some conditions minerals in aqueous ... 9/9-1-468.pdfsome conditions affecting the adsorption of...

SOME C O N D I T I O N S A F F E C T I N G T H E

A D S O R P T I O N O F Q U I N O L I N E B Y C L A Y

M I N E R A L S I N A Q U E O U S S U S P E N S I O N S

by

1~. W . DOEtILER AND W . A . YOUNG

Jersey Production Research Company, Tulsa, Oklahoma

A B S T R A C T

The adsorption of quinoline by Na +- and CaZ+-montmorillonite, illite, and kaolinite in water suspensions was studied for varying physico-ehemical conditions. The shapes of the adsorption isotherms depended upon these imposed environmental conditions, which were quinoline concentration, pH, salinity, time, and temperature.

In order to be in the range of concentrations of organic materials in natural waters, these studies covered the concentration range, from 0 to several hundred ppm. Of the variables studied, pI-I was critical. Throughout the pH range 8.5-6.0, adsorption increased as p i t decreased. The change in adsorption as salinity increased depended on pi t , clay mineral, and quinoline concentration. In our experiments, samples reached equilibrium within 2-3 hr, and moderate temperature changes made little difference in adsorption amounts.

Under the same conditions, Na+-montmorfllonite adsorbed the most quinoline, kaolinite the least, and Ca2~-montmorillonite and illite intermediate amounts.

Two mechanisms seem to control this adsorption : ion exchange and molecular adsorption. This paper a t tempts to explain the effects of the physico-chemical environment on adsorption by these two mechanisms.

I N T R O D U C T I O N

~Iany excellent articles deal with the adsorption of organic material by clay minerals. References to many of these articles, as well as general surveys of clay-organic reactions, have been given by MacEwan (1951) and Grim (1953, pp. 250-277). For the most part, however, these investigations have been concerned with adsorption of organic liquids and vapors by montmorillonite and vermiculite. The studies have been focused primarily on the swelling of the clay lattice due to organic adsorption, the bonding mechanisms operative between organic and clay, and the orientation of the organic molecules between clay layers.

More recently Brindley and Rustom (1958), Hoffmann and Brindley (1959), and Bader and Smith (1959) specifically studied organic adsorption by clays in water suspensions.

468

SOME CONDITIONS AFFECTING THE ADSORPTION OF QUINOLINE 469

The mere presence of water in a clay-organic reaction is important in that the water must act in competition with the organic material for sites on the clay surface. The pH of the water is a consideration since some organic types may change in their ionic-nonionic form in response to changes in hydrogen ion availability. Adsorption characteristics by clay may be quite different depending upon whether or not the organic material is ionic or nonionic. If buffer solutions are added in order to keep pH constant, the question arises as to the significance of ionic strength of the aqueous medium on adsorption. I t is quickly seen that a whole series of variables are soon involved in such experiments.

This study is an a t tempt to show the importance of some of the physico- chemical conditions of the aqueous medium in which clay-organic reactions occur. When the term "environment" is used in this paper, the reference is to these imposed physieo-chemical conditions.

A C K N O W L E D G M E N T S

The authors wish to thank the management of the Jersey Production Research Company for permission to publish this work. Further thanks are expressed to Prof. R. E. Grim, Dr. W. F. Bradley, Prof. P. F. Low, and Dr. W. A. White for their discussions with the writers and comments con- cerning interpretations of the data.

M A T E R I A L S A N D M E T H O D S

Clay Minerals

The clay minerals used in this investigation were Na+-montmorillonite from Clay Spur, Wyoming; Ca2+-montmorillonite from Chambers, Arizona: illite from Fithian and Morris, Illinois; and kaolinite of the Georgia type. The exact source of the kaolinite sample is not known. The effects of varying environmental conditions were our chief concern, and not maximum adsorption capacities of the clays. Consequently, the montmorillonite and kaolinite samples were used without any prior t reatment ; that is, small amounts of nonclay material were not separated from the clay. The illite samples, however, were dispersed in distilled water, and the < 2 # fraction was separated by centrifugation and used in the experiments. An imposed pH was difficult to maintain on this material. Accordingly, before using it, the clay was soaked in 0.2 N K O H for 1 hr, washed free of excess K 0 H with distilled water, and air-dried.

