Kaolin when thermally heated at specific temperatures gives products of industrial significance called “calcined kaolin”, an anhydrous aluminium silicate form of kaolin with characteristic properties such as high brightness, hydrophobicity, abrasive nature and improved electrical properties. Calcinations also alter both the size and shape of kaolin particles.
Calcinations occur in two stages which are from 450oC to 700oC. At 700oC, the dehydration of kaolin is completed forming metakaolin mostly used to improve the dielectric properties of PVC.
Calcined kaolin is also used in the paint industry as an effective opacifying extender in paint formulation, partially replacing titanium dioxide thereby reducing the overall cost of paint formulation but maintain paint film quality.
Pigment is one of the main components in paint formulation which is dominated with the use of titanium dioxide. However, due to increasing demand of this important pigment and the attendant increase in price, it has become imperative to develop cheaper alternative source with properties similar to titanium dioxide. Calcined kaolin can partially replace titanium dioxide thereby reducing the cost of paint production.
Nigeria has a huge reserve of kaolin with an estimated reserve of about 3billion metric tonnes scattered in different parts of the country. There are at least 45 known deposits of kaolin in Nigeria. There is no state in the country without at least one deposit. The market for kaolin in Nigeria is large, sustainable and expanding because of the numerous applications of the product.
The first phase of the project commenced in 2003 and kaolin from the Alkaleri deposit was used. The raw kaolin was calcined without beneficiations which produce 5% substitution after industrial test. The research was completed in 2004.
The second phase of the project commenced in 2009 and involved the calcination of kaolin from seven deposits across the six geo-political zones of the country. 20% substitution was achieved after industrial test.
The third phase of the project which is aimed at addressing the issues identified in the second phase started in 2014. Hence the Council has commissioned a contractor to fabricate and install a gas suspended Calciner. The company has since commenced the fabrication of the Calciner.
From the company’s status report forwarded to the Council last year, the Cooling section has been installed along with Calciner Riser Column. The installation of the preheating cyclones is on-going after which, the system will be tested without heat to ascertain the aero - solid dynamic behaviour. The refractory lining and external insulation is expected to be applied during the final installation at the council’s approved location. Also the base of the Calciner Riser Column has been modified to accommodate heating with LPG gas.
However, from the report of monitoring visit this year, the fabrication of all component parts have been completed. It is being awaited for final coupling at the RMRDC demonstration centre which will be followed by continuous test running for the purpose of operational optimization.