Chemical Enrichment and Acid Activation of Bentonite Clay

Bentonite clay with high amorphous SiO₂ content up to 50% has been enriched via the caustic treatment. Caustic concentration varied between 5 to 25%. Operation time and temperature were the other parameters when driving the optimum enrichment conditions. It was found that amorphous silica was successfully removed when the caustic concentration is 15% or above. Operation temperature of 80 C and duration of 90 minutes were the other limitations in order to have an efficient SiO₂ extraction. Recovery of SiO₂ as sodium silicate solution during this enrichment was another concern that might be important affecting the process economy. Acid activation was applied to the enriched clay to obtain a bleaching earth. The so-called bleaching earth showed bleaching efficiencies of 98.3% and 93.3 regarding to the chlorophyll-a and β-carotene, respectively. In agreement with the recorded decreases in chlorophyll-a and β-carotene components, lovibond red and yellow values were also decreased considerably. This study showed that the unpleasant color changes coming from the presence of pigments, such as chlorophyll-a and β-carotene, can be avoided by the use of chemically enriched and acid activated bentonite as the bleaching earth.