Digestion technology of Guizhou diasporic bauxite with low and medium grades by lime Bayer process

The digestion experiments of lime Bayer process using diasporic bauxite from Guizhou Province with low and medium grades(alumina-silica ratio is 5.48) were completed. The influences of lime amount, proportioning molar ratio, spent liquor's caustic soda mass concentration, digestion temperature and digestion time on the digestion process were investigated systematically. The results show that alumina-sillicon ratio and sodium-sillicon ratio of red mud decrease obviously with increasing lime amount. Increase of lime charge will effectively reduce soda consumption. The suitable conditions for digestion of lime Bayer process is as follows: lime amount is 10% to bauxite, proportioning molar ratio is 1.45, spent liquor's caustic soda mass concentration is controlled to about 200 g/L, digestion temperature is about 270 ℃and digestion time is of 50 min. When adopting the above conditions in the digestion process, αk of digested solution reaches less than 1.40, alumina-silica ratio of red mud is below 1.20, sodium-silica ratio of red mud is smaller than 0.38 and relative extraction yield of alumina is above 95%.