CHARACTERIZATION OF SMECTITES SYNTHESISED FROM ZEOLITES AND MECHANISM OF SMECTITE SYNTHESIS

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1 Clay Minerals (1985) 20, CHARACTERZATON OF SMECTTES SYNTHESSED FROM ZEOLTES AND MECHANSM OF SMECTTE SYNTHESS S. KOMARNEN AND E. BREVAL Materials Research Laboratory, The Pennsylvania State University, University Park, PA 16802, USA Received 24 May 1984; rev&ed 10 August 1984) A B ST R A C T: Smectites were synthesised hydrothermally from zeolites in an Mg-rich brine at 300~ under a confining pressure of 30 MPa and characterized by XRD using the Greene-Kelley Li-saturation test and the K+-saturation/glycolation test. The synthetic smectites were found to be dioctahedral with only tetrahedral negative layer charge; the layer charge was also deduced to be low and they are classified as beidellites. The mechanism of formation includes H + saturation of zeolites by the hydrolysis of Mg 2+ under hydrothermal conditions, followed by decomposition of the zeolites and recrystallization to beidellites. These results show that solution chemistry is an important factor affecting stability of zeolites under hydrothermal conditions. Transformation of zeolites to smectites in an Mg-rich brine under hydrothermal conditions has been reported by Komarneni & Roy (1983). The objectives of this investigation were (i) to elucidate the mechanisms of smectite formation from zeolites and (ii) to characterize these synthetic smectites. Understanding the mechanism of smectite formation from zeolites is helpful in determining the precise conditions for possible commercial manufacture of smectites and also in the interpretation of zeolite diagenesis. Characterization of these synthetic smectites could indicate likely industrial applications, e.g. viscosity control agents or in catalysis. EXPERMENTAL Materials Six smectites synthesised earlier from six different zeolites in Mg-rich brine (Komarneni & Roy, 1983) were used for this study. Two of the zeolites, namely phillipsite from Pine Valley, Nevada (reference zeolite 27134) and erionite from Shoshone, California (reference zeolite 27104), were again hydrothermally treated to synthesise smectite in order to investigate the mechanism of smectite formation. The zeolite samples were supplied as < 200 mesh (<75 /tm) powders by Minerals Research, P.O. Box 591, Clarkson, New York. An Mg-rich (on a normality basis) brine composed of 10% MgC12, 10% CaC12, 5% KC1, 5% NaC1 and 70% H20 was used as the mineralizer in the hydrothermal treatment The Mineralogical Society

