Kaolin

Kaolinite has a low shrink-swell capacity and a low cation exchange capacity (1-15 meq/100g). It is a soft, earthy, usually white mineral (dioctahedral phyllosilicate clay), produced by the chemical weathering of aluminium silicate minerals like feldspar. In many parts of the world, it is colored pink-orange-red byiron oxide giving it a distinct rust hue. Lighter concentrations yield white, yellow or light orange colors.

Category:                                  Silicate material

Chemical formula:                      Al₂Si₂O₅(OH)₄

Color:                                       White, sometimes red, blue or brown tints from impurities

Crystal habit:                             Rarely as crystals, thin platy or stacked, More commonly as

                                                microscopic pseudohexagonal plates and clusters of plates,

                                                aggregated into compact, claylike masses

Crystal system:                           Triclinic

Cleavage:                                  Perfect on {001}

Tenacity:                                    Flexible but inelastic

Mohs scale hardness:                 2–2.5

Luster:                                      Pearly to dull earthy

Streak:                                      White

Specific gravity:                         2.16–2.68

Optical properties:                      Biaxial (–)

Refractive index:                          n_α = 1.553–1.565,
                                                  n_β = 1.559–1.569,
                                                  n_γ = 1.569–1.570

Kaolin is found in the following states: Ogun, Kogi, Imo, Rivers, Anambra, Bauchi, Kebbi, Ondo, Ekiti, Akwa Ibom, Kano, Katsina and Plateau.

Availability

Fortunately, abundant kaolinitic clay deposits have been identified all over the country.  Some of these are shown below:

State                     Location                             Reserve in million Tonnes

Anambra             Ozubulu                                   4.2

Enugu                 Enugu                                      50

Oyo                      Tede                                     1.5

Kaduna               Mararaba-Rido                         5.5

Katsina               Kankara                                  3.5

Kebbi                   Illo                                       Very large

                          Kaoje                                      Very large

Ogun                   Ibamaje                                  Large

                            Onibode                               Large

                               Miroko                                Large

Plateau                 Jos                                        Large

Borno                   Maiduguri                        Large

Kwara                 Lafiagi                                 Large

Raw kaolinic clay is first crushed and mixed with water into a slurry. At this stage, some amount of diatomite reagent may be added to decolorise the clay (if necessary), after which the slurry is pumped into a vibro-screen to extract foreign particles and impurities.  The slurry is, thereafter, pumped into a filter press to eject the water. The filtered cakes of kaolin are dried, pulverized, milled and classified.  The final product is then packaged for industrial use.  Further treatment with acid and other chemicals is needed for pharmaceutical and paper grades.

The total national demand of kaolin in Nigeria is about 60,000 tonnes per annum for the soap, detergent and pharmaceutical industries. 

Medically, kaolin is used as an absorbent and has also found tremendous use in anti-diarrhea formulations.  It is sometimes used in combination with pectin, a polygalacturic acid extracted from the pulp residues of citrus fruits.  Conservatively, about 500 tonnes of kaolin (worth about N5.0 million) is required annually for the formulation of anti-diarrheal mixture alone.  Thus local sourcing of kaolin would not only enhance input into the pharmaceutical industries but also conserve some foreign exchange for the country.

The estimated annual demand of Kaolin is over 350,000 tones, while local production is put at about 25,000,000 tones. There is therefore a huge demand gap that must be bridged to reduce importation by paper, chalk, paint and pharmaceutical industries among others.