Organic Material

Quinoline was selected as the organic material in this study because it has a favorable solubility in water, and it can be rather easily analyzed. quantitatively, by its absorption spectra in ultraviolet light (Fig. 1). Quino-

470 NINTH NATION~ CONFERENCE ON CLAYS AND CLAY MINERALS

line (synthetic) from Eastman Organic Chemicals was dissolved in distilled water and used in all experiments.

Buyers

In order to control the pH of the sample environment, i t was necessary to use buffer solutions. Phosphate buffers were used for the pI-I range 6.0-8.0, and borate buffers for the range 8.0-10.0. Sodium phosphate or

AB$ORBANGE IN I CI, I GELL FOR ~0 PpM SOLUTION

I ~ I I I ~ ~ .... ~ 240 ~60 2ao 300 ~2o 340 360 3Bo

MILLIMIC, RONS

FIGURE l.-- (.4) Absorption spectra of quinoline in ultraviolet light, and (B) structural formula of quinoline.

borate buffers were used with Na+-montmorillonite and kaolinite, potassium buffers with illites, and ammonium buffers with Ca2+-montmorillonite clay.

Procedure

One-quarter gram portions of the air-dried clays were weighed, placed in screw-top flasks, and allowed to disaggregate by soaking in distilled water. In several instances, 0.50 g samples of kaolinite and illite were used, and these are noted in the paper. The combined volume of water, buffer, and quinohne solution in each sample was 10 ml. The quinoline was in contact with the clay for 3 4 days, after which the samples were centrifuged in order to separate the clay from the supernatant liquid. Quinoline concentration and pH measurements were made on the supcrnatant liquid. Quinoline concentration was determined by absorption of ultraviolet light at 314 m# (Fig. 1A). All quinoline determinations were made in alkaline solutions, since the ultraviolet light absorption is somewhat pI-I sensitive. The amount of quinoline in the supernatant liquid was calculated, and then by difference the amount retained by the clay.


E X P E R I M E N T A L R E S U L T S

Quinoline Concentration

Fig. 2 shows adsorption isotherms for four clay minerals, at about the same pH, with qninoline concentration as the variable. The curves describe equilibrium conditions of the samples; that is, the quinoline concentrations

J ~o IOOC - -

=~ s o c - - - -

60C - - - - -

::L

f60C "]

I

140C - - - - - - - - - -

120C - -

F

40C

20C - -

/ T q T q L , !

0 NA ~' MONTMORILLONITE - p H 7.5 i h, GA'r'+MONTMORILLONITE-pH 7.5 ~ j ~ ~

t

D ILLITE " "pH 7B / X KAOLINITE ~" pH 7.6

[ [

OUINOLINE IN EQUILIBRIUM - PPM

FIou~ 2.--Isotherms showing quinoline adsorption by four clay minerals in response to changing quinoline concentration.

at the end of the experiments are plotted against the amounts adsorbed by the clays. As higher concentrations of quinoline became available to the clays, more was retained. The adsorption mechanism or mechanisms, in some cases, became more efficient as the quinoline concentration increased. The data show that some of the isotherms swing upward at higher quinoline concentrations. The concentrations studied here ranged from 0 to 200 ppm, well below the value for quinoline solubility in water. For similar environmental conditions, Na+-montmorillonite retained the most quinoline, kaohnite the least, and Ca2+-montmorillonite and Fithian illite intermediate amounts. No correlations have been made for clay hydration state at room conditions.

472 NINTH NATIONAL CONFERENCE ON CLAYS AND CLAY MINERALS

pH

Adsorption of quinolinc by the clay increased as the pit of the environment decreased throughout the range of pH values investigated. Adsorption was more sensitive to pH changes in the case of the three-layer clays than with kaolinite. Fig. 3 and 4 show that adsorption from slightly acidic environments was always greater than from alkaline environments, regardless of the quinoline concentration or type of clay present. Particularly with Fithian illite and Ca~§ the shapes of the adsorption isotherms varied in response to pH changes.

Fig. 5 and 6 illustrate, a little more clearly, the dependence of adsorption values on pH throughout the range of approximately 6.0-8.0. Note that 0.50 g samples of kaolinite and illite were used for the curves in Fig. 5, but the same quinoline concentration was available to all samples plotted in both figures.

