Straight synthesis of α and γ alumina from kaolin by HCl acid leaching

This paper investigates the production of alumina from kaolinite by leaching method using hydrochloric acid. Raw kaolin was calcined at 850?C then leached with 6 M hydrochloric acid at 90?C, followed by the addition of 6 M HCl solution to the leachate the aluminum hydroxide was precipitated. Finally, precipitated aluminum hydroxide was heated at 1100?C and turned into aluminum oxide. Materials were identified by XRF, XRD and SEM-EDX techniques. Alumina recovery percentage was determined at different kaolin particle sizes (-200 to -400 standard Tyler screen mesh), different times (1, 2, 3 and 4 h), different leaching temperatures (80, 90, 100 and 104?C) and different concentrations of hydrochloric acid (20, 25, 30 and 37%). Alumina phase changes were also investigated at two calcination temperatures (1100 and 1200?C). The purity of aluminum oxide obtained from this process is about 97% and its recovery percentage is about 98%. It was observed that kaolin granulation with dimensions less than 75 ?m had no significant effect on alumina recovery percentage. It was also found that, the alumina recovery percentage increased with increasing leaching temperature.