Extraction of alumina from local clays by hydrochloric acid process

Abstract EN

A bench work study was carried out to investigate the use of kaolinitic clay containing 29.4 % Al2O3 extremely abundant in Saudi Arabia for the production of pure alumina by calcination at 700 o C for 1h (recommended by previous investigators) then leached by hydrochloric acid.

The effects of leaching temperature (25 o C to boiling temperature), period of activation (10-150 minutes), acid concentration (1M–6M), particle size (–8 to –200 standard Tyler screen 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 acid concentration at boiling conditions under reflux, one hour for leaching time, –100 mesh standard Tyler screens for particle size of calcined clay and 10 ml acid / gm clay for acid to clay weight ratio.

Leaching this local clay sample under these conditions resulted in 32 % alumina extraction.

Local kaolinitic clay were calcined at temperatures varying between 400 o C and 800 o C at different calcination periods (5 to 120 minutes).

The calcined clay was then leached with 3M HCl acid under the above-recommended leaching conditions.

The optimum calcination conditions were 600 o C and 1 hour for calcination temperature and time period, respectively.

The corresponding alumina extraction from local clay sample is about 63 %.