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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)




Clay-natural organic matter (NOM) complexes are dynamic components of soils and sediments. The movement and fate of NOM in the environment is strongly influenced by the formation of these complexes. As a consequence, clay-NOM complexes have been the focus of many complexes. Structural and dynamic aspects of clay-NOM complexes have been studied, for example the type and frequency of organic matter bound to the clay mineral surfaces and ultimately its effects on aggregation processes. Yet there are many structural aspects of the products of this aggregation that are not yet well understood, such as what happens at the molecular level when the organic matter approaches and binds to the clay material surfaces. These interactions are difficult to study because of the uncertainties concerning the nature of NOM and the precise condition of the clay particle surfaces is seldom known. Even when the clay minerals are well purified, the surface charge distribution is not known precisely. There are ways to estimate and closely model these interactions using simple, model organic compounds for NOM such as polysaccharides, surfactants, proteins, lipids. The surface charge of the clay minerals can be estimated from the point of zero charge (pzc) and the shape can be estimated by mathematical analysis of light scattering measurements. The objective of this work was to characterize the aggregation properties and aggregate structure of illite and the effect of organic matter coating on that aggregation using laser light scattering (LLS). Using LLS, the types of particle interactions are found to be pH dependent. At high pH values, and electrolyte concentration, face-to-face aggregation of the particle is dominant but not the only interaction mechanism. The presence of interlayer cations has a much larger effect on the aggregate structure than the pH. High pH values stabilize the clay particles in water. Studying the rate of aggregation provided the doublet to singlet hydrodynamic radius. This characterizes the structure of the aggregates. Structural details were also examined through the fractal dimension measured by LLS in the presence of exchange cations and/or NOM. The fine structural details change when these conditions change, allowing greater insight into the structural details of clay-NOM complexes.

Library of Congress Subject Headings

Clay minerals


Soil structure

Aggregation (Chemistry)

Light -- Scattering



Number of Pages



South Dakota State University