effect of non-swelling layers on the … · dissolution of reduced-charge montmorillonite in...

Clay Minerals (1996) 31, 333-345

EFFE CT OF N O N - S W E L L I N G L A Y E R S ON THE D I S S O L U T I O N OF R E D U C E D - C H A R G E

M O N T M O R I L L O N I T E IN H Y D R O C H L O R I C ACID

P. K O M A D E L , J . B U J D A K , J . M A D E J O V A , V . S U C H A * AND F . E L S A S S t

Institute oflnorganic Chemistry, Slovak Academy of Sciences, 842 36 Bratislava, Slovakia, *Department (?['Geology of Mineral Deposits, Comenius University, 842 15 Bratislava, Slovakia, and t Station de Science du Sol, 1NRA Versailles,

France

(Received 15 August 1995; revised 15 February 1996)

A B S T R A C T : A series of reduced-charge montmorillonites (RCM), prepared from the same parent Li-montmorillonite (Jelgov2? Potok, Slovakia) by heating at various temperatures (105-210~ for 24 h, was treated with 6 M HC1 at 95~ for periods up to 30 h. Reaction solutions obtained were analysed for A1, Fe, Mg and Li and the solid reaction products were investigated by Fr lR spectroscopy. Both analyses provided evidence that the extent of dissolution decreased with increased amounts of Li fixed within the montmorillonite structure, i.e. with increased heating temperature. Differences in the acid dissolution process were reflected in the structural changes which occurred within the RCM samples, due presumably to different positions of fixed Li. The ethylene glycol monoethyl ether (EGME) surface areas, and XRD and HRTEM analyses of the RCM series revealed an increased amount of non-swelling layers in the samples prepared at higher temperatures, which caused a substantially slower decomposition of M7 and M8 in HC1. The calculated XRD patterns of M6 and M7 confirmed the presence of 20% and 45% pyrophyllite-like layers, respectively, in these samples. Mixed-layer pyrophyllite-like-smectite and pyrophyllite-like crystals, containing only non-swelling layers, were found in sample M8. The results confirmed that the amount of swelling layers in RCM significantly affects their dissolution rate in HC1.

The use of acid treatments of clay minerals, which have been applied for decades to obtain information regarding mineral structure, was reviewed recently by (~f~el & Komadel (1994). Acid treatment removes tetrahedral and octahedral cations from the smectite structure at similar rates (Luca & MacLachlan, 1992; Tk~i~ et al., 1994). Readily soluble, octahedral plus tetrahedral and 'insoluble' portions of constituent atoms can be calculated from the dissolution curves, thus providing information on the distribution of atoms in the sample. Readily soluble portions include exchangeable cations and easily soluble admixtures such as goe th i te (Komadel et al., 1993). Common 'insoluble' phases found in the fine fractions of bentonites are kaolinite, quartz, anatase and volcanic glass ((~f~el & Komadel, 1994). Kato et al. (1966) reported that the A1 content retained in the solid reaction products after 2 h reaction with 25% HzSO4 was 24% for montmorillonite, 88% for

pyrophyllite and 94% for kaolinite. Nov~ik & (~f~el (1978) found that the rate of dissolution of dioctahedral smectites increased with octahedral Fe and Mg for A1 substitution. Low octahedral substitution is one of the reasons for the observed lower dissolution rate of pyrophyllite compared to montmorillonite. However, the effect of swelling on dissolution rate is unclear.

Fixation of Li and reduction of layer charge was observed after heating Li-montmorillonite at about 200-300~ (e.g. Hofmann & Klemen, 1950). Bujd~ik et al. (1991, 1992) prepared a series of reduced-charge montmori l loni tes (RCMs) by heating Li-montmorillonite at various temperatures (105-210~ for 1 -24 h. Individual examples of this series, prepared from the same parent clay, have similar Si, A1, Fe and Mg contents but different layer charges and different amounts of non-swelling layers due to the various contents of fixed Li.

�9 1996 The Mineralogical Society

334 P. Komadel et al.

The objective of this paper was to investigate the effect of the swelling/non-swelling layer ratio on the dissolution of a series of RCMs in hydrochloric acid.

