DIGESTION OF DIASPORIC BAUXITE WITH MASS RATIO OF Al_2O_3/SiO_2 NO GREATER THAN 7 BY BAYER PROCESS WITH AN EXCESSIVE ADDITION OF LIME

摘要

It is usually believed that digestion of the diasporic bauxite with mass ratio of Al_2O_3/SiO_2 no greater than 7, which constitutes over 70 percent of China proved bauxite reserves, by adopting ordinary Bayer Process, is uneconomically viable because of consumption of higher caustic soda. At higher digestion temperature simultaneously with a more addition of inexpensive lime than in ordinary Bayer Process, the bauxite can be economically digested through Bayer Process. Leaching rate of alumina from the bauxites can reach over 85% after 60 minutes of digestion at 280℃, with Na_2O_k( 220g/l of sodium aluminate liquor and with lime addition of over 16%wt. of bauxite. The content of Na_2O in the produced red mud is under 2.5%wt. The XRD analysis results of the red mud indicate that an excessive addition of lime causes big changes of constituents of red mud. The improved Bayer Process is of significance for exploitation of China bauxite.