Preparation and properties of barium clinoptilolite

Mat. Res. Bull. Vol. 7, pp. 543-550, 1972. Pergamon Press, Inc. Printed in the United States.

PREPARATION AND PROPERTIES OF BARIUM CLINOPTILOLITE Daniel B. Hawkins and Jose L. Ordonez* Geology Department, University of Alaska, Fairbanks, Alaska

(Received April 11, 1972; Communicated by R. Roy) ABSTRACT Barium c l i n o p t i l o l i t e was prepared by ion exchange of natural c l i n o p t i l o l i t e with 0.2 normal barium chloride solution at 85°C for 16 hours. Barium c l i n o p t i l o l i t e is stable to 650°C, a thermal s t a b i l i t y less than potassium c l i n o p t i l o l i t e , greater than calcium c l i n o p t i l o l i t e and similar to natural c l i n o p t i l o l i t e . Barium c l i n o p t i l o l i t e transforms hydrothermally at 425°C and 15,000 psi. to hexagonal celsian-cymrite, quartz and water; unlike natural clinop t i l o l i t e which converts at 350°C and 15,000 psi. to mordenite then to plagioclase, quartz and water at 425°C. X-ray d i f f r a c t i o n patterns and electron micrography suggest that structural or morphological differences relative to natural c l i n o p t i l o l i t e may also exist. Barium c l i n o p t i l o l i t e showed low ion exchange s e l e c t i v i t y for strontium relative to calcium; much less than that of natural c l i n o p t i l o l i t e . I t is suggested that barium c l i n o p t i l o l i t e might exhibit ion exchange s e l e c t i v i t y for barium or radium and might be of use in radioactive waste treatment. Introduction The purpose of this study was to determine i f barium c l i n o p t i l o l i t e similar to that synthesized hydrothermally ( I ) could be produced from the natural high-silica zeolite under less rigorous conditions by ion exchange. A more detailed account of this work is given elsewhere (2). The c l i n o p t i l o l i t e used in this study came from Mink Creek, near Preston, Idaho, where the mineral occurs in the t u f f of the Salt Lake Group of late Tertiary age (3).

The i d e n t i f i c a t i o n of c l i n o p t i l o l i t e in this t u f f was based

upon X-ray d i f f r a c t i o n and confirmed by heating the zeolitized t u f f overnight at 500°C with no subsequent modification of structure (4).

*PresentAddress: Prospecciones Geologico-Mineras, S.A., Pedro Muguruza, l-6°A, Madrid-16, Spain.

543

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BARIUM CLINOPTILOLITE

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The mineralogical composition of the t u f f was estimated by X-ray diffraction and optical microscopy. The material studied consisted of more than 80% clinoptilolite,-lO% quartz, less than 4% potassium feldspar, less than 2% calcite and minor amounts of plagioclase, chlorite, montmorillonite, limonite and pryolusite.

No chemical analysis of this material is available. Preparation of Barium Clinoptilolite

The t u f f was ground and sieved to less than lO0 mesh. The size fraction lying between lO0 and 200 mesh was used for further treatment.

This material

was washed in I0% hydrochloric acid at 25°C for one hour to remove calcite, limonite and pyrolusite.

The acid-washed material was treated with O.l molar

di-sodium ethylene d i n i t r i l o tetraacetic acid (di-sodium EDTA) for 16-24 hours at 85°C. The purpose of the EDTA treatment was to remove alkaline-earth cations from the exchange sites of the zeolite and to convert the zeolite to the sodium form. The material was washed four times with d i s t i l l e d water to remove the EDTA solution.

Next, the material was treated with O.l molar barium chloride

solution for 16-24 hours at 85°C to convert the zeolite to the barium form. Finally the material was washed with d i s t i l l e d water to remove the remaining barium chloride solution.

The material so treated is referred to hereafter as

barium c l i n o p t i l o l i t e in contrast to the original material called here natural clinoptilolite.

The X-ray diffraction pattern of barium c l i n o p t i l o l i t e

indicated the presence of opaline silica as a result of the treatment above. The treatment described here for the preparation of barium c l i n o p t i l o l i t e is very harsh.

I t is certain that aluminum and silicon were removed from the

zeolite as a result of the various chemical treatments, since others have noticed such a loss under similar conditions (5). loss of the zeolite by dissolution was noted.

In this work considerable

To avoid this degradation, i t is

suggested that the acid wash and EDTAtreatment be deleted and a sodium chloride ion-exchange step be substituted for the latter. Properties of Barium Clinoptilolite Structural Properties.

The X-ray diffraction pattern of barium c l i n o p t i l o l i t e

is very characteristic and is the same as that obtained for barium clinoptilol i t e hydrothermally synthesized from barium alumino-silicate gels and calcined kaolinite (1).

