Abstract: In order to obtain some strains of bacterium which may liberate silicate from bauxite with a high Si content, some strains of bacterium were isolated from materials such as garden soil, biological fertilizer and bauxite mineral using nitrogen media. The phenotype characteristics such as morphology, physiology and biochemical tests show that GSY—5^# bacteria belong to Bacillus sp because they are rod shaped and can produce oval endospore. The sizes of bacteria and endospore are (1-1.2)μm×(4-7)μm and (1.5-1.7)μm×(3-4)μm, respectively. The cultivating conditions of GSY—5^# on solid media and in liquid media were identified. The results show that GSY—5^# grows best within pH range of 7.3-8.4, and the optimum temperature for the growth is 30℃.The microorganism can fix nitrogen because it grows very well on solid nitrogen-free mineral media and show apparent capsule. It can produce a rich variety of exo-polysacchoride in liquid nitrogen-free media. In comparison of characteristics of GSY—5^# bacteria with those of mold strain of Bacillus mucilaginosus, GSY—5^# bacteria are a strain of Bacillus mucilaginosus. In this experiment five bauxite samples containing aluminosilicates as impurities were leached with silicate bacteria GSY—5^# at pH 7.2, 30℃, 200r/min, for 7 days, and the ratio of Al₂O₃ to SiO₂(A/S) in samples is increased from 4.58 to 5.88, from 6.74 to 8.45, from 6.03 to 8.55, from 5.09 to 6.79 and from 2.93 to 13.54, respectively. The leaching results indicate that leaching with silicate bacteria is useful in the improvement of low-grade high-SiO₂ bauxite.

Key words: silicate bacteria; bacillus mucilaginosus; screening; mold strain; phenotype characteristics; bauxite