The Suitable Industrial Application Of Kaolin
[KPANKOROGI AND IJERO EKITI]

CHAPTER TWO
2.0    LITERATURE REVIEW
2.1    BACKGROUND OF THE STUDY
The importance of kaolin is remarkable as one of the most abundant clay rock in soil and sediments, its properties are such that it interacts with other soil element to contribute to the mechanical stability of the soil column (Huertas et al, 1999; Chen et al., 2000).
            Kaolin is a layered clay rock and product of advanced weathering process. One layer of the clay consists of an alumina octahedral shut and a silica tetrahedral sheet that share a common plane of oxygen atoms and repeating layers of the mineral are hydrogen bounded together. As a consequence of this structure, the silica/oxygen and alumina/hydroxyl sheets are exposed and interact with different components in the soil. (Grim,1968).
           Frost (1998) discusses outer and the inner hydroxyl sheet. The outer groups are situated along the unshared plane of the alumina sheets while the inner groups are located along the plane that is shared with and borders on the silica oxide sheets. Hendershot et al.(1993).
The movement of the inner hydroxyl plane is restricted as a result of chemical bonding between the silica and alumina sheet.
    As a consequence of its well-packed structure, kaolin particles are not easily broken or separated. Hence, most sorption activity occurs along the edge and surface of the structure.
Kaolin can form a barrier that is not easily degraded and naturally occurring sediments and deposits containing an abundance of kaolin interspersed with other minerals are effective.
      In controlling the migration of dissolved species (Devidal et al, 1996). Clay impurities will depend on the genesis of the clay and will affect the degree of disorder and the particle size of the clay (Balan et al, 1999).
Unlike smectites, kaolin is non-expanding and as a result of its high molecular stability, isomorphorous substitution is limited or nonexistent (Mitch-ell, 1993). Kaolin is the last reactive clay (Suraj et al, 1998) however, it has high Ph dependency enhance or inhibit the adsorption of metals according to the ph of the environment (Mitchell,1993), and this metal adsorption is usually accompanied by the release of hydrogen (H+) ions from the edge sites of the mineral.
Adsorption may also take place on the flat exposed, plane of the silica and the alumina sheets (spark et al., 1995).
The Cation Exchange Capacity (CEC) quantifies the clay ability to exchange cat ion and retain nutrients and is a measure of the clay quality.