Characteristically, the 8.9A(020) X-ray diffraction peak of

barium c l i n o p t i l o l i t e is much less intense than the most intense 7.9A(002) peak. These intensities are reversed for natural c l i n o p t i l o l i t e .

X-ray diffraction

data for barium c l i n o p t i l o l i t e and natural c l i n o p t i l o l i t e are shown in Table I.

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BARIUM C L I N O P T I L O L I T E

The change in i n t e n s i t y of the X-ray d i f f r a c t i o n

545

peaks of c l i n o p t i l o l i t e

upon treatment with barium is due mainly to the increased X-ray s c a t t e r i n g power of the heavy barium atom r e l a t i v e to the l i g h t e r a l k a l i - m e t a l a l k a l i n e - e a r t h cations present in the natural mineral.

and

Also, morphological or

s t r u c t u r a l changes may c o n t r i b u t e in part to the c h a r a c t e r i s t i c X-ray d i f f r a c tion pattern of barium c l i n o p t i l o l i t e . TABLE 1 X-ray D i f f r a c t i o n Data on Natural C l i n o p t i l o l i t e , Barium-Exchanged C l i n o p t i l o l i t e and Hydrothermally Synthesized Barium C l i n o p t i l o l i t e

Natural Clinoptilolite d

Barium- Exchanged Clinoptilolite

I/I o

8.93 I0 7.89 6 6.80 2 5.91 1 . . . . 5.25 2 5.09 3 4.67 2 . . . . . 4.35 1 4.25 3 4.04 2 3,95 I0 3.88 5 3.71 1 3.56 1 3.45 2 3.40 3 3.34 I0 3.21 3 3.16 2 . . . . . . . . 2.96 4 2.79 3 2.71 1 . . . . . Interfacial

d

.

.

.

. .

.

. .

.

. .

. .

I/I o

8.81 5 7.83 I0 . . . . 5.90 4 . . . . . 5.07 4 . . . . . 4.59 3 4.31 2 . . . . 4.04 3 3.95 7 3.90 3 3.69 2 3.52 2 . . . . 3.40 3 3.33 2 3.21 2 3.15 4 . . 2.97 4 2.78 2 2.71 2 2.52 1

. .

.

.

. .

.

.

. .

.

.

. .

.

.

d

I/I o

8,97 7.93 . . 5.95 5.37 . . 5.10 4.65 . . . 4.35 . . . . . 3.97 . . . 3.71 3.55 . . 3.40 . . . . . . 3.16 3.07 3.00 2.97 2.80 2.72 2.52

3 I0 7 4 5 5 . . 4 . . I0 . . 6 6 7 . . . . 7 5 5 9 6 6 4

angles were measured from electron micrographs of barium and

natural c l i n o p t i l o l i t e . the i n t e r f a c i a l

.

Synthetic Barium Clinoptilolite (I)

For the 62 i n t e r f a c i a l

angles of barium c l i n o p t i l o l i t e

angles measured, 50 per cent of fell

between 85 and 95 degrees.

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BARIUM CLINOPTILOLITE

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Only II per cent of the 61 interfacial angles measured for natural c l i n o p t i l o l i t e were in this range. These data suggest a tendency for barium c l i n o p t i l o l i t e to occur with a crystal habit characterized by an abundance of 90 degree interfacial angles. The reason for this apparent morphological change is unknown. Ion-Exchange Properties.

The strontium-calcium ion-exchange properties of

natural and barium c l i n o p t i l o l i t e were investigated using aqueous chloride solutions O.OOl molar in strontium and 0.017 molar in calcium. The strontium and calcium concentrations of the solutions in equilibrium with the zeolites were determined by atomic absorption spectrometry. The strontium content of the zeolite was determined by difference between the amount of strontium originally present in solution and that remaining in solution upon equilibration with the zeolite. TABLE 2 Strontium Distribution Coefficients for Natural and Barium Clinoptilolite

Sample

K~r(ml/g)

Natural c l i n o p t i l o l i t e

61

Natural c l i n o p t i l o l i t e

71

Barium c l i n o p t i l o l i t e

9

Barium c l i n o p t i l o l i t e Barium c l i n o p t i l o l i t e , sodium form

9 40

Barium c l i n o p t i l o l i t e , sodium form

48

~r for strontium exchange as determined by The distribution coefficient K~ batchwise equilibration of 0.50 g samples of barium c l i n o p t i l o l i t e in 50 ml of the above solution is shown in Table 2.

The distribution coefficient for

strontium is defined as KSr ppm Sr/g zeolite d = ppm Sr/ml solution

at equilibrium.

From the data in Table 2, i t is evident that conversion of natural clinop t i l o l i t e to the barium form drastically reduced the strontium uptake by the zeolite. Conversion of barium c l i n o p t i l o l i t e to the sodium form only partially restored the i n i t i a l strontium sorptive capacity of the natural c l i n o p t i l o l i t e .