1600 ! A "

0 NA* MON3"MORILLONITE i pH 6.4 1400 - J J" NA+ MONTMORILLONITF - pH 75

CA§ - pH 63 - - Xl~ CA++iNT MOR' LLONtT'I- pH 73

1200 I

1 I ! l C

> -

51~176 . . . . i o i

~ , f ~ ,

600 . . . .

t .oo,

200 . . . . . . .

' i n ~

f

0 .20 40 60 80 I00 120 140 Q4JINO(..INE IN EG4.11UBRIUM - PPM

FIGURE 3.--Isotherms showing changes in quinoline adsorption by Na +- and Ca z+- montmorillonite in response to changing pH.


I O 0 0

/

(5

m

:L

J

0 20 40

0 ILLITE - pH 6.5 ,~ ILLITE - pH 7.5 r l KAOLINITE - pH 6.7

--X

60 80 I00 120 140 160 QUINOLINE iN EQUILIBRIUM - PPM

F m v ~ 4.--Isotherms showing changes in quinoline adsorption by illite and kaolinite in response to changing pH.

I00 PPM OUINOLINE 0 ILLITE A KAOLINITE

cu

20C A - - ~ A A

6.4 6.8 7.2 7.6 8.0 8.4

CH

FI(]u~ 5. - Curves showing changes in quinoline adsorption by illite and kaolinite in response to changing pH.

cog 31


Time and Temperature

Time vs. adsorption and temperature vs. adsorption curves are included here primarily to show tha t equilibrium was being reached in the time the samples were allowed to remain mixed, and tha t moderate temperature

tO00

60(

8

0

g <o 40(

::L. "....

IOO PPM QOINOLIN( NA 4" MQ~ITMO4~IL NITE GA ~ ~'MON TMORiL~NIT r

1

6 ' ; 6.8 7.2 76 8.O pH

FmuR~ 6.-Curves showing changes in quinoline adsorption by Na +- and Ca ~+- montmorillonite in response to changing pit.

variations caused very little change in adsorption amounts. Fig. 7 shows that about 200 min after mixing, 0.25 g samples of Na+-montmorillonite reached equilibrium with their environments. To be sure, this t ime factor undoubtedly would change as sample size and organic concentration change. The samples taken 15 min after mixing were probably abnormally high in quinoline owing to the high organic concentration around the point in the suspension at which the quinoline was introduced.

There was only a slight decrease in adsorption as the temperature was raised from 4 ~ to 60 ~ (Fig.8).

Sal ini ty

The overall effect of salinity in the range 0-68,000 ppm was to reduce the amount of quinoline adsorbed by the clay. Salinity, as used here, was


a combination of buffer and NaC1. The strength of the buffer solution of a median pH was about 8400 ppm.

Adsorption v s . salinity curves are shown in Fig. 9 for three clay minerals in comparable organic and pH environments. The isotherm for Na*-mont -

I000

800

6OO

.o

8 400

2 0 0 - -

/ /

A

s /,.--- /

I

/ / /

'X

v

MA + MQNTMOR(LLONffE I00 PPM QUINOLtNE

O pH6~ Z~ pH 78

X pH92

200 300 400 " 1 4 MINUTES AFTER MIXPNG DAYS

FtcuR~ Z--Curves showing adsorption of quinoline by Na+-montmorillonite in relation to time after mixing.

morillonite shows a minimum at about 16,000 ppm, whereas the curves for Morris illite and the kaolinite do not. The minimum on the Na+-montmoril- lonitc curve was, at least in part, related to pH. This relation is illustrated in Fig. 10 where the quinoline concentration was the same for each curve, but the pH was varied. The minimum became more pronounced and moved from lower to higher salinities as the pH changed from 6.4 to 8.3. This minimum also was related to quinoline concentration (Fig. l 1). Percent adsorption was plotted v s . salinity because of the varying organic concentration. The curve at 300 ppm quinoline shows little effect due to salinity, while the curve at 12 ppm quinoline, at least in shape, approaches those for kaolinite and illite.