1 . 0

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

Sample M1 is the <2 I.tm fraction of Ca2+-saturated ' 0.5- bentonite Jelgov3 ~ Potok (JP) from the clay deposit in the Kremnica mountains in central Slovakia (Sucha et al., 1992; Samajov~i et al., 1992). Reduced-charge samples M 2 - M 8 were prepared by heating Li+-saturated JP for 24 h at temperatures of 105, 110, 120, 130, 135, 160 and 210~ respectively. After heating, the exchangeable Li § 0 . 0

in M 2 - M 8 was back-exchanged for Ca 2+. The CEC (cation exchange capacity) and EGME (ethylene glycol monoethyl ether) surface areas are listed in Table 1. Details of preparation and the structural formulae of the materials obtained are given in Madejowl et al. (1996).

&

0 ~ +

o

I l l l [ I

10

M3

' ' �9 I ' ' ' ' ' 1 20 30

hours

FiG. 1. Dissolution of AI, Fe, Mg and Li from sample M3 in 6 M HC1 at 95~

Acid dissolution

A portion of each sample weighing 1 g was mixed with 100 ml of 6 M HC1 at 95~ in a 250 ml Pyrex flask with reflux and placed in a water thermostat. The mixture was reacted, with occa- sional stirring, for 30 h. After specified times (ranging from 0.25 to 30 h), 5 ml of the reaction supematant was sampled from the reaction mixture and retained for A1, Fe absorption photometry, and for Mg and Li atomic absorption spectroscopy analyses; and 5 ml of 6 M HC1 was added to the reaction vessel. Amounts of dissolved octahedral cations (wt) were calculated and dissolution curves (Figs. 1 -3 ) were constructed by plotting the undissolved portions of the atoms (1-at) as a function of time, t. The value of at was calculated from the relation

O~ ~ Wt /W 0

where Wo is the total content of the cation in the undissolved sample.

Fourier transform infrared spectroscopy (FTIR)

The solid reaction products, obtained after 0.5, 6 and 30 h, were washed with water, dried at 60~ ground to pass a 0.2 mm sieve and analysed by FI'IR spectroscopy. The spectra were obtained on a FTIR spectrometer Nicolet Magna 750 equipped with a DTGS detector. For each sample 128 scans were recorded in the 4000-400 cm - I spectral range in the transmittance mode with a resolution of 4 cm - I . The KBr pressed disk technique (0.4 mg of sample and 200 mg of KBr) was used.

TABLE 1. Temperature (~ of preparation, CEC (mEq.100g -1) and EGME surface a r e a s (m2.g -1) of samples M l - M 8 .

Sample M 1 M2 M3 M4 M5 M6 M7 M8

Temperature - 105 110 120 130 135 160 210 CEC 83 71 65 60 50 46 26 14 Surface area 786 836 826 825 799 780 586 365

Dissolution of reduced-charge montmorillonite in HCI 335

1 . 0 ! . 0

! : i i I Li

�9 . . : : A' . . .

t fl~alt +A �9 �9 eA ' 0 . 5 �9 ' 0 . 5 �9

2 ,O, �9 �9 -I- �9 4-

4" �9 § �9 &

0 . 0 I ' ' ' I ' ' " ' I ' I v

0 10 20 30 0 10 20 30

hours hours

FIG. 2. Dissolution of A1 from samples M1-M8 in 6 M FIG. 3. Dissolution of Li from samples M1-M8 in 6 M HCI at 95~ HCI at 95~

X-ray diffraction (XRD)

Oriented specimens (10 mg/cm z) were prepared by sedimentation of the clay suspension on glass slides. Both air-dried and ethylene glycol (EG) saturated (prepared in EG atmosphere at 60~ samples were analysed by XRD using a Philips PW 1710 diffractometer (Ni-filtered Cu-K~ radiation).

The NEWMOD computer program (Reynolds, 1985) was used to evaluate the experimental XRD patterns. The parameters used for the calculation were as follows: .pyrophyllite Fe = 0.1 per half unit- cell, dool = 9.2 A; smectite Fe = 0.1 per half unit- cell, dool = 16.9 A; R = 0, 0.5, 3.

