PDF《博士学位论文公示材料》

350 o C for

180 min with the molar ratio of sulphuric acid to bauxite 2.75:1, and the leaching conditions was

95 o C 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 temperature, pyrite was superior to diaspore in the sulphuric roasting process of high sulfur bauxite. 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 α-Al2O3 和α-Fe2O3 were obtained. Second, in order to reduce the environmental impact of flue 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. 94.0% of aluminum was extracted at roasting temperature of

375 o C for

210 min with the molar ratio of NH4HSO4 to bauxite 7:1, and the leaching conditions was

95 o C for

20 min with liquid-solid ratio 4:1. In the range of temperature, pyrite was superior to diaspore in the sulphuric roasting process of high sulfur bauxite. The sequence of product generation was of 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 using 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 decomposition temperature of sulfuric acid. It was further explained that the decomposition of sulfuric acid after

350 o C was the main reason for the decrease of aluminum leaching rate. The optimum roasting temperature of ammonium bisulfate system was

375 o C, 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 o C. 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 ―3― carried out. Green biodegradable biomass persimmon tannin after chemical modification was selected as the separation medium, which can be used as an adsorbent for selective adsorption of trace titanium. Selective adsorption for Ti (IV) was successfully realized from

220 mg・ L-1 Ti(IV)-780 mg・ L-1 Fe(III)-2440 mg・ L-1 Al(III) leaching solution at pH 1.45. The maximum uptake of Ti (IV) was found to be 34.82 mg・ g-1 , which had no adsorption capacity for Fe(III) and Al(III). The adsorption mechanism was that the N atom of the C=N group on the adsorbent is coordinated with Ti (IV), and cation exchange between H+ from hydroxyl group on the 2,3 position from 2,3,4-trihydroxybenzaldehyde occurs inferred by FT-IR, XPS and theoretical calculation of quantum chemistry. This study also offers the basic data for the practical application of the mesoporous silica adsorbents through recycling experiment. The adsorbent can realize selective recovery of Ti (IV) from leaching solution of high sulphur bauxite, which provides a new method and research idea for the removal of trace impurities from leaching solution. ―4― 论文主要创新点 1.以硫酸或硫酸氢铵作为高硫铝土矿的预焙烧助剂, 既降低了焙烧脱硫温度, 又避免用强酸或强碱浸出. 建立了硫酸和硫酸氢铵体系的最佳提铝工艺条件,硫酸体系铝的提取率为 83.8%,硫酸氢铵体系铝的 提取率可达到 94.0%. 2.从硫酸、硫酸铵、硫酸氢铵的基本性质和热分解规律入手,结合高硫铝土矿和三种助剂焙烧反应的热 力学计算,对比分析了三种体系提铝效率产生差异的主要原因,预测 (NH4)2S2O7 是影响焙烧过程的 关键性组分. 3.首次尝试用 HSC 热力学计算软件计算硫酸、硫酸铵、硫酸氢铵焙烧体系所发生的焙烧反应的Gθ, 据此来判断反应进行的难易程度和先后顺序,并通过 XRD 分析加以验证.分析结果为硫酸体系焙烧 反应的先后顺序为黄铁矿>