31"


Reversibility

The reversibility of the adsorption reaction, or the ease with which the quinoline was desorbed in response to changing conditions, was studied for Na+-montmorillonite, Fithian illite, and kaolinite. The procedure in the

NA + MONTMORILLONITE - pH 7 I 0 80 PPM OUINOLINE /~ 40 PPM OUINOLINE

o l 0 20 30 40 50 60 70 TEMPERATURE - "C

FmURE 8.--Curves showing adsorption of quinoline by Na+-montmorillonite in relation to temperature.

reversibility experiments was to prepare two identical sets bf samples. Each set initially covered the concentration range 400-2000/zg (40-200 ppm) quinoline per 10 ml of water. The samples in one set were analyzed 3 days after they were mixed, and at the same time the other set was diluted so that the new quinoline concentration in each sample was only 200 fig per I0 ml of water. The solution used for diluting the samples was such that the proportion of buffer to water remained constant. After 4 days at this new concentration, these samples were analyzed. With this concentration a completely reversible reaction would leave an amount of quinoline on the clay equal to that adsorbed if the concentration had always been 200 fig per 10 ml of water.

SOME CONDITIONS AFFECTING THE ADSORPTZON OF QU]NOLINE 477

IO00

SO0

d

\

I

I00 PPM QUINOLtNE NA P MONTMORILLONITE - pH 7,2 ILLtTE -- pH 7.3 KAOLINITE - =H 7.2

J

f

200

0(~ 8000 16,000 24 jO00 32,000 40,000 48,000 56,000 64,000 72,000 80~000 SALINITY - PPM

FIGURE 10. -- Curves showing changes in adsorption of quinoline by Na+-montmorillonite in response to changing salinity and pH.

f

NA 4" MONTMORILLONITE IO0 PPM OUINOLINE

[] pH 6.4 0 pH 7.~ ~, pH S.8

~oo~ (

IE : 6oc ~

~u;400 /

0 0 8000 16,000 24000 32,000 40,000 48,000 56~00 64,000 ?'2,000

SALINITY - PPM

FmvRE 9.--Curves showing changes in adsorption of quinoline by three clays in response to changing salinity.

478 NI]NT]-I NATIONAL CO1WFERE1WCE ON CLAYS AND CLAY MINEI~ALS

IOC

d

so

d

80 ~

k~

4ol ~

~o ~

1 0 1 0 5000 16,000

1

NA + MONTMORiLLONITE - pH "~2 0 300 PPM OUINOLINE

I00 PPM OUINOLINE I ~ PPM QUINOLINE

32,000 40,000 48 ,000 SAUNITY - PPM

24,000 56,000

0

I I

I

64,000 72,000 80,OCO

F m u ~ 11.-Curves showing changes in adsorption of quinoline by Na+-montmorillonite in response to cha~nging salinity and quinoline concentration.

210C

180C

150C - -

IZOC o

=o r 80G o

m 60C

300

NA* MONTMORILLONITE - pH 6.4 0 INITIAL SAMPLES Z~ SAMEAS 0 LATER D[LIJTED TO

200/r GM/IO~;C X COMPLETE REVERSIBILITY

0 I

/

X

500 1000 1500 2000

~GM QUINOLINE IN I0 C0 H 2 0 INITIALLY

Fmvg~ 12.-Reversibility of quinolhle udsorptlon by Na+-montmoritlonite at pl:~ 6.4.

SOME CONDITIONS AFFEOTING THE ADSORPTION OF QUINOLINE 479

Comparison of Figs; 12 and 13 shows that quinoline adsorption was more reversible from Na%montmoIil lonite when the pH was 7.5 rather than 6.4. Even at pH 7.5, however, the adsorption reaction was not completely reversible.

Reversibility data for both Fithian fllite and kaolinite were for 0.50 g samples. Fig. 14 and 15 show t h a t quinoline adsorption was rather

180C j r

i

, i 50C 0 INITIAL NAt MONTMORILLONIT[sAMPLES pH 7,5 ~/ . . . . . . ~

120C . . . . . . . . . x COM PLETs R s . . . . . . . . . . . . . . . . . . . .

i i -

~oo~ ...... ~ ~ ......................

~ 5bo ~0oo ~ ~oo ~ o o ~GM QUINOLINE IN I0 {;C H20 INITIALLY

FIGURE 13.-- Reversibility of quinoline adsorption by Na+-montmorillonite at pH 7.5.

