Removal of iron oxides in Meetiyagoda kaolin by chemical leaching to improve whiteness

Abstract

Industrial grade Kaolin deposits in Sri Lanka are located in Boralesgamuwa and Meetiyagoda. Two distinct grades of Kaolin are produced at Meetiyagoda refinery, based on the whiteness index (WI). The presence of iron oxides significantly affects the WI of the Kaolin. Upgrading of the whiteness will result in a huge increase in the product prices as high as 35%. However, no effective methods are currently in place for the whiteness improvement at Meetiyagoda Kaolin refinery. Hence, this study was carried out to assess the whiteness enhancement capability of Meetiyagoda Kaolin by chemical leaching process using oxalic and citric acids. The treatment time (0–120 min) in steps and concentration of acids (0.01, 0.1, 0.2, 0.3, 0.4 and 0.5 M) were considered as the main variables of this study. Leachate and treated samples were analysed by using spectrophotometric and XRF methods respectively. The results depict that the oxalic acid is more effective in leaching iron oxides from Kaolin compared to citric acid for the Kaolin at Meetiyagoda. It was observed that 25% and 14% of Fe in Kaolin filter cakes can be removed by 0.4 M oxalic and 0.5 M citric acid respectively, within a treatment time of 120 mins at the room temperature.