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During the weathering of intrusive rocks a process known as “kaolinization” occurs wherein the sodium feldspar breaks down into kaolin group minerals – kaolinite and halloysite. Both are hydrated aluminosilicate minerals. Kaolinite (Al2Si2O5(OH)4 ) occurs as plate-like sheets that commonly appear as “stacked books”. Aggregates of the microscopic kaolinite platelets (commonly termed “kaolin”), are typically soft with increasingly purer varieties displaying greater whiteness and brightness.
When kaolin is calcined (heated to about 800o C) it is transformed into a dehydrated, amorphous phase called “metakaolin.” The heating causes metakaolin to become activated and metastable – a pozzolan. When metakaolin (or any pozzolan) is added to cement-based mortars, it causes an aggressive reaction with calcium hydroxide (lime) to form compounds with enhanced performance characteristics including increased strength; reduced permeability; greater durability; effective control of efflorescence; and control of degradation caused by Alkali-Silica Reaction. The quality of a metakaolin is determined by (i) the amount of lime it is able to bind, (ii) the velocity at which the hydrated lime is reacted, (iii) the mechanical properties of mortars and concrete and (iv) the color (whiter metakaolin can be more easily colored).
I-Minerals will move its kaolin into metakaolin market under the brand name Bovill Metakaolin. Long term testing by a leading cement laboratory has demonstrated its initial metakaolin product performed at least as well as fly ash, a more common pozzolan in the Pacific Northwest. Bovill Metakaolin has a finer particle size than I-Minerals’ initial metakaolin product and is now generating pozzolanic results more comparable with higher cost pozzolans such as silica fume. At present there is no metakaolin production in the Pacific Northwest and transportation costs to bring a Georgia sourced metakaolin make it a high priced pozzolan. Fly ash, lower cost and generally inferior pozzolan compared to metakaolin is coming under ever increasing environmental pressures presenting a significant market opportunity for I-Mineral’s Bovill Metakaolin.
Beyond standard ceramic applications, other uses for kaolin include paper coating, filler, paint, plastics, fiberglass, catalysts, and other specialty applications. It is also used as a key ingredient in natural pesticides that are suitable for organic farming applications. I-Minerals however will focus almost exclusively on the metakaolin markets. A bridge deck in a northern climate where it is subject to the wear and tear associated with plowing and salting is a prime metakaolin application.