I 0 0 0 ' I J

I LL ITE - pH 8,2 | 0 INITIAL SAMPLES ~ (

t . . . . ~ TO 200 FcGM/IOCC | 8 0 0 z'k SAME AS O, LATER . . . . . .

X COMPLETE' REVERSIBILITY

. . . . . . i , - =

400 . . . . . . . . I . . . . ,,

200 .............................

n o I 500 1000 1500

~ G M OUINOUNE ~N IO cc H20 INmALLY

FIGURE 14. - Reversibility of quinoline adsorption by iUite at pH 8.2.

2000


irreversible with both illite and kaolinite, even though the p H of the illite experiment was 8.2.

600

500

i KAOLINITE L pH 6 7

0 INITIAL SAMPLES

d 4 0 0 $

o 0

5DO

o

Z00

$ :L

I 0 0

Z~. SAME AS O, LATER DILUTED TO 200 /r

X COMPLETE REVERSIBILITY

!

L X ~ X I x '

/ 0

O 500 IOOO 1500 P'GM QUINOLINE IN IO CC H20 INITIALLY

FmURE 15. -- Reversibility of quinoline adsorption by kaolinite at pH 6.7.

Y

2000

D I S C U S S I O N

Before the relations between clay and quinoline in various environments can be discussed, the effect of changing environment on quinoline alone must be understood. At p H 5, quinoline in solution exists in about equal portions of ionic and nonionic molecules. As pH increases, the percent of quinohne cations decreases, and at a pH of 7.0, only about 1 percent are cations. Accordingly, the quinoline exists in both ionic and nonionic forms in these experiments. The ratio of the two forms depends on pi t .

Buffers, of the variety used in this study, and NaC1 have no apparent effect on the quinohne spectra in solution for the range of concentrations in which these components were mixed.

I t appears tha t the clay minerals adsorbed quinoline from solution by two mechanisms: cation exchange and molecular adsorption. The latter mechanism may be due to van der Waals ' at tractive forces or to those forces resulting from polarization of the aromatic rings as a whole, or both (Bradley, 1945).

Quinohne must compete with water for sites on the clay surfaces. The state of order or disorder of the water net, therefore, is somewhat a measure of the energy acting to keep the quinohne in solution and not adsorbed on the clay. Any condition which tends to disrupt the water net, accordingly, should promote adsorption of quinoline in relatively larger amounts.


Initially adsorbed quinoline apparently has a disruptive effect on the water nets of the three-layer clays. The data show that, as a result, the adsorbing mechanisms become more efficient at higher quinoline concentrations.

The pr imary effect of pH is to produce a greater number of quinoline cations at lower, rather than higher, pH values. The adsorption v s . pH relationship, then, apparently reflects the extent of exchange between organic and inorganic cations for sites on the clay surfaces. When large amounts of quinoline can be adsorbed through cation exchange, the upswing 4n the adsorption isotherm, or the increased efficiency of overall quinoline adsorption, occurs at lower organic equilibrium concentrations (Fig. 3). This suggests that quinoline cations on exchange sites exert a greater disruptive effect on the water net around clay flakes than equivalent adsorption as the free base would exert.

The adsorption v s . salinity curves show an initial decrease in adsorption values as salinity increases. This is interpreted as a cation exchange phenomenon; that is, fewer quinoline cations become adsorbed as Na + concentration increases. Since adsorption values never approached zero, even at the highest salinities, quinoline must be adsorbed, therefore, by molecular forces as well as by ionic forces.

Sodium concentration, in addition to competing with quinoline cations, disrupts the water net around clay flakes. According to Norrish (1954), the lattice expansion data for montmorillonite in NaC1 solutions show an abrupt change toward smaller interplanar spacings at a concentration of about 16,000 ppm. The adsorption v s . salinity data for Na+-montmorillonite, in general, indicate adsorption increases at salinities greater than the range 16,000-24,000 ppm, when the initial quinoline concentration is 100 ppm (Fig. 10). These data appear to be further evidence that structure of the water net and quinoline adsorption are related. The shapes of the curves, in particular the minima, may result from the interaction of both adsorption mechanisms--ion exchange and molecular adsorption.

