It is well known that as the content of iron in the bauxite decreases its concentration in the liquor increases and, as a consequence, its content in alumina increases. It is believed that this soluble iron in the liquor could be due to the presence of Algoethite and its transformation of hematite during the digestion process. In order to minimize the content of iron in the liquor (DBO), the digestion process was carried out with two bauxite samples with recycles of red mud, fine and coarse part (sand), at different percentages to reach the Fe_2O_3 grade from 10 to 15% at the process feed. The bauxite and red mud mixtures were digested at 145°C, during 60 minutes, with caustic soda concentration at 280g Na_2CO_3/L and initial an A/C of 0.38 and the final A/C reached the value of 0.74. The results demonstrated that fine red mud added to the bauxite did not contribute to a decrease in the iron content of the liquor, instead, the iron content increased. However, the coarse part of red mud, called sand, decreased the iron in the liquor from 0.027g/L to less than 0.004/L.
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