2 182 S. Komarneni and E. Breval Methods For smectite synthesis, 100 rng of each zeolite were loaded into a gold capsule, 200 ~tl of the Mg-rich brine were added, and the capsule sealed by cold-welding (Komarneni et al., 1979). The sealed gold capsules were treated hydrothermally for 4 weeks in a cold-seal vessel at 300~ using a confining pressure of 30 MPa. After completion of the hydrothermal treatment, the gold capsules were weighed to check for leaks and the contents of the capsules without any leaks were further investigated. After the gold capsules were cut and opened with a scissors, the ph of the capsule fluid was determined immediately using ph papers. The fluid phase from these two capsules was removed with a micropipette and centrifuged to remove any suspended particles before analysis for A, Ca, Fe, K, Mg, Na and Si by atomic emission spectroscopy (AES) using a SpectraMetrics Spectra-Span instrument. All the smectites were characterized by XRD techniques involving K +- and Li+-saturation. X-ray diffraction was carried out with a Philips APD-3600 diffractometer using graphite-monochromated C u-k~z radiation. Determination of the magnitude of layer charge A portion of each sample was saturated repeatedly with 1 N KC solution and washed free of excess salt with water. An oriented slide was prepared and allowed to air dry before X-ray analysis. The sample was then solvated with ethylene glycol and X-rayed again. The approximate magnitude of the layer charge of these synthetic smectites was inferred from their behaviour on K+-saturation, on the basis that expandable layers with low negative layer charge do not collapse to 10 A when K + is the interlayer cation (Jackson, 1969; Schultz, 1969), whereas interlayers with higher negative layer charges (as in vermiculite) do collapse to 10 A. Determination of the location of layer charge The Hofmann-Klemen and Greene-Kelley Li-test (Hofmann & Klemen, 1950; Greene-Kelley, 1955; Shultz, 1969) was used to help distinguish between octahedral and tetrahedral negative layer-charge deficiencies in the smectites. Another portion of each sample was saturated with 1 N LiC1 solution and washed free of excess salt with water. The LiCl washings were analysed for the displaced exchangeable cations by AES. An oriented slide was prepared by drying a suspension at room temperature. The slide was initially X-rayed before Li was fixed into interlayers and/or octahedral vacancies by heating the slide to 225~ for 8 h. The slide was X-rayed after cooling and again X-rayed following glycerol treatment. According to the Greene-Kelley test, the expandable layers would remain collapsed after Li + saturation, heat treatment and glycerolation (solvation with glycerol) if the negative charge is located predominantly in the octahedral sheet. Determination of di- or trioctahedral nature The (060) XRD reflection was measured for a randomly oriented sample on a glass slide using a slow scan of 0.4~ A d(060) spacing of A indicates a dioctahedral smectite whereas a spacing of ~ indicates a trioctahedral species (Brindley & Brown, 1980).

3 Morphology of the synthetic smectites Smectites synthesised from zeolites 183 Particle morphology of the synthetic smectites was determined by transmission electron microscopy using a Philips 420 microscope. Synthes& of smeetite RESULTS X-ray diffraction analysis revealed the formation of smectite from both phillipsite and erionite (Figs 1 and 2) confirming earlier results (Komarneni & Roy, 1983). The two zeolites appear to have completely transformed to smectite since no residual zeolites were detected by XRD. Other minor crystalline phases detected by XRD were albite and mica for the chabazite transformation (Fig. 3). Mica was present as a trace impurity in the original chabazite sample and albite appears to have formed during the transformation. Solution analyses Concentrations of elements such as Mg, Ca, K, Na, A1, Fe and Si and ph of the fluids from the hydrothermal reaction of Mg-rich brine with phillipsite and erionite are presented in Table 1 and compared with the initial concentrations of cations in the Mg-rich brine. The concentrations of Mg 2+ decreased significantly after the hydrothermal reaction while the concentrations of Ca 2+, K + and Na + were affected only slightly. The decomposition of zeolites affected the concentrations of the latter three elements since the zeolites were 0 2, DEGREES TWO THETA (CuKa) Fro. 1. XRD traces of K+-saturated and ethylene glycolated smectites formed from: (A) erionite, Shoshone, California; (B) elinoptilolite, Hector, California; (C) mordenite, Lovelock, Nevada; (D) clinoptilolite, Castle Creek, daho.

