Technology and mechanism of desilication from roasted diasporic bauxite in atmosphere

The leaching desilication technology of roasted diasporic bauxite in atmosphere by caustic soda solution was investigated. The optimum parameters were: the grinding fineness of the roasted bauxite -0.076mm and 80%～85%, leaching time 2h, Na2Ok 100～150g/L, L/S 4～5, leaching temperature 90～95℃. The desilication rate 55.20% and concentrate A/S (mass ratio of Al2O3 to SiO2) 9.90, as good as those obtained at pressure, were obtained respectively. Investigation of two-stage leaching shows that it can both improve desilication rate of roasted ore and reduce leaching time. When time of the first stage and the second stage is 30min and 30min respectively, desilication rate can reach 59.65%. X-ray diffraction analysis of the concentrate has proved that desilication procedure is accompanied with the formation of sodium aluminosilicate hydrate. X-ray spectra also show that silica removed during leaching is amorphous silica. SiO2 occurring as quartz in raw ore or mullite formed during roasting can not dissolve in alkali solution.