PRODUCTION OF ALUMINA FROM SAUDI CLAY BY SULFURIC ACID LEACHING

Aluminum is obtained by electrolysis of pure alumina obtained from bauxite by Bayer process. Bauxite ore has been discovered in limited amounts in the Kingdom's land, so, it appears to be very important to search for a local substitute for alumina producti on in the Kingdom. Local kaolinitic clay containing 29.4% Al 2 O 3 was grinded , activated by calcination at 700 ° C for 1h and leaching with 40% wt. sulfuric acid under boiling conditions. The extracted aluminum sulfate was purified from dissolved iron impurities by adding hot saturated ammonium sulfate solution to the leached liquor and cooling to crystallize pure ammonium alum ((NH 4 ) 2 SO 4 Al 2 (SO 4 ) 3 ? 24 H 2 O) which is calcined to give pure alumina. Investigation of the effect of leaching time and acid to clay ratio revealed that 90.9 % and 48.1% extraction of alumina and iron oxide are obtained when using the stoichiometric acid requirement at leaching period of 1h. Investigation of the effect of crystallization conditions on the purity of the obtained alu mina showed that alum yield increase s with decreasing final crystallization temperature. Decreasing the final crystallization temperature from 30 ° C to 0 ° C increase alum yield from 74.5 % to 95.4 %, with alum purity exceeding 99.9 % . The results indicate d that alum yield increase s with decreasing final crystallization temperature and initial liquor concentration. However, the final crystallization temperature was the most important parameter affecting the alum crystallization process. Calcination of produced al um at 950 ° C for 30 minutes gave alumina containing 99.9% Al 2 O 3 and 0.01% Fe 2 O 3 which is within specifications of metallurgical grade alumina .