4 184 S. Komarneni and E. Breval TABLE 1. Solution ph and concentrations (/~g/ml) of fluids. Mg-rich Phillipsite (Nevada) Erionite (California) brine, + Mg rich brine + Mg-rich brine control at 300~ MPa at 300~ MPa ph Mg Ca K Na A Fe Si naturally saturated mainly with Na +, K + and Ca 2+ with little or no Mg 2+. The high concentrations of Fe in the capsule fluids suggest acidic conditions which are substantiated by the low ph values measured (Table 1). On the other hand, the concentrations of Al and Si are quite low which suggests their incorporation in solid phases. Magnitude of layer charge All these synthetic smectites gave basal spacings of ~12,~ on K + saturation but expanded to ~ 17/k on glycolation (Figs 1 and 2). This c-axis expansion on K + saturation and glycolation is quite typical of low-charge smectites and it is assumed, therefore, that the synthetic smectites have low negative charges. The exact amount of charge could not be determined because of contamination from trace to moderate amounts of starting zeolites and also probably from amorphous solids in the reaction mixtures (Komarneni & Roy, 1983). Location of layer charge The Li+-saturated and air-dried smectites exhibited a c-axis spacing of ~ 15,~. However, the various synthetic smectites collapsed to ~ 10 ~ on Li+-saturation and heat treatment at 225 ~ for 8 h but re-expanded to 18/k with a regular series of higher orders on treatment with glycerol (Fig. 3). This result suggests that the layer charge is mainly located in the tetrahedral sheets (Greene-Kelley, 1955; Schultz, 1969). Analyses of the exchangeable cations displaced by 1 y LiC1 indicated the presence of Ca 2+, K +, Mg 2+ and Na + ions as would be expected since the Mg-rich brine contained all these ions. Di- or trioctahedral nature All the synthetic smectites gave a d(060) spacing of 1.50 A (Fig. 4) which clearly indicated that they were dioctahedral. Thus, Mg 2+ from the Mg-rich brine was not incorporated in the octahedral sheet of the smectites. Particle morphology Fig. 5 shows that the synthetic clays are composed of foliated aggregates consisting of irregularly folded sheets. This type of morphology is typical of smectites (Grim & G/iven, 1978).

5 Smectites synthesised from zeolites 185 -<-< ~2 0 0 ~ 4 F ~ X >-- J d " ~ d o +" 4-_ 9 ~ ~'~ 0 N2oeo~a r'~ 0 nq ~. oj to 0 0 ~ ~o u~o ~2

186 S. Komarneni and E. Breval 1 6,3 1 65 f A 55 57 1 59 61 DEGREES TWO THETA (CuKa) FG. 4.

Transmission electron micrographs of synthetic smectites: (A) smectite after phillipsite, Nevada; (B) smectite after erionite, Shoshone, California.

6 186 S. Komarneni and E. Breval 1 6, f A DEGREES TWO THETA (CuKa) FG. 4. d(060) spacings of synthetic smectitesformed from: (A) phillipsite, Pine Valley, Nevada; (B) chabazite, Christamas, Arizona; (C) erionite, Shoshone, California. FG. 5. Transmission electron micrographs of synthetic smectites: (A) smectite after phillipsite, Nevada; (B) smectite after erionite, Shoshone, California. DSCUSSON Results presented above clearly show that the synthetic smectites formed from zeolites in an Mg-rich brine have three characteristics in common: (i) they have a low negative layer charge, (ii) their charge is located in the tetrahedral sheets and (iii) they are dioctahedral in nature. The smectites can therefore be classified as beidellites (Grim, 1968; Brindley & Brown, 1980). The mechanism of formation of beidellites from zeolites is proposed as follows. Under the hydrothermal treatment used here, acidic conditions are generated by the hydrolysis of Mg 2+ (Komarneni, 1981) from the Mg-rich brine. H+-saturation of the

Smectites synthesised from zeolites 187 zeolites followed their decomposition and recrystallization to beidellite. Development of acidic conditions was confirmed by the low ph (3.

