
(ii) Substanceswith low volatility which show little or no adsorption
from aqueoussolution, may still form complexeson drying becausethe
water evaporatesleaving the clay and organic material behind.
The secondmechanismhas already been proposedby Bradley (19a5)
who suggestedthat ethylene glycol may form complexeswith montmorillonite by replacementof the adsorbedwater due to their difference
in volatility. This is now confirmedexperimentally. Ethylene glycol and
glycerol belong to the secondgroup since they show no preferential adsorption from aqueoussolution under equilibrium conditions but form
complexesafter drying due to their low volatility comparedwith that of
lvater.
Grateful acknowledgementis made to the donors of the Petroleum
Research Fund, administered by the American Chemical Society, for
support of this reasearch.
Rnlnnexcrs
Bnaolrv, W. F., (1945), Molecular associations between montmorillonite and some polyfunctional organic liquids. f . Am. Chem. Soc.67,975481.
BnrNor.ev, G W., HorruaxN, R. W., ANt Brvorn, R, (1960), unpublished data.
Bntnolnv, G. W., awn RusroM, M*ntouo, (1958), Adsorption and retention of an organic
material by montmorillonite in the presenceof water, Am. Mineral.,43r 627-640.
HolrueNN, R. W., axn BnrNnrnv, G. W., (1960), Adsorption of nonionic aliphatic molecules from aqueous solution on montmorillonite (Clay-Organic Studies, Part II).
Geochim et Cosmocltim.Acta,20, 15-29.
HorluaNn, R. W., aNn BnrNolrv, G. W., (1961), Infrared extinction coefficients of
ketones adsorbed on Ca-montmorillonite in relation to surface coverage (ClayOrganic Studies, Part IV). Submitted b f . Phys. CIum.