Graduate Thesis Or Dissertation
 

Formation and stability of Al, Fe, and Mg interlayers in montmorillonite and vermiculite

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  • 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 stable. 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 alkaline media. 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 behavioral differences.
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