High-resolution transmission electron microscopy (HRTEM)

The HRTEM measurements were obtained using a Philips 420 STEM microscope operated at 120 kV. The specimens were prepared from the Li treated samples as a clay paste. The paste was first coated with agar before the embedding procedure which was applied according to the method described by Tessier (1984). Samples were equili- brated with water at a pressure of 32 kPa. Water was first replaced by methanol, then propylene oxide and finally with Spurr's resin. The resin was polymerized at 65~ for 24 h. Ultra-thin sections,

50 nm thick, were cut with a diamond knife on a Reichert-Jung Ultracut E microtome. This method preserves the fabric of clay minerals and prevents the collapse of the swelling phases (Tessier, 1984). During the embedding procedure, the swelling smectite interlayers are intercalated by organic compounds of the resin and d(001) is thus maintained at 1.35 nm. The porosity existing between the loose fundamental particles or individual mixed-layer crystals is preserved. Photographs were taken in underfocus conditions close to the Sherzer defocus at a magnification of 51 000. Measurements were done using a binocular at a magnification of 40. Stacking periodicity was calculated from the distance between the two intensity maxima corresponding with the centre of the layers.

R E S U L T S A N D D I S C U S S I O N

The CEC data (Table 1) prove that the layer charge of the samples gradually decreases in the M 1 - M 8 series. However, the EGME data show minor changes in the surface areas of M1-M6, followed by gradually decreasing values for M7 and M8. These results indicate the presence of significant amounts of non-swelling layers in M7 and even more in M8.


So lu t ion ana ly s i s

Typical dissolution curves of A1, Fe, Mg and Li leached from samples M 1 - M 8 in 6 M HC1 at 95~ are shown in Figs. 1-3 . Only minor differences were observed in the shapes of these curves for various cations dissolved from the same sample for M 1 - M 6 (e.g. M3 in Fig. 1). These metals were almost completely (>95% of total content in the sample) dissolved in 6 M HC1 within 30 h; the only exception being Mg. Up to 20% of the total Mg was found to be 'insoluble' under the conditions used. Variation of the amount of 'insoluble' Mg between 5% (in M3) and 20% of total Mg (in M5 and M6) in the samples suggests that this part of Mg is bound in an 'insoluble' admixture, such as volcanic glass. Variation either in the volcanic glass content in the samples used for acid dissolution and/or in the Mg content in the volcanic glass may have caused the variation in ' insoluble' Mg. Absence of any identifiable amount of a crystalline compound in the solid reaction products after acid treatment was confirmed by XRD.

Dissolution of A1 and Li from samples M 1 - M 8 is shown in Figs. 2 and 3, respectively. The curves for M 1 - M 4 overlap indicating that the effect of Li fixation on acid treatment was negligible in these samples. However, a gradual decrease in the leaching progress was observed for M5 through M8. Samples M7 and M8 were not dissolved within 30 h. The very slow dissolution of M8 resulted in only approxi- mately 23% leaching of AI and Li after 30 h. Due to preparation of all samples from the same parent clay, only minor, if any, differences are supposed to occur in the original particle sizes and distributions, which may affect the leaching. In addition, a similar level of Mg and Fe for A1 substitution in all samples minimizes the effect of octahedral substitution on the dissolution rate (NovLk & ~f~el, 1978). 'Swellability' which is known to decrease with increasing Li fixation in montmorillonite (Brindley & Ertem, 1971), affects the accessibility of the sheets for protons and thus the reaction rate. The high swelling of smectite has been considered to be the main reason for its faster dissolution in HC1 compared with kaolinite (Miller, 1965). The possibility exists that the lower dissolution rates measured for M7 and M8 compared with the rest of the series reflects changes in 'swellability'. Thus, detailed XRD and HRTEM examination of samples M7 and M8 were performed to examine the possible development of non-swelling layers (see below).

No significant difference was found between the dissolution curves of Li and those of octahedral cations (Figs. 1-3). In other words, the leaching process of Li was similar to that of octahedral A1, Fe or Mg. Our previous assay of these samples has shown that Li is fixed in three different positions in the structure, i.e. in the hexagonal holes of the tetrahedral sheet (M2-M8), in the Li-substituted OH groups (M5-M8) and in the previously vacant octahedra (M7 and M8; Madejowl et al., 1996). Recent results of Luca & MacLachlan (1992) and T k ~ et al. (1994) have proved that the dissolution rates of tetrahedral and octahedral atoms of smectites are comparable and that the structure of the smectite beyond the dissolution front remains intact. The final reaction product of the dissolved portion is amorphous silica formed by a three- dimensional cross-linked SiO4 framework with some Si atoms bearing one OH group (Tk~6 et al., 1994). Complete dissolution of the octahedral sheet of a Li-containing montmori l loni te is expected to produce a similar product with virtually all Li dissolved. Smooth dissolution curves of Li for all samples (Fig. 3) show that this method failed to distinguish clearly between the different positions of Li in the structure. Infrared spectroscopy was used to further characterize the acid-treated clays.

