Precipitation profiles of Chinese refineries are generally characterized by high solid content, high caustic concentration and growth only process plus relatively loose product quality target control. Usually diasporic type bauxite is exploited and processed in China due to the formation under an oriental natural environment. Processing this type of bauxite requires digestion conditions with high temperature (+260 °C) and high caustic concentration (+410 g/L, expressed as Na2CO3) to achieve good alumina extraction efficiency. Furthermore, extremely large circulation of seed (+800 g/L, 1st precipitator) is adopted to give high productivity and "adequate" product quality.
This study reports typical precipitation process and key performance indicators (KPls) used in Chinese alumina refineries. It highlights the influence of several factors such as slurry solid concentration, interstage cooling profile and seed moisture on precipitation yield and rate. An objective process used in China has also been stated and forms a basis for presenting optimized precipitation profile which is currently applicable and unique to diasporic bauxite refining in China.