Degree Type

Dissertation

Date of Award

1981

Degree Name

Doctor of Philosophy

Department

Agronomy

Abstract

The exchangeability of interlayer K in micaceous minerals is governed by the conditions imposed by the solution around the particles and the mineral properties themselves. This study focused on the role of mineral properties by relating the K extracted by NaCl-NaTPB solutions to differences in existing and thermally altered properties of selected minerals. The relevance of particle size, mixed layering and dioctahedral structures were emphasized by using size-fractions of ground muscovite, < 2 (mu)m fractions of Tumut and Grundite illites and four trioctahedral mica-vermiculites;When the micaceous minerals were heated, several changes in K exchangeability occurred and the minerals lost weight by dehydration and dehydroxylation. Dehydroxylation enhanced the rate and amount of K release in all the dioctahedral minerals by increasing the interlayer spacing. Mica-vermiculites with mixed layering yielded the same thermal response even though trioctahedral micas behaved otherwise and there was no evidence of dehydroxylation involvement. The minerals varied in their response to temperatures under 400(DEGREES)C, but dehydration was not an obvious factor. These low temperatures reduced layer weathering and thereby provided a means of detecting this mechanism of K release. Layer weathering was a significant factor in ground micas, not in the illites. In the absence of dehydroxylation, reductions in edge weathering also occurred in many heated samples. The thermally induced changes in layer and edge weathering probably stemmed from a reduction in interlayer spacing. If so, a similar explanation should be considered for the limited K release in small particles because the relevance of layer weathering was eliminated by comparisons of heated illites and ground mica. X-ray diffraction studies verified the occurrence of structural alterations but not a measurable decrease in interlayer spacing. However, the small particle effect in illites was circumvented by the expanding effects of dehydroxylation. Mixed layering plays a major role in the thermal responses of mica-vermiculites but has no identifiable effect on K exchange in unheated minerals;The interlayer spacing and condition of the lateral edges of the mineral particles appear to dominate the exchangeability of interlayer K.

DOI

https://doi.org/10.31274/rtd-180813-6025

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Jia Shung Wang

Language

en

Proquest ID

AAI8209187

File Format

application/pdf

File Size

157 pages

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