In f rared s p e c t r o s c o p y

The IR spectra provide a sensitive measure of the changes of the smectite structure due to Li-fixation (Calvet & Prost, 1971, Madejov~t et al., 1996) and acid dissolution (Madejov~i et al., 1993; Breen et al., 1995). The assignment of the montmorillonite bands in the 1300-400 cm-~ region, where most of the changes due to acid dissolution occur, is according to Farmer (1974). Fixation of Li in the structure of montmorillonite upon heating induced a shift of the S i - O stretching band from 1035 cm - l (M1) to 1047 cm -~ (M8) and the appearance of small pyrophyllite-like bands at 1120 cm -1 and 420 cm - l . The OH-bending bands (A1A1OH at 915 cm -1 and A1MgOH at 843 cm -1 for M1) moved to higher wavenumbers and substantially decreased in intensity. The positions of the S i - O - A 1 and S i - O - S i bending vibrat ions remained unchanged after Li-fixation (Madejov~ et al., 1996).

Acid dissolution for 6 h caused pronounced changes in the IR spectra of all clays. The spectra of M1 through M4 samples are similar and reflect a

Dissolution o f reduced-charge montmorillonite in HCl 337

high level of clay decomposition. The S i - O stretching band identified for untreated M1 at 1035 cm -1 disappeared and only the S i - O absorption of amorphous SiO2 near 1100 cm - l (Moenke, 1974) is present in the spectra of the M 1 - M 4 samples (Fig. 4). The increased amount of amorphous SiOz content is also proven due to an increase in intensity of the band at 799 cm -1.

The dissolution process of dioctahedral smectites is assumed to be complete when no vibrations of octahedral atoms (A1AIOH and A I - O - S i bending) are present in their IR spectra (Komadel et al., 1990).

However, OH-bending bands decrease in intensity also as a consequence of Li fixation in the structure (Calvet & Prost, 1971; Madejov~i et aL, 1996). The A 1 - O - S i band near 520 cm -1 is the most sensitive diagnostic absorption of Al-rich dioctahedral smectites in the process of acid dissolution (Madejov~i et al., 1993), since the band is unaffected by Li fixation (Madejov~i et al., 1996). The IR spectra of samples M 1 - M 4 treated for 6 h, show the absence of OH- bending vibrations and only a shoulder near 520 cm -1 (Fig. 4) reflecting high, but incomplete, A1 dissolution (Fig. 2). The IR spectra of M5 and M6 as

, \

1120 932

928

803 \ \ 420

803 61!

a 799

519

467

,. .~ 1099

I I I I I

1200 1000 800 600

Wavenumbers (cm "1) Fie. 4. IR spectra of MI (a), M4 (b), M5 (c), M6 (d), M7 (e) and M8 (f) samples treated for 6 h in 6 M HCI at

95~


f \ / 853 803

801 615

o~ N 120

106, 976 800

467

~ J 1 0 9 9 I I I I

1200 1000 800 600

Wavenumbers(cm -I)

FIG. 5. IR spectra of M1 (a), M4 (b), M5 (c), M6 (d), M7 (e) and M8 (f) samples treated for 30 h in 6 M HCI at 95~

compared with M 1 - M 4 revealed a lower level of acid attack (Fig. 4). The main S i - O stretching band at 1057 cm -1 with a shoulder near 1093 cm -1 together with the increased intensity of an A I - O - S i band compared with M4 indicate a higher AI content in these samples. This is in accord with the solution analyses, which indicated ~ 50% of undissolved A1 in samples M5 and M6 treated for 6 h (Fig. 2). An even lower extent of A1 dissolution after 6 h of treatment was found (Figs. 2 and 4) for samples M7 and M8, using both methods. The IR spectra of M7

and M8 treated for 6 h in HCI (Fig. 4) look very similar to the spectra of acid-untreated M7 and M8 (Madejov~ et al., 1996). However, the area of the A 1 - O - S i band in M7, normalized to the S i - O - S i band at 469 cm -1, is lower by ~13% than that of M8, indicating a lower A1 content in 6 h HC1 treated sample M7 as compared with M8 (Fig. 4). This result is in agreement with the solution analyses of these samples (Fig. 2), in which 73 and 90% of undissolved AI were found for M7 and M8, respectively.


