Clay Mineral Formation at Ambient Conditions

Clays are one of the most common and the most diverse group of minerals on the Earth’s surface. They are formed during a chemical or a combined mechanical and chemical weathering processes of crystalline rocks. This process is complex and seemingly small changes in the source rock or the weathering process and conditions can significantly affect the observed weathering products.

Despite widespread abundance the mechanism of clay mineral formation is largely uncertain. This is largely due to formation conditions that are hard to replicate and monitor in a laboratory setting. Natural processes that produce clays happen at low temperatures and takes place over a timescale of many if not many hundreds of years and yields crystals with large density of defects and grain size of few microns. Laboratory methods cannot exactly replicate this process if experiments are to be conducted over reasonable timescales and particles large enough to be identified as clays are to be produced. Therefore, the synthesis process has to be modified, conditions changed and conclusions about the natural processes have to be made indirectly. Natural clay formation takes place in a complex chemical environment containing ions and organic molecules that may not be constituents of clay minerals formed but still impacts the process. Although many laboratory synthesis methods also feature such components, especially organic additives, their role and whether they are essential or not is not sufficiently explained.

Our research in clay formation mechanisms focuses on the interface between a primary mineral and the solution as the mineral surface is first amorphized and then converted into a clay. Alternatively, a direct precipitation pathway is considered. We are interested in determining what conditions are necessary for clay formation to occur and how do changes in the reaction environment affect clay formation.

Due to their widespread abundance clays have also been an important resource for humans as a precursor to various building materials such as bricks, cement. Clay minerals are also used in production of ceramics and clay mineral kaolinite is used in production of porcelain. However, there are also more specialist applications of clay minerals such as adsorbent materials, catalyst supports and nanocomposites. Clays with consistent, well known and preferably tunable properties are required for these, more specific, applications. Such clays cannot be always obtained from natural sources due to purity and consistency issues. Therefore, for applications like catalysis clay minerals, with few exceptions, currently have a relatively minor role compared to another silicate mineral group, zeolites. Zeolites are much easier to produce and their properties can be easily tuned by modifying the synthesis process or by post-synthesis modifications. Understanding the mechanisms of various clay mineral formation may enable the discovery of synthesis procedures of clays with desirable properties of catalysis or nanocomposite applications.

Recent Publications

(authors from the group in bold)

Besselink, R., Stawski, T.M., Freeman, H.M., Hövelmann, J., Tobler, D.J., Benning, L.G. (2020). Mechanism of saponite crystallization from a rapidly formed amorphous intermediate. Crystal Growth & Design, 20, 5, 3365-3373. DOI: 10.1021/acs.cgd.0c00151.

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