The salinity at which the minimum occurs in each adsorption curve varies with pH. At pI-I 6.4, relatively large amohnts of adsorbed quinoline plus the Na + concentration both act to disrupt the water net around the clay flakes. Collapse of the water net can occur, therefore, at a lower salinity when the pH is 6.4 than when the pH is 8.3, owing to the relative amounts of adsorbed quinoline at each pH. Consequently the minima trend toward higher salinities as pH increases.

The shapes of the adsorption v s . salinity curves for Na+-montmorfllonite also change with quinoline concentration. The 300-ppm quinoline concentration is evidently adequate to compete with Na + up to considerable concentrations, so tha t essentially no minimum is detected. Adsorption by ion


exchange and molecular forces interact so tha t percent adsorption is nearly constant over this salinity range. At 12 ppm, there is an initial decrease in adsorption; however, this concentration is inadequate to define a minimum in the curve.

The adsorption v s . salinity curves for illite and kaolinite show little in- crease in adsorption at the higher salinities, even though the Na+-montmorillonite did adsorb more under comparable conditions. The illite and kaolinite clays possess substantially less surface area on which water nets can develop; accordingly, they can be expected to show only a small effect in relation to changes in their adsorbed water.

The reversibility of quinoline adsorption by Na§ is more complete at pH 7.5 than at pH 6.4. Evidently these data result from a greater degree of cation exchange which occurs in the acid environment. Ion exchange, therefore, seems to bond the quinoline less reversibly to the clay than the molecular forces.

Reversibility of quinoline adsorption on illite and kaolinite appears to have a control in addition to pH. The degree of reversibility is less than expected for both clay types, even though the amount of quinoline involved is considerably less than tha t with Na+-montmorillonite. I t is suggested that the variation in surface charge and in surface composition of illite and kaolinite, as compared to Na+-montmorillonite, may explain these reversibility data.

S U M M A R Y A N D C O N C L U S I O N S

Experiments were performed in which quinoline, as the organic material, was adsorbed by clay minerals in water suspensions. The clay minerals were Na +- and Ca2+-montmorillonite, iilite and kaolinite. The physico- chemical environments of the samples were varied in regard to quinoline concentration, pH, salinity, time, and temperature, and the adsorption data were found to vary in response to these conditions.

Both cation exchange and molecular adsorption caused quinoline to be retained by the clay. The nature of the water net around clay layers was important in that the water competes with quinoline for the clay surfaces. As the water net was disrupted, quinoline adsorption proceeded more efficiently.

The reversibility of quinoline adsorption was controlled, at least in part, by the pH of the environment and by the type of clay mineral.

From the data presented, it can be seen that the reactions between quinoline and clay minerals in water suspensions are quite sensitive to some changing environmental conditions. Different types of organic material can be expected to react differently to the same environmental changes.

SOME CO~NDITIO~NS AFFECTING THE ADSORPTION OF QUINOLINE 483

R E F E R E N C E S

Bader, R. G. and Smith, J .B. (1959)Significance of adsorption isotherms for specific organic materials on sedimentary minerals (abstr.): Bull. Geol. Soc. Amer., v. 70, p. 1564.

Bradley, W.F. (1945) !VIolecular associations between montmorillonite and some poly- functional organic liquids: J. Amer. Chem. Soc., v. 67, pp. 975-981.

Brindley, G. W. and Rustom, Mahmoud (1958) Adsorption and retention of an organic material by montmorillonite in the presence of water: Amer. Min., v. 43, pp. 627-640.

Grim, R. E. (1953) Clay Mineralogy: McGraw-Hill Book Co., Inc., New York, 384 pp. Hoffmann, R. W. and Brindley, G. W. (1959) Adsorption of organic molecules from aqueous

solutions on montmorillonite (abstr.): Bull. Geol. Soc. Amer., v. 70, pp. 1618-1619. MacEwan, D. M. C. (1951) The montmorillonite minerals (montmorillonoids): in X-ray

Identification and Crystal Structures o] Clay Minerals: Mineralogical Society, London, pp. 86-137.

Norrish, K. (1954) The sweUing of montnlorillonite: Faraday Soc. Disc., no. 18, pp. 120-134.

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