The IR spectra of samples M 1 - M 6 , treated for 30 h, (Fig. 5) are almost the same and confirm complete dissolution of these clays as indicated in the dissolution curves (Fig. 2). In addition to the 1099, 800 and 467 cm -1 bands attributed to four- coordinated amorphous silica, a medium intensity band near 976 cm -1 due to S i - O stretching of SiOH groups is observed (Moenke, 1974). A slight decrease of the SiOH band intensity for M5 and M6

indicated lower protonation of the reaction products of these clays.

Significantly lower degradation of sample M7 after 30 h of acid treatment, shown in the dissolution curves (Fig. 2), was reflected also in the IR spectrum (Fig. 5). The S i - O stretching band was at 1060 cm -1 and the A I - O - S i band (not observed for M 1 - M 6 ) was clearly identifiable at 522 cm -1. The IR spectrum of M8 indicated that

9.86

11.63

3.17

4.8

.26

4.9

3.09

4.49 J \ b

3.07 5.0

a

I !

4 1o 5'o ~

FIG. 6. XRD patterns of air-dry oriented specimens, a - M6; b - M7; c - M8; spacings in ~,; Cu-Ktz radiation.


structural changes of this sample, resulting from the 30 h acid attack, are minor (Fig. 5). The bands present in this spectrum and in that of the untreated M8 (Madejov~i et at., 1996) are nearly identical. However, a minor decrease in the A 1 - O - S i band intensity of acid-treated M8 compared with that of the acid-untreated M8 reflects some leaching of A1, which is in accord with the results of solution analysis (Fig. 2). The most significant differences in the acid dissolution process within the M 1 - M 8 series were found for samples M6, M7 and M8, where a substantial increase of non-swelling layers is supposed to cause the decrease in the EGME surface areas (Table 1). These samples were further examined by XRD and HRTEM.

X-ray diffraction

The XRD patterns of air-dry oriented samples M 6 - M 8 are shown in Fig. 6. The most intensive XRD peaks of these samples are 001,002 and 003. Other peaks are much less pronounced and diffuse. In addition to the basal reflections, a small hkl peak was also observed with a d-value of 4.48 ,~. The intensity of this reflection increased from M6 to M8. This could be explained by an increase of the crystal thickness. The thickness of the fundamental particles without expandable interlayers increased for the M 6 - M 8 samples while the a and b dimensions were the same as those for the smectite precursor. The a, b and c dimensions become more

9.20

1692

16.92 1 A 1 / .I %

8.74

5.53 4.35 3.37

2.91 2.16 1.9 b

~ , ~ 5.68 3.40

lb 3'0 *20

FIG. 7. XRD patterns of oriented specimens after ethylene glycol saturation, a - M6; b - M7; c - M8; spacings in ,~; Cu-Ka radiation.

Dissolution of reduced-charge montmorillonite in HCl 341

FIG. 8. Comparison of Li-fixation on the particles and crystals. A - M1; B - M6; C - MS.

similar with increasing Li-content . This also decreased the orientation of layer stacks parallel to 001. The 001 and 002 basal reflections shifted

toward a smaller d-value, while the 003 peak shifted in the opposite direction with increasing Li- content. Decreasing 001 spacings confirmed lower


swelling and thus suggest the presence of non- swelling layers in the examined samples.

Significant changes in XRD patterns occurred after EG saturation (Fig. 7). The Li-fixation brings about a substantial decrease of the layer charge (Table 1). This is supposed to cause collapse of some smectitic, i.e. expandable, interlayers and the subsequent development of pyrophyllite-like (unexpandable) layers. In this way mixed-layer pyrophyllite-like-smectite crystals could be formed. The computer program NEWMOD (Reynolds, 1985) was used to calculate the XRD patterns of EG saturated samples. A very good correlation was found between the experimental trace of M6 and the calculated pattern with 80% smectitic and 20% pyrophyllite-like layers, while 55% smectite and 45% pyrophyllite-like layers produced the best result for M7. For both samples, an R = 0 type of interstratification was used in the calculations (Reynolds, 1985). The experimental trace of M8 could not be calculated in the same way. A mixture of two different mineral phases, namely a pure pyrophyllite-like phase and a mixed-layer pyrophyll i te-l ike-smecti te with 60-70% pyrophyllite-like and 30-40% smectite in a transition stage between random and ordered interstratification (R=0.5) provided the best result.