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BARIUM CLINOPTILOLITE

547

The reduced strontium sorption by barium c l i n o p t i l o l i t e is due apparently to the fact that the smaller, r e l a t i v e l y hydrated strontium ions w i l l not displace the larger less hydrated barium ions from the exchange sites. I t was thought that enhanced strontium sorption could be produced in natural c l i n o p t i l o l i t e by conversion f i r s t to the barium form as suggested e a r l i e r (6) for synthetic strontium and calcium varieties of c l i n o p t i l o l i t e . This study showed that the sodium form of barium c l i n o p t i l o l i t e had a reduced strontium sorptive capacity relative to natural c l i n o p t i l o l i t e . The reduced strontium sorption of the sodium form of barium c l i n o p t i l o l i t e may be due to a combination of the following: A.

Incomplete removal of barium.

B.

Partial destruction of the zeolite by the chemical treatment.

C.

Partial irreversible conversion of the zeolite to a barium selective form.

Laboratory f a c i l i t i e s were inadequate to test the barium s e l e c t i v i t y of the sodium form of barium c l i n o p t i l o l i t e .

I t should be noted, also, that

radium is very similar in size and identical in charge to barium.

I t is pos-

sible that barium c l i n o p t i l o l i t e in the sodium form might be quite selective for radium.

I t is suggested that the radium sorptive properties of barium

c l i n o p t i l o l i t e be investigated for possible use in radioactive waste treatment. Thermal S t a b i l i t y .

The thermal s t a b i l i t y l i m i t as defined here is that

temperature at which the mineral structure is destroyed upon heating for four hours.

The thermal s t a b i l i t y l i m i t for c l i n o p t i l o l i t e s containing different

ions is as follows: ptilolite

calcium c l i n o p t i l o l i t e

(7,8) 400-450°C; barium clino-

(this study) 650-700°C; natural c l i n o p t i l o l i t e

potassium c l i n o p t i l o l i t e

(8) 650-700°C; and

(7) 800%.

As shown by the above data, the thermal s t a b i l i t y of c l i n o p t i l o l i t e is profoundly affected by the nature of the exchangeable cation.

I t appears

that barium and potassium ions tend to stabilize the structure relative to calcium ions.

The thermal s t a b i l i t y of c l i n o p t i l o l i t e seems to be a function

of the size and charge of the cation; the larger the cation and the lower the charge, the greater the thermal s t a b i l i t y .

As suggested by Minato and

Utada (8), the difference in thermal s t a b i l i t y of the d i f f e r e n t c l i n o p t i l o l i t e s is related to the dehydration behavior of these zeolites; with calcium c l i n o p t i l o l i t e being dehydrated at a much lower temperature than the sodium

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BARIUM CLINOPTILOLITE

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and potassium forms. This dehydration behavior must be related to the size and charge of the exchangeable cations as Barrer and Cram (5) have discussed. A detailed explanation of the effect of the exchangeable cation and the sorbed water on the thermal s t a b i l i t y of c l i n o p t i l o l i t e is lacking at present. Hydrothermal Stability.

The hydrothermal behavior of c l i n o p t i l o l i t e , studied

using the well known hydrothermal technique (9), is su~=narized by the data shown in Table 3.

These data refer to the observed synthesis conditions only

and do not indicate equilibrium conditions for the suggested reactions.

Since

the conditions of zeolite formation are dependent upon the activity of silica (lO), i t is stressed that these hydrothermal studies were carried out in the presence of quartz, which would control the silica activity. TABLE 3 Hydrothermal Reactions of Natural and Barium Clinoptilolite at 15,000 psi Pressure

Reactants

Products 200-350%

350-425%

425-500°C

500-625°C

Clino.

Clino.

Mordenite

Qtz.+Plag.

Qtz.+Plag,

Ba-clino.

Ba-clino.

Ba-clino.

Hex.Cels-Cym. Cels.+Qtz. +Qtz.

Abbreviations used in Table 3:

Clino. : natural c l i n o p t i l o l i t e ; Ba-clino. =

barium c l i n o p t i l o l i t e ; Qtz. : quartz; Plag. = plagioclase; Hex.Cels-Cym. = hexagonal celsian-cymrite solid solution; Cels. = celsian.

As shown in Table 3, i t appears that the hydrothermal "stability" range of barium c l i n o p t i l o l i t e is somewhat greater than that of natural clinoptilol i t e although both forms of c l i n o p t i l o l l t e convert to feldspar at about 425°C. The lower "stability" range of natural c l i n o p t i l o l i t e is related to the formation of mordenite. Note that natural clinopt~lolite under hydrothermal conditions converts to mordenite around 350°C and that mordenite persists over a f a i r l y wide temperature range before converting to quartz and plagioclase.

