Study On Desilication Of Low Grade High Sulfur Roasted Bauxite

At present,Chinese aluminium industry is booming,but Chinese aluminium resources account for only about 3% of the world's aluminium resources,while its production capacity accounts for 25% of the world's production capacity.Most bauxite resources in China are diaspore,of which 42.8% are low grade bauxite with A/S less than 5.It has the characteristics of high sulfur,high silicon,medium-high iron and titanium.The mineral phase structure is complex,which is not conducive to direct Bayer leaching,making most of this kind of ore in a state of unexploited utilization.Therefore,this paper combines roasting desulfurization and alkali leaching desilication ideas to carry out research,improve ore A/S,and provide qualified raw materials for Bayer process.Based on the analysis of the chemical composition and phase structure of the ore,the effects of a series of important parameters on the desilication of roasted ore by alkali leaching were systematically studied by using suspension and muffle furnace roasting methods.The change rules of phase structure and micro-morphology were investigated,and the mechanism of desilication by alkali leaching was analyzed by combining kinetics.The main conclusions are as follows:The three primary mineral phases are basically identical,mainly consisting of diaspore,kaolinite,quartz,pyrite and anatase.Static roasting has a longer time and a better desulfurization effect than suspension roasting because the ore is heated up in the furnace.The optimum conditions for alkali leaching desilication of static roasted ore are roasting temperature 950?,desilication condition L/S=10,desilication time30 min,caustic soda concentration 110 g/L,desilication temperature 95?,desilication rate 68.99%,alumina loss rate 2.01%,concentrate A/S increased to 10.82.When the suspension calcination temperature is 930?,the desilication condition is L/S=8,the desilication time is 30 min,the caustic soda concentration is 110 g/L,the desilication rate is 49.24%,the alumina loss rate is 2.03%,and the concentrate A/S =8.21.Under the same conditions,the actual dissolution rate of static roasting desiliconization concentrate is 75.37%,while that of suspension roasting desiliconization concentrate is 80.53%.The phase structure analysis of roasted ore and desiliconized concentrate shows that there are more holes in static roasted ore at 900-950?,which makes it easier for ore particles to fully contact with alkali solution and has a higher desiliconization rate.Static roasting has higher crystallinity than suspension roasting,which makes the dissolution effect of suspension roasting desiliconization concentrate better than static roasting.Kinetic analysis of desilication process by alkali leaching: activation energy Ea=31.04KJ/mol for static roasting,Ea=244.20KJ/mol for suspension roasting,mixed control for static roasting and chemical reaction control for suspension roasting.With lime as desiliconizing agent,desiliconization of alkali liquor containing silicon is carried out,and the ratio of calcium to silicon has a great influence on the overall desiliconization cycle effect;with fixed ratio of calcium to silicon,the desiliconization rate is basically unchanged,and the A/S ratio of concentrate after desiliconization of roasted ore can reach more than 7,and the desiliconized alkali liquor can be recycled realistically.