Thus, the presence of non-swelling layers, increasing from M6 to M8, was confirmed by both EGME surface areas (Table 1) and XRD.

HRTEM (high-resolution transmission electron microscopy)

Three samples (M1, M6 and M8) were observed by transmission electron microscopy of ultra-thin sections. Significant differences were found between the photomicrographs. Arrangement of the particles was observed at low magnification (Fig. 8). The Li-untreated smectite (MI) consists of regularly distributed thin 3 -5 layer crystals and a number of loose monolayers. Samples M6 and M8, which were strongly affected by the Li treatment, had more irregularly distributed crystals of different thicknesses with visible bendings. The degree of crystal deformation was higher in sample M8 than M6. At higher magnification, mixed-layer pyrophyllite-like-smectite crystals consisting of 5-10 (maximum 15) 2:1 layers were observed in M6. Smectite crystals occurred only occasionally and loose crystals with one or two layers were frequent (Fig. 9). Bilayers and trilayers without any expandable interlayers arranged to thick mixed layer crystals were typical for the sample M8

FIG. 9. HRTEM photograph of mixed-layer crystals (marked with arrows) in sample M6.


(Fig. 10A). The number of 2:1 layers per crystal increased up to 30 and loose monolayers were much less frequent. Relatively thick crystals (4 -10 layers) with the mean stacking periodicity of 9.2 ,~

(pyrophyllite-like crystals) were also observed in the sample M8 (Fig. 10B),

The development of mixed-layer pyrophyllite- like-smectite and pyrophyllite-like crystals in M8

FiG. 10. HRTEM photographs of layer arrangement in sample M8. A - mixed-layer crystals built mainly by bi- and trilayers; B - pyrophyllite-like crystal with no swelling interlayers.


suggests that the distribution of the layer charge in the crystals of Jelgov37 Potok smectite may not be homogeneous. Variation in the amount of layer charge and/or charge distribution within the octahedral and tetrahedral sheets is considered to affect the formation of mixed-layer pyrophyllite- like-smectite or pyrophyllite-like crystals in the course of Li-fixation.

C O N C L U S I O N S

Analyses of both solution and solid reaction products of HCI dissolution of a series of RCMs prepared from the same parent clay showed that the greatest extent of dissolution occurred for the M 1 to M4 samples, where Li is fixed only in the h e x a g o n a l ho les o f the t e t r ahedra l shee t (Madejov~i et al., 1996). Slower dissolution of samples M5 and M6 is connected with the lower swelling ability of these samples. These two samples contain fixed Li in both the hexagonal holes of the tetrahedral sheet and in the OLi (previously OH) groups. The M6 sample contains ~ 2 0 % of non-swelling pyrophyllite-like layers. An increased amount of non-swelling layers in M7 and M8 caused substantially slower dissolution of these samples in HC1. Two kinds of crystals were present in sample M8: mixed-layer pyrophyllite-like-smectite and pyrophyll i te- l ike crystals, the latter containing only non-swelling layers.

ACKNOWLEDGMENTS

The authors acknowledge the financial support of the Slovak Grant Agency for Science (grant No. 2/1167/ 95), the technical assistance of R. Hanicov~i, Z. Luk,4~ov~i and L. Pugkelovh and critical comments of J. Srodofi, W.P. Gates and B. (~f~el. V.~. thanks INRA for supporting his visit to Versailles.

REFERENCES

BREEN C., MADEJOVA J. & KOMADEL P. (1995) Characterisation of moderately acid-treated, size- fractionated montmorillonites using IR and MAS NMR spectroscopy and thermal analysis. J. Mater. Chem. 5, 469-474.

BRINDLEY G.W. & ERTEM G. (1971) Preparation and solvation properties of some variable charge montmorillonites. Clays Clay Miner. 19, 399-404.

BUJDAK J., SLOSIARIKOVA H., NOWkKOVA L'. & ~(~EL B. (1991) F i x a t i o n o f l i t h i u m ca t i ons in montmorillonite. Chem. Papers, 45, 499-507.

