Sustainable Mining and Metallurgy

In the production of alumina by the Bayer process, after each cycle of the mother liquor, the caustic alkali is lost and the invalid alkali is increased, resulting in a decrease in the efficiency of evaporation and salt discharge, and an increase in energy consumption and alkali consumption. In order to recover the lost caustic alkali and reduce the invalid alkali, this paper took the domestic diaspore alumina production system with high carbon content as an example, and designed three process conditions: evaporation salt discharge causticization, evaporation salt discharge causticization+red mud dealkalization and recovery, evaporation salt discharge causticization+red mud dealkalization and recovery+first washing solution causticization. The flow direction of Na₂O in the production process was studied, and the loss, conversion and recovery of effective alkali in the system were calculated. From the technical and economic aspects, the characteristics of red mud alkali removal and causticization of primary lotion were analyzed and compared. The dealkalization of red mud can remove and recover the Na₂O in the sodium silicon slag of red mud and return it to the production system. The causticization of the first lotion can convert Na₂CO³ in the mother liquor into NaOH and reduce the carbon-alkali content of the system. Dealkalization of red mud and causticization of primary lotion can reduce the alkali consumption of alumina production and save production costs. Taking an alumina plant with a capacity of 100t/a as an example, the alkali consumption of production can be reduced by 66~70_kg/t by using red mud alkali removal and causticization of primary washing liquid, and the production cost of alumina can be saved by 85~134yuan/t.