|Abstract or Summary
- The effects of pH and time on the formation of hydroxy-Al, Fe,
and Mg interlayer were compared for montmorillonite and vermiculite.
The stability of interlayers was evaluated by sequentially increasing
the severity of dissolution treatments and by subjecting the inter-layers to an HC1 treatment. The interlayer formation and stability
were evaluated by X-ray diffraction analysis and CEC measurements.
In montmorillonite, aluminum interlayers were formed at all
pH levels. Systems equilibrated in acid media exhibited the greatest
degree of interlayering and the resulting material showed the essential
X-ray diffraction characteristics of chlorite. However, the amount
of interlayers decreased after six months and one year. Those inter-layers formed in alkaline media exhibited increased interlayering
after one year. Boiling Na₂CO₃ and particularly boiling NaOH
generally removed part of interlayers. This removal was more
pronounced for neutral and alkaline media than for acid media. The interlayer formed in alkaline conditions showed the highest stability
to HC1 treatment, whereas that formed in acid medium was the least
In vermiculite, aluminum interlayers were also greater for
acid than for alkaline media. In contrast to montmorillonite, the
amount of interlayer in vermiculite in acid media increased with
time. For alkaline media there was some increase in the inter-layering after six months followed by decrease after one year. As
the severity of dissolution treatments increased the degree of collapse
increased. However, chloritic components, in addition to dominant
collapsible components, were evident after NaOH treatment for
systems formed at intermediate pH levels. The stability to the HC1
treatment decreased toward alkaline media.
Moderate amounts of iron interlayers were formed in montmorillonite
at all pH levels. The interlayers did not inhibit expansion
on solvation but the systems exhibited moderate resistance to collapse.
Diffraction patterns were characterized by diffuse peaks and plateaus
suggesting mixed layer systems. Some reorganization or decrease
of interlayers occurred after equilibration for one year. The interlayers
were partially removed by dissolution treatments. Interlayers
formed at intermediate pH values were, presumably, more stable
than those formed in other media. Iron interlayers from all media
exhibited a high stability to the HC1 treatments. Iron interlayers in vermiculite were favored by alkaline environments.
Formation was greatest after ten days and less after six
months or one year. Iron removal and particularly boiling NaOH
treatments resulted in resolution of collapsible and non-collapsible
components. In the latter case, definite chlorite lines were observed.
The interlayer from alkaline media exhibited somewhat higher
stability to sequential treatments than those from other media. The
HC1 treatments removed more interlayer from acid media than from
Magnesium interlayers in montmorillonite and vermiculite were
formed only in alkaline environments (pH > 10). After ten days, in
both systems, the degree of interlayers formation decreased as the
pH increased. The montmorillonite system showed only a slight
dissolution of interlayers after 6 months and one year, whereas a
strong interlayer decrease was observed for the vermiculite system.
The interlayered montmorillonite formed at an initial pH of 11 became
nearly amorphous to X-ray diffraction following a 6-month period.
The boiling NaOH treatment produced a partial resolution of the
montmorillonite system into collapsible and non-collapsible components.
In vermiculite, the second dithionite-citrate removed most
of the interlayers and induced a high degree of collapse and a high
CEC. The boiling NaOH treatment resolved a small 14 A[superscript °] component
in addition to a dominant 10 A[superscript °] component after K-saturation. The interlayers in montmorillonite showed a high stability to HC1 treatments.
In contrast, most of the magnesium interlayers in vermiculite
were removed by the HC1 treatments.
In conclusion, the hydroxy-Al, Fe, and Mg interlayers in
montmorillonite showed a higher degree of formation and exhibited a
higher stability to sequential and HC1 treatments than the interlayers
formed in vermiculite. Reasons were given in order to explain these