Chemical Activation of Kaolin under Acid and Alkaline Conditions

In this study chemical activation of kaolin under acid and alkaline conditions was investigated. For this purpose the natural kaolin was heated in a furnace until the metakaolin was formed. Then this reactive kaolin was used for chemical activation. For increasing or decreasing of silica or alumina contents, metakaolin was leached by acids and alkaline [1,2]. The extraction of aluminum and silicon was done by HF and NaOH. After calcination, the percentages of alumina and silica were reached to 41% and 54%, respectively. For reducing silica content and producing higher alumina materials, metakaolin was leached by caustic soda solution at 100 °C. Consequently, the amount of alumina and silica reached to 46% and 48%, respectively. In order to increase the silica content in kaolin, metakaolin has been leached by HF diluted solution at room temperature, in which the amount of alumina and silica reached to 35% and 61%, respectively. In particular, the treated kaolin in this way could be used as raw material to produce zeolite 4A or as a valuable additive in concrete. The XRD patterns of kaolin, metakaolin and leaching process with NaOH were presented in Fig 1: a-c.