KaolinDuring the weathering of intrusive rocks the sodium feldspar contained therein 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 (are commonly termed "kaolin"), are typically soft with increasingly purer varieties displaying greater whiteness and brightness. Kaolinite is hydrophilic, meaning that it can be relatively easily dispersed in water, a property desirable for many of its uses.
Particle size and brightness are primary attributes that determine kaolin's value. The brightness is a measure of the amount of light kaolin reflects back. The higher the reflective characteristics of kaolin and the smaller the particle size, the greater the number of uses it has. Kaolin minerals long have been the basic raw materials used in the ceramic industry, especially in fine porcelains. They can be easily molded and are white when fired. Large quantities of kaolin are used in 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.
High Value Applications
When kaolin is calcined (heated to between 600° and 850°) it is transformed into an amorphous phase called "metakaolin." The heating causes metakaolin to become activated and metastable. When metakaolin 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). 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. I-Minerals is currently undertaking a long term testing process of a metakaolin product produced from the Bovill Kaolin property to confirm its quality in the metakaolin markets. Results to date are very favorable.
Cosmetic grade kaolin, which is very low in trace elements such as iron, is used in cosmetic products as it is has an opaque white base. Its oil control properties allow a cosmetic makeup to stay on longer, withstand perspiration and wet or humid conditions. Cosmetic grade kaolin does not draw the oil of the skin and provides effective sun protection