The alumina recovery from low grade kaolin （K-JS） treated through thermal and mechanical methods was investigated. High grade kaolin （K-SX） was used as comparison. The optimum calcination temperatures for K-JS and K-SX were both 600 ℃, which resulted in 89.34wt% of alumina extraction from K-JS and 83.37wt% from K-SX. With the increase in calcination temperature, the chemical reactivity of calcined K-JS and K-SX to acid decreased. Mechanical treatment was much more effective in increasing the alumina extraction from activated kaolin. Around 99wt% of alumina was extracted from K-JS ground for 10 hours and 95wt% of alumina was extracted from K-SX ground for 20 hours. The IR results showed that the substitute of A1 for Si occurred in calcined K-SX, however, the impurities in K-JS decreased this substitute. More alumina could be extracted from low grade kaolin than that from high grade kaolin under identical thermal or mechanical conditions.