No mordenite was observed to form from barium c l i n o p t i l o l i t e implying

perhaps that barium inhibits mordenite formation.

I t is of interest that

attempts to synthesize barium mordenite from other reactants in earlier studies (1) were also unsuccessful.

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BARIUM CLINOPTILOLITE

The phases formed from barium c l i n o p t i l o l i t e

549

at higher temperature

suggest the occurrence of the following reactions (where the abbreviations are the same as those used in Table 3 . ) : I.

Ba-clino. = Hex.Cels-Cjn~. + Qtz. + Water, T = 450°C, PH20 = 1 Kbar.

2.

Hex.Cels-Cym. = Cels. + Qtz. + Water, T = 550°C, PH20 = 1 Kbar.

Possibly the coupled reaction, e . g . , 3.

(3) occurs also:

Ba-clino. = Cels. + Qtz. + Water, T = ?

The temperatures shown for the above reactions are those for the midrange of the observed synthesis conditions. reversed, these temperatures are l i t t l e rium temperature for these reactions.

Since the reactions were not

better than guesses at the e q u i l i b Seki and Kennedy ( I I ) determined that

for the reaction 2[Hex.Cels-Cym.] = Cels. + Sanbornite + 2 Qtz. + water, only the Hex. Cels-Cym. solid solution was stable in the p-t region 500-625°C and 20,000 psi.

Thus, in the present work i t appears that monoclinic celsian

occurs metastably in the temperature range 500-625°C. Occurrence.

To our knowledge, no natural analog of barium c l i n o p t i l o l i t e

been reported.

has

The natural barium zeolites harmotome, eddingtonite, and

brewsterite are all

l o w - s i l i c a zeolites and probably form under conditions of

lower s i l i c a a c t i v i t y than does c l i n o p t i l o l i t e .

Barium c l i n o p t i l o l i t e

form in nature as a hydrothermal a l t e r a t i o n product of a v i t r i c

might

t u f f or more

l i k e l y by ion-exchange of barium-rich solutions on preexisting c l i n o p t i l o l i t e The formation of barium c l i n o p t i l o l i t e

by reactions ( I ) and (3) above, while

possible is not considered to be too l i k e l y , since natural c l i n o p t i l o l i t e

doe~

not seem to form in nature by the analogous reactions but rather occurs as an a l t e r a t i o n product of v i t r i c ptilolite

tuffs.

I t is very u n l i k e l y that a barium c l i n o -

of sedimentary o r i g i n would be encountered in nature.

Barium

concentrations s u f f i c i e n t for the formation of barium c l i n o p t i l o l i t e

are

u n l i k e l y to be found in the sedimentary environment where the barium concent r a t i o n is controlled usually by the s o l u b i l i t y of barite. The assistance of Mr. George Lindholm for the electron microscopy and the helpful c r i t i c i s m s and discussions of Dr. Michael Wood are g r a t e f u l l y acknowledged. manuscript.

Thanks are extended to Dr. R. B. Forbes for his review of this This work was supported by U.S. Atomic Energy Comission

Contract No. AT/I0-I/1286 and a University of Alaska, Water Resources I n s t i tute Grant.

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BARIUM CLINOPTILOLITE

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References I.

D. B. Hawkins, Mat. Res. Bull.

2.

Jose L. Ordonez, Unpublished M.S. Thesis, Univ. of Alaska, Geology Dept. (l 970).

3.

R. A. Sheppard, Preprints of the 2nd I n t n ' l . Conf. on Molecular Sieve Zeolites. Am. Chem. Soc., Washington, D.C., 428 (1970).

4.

F. Mumpton, Am. Nin. 45, 351 (1960)

5.

R. M. Barrer and P. J. Cram, Preprints of the 2nd I n t n ' l . Conf. on Molecular Sieve Zeolites. Am. Chem. Soc., Washington, D.C., 328 (1970).

.

7.

2_, 951 (1967).

D. B. Hawkins, Mat. Res. Bull. 2_, 1021 (1967).

A. O. Shepard and H. C. Starkey, Art. 138 in U.S. Geol. Survey Prof. Paper, 475-D, D89 (1964).

.

H. Minato and M. Utada, Preprints of the 2nd I n t n ' l . Conf. on Molecular Sieve Zeolites. Am. Chem. Soc., Washington, D.C., 535 (1970).

.

R. Roy and O. F. Tuttle, Physics and Chemistry of the Earth Press, London (1956).

I0.

D. S. Coombs, A. J. E l l i s , W. S. Fyfe Cosmochim. Acta 17 (I/2) 53 (1959).

II.

Y. Seki and G. C. Kennedy, Am. Min. 49, 1407 (1964).

~, Pergammon

and A. M. Taylor, Geochim. et