Digestion temperature is the controlled operating temperature at which the bauxite ore and caustic soda solution are maintained inside the digestion vessels during the Bayer Process alumina refining operation, and it is one of the most influential parameters determining the rate and completeness of aluminium mineral dissolution. The optimal digestion temperature varies depending on the mineralogy of the bauxite being processed: gibbsite (Al(OH)₃), the most readily soluble aluminium mineral, dissolves efficiently at relatively low temperatures of 140–150°C; boehmite (AlOOH) requires intermediate temperatures of 200–240°C; and diaspore (AlOOH polymorph) demands the highest temperatures, often in excess of 260–300°C, to achieve economical dissolution rates. Higher digestion temperatures generally increase aluminium extraction rates and reduce required residence times but also increase energy consumption, caustic degradation, and wear on process equipment. Precise temperature control through steam injection, heat exchange, and process automation is essential for optimising alumina yield while minimising operating costs. Temperature profiling along the digestion train enables process engineers to balance extraction efficiency against energy input. Digestion temperature also affects the degree of silica dissolution, influencing the formation of desilication products and the management of the sodium-aluminium-silicate scale within the digestion circuit.
