A digester is a large pressure vessel or autoclave used in the Bayer Process of alumina production from bauxite ore, designed to carry out the chemical dissolution of aluminium-bearing minerals — principally gibbsite, boehmite, and diaspore — in hot, concentrated sodium hydroxide (caustic soda) solution under elevated temperature and pressure conditions. In bauxite mining and processing operations, the digester is one of the most critical pieces of equipment in the alumina refinery, determining both the recovery efficiency of alumina and the throughput of the processing plant. Digesters are typically cylindrical steel vessels, often arranged in series as digestion trains, and can operate either in batch or continuous flow mode. Modern refineries favour continuous tube digesters for their operational efficiency, reduced heat losses, and greater control over process conditions. The digester must withstand highly corrosive caustic conditions at temperatures up to 300°C and pressures corresponding to the steam saturation point. Proper sealing, materials selection, and instrumentation are essential for safe operation. Digester performance directly affects the overall alumina extraction rate and the quality of the resulting alumina trihydrate product.