BUJDAK J,, PETROVI(~OV~ I. & SLOSIARIKOVA H. (1992) Study of water-reduced charge montmorillonite system. Geol. Carpath., Ser. Clays, 43, 109-111.

CALVET R. & PROST R. (1971) Cation migration into empty octahedral sites and surface properties of clays. Clays Clay Miner. 19, 175-186.

Ci~EL B. & KOMADEL P. (1994) Structural formulae of layer silicates. Pp. 114-136 in: Quantitative Methods in Soil Mineralogy (J.E. Amonette & L.W. Zelazny, editors). SSSA Misc. Publ., Soil Science Society of America, Madison, WI, USA.

FARMER V.C. (1974) Layer silicates. Pp. 331-363 in: Infrared Spectra of Minerals (V.C. Farmer, editor). Mineralogical Society, London.

HOFMANN U. & KLEMEN R. (1950) Verlust der Austauschf~igkeit von Lithiumionen an Bentonit durch Erhitzung. Z. Anorg. Allg. Chem. 262, 95-99.

KATO C., SUZUKI T. & FUJIWARA T. (1966) Decomposition and structural change of clay minerals by acid. Mem. School Sci. Eng., Waseda Univ. 30, 1 3 - 24.

KOMADEL P., SCHMIDT D., MADEJOV,~ J. & CI(~EL B. (1990) Alteration of smectites by treatments with hydrochloric acid and sodium carbonate solutions. Appl. Clay Sci. 5, 113-122.

KOMADEL P., SaVCKI J.W. & ~I~EL B. (1993) Readily HCl-soluble iron in the fine fractions of some Czech bentonites. Geol. Carpathica, Ser. Clays, 44, 11-16.

LUCA V. & MACLACnLAN D.J. (1992) Site occupancy in nontronite studied by acid dissolution and MOssbauer spectroscopy. Clays Clay Miner. 40, 1-7.

MADEJOV,/t J., BEDN./~RIKOV,'k E., KOMADEL P. & CI(~EL B. (1993) Structural study of acid-treated smectites by IR spectroscopy. Proc. l l th Conf. Clay Miner. Petrol. (1990) C. Bud~jovice, 267-271.

MADEJOV/t J., BUJD,/~K J., GATES W.P. & KOMADEL P. (1996) Preparation and infrared spectroscopic char- acterization of reduced-charge montmorillonite with various Li content. Clay Miner. 31, 233-241.

MILLER R.J. (1965) Mechanisms for hydrogen to aluminum transformations in clays. Soil ScL Soc. Am. Proc. 29, 36-39.

MOENKE H.H.W. (1974) Silica, the three-dimensional silicates, borosilicates, and berylium silicates. Pp. 365-382 in: Infrared Spectra of Minerals (V.C. Farmer, editor). Mineralogical Society, London.

NOVAK I. & ~i~EL B. (1978) Dissolution of smectites in hydrochloric acid: II. Dissolution rate as a function of crystallochemical composition. Clays Clay Miner. 26, 141-144.

REYNOLDS R.C. JR. (1985) NEWMOD, a computer program fi)r the calculation of basal X-ray diffraction intensities and mixed-layered clays. R.C. Reynolds Jr., Hanover, New Hampshire.

~AMAJOV,~ E., KRAUS 1. t~ LAJ~.~KOV.~ A. (1992) Diagenetic alteration of Miocene acidic vitric tufts of the Jastrab~i formation (Kremnick6 vrchy Mts.,


Western Carpathians). Geol. Carpath., Ser. Clays, 43, 21-26.

SUCHA V., KRAUS I., MOSSER C., HRONCOV/~ Z., SOBOLEVA K.A. & S1RA~OVA V. (1992) Mixed-layer illite/smectite from the Doln~i Ves hydrothermal deposit, the Western Carpathians Kremnica Mts. Geol. Carpath., Ser. Clays, 43, 13-19.

TESSIER D. (1984) Etude experimental de l'organisation des materiaux argileux: Dr. Science thesis, Univ. Paris VII.

TKA~ I., KOMADEL P. & MOLLER D. (1994) Acid-treated montmorillonites - a study by 29Si and Z7AI MAS- NMR. Clay Miner. 29, 11-19.

effect of non-swelling layers on the … · dissolution of reduced-charge montmorillonite in...

Documents