Reference smectites were examined to determine relationships between Li uptake, cation-exchange capacity (CEC), and octahedral layer charge after Li saturation and heating at 250°C (Hofmann-Klemen effect). Direct measurements of exchangeable Li after heating led to overestimates of charge reduction due to entrapment of Li in collapsed interlayers. Expansion of interlayers by sequential washings with 1 N MgCl2, 0.01 N MgCl2, and ethanol and subsequent determinations of exchangeable Mg provided accurate measurements of reduced charge. The CEC reductions observed in dioctahedral samples as a result of Li saturation and heating equaled octahedral charge values derived from published mineral formulae, and interlayer charge estimates obtained by alkylammonium exchange confirmed that measured CEC reductions were a consequence of uniform decreases in octahedral layer charge.

Dioctahedral specimens retained 1 to 10 meq/100 g of non-exchangeable Li in excess of CEC reduction and were acidified in direct proportion to their total Fe contents, apparently as a result of the deprotonation of structural hydroxyl groups. Mild acid treatment reprotonated these hydroxyl groups, released excess Li, and resulted in total Li contents comparable to measured CEC reductions. Heating (250°C) Mg-saturated hectorite induced a loss of octahedral Li, acidification, and a reduction of CEC, indicating that Mg had partially replaced octahedral Li. These results suggest that octahedral Li is mobile at low temperatures and that cation movement into or out of the octahedral sheet is favored if the layer charge is reduced.

A series of reduced-charge (RC) hectorites were prepared by multiple heat (250°C) treatments of Mg-saturated hectorites (SHCa-1 ). Cation exchange capacity (CEC) measurements and alkylammonium exchange indicated that a decrease in layer charge occurred with each Mg-250 treatment. Chemical analyses showed that decreases in structural Li and increases in structural Mg contents coincided with charge reduction. Fluorescence measurements of adsorbed quinoline indicated that the hectorite surface was acidified during charge reduction; hydroxyl group deprotonation is a possible source for the acidity. Fourier transform infrared spectra (FTIR) indicated that the Mg-250 treatment induced the loss of structural Li and shifted the SiO stretch band to a position similar to that in talc. The relative intensities of the OH and SiO stretch bands in FTIR spectra suggest that some of the hydroxyl groups in hectorite were lost, possibly by deprotonation. However, thermogravimetric data (TG) reveal no significant difference in the hydroxyl contents of the hectorites.

The FTIR spectra, CEC, layer charge, chemical, and TG data all supported the view that Mg substitution for octahedral Li occurred which resulted in a more “talc-like” structure. Charge reduction in smectites is evidently a general phenomenon and can be induced by heat treatment with the proper exchangeable cation. The ability to reduce the charge of hectorites makes it possible to prepare a series of clays which vary in charge but lack structural Fe. Such RC smectites should be suitable for expandable clay mineral studies which utilize spectroscopic techniques that are sensitive to Fe content.

For a series of mixed-layer illite-smectite (I-S) minerals from a drillhole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Casaturated specimens in both air-dried and ethylene glycol-solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li saturation. The K content in the illite layers was 1.5–1.7/O20(OH)4 in the I-S series from 3 to 85% of I-layer content (% I). The layer charge of the smectite layer varied slightly within the range of 0.3–0.5/O10(OH)2 by alkylammonium exchange experiments and the expandability was independent of the beidellite content within a range of 0–0.5 by the Li-saturation test. The degree of long-range ordering represented by Reichweite (R) parameters varied from R0 to R3 via R1 and R2 with increase in % I. The I-S samples contained <10% vermiculite as the third component and the vermiculite content tended to decrease with progressive illitization.

In contrast to the smectitic R0 samples (<10% I), more illitic R0 (e.g. 35% I) and >R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium-exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quartets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites.

Smectites from the E horizon of podzols dated at 1200–10,000 y in central and northern Finland were studied. Clay minerals in the fine (<0.1 μm) and coarse (0.1–2 μm) fractions were examined by X-ray diffraction. The distribution (octahedral or tetrahedral) and magnitude of the layer charge of expandable minerals were estimated using intercalation of alkylammonium ions (nC = 12) associated with the Hofmann & Klemen effect. In addition, charge alteration following desaturation (H+ exchange) and autotransformation was investigated. Smectites from the E horizons of podzols are not homogeneous but constitute a mixture of several populations with various layer charges. Smectites with lower layer charge are present in podzols having a longer effective time of pedogenesis, suggesting alteration of the high-charge smectites with time. Experimental alteration of the smectites by autotransformation shows that a decrease of the layer charge is easily produced by desaturation of the smectite clays.