Extraction of Alumina from Local Clays by Hydrochloric Acid Process

A bench work study was carried out to investigate the use ofkaolinitic clay containing 29.4% Al2O3 extremely abundant in SaudiArabia for the production of pure alumina by calcination at 700oC for1h (recommended by previous investigators) then leached byhydrochloric acid.The effects of leaching temperature (25oC to boilingtemperature), period of activation (10-150 minutes), acidconcentration (1M – 6M), particle size (–8 to –200 standard Tylerscreen mesh), acid to clay weight ratio (4:1 to 15 :1ml acid/gm clay)on alumina extraction were investigated.The recommended leaching conditions are: 6 molar for acidconcentration at boiling conditions under reflux, one hour forleaching time, –100 mesh standard Tyler screens for particle size ofcalcined clay and 10 ml acid/gm clay for acid to clay weight ratio.Leaching this local clay sample under these conditions resulted in32% alumina extraction.Local kaolinitic clay were calcined at temperatures varyingbetween 400oC and 800oC at different calcination periods (5 to 120minutes). The calcined clay was then leached with 3M HCl acid underthe above-recommended leaching conditions. The optimumcalcination conditions were 600oC and 1 hour for calcinationtemperature and time period, respectively. The corresponding aluminaextraction from local clay sample is about 63%.