Technology of desilication from diasporic bauxite by roasting-alkali leaching process(II)

The roasting process of the desilication from diasporic bauxite was studied on sintering cup simulating grate machine. It is shown that using grate machine as the roasting apparatus of bauxite is practicable. The optimum roasting parameters for grate machine are: size of ore 0～5 mm, coke (size 1 mm and coated on mixer surface) consumption 3.4%, ignition temperature 950 ℃, ignition time 1 min, thermal insulation at 800 ℃ for 2 min, water content 7.5%, negative pressure of ignition 3 kPa, negative pressure of roasting 7 kPa, dosage of F additive 0.6%. By alkali leaching, rate of desilication 43.45% and A/S of the concentrate 8.31, were obtained. By means of X ray diffraction analysis, the following conclusions can be made: only Si existing in kaolinite can be changed into noncrystalline SiO 2, during the digestion, this kind of SiO 2 is dissolved in NaOH solution, but α SiO 2 does not dissolve, so it is not contributive to desilication. The digestion of the concentrate by Bayer process also shows that the digestion ratio of Al 2O 3 of the concentrate is higher than that of the raw ore. [