Extraction of Alumina from Local Clays by Hydrochloric Acid Process@@@إنتاج الألومينا من الطفلة الوطنية بالمعالجة بحامض الأيدروكلوريك
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%.
Methods for producing alumina from clay—an evaluation
This paper summarizes and compares Bureau of Mines cost estimates for seven selected processes to produce metallurgical-grade alumina from clay. Processes discussed include acid-leaching, alum intermediate, and alkaline-sinter techniques. The effects of varying the principal operating-cost components—clay, reagents, electricity, fuel, and labor—are presented. Individual nomographs were prepared that permit easy assessment of several processes deemed most likely to be of commercial interest.
Production of Liquid Alum from Aluminum-Anodizing Sludges
The potential for reclamation of dewatered aluminum-anodizing sludges as liquid alum was investigated. Batch extractions with sulfuric acid at elevated temperatures indicated that liquid alum production was feasible. Sludge solids content was shown to be a critical variable if commercial-strength products (8.0 to 8.3 percent as Al2O3) are to be produced.