Calculation of the expected economic efficiency of aluminium production by increasing the use of domestic alumina

In this work, we aim to calculate gains in the economic efficiency of primary aluminium production (on the example of RUSAL Krasnoyarsk JSC) when increasing the use of alumina obtained from sintering nepheline raw materials at the Achinsk alumina plant. A series of experiments was conducted to determine the optimal conditions for cooling of nepheline cakes using a SNOL 6.7/1300 laboratory muffle furnace. An industrial sample of limestone-nepheline-soda mixture was used as a research object. In order to determine the phase composition of nepheline cakes, a DRON-6 diffractometer (Russia) was used. The sintering conditions of charges were as follows: the heating rate of the sample charge was 10.4ºC/min; exposure at the temperature of 1250 ºC was 15 minutes. It is determined that the effect of the cooling rate on the content of α'-modification in 2CaO.SiO2 cake is inverse. The analysis of phase data does not demonstrate any changes in the qualitative and quantitative composition of other phases (sodium aluminate, calcium ferrite, carnegieite) that make up the cake structure. This indicates that solid-phase 2CaO.SiO2 recrystallisation reactions develop exclusively under cooling. The obtained dependences of modification content variation upon cake cooling with different rates show that there is a characteristic change in the slope of the curve, which reflects the content of α'-, β-forms of 2CaO.SiO2 in cakes at the temperature of 1000ºС for all cooling rates. It was found that slow cooling (at the rate of no more than 15°C/min) of nepheline cake up to only 1000ºC is sufficient for the completion of 2CaO.SiO2 transition from α'- to β-modification. The results of the conducted technological leaching of the obtained cakes and the processing of experimental data of cake cooling (at 1250-1000 ºC) for the content of 2CaO.SiO2 α'-form in cakes demonstrate that a 1% decrease in this modification content provides a 0.2% increase in alumina extraction. The expected annual effect of reducing the production cost of 1 tonne of primary aluminium due to savings on purchase of imported alumina amounts to 55.83 million rubles.

alumina production, nepheline sintering, alumina extraction, economic efficiency, technological leaching, nepheline ores