低品位高硫铝土矿闪速焙烧脱硫与碱溶脱硅的调控机制

Determining the way and temperature of roasting is the key to realize efficient desulfurization and desilification with low-grade high-sulfur high-silicon bauxite. The project put forward using the technique of flash roasting desulfurization - alkali solution desilification, which make efficient desilification by alkali solution at low temperature come true and avoid the loss of aluminum by dissolving in the solution meanwhile. By study on interaction of multiple mineral and evolution of mineral phase structure in roasting process as well as non-isothermal interface/macrokinetics of sulphur mineral oxidation in heterogeneous mineral phase, quantitative relation between roasting temperature and crystalline degree of alumina in transfer form will be established, as well as the quantitative relation between roasting temperature and active silica. Reveal the generation mechanism of iron titanium hydrate garnet in alkali solution and build the thermodynamic and dynamic model of heterogeneous reaction by research the selectively solubilization of multiple mineral and laws of effect between liquid-solid phase in the process of alkali dissolution, dynamic behavior of silicon containing minerals at solid-liquid interface and dissolve-transfer mechanism, high temperature activation of silicon minerals and co-strengthening digestion desilification mechanism of mineralogical structure. Scientific and reasonable roasting scheme can be determined combine digestion results of aluminium concentrate by Bayer process and results of desilification by alkali solution.

低品位高硫高硅铝土矿实现高效脱硫脱硅的关键是焙烧方式与焙烧温度确定。项目提出采用“闪速悬浮焙烧脱硫-碱溶湿法脱硅”技术，实现低温碱溶高效脱硅的同时，避免铝转入溶液造成的损失。通过研究焙烧过程多元矿物相互作用及矿相结构演变，非均质矿相中硫矿物氧化的非等温介/宏观动力学，建立焙烧温度与过渡形态氧化铝结晶程度及活性氧化硅的量化关系；研究碱溶过程中多元矿物选择性溶解及液-固相之间的作用规律，含硅矿物在固液界面的动力学行为及界面的溶解—迁移机制，硅矿物的高温活化与矿相结构协同强化溶出脱硅机制，揭示碱液中铁钛水化石榴石的生成机理，建立多相反应热力学与动力学模型；结合碱溶脱硅与铝精矿拜耳溶出结果，确定科学合理的焙烧方案。

针对典型的高硫低品位铝土矿，采用“悬浮焙烧脱硫-碱溶脱硅-拜尔溶出”的方式，重点考查脱硫、矿石脱硅、溶液脱硅、溶出共性的指标，实现脱硅精矿品质提升、溶出性能明显提高的目的，并分析矿物演变规律、脱硅机制及溶出动力学，主要结论为（1）悬浮焙烧时间短，脱硫效果好。随着焙烧温度的增加，矿石中硫含量明显降低，1000℃焙烧时，S2-降低至0.01%，几乎完全脱除，结构疏松多孔；高岭石分解，硅、铁实现结构重排。（2）800℃、1000℃生成的硅酸铁分别为Fe2(Fe0.565Si0.435)O4、Fe2.45Si0.55O4，碱浸脱硅后硅酸亚铁消失，当温度高于1100℃，Al2O3发生钝化、SiO2晶体趋于完整，不利于溶出和脱硅。因此，焙烧温度不能高于1000℃。（3）悬浮焙烧后一水硬铝石、高岭石主要分解成Al2O3、SiO2及Al2O3·2SiO2，与NaOH反应活性为Al2O3·2SiO2 > SiO2> Al2O3。较佳条件为1000℃焙烧、L/S10、Nk110g/L、95℃、20min，SiO2脱除率为46.3%，Al2O3损仅2.4%，A/S均达到7.2以上。（4）含硅溶液的脱硅控制步骤为扩散控制，表观活化能为29.35 kJ / mol，脱硅动力学方程为1−2/3XB−(1−XB)2/3=15.80exp[−29350/(RT)]·t，形成的C-S-H和Ca4Si5AlO15(OH)2·5H2O在Ca(OH)2表面生成固体膜，阻碍SiO2(OH)22-的扩散。（5）焙烧矿和脱硅精矿的溶出表观活化能分别为48.89 kJ/mol和63.99 kJ/mol，在特定溶出条件下，氧化铝相对溶出率与温度分别满足如下关系：y=u(T)=-372.59+2.80053T-0.00406T2和y=u(T)=-563.42+4.32469T-0.00714T2。研究结果为该类矿石的应用奠定了坚实基础。