Basic Study On Aluminum Extraction By Activated Roasting From High Sulfur Bauxite

High sulfur bauxite has a large proportion of bauxite resources in China.Research on the development and utilization of high sulfur bauxite mainly has been focused on how to reduce the sulfur content in high sulfur bauxite.The main desulfurization methods are flotation desulfurization,roasting desulfurization,mineral separation desulfurization,biological desulfurization,electrolysis desulfurization,etc.However,there are various problems in the above desulphurization methods,such as high energy consumption,low aluminum extraction efficiency,and high cost,so it is difficult to realize industrialization.This paper focused on the comprehensive utilization of high sulfur bauxite resources.In view of the difficult leaching of diaspore bauxite,methods of pre-activation by sulfuric acid or ammonium bisulfate were proposed.The effects of two kinds of pre-roasting additives on aluminum extraction and roasting mechanism were studied in order to establish a new mild and high efficiency aluminum extraction process.At the same time,the removal of trace titanium in leaching solution was studied.The results of the study were followed as:First,the optimum conditions for H2SO4 roasting and leaching of high sulfur bauxite were explored.83.8%of aluminum was extracted at roasting temperature of 350? for 180 min with the molar ratio of sulphuric acid to bauxite 2.75:1,and the leaching conditions was 95? for 30 min with liquid-solid ratio 6:1.The thermodynamic laws of the roasting reaction for each phase were discussed by thermodynamic calculation with HSC software.In the range of examined temperature,pyrite reated preferentially with sulphuric acid compared with diaspore.The roasting kinetics experiment and the calculation of apparent activation energy were carried out,which showed that the roasting process was controlled by chemical reaction.The separation of aluminum and iron has been realized by coprecipitation and alkali dissolution.The corresponding products Al2O3 and ?-Fe2O3 were obtained.Second,in order to reduce the environmental impact of gas generated during sulphation roasting process,ammonium bisulfate was used as a pre-roasing additive,which was less acidic than sulfuric acid.The optimum conditions for NH4HSO4 roasting and leaching of high sulfur bauxite were set up.93%of aluminum was extracted at roasting temperature of 375? for 210 min with the molar ratio of NH4HSO4 to bauxite 7:1,and the leaching conditions was 90? for 20 min with liquid-solid ratio 4:1.In the range of examined temperature,pyrite reated preferentially with sulphuric acid compared with diaspore.The sequence of product generation was ferric sulfate,ammonium sulfate and ammonium ferric sulfate.The roasting and leaching kinetics experiments and the calculation of apparent activation energy were carried out,which showed that both of them were controlled by chemical reaction.The separation of aluminum and iron can be achieved by different decomposition temperatures of sulfate.Third,according to the basic properties and thermal decomposition rules of three pre-roasing additives and based on the thermodynamic calculation of roasting reaction of high sulfur bauxite with three kinds of additives,the main reasons for the difference of aluminum extraction efficiency were analyzed.The optimum roasting temperature of sulfuric acid system was close to the boiling point of sulfuric acid(337?).It was further explained that the volatilization of sulfuric acid after 350? was the main reason for the decrease of aluminum leaching rate.The optimum roasting temperature of ammonium bisulfate system was 375?,at which NH4HSO4 has been completely decomposed into(NH4)2S2O7.It is speculated that(NH4)2S2O7 played a key role and deserved further study.In addition,NH4HSO4 changes from solid phase to molten state at 150?.The roasting reaction was transformed from solid-solid system to solid-liquid system.The contact area of high sulphur bauxite and ammonium bisulfate and mass transfer rate between particles increased,which were beneficial to the roasting reaction.Fourth,there was trace titanium in the leaching solution,which affected the dissolution of aluminum and the purity of aluminum products,so the separation and removal of titanium from leaching solution were carried out.Green biodegradable biomass persimmon tannin after chemical modification was selected as the separation material,which can be used as an adsorbent for selective adsorption of trace titanium.Selective adsorption for Ti(?)was successfully realized from 220 mg·L-1 Ti(?)-780 mg·L-1 Fe(?)-2440 mg·L-1 Al(?)leaching solution at pH 1.45.The maximum uptake of Ti(?)was found to be 34.82 mg·g-1,which had no adsorption capacity for Fe(?)and Al(?).The adsorption mechanism was that the N atom of the C=N group on the adsorbent was coordinated with Ti(?),and cation exchange occurred between H+from 2,3 position hydroxyl group of 2,3,4-trihydroxybenzaldehyde and TiO2+,which were inferred by FT-IR,XPS and theoretical calculation of quantum chemistry.The adsorbent can realize selective recovery of Ti(?)from leaching solution of high sulphur bauxite,which provides a new method and research idea for the removal of trace impurities from leaching solution.