7 Smectites synthesised from zeolites 187 zeolites followed their decomposition and recrystallization to beidellite. Development of acidic conditions was confirmed by the low ph (3.8) in capsule fluids (Table 1). Under hydrothermal conditions, acidic ph develops in saline solutions because of changes in hydrolysis constants and the association of ion-pair complexes. Braithwaite & Molecke (1980) reported a ph of 3 in Mg-rich brine at 300~ which confirms the findings here. Thus, for an example, the transformation of phillipsite to beidellite can be represented by the following equations: Separately 2MgC12 + 4H20 = 2Mg(OH)2 + 4HC1 2.33Na2[SivA12]Ols-xH20 + 4HC1 (phillipsite) Na0.66[SiT.34A10.66]A14020(OH)4.xH SO 2 + 4NaC1 (beidellite) Overall 2-33Na2[SiTA12]Ols. xh20 + 2MgC12 + 4H20 Na0.66[SiT.34A10.6jA14020(OH)4. xh20 + 2Mg(OH) SO2 + 4NaC1 The analysed Si and A compositions are those for phillipsite from Nevada. The exchangeable cations of this zeolite are K Na + and Ca 2+ but in the equations Na is used as the exchangeable cation for simplicity. XRD analysis did not reveal the presence of either crystalline SiO 2 or Mg(OH) 2 and therefore they may be present as amorphous phases. The concentration of Mg 2+ detected in the capsule fluids is considerably lower than the initial Mg 2 concentration (Table 1) which indicates that some of the Mg is in a hydrolysed but noncrystalline phase, probably because of the acidic ph of the capsule fluids. The crystallization of brucite can occur only when there is a good sink for protons as in the case of SrZrO 3 transformation in this Mg-rich brine under hydrothermal conditions (Komarneni, 1981). The formation of beidellite under these acidic conditions is an indication of its stability over saponite or mica, which could also have formed because of the availability of abundant Mg and K in the solution (Table 1). A small amount of albite was detected only in the case of chabazite interaction with Mg-rich brine. This phase may have formed during the quenching process of the hydrothermal runs. t is clear from the solution analyses (Table 1) that Fe 3+, which is present as iron oxides in the starting zeolites, also seems to have been excluded from the structure, as indicated by the large concentrations of Fe 3+ in solution. These results show that (i) beidellite is very stable under acidic conditions and (ii) pure beidellite can probably be synthesised by adjusting the stoichiometry of the starting materials using Mg-brine under hydrothermal conditions. CONCLUSONS Smectites synthesised from zeolites in an Mg-rich brine under hydrothermal conditions are beidellites. H+-saturation of zeolite by the hydrolysis of Mg 2 followed by its decomposition and recrystallization is the mechanism of beidellite formation in this instance.

188 S. Komarneni and E. Breval REFERENCES BRArrHWATE J.W. & MOLECKE M.A. (1980) Nuclear waste canister corrosion studies pertinent to geologic isolation. Nuel. Chem. Waste Management 1, 37-50.

8 188 S. Komarneni and E. Breval REFERENCES BRArrHWATE J.W. & MOLECKE M.A. (1980) Nuclear waste canister corrosion studies pertinent to geologic isolation. Nuel. Chem. Waste Management 1, BRNDLEY G.W. & BROWN G. (1980) Crystal Structures of Clay Minerals and their X-ray dentification, pp. 170 and 328. Mineralogical Society, London. GREEN,-KELLEY R. (1955) Dehydration of the montmorillonite minerals. Mineral. Mag. 30, GRM R.E. (1968) Clay Mineralogy, p. 86. McGraw-Hill Book Company, New York. GRM R.E. & GUVEN N. (19"78) Bentonites; Geology, Mineralogy, Properties and Uses, p. 21. Elsevier, Amsterdam. HOFMANN U. & KLEMEN E. (1950) Loss of exchangeability of lithium ions in bentonite on heating. Z. anorg. allg. Chem. 262, JACKSON M.L. (1969) Soil Chemical Analysis--Advanced Course, p Published by the author, Department of Soil Science, University of Wisconsin, Madison, W KOMARNEN S. (1981) Hydrothermal stability of fl-cs2u207 and SrZrO 3 in fluids, J. norg. NucL Chem. 43, KOMARNEN S., FREEaORN W.P. & SMTh C.A. (1979) Simple cold-weld sealing of noble metal tubes, Am. Miner. 64, KOMARNEN S. & RoY D.M. (1983) Alteration of clay minerals and zeolites in hydrothermal brines, Clays Clay Miner. 31, SCm~LTZ L.G. (1969) Lithium and potassium absorption, dehydroxylation temperature, and structural water content of aluminous smectites. Clays Clay Miner. 17,

Analysis of Clays and Soils by XRD

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