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攀枝花钛铁矿氧化还原中的物相和形貌变化及其对盐酸浸出的影响机理
Alternative TitlePhase and microstructure changes of Panzhihua ilmenite during oxidation-reduction pretreatment and their influence mechanisms on the hydrochloric acid leaching
张溅波
Subtype博士
Thesis Advisor朱庆山
2014-02
Degree Grantor中国科学院研究生院
Degree Discipline化学工程
Keyword钛铁矿   人造金红石   氧化   还原   盐酸浸出
Abstract以钛铁矿为原料制备人造金红石是氯化法钛白生产的重要环节,而盐酸法是一种制备优质人造金红石的先进技术。探求合适的钛铁矿焙烧预处理方法以改善钛铁矿的物相组成、微观形貌结构,解决钛铁矿酸浸过程中存在的浸出速度慢、产品粉化率高等问题一直是盐酸法发展亟需解决的技术问题。前人的研究结果尚不能够全面地揭示钛铁矿焙烧过程物相和微观结构变化对盐酸浸出的影响规律,无法对焙烧-浸出工艺进行系统地优化。因此,本文对钛铁矿的氧化、还原焙烧过程物相和微观结构变化规律及其对后续酸浸过程的影响机理进行了系统研究。本文取得的创新性研究结果如下: (1)在600-1000 ℃温度范围内对攀枝花钛铁矿氧化焙烧过程的研究结果表明钛铁矿的氧化焙烧过程有两种不同的反应历程。当T<800 ℃时(中低温区域),钛铁矿仅发生氧化反应,主要生成Fe2O3和TiO2。反应初期,钛铁矿中二价铁的氧化是通过Fe离子的向外扩散实现,钛铁矿颗粒表面生成一层Fe2O3(另一产物为Fe2Ti3O9);但是当Fe2O3层厚度达到1-2 μm时,O离子的向内扩散替代了Fe离子扩散来实现剩余二价铁的氧化,颗粒内部生成相互混杂的Fe2O3和针状TiO2晶体;氧化产物在焙烧过程中不断生长长大,最终TiO2晶体形成包裹着Fe2O3晶体的网络结构。当T≥800 ℃时(高温区域),钛铁矿先经历相同的氧化反应,颗粒内部生成包裹Fe2O3晶体的TiO2网络。但是由于热力学不稳定,Fe2O3和TiO2逐渐发生化合反应生成Fe2TiO5,Fe2TiO5变成主相,残留Fe2O3和TiO2分别以点状或岛状形态分散在Fe2TiO5主相中。在这两个温度区域内,温度仅影响反应和晶体生成的速率。 (2)对两种典型的热力学稳定(氧化温度:T<800 ℃和T≥800 ℃)预氧化矿在600-800 ℃温度范围内弱还原焙烧过程的研究结果表明预氧化矿的弱还原焙烧有两种相互竞争的反应路径。当还原温度高时(如750和800 ℃),预氧化生成的TiO2参与还原反应而被消耗。在T<800 ℃和T≥800 ℃下分别预氧化的钛铁矿都被还原成FeTiO3。只不过前者得到的是网络状多孔FeTiO3;而后者得到的是被微孔分散的微米级FeTiO3晶粒。当还原温度较低时(如600 ℃),TiO2不参与反应。在T<800 ℃预氧化钛铁矿的Fe2O3被还原为金属Fe,TiO2网络保留完好;而在T≥800 ℃预氧化钛铁矿的Fe2TiO5被还原为FeTiO3,颗粒内部的少量岛状TiO2晶体也保存下来。 (3)对预氧化、氧化-高温弱还原对盐酸浸出影响机制的研究结果表明钛铁矿浸出速率受矿物结构和物相组成的共同影响。为了研究物相对浸出速率的影响,对分析纯的FeTiO3、Fe2O3和Fe2TiO5的盐酸浸出动力学进行研究。结果表明它们在盐酸中的浸出速率大小为:Fe2O3 > FeTiO3>> Fe2TiO5,文献中常用来解释氧化预处理影响的“三价铁化合物在盐酸的浸出速率要比二价铁化合物高”的结论是不正确的。预氧化(600-1000 ℃-4 h)预处理不能破坏钛铁矿的致密结构,它对浸出速率的影响主要是由物相转变导致的:600-700 ℃弱氧化因易溶Fe2O3的生成会小幅度提高浸出速率;而900-1000 ℃强氧化因难溶Fe2TiO5相的生成会严重限制反应活性。但是,氧化-高温弱还原(750 ℃-0.5 h)预处理使钛铁矿变为多孔的FeTiO3,能够显著提升浸出反应活性。攀枝花钛铁矿直接浸出的产品是通过Ti溶解-水解异相成核沉积而来,它们的抗机械力差,在搅拌等外力下会发生严重物理粉化。焙烧预处理在钛铁矿颗粒内部生成的TiO2晶体对抑制浸出产品的粉化发挥关键作用。T≤800 ℃氧化预处理生成网络状的TiO2,能够维持颗粒粒径,有效抑制产品粉化。但是氧化-高温弱还原预处理只能生成少量TiO2晶体,预处理后钛铁矿的浸出产品也是通过溶解-水解而来,它们能在不带搅拌的浸出过程中基本维持初始粒径,但是在有搅拌的浸出过程中会发生严重粉化。 (4)中低温氧化-低温弱还原和氧化-高温弱还原-弱氧化焙烧预处理新工艺,即能破坏钛铁矿的致密结构,显著提高矿物反应活性;又能使颗粒内部生产TiO2网络,能极大抑制产品粉化。 (5)弱氧化-盐酸浸出和中低温氧化-低温弱还原-盐酸浸出工艺可以以攀枝花钛铁矿为原料,制备微米和亚微米级大孔(金红石型)TiO2材料。TiO2晶体和孔洞尺寸随着氧化温度和焙烧时间的增大而增大。
Other AbstractUpgrading ilmenite to obtain synthetic rutile is a key step of chlorination process to produce titanium dioxide. Hydrochloric acid leaching is a preponderant process to produce high quality synthetic rutile. Ascertaining appropriate roasting pretreatments to alter the phase compositions and microstructure of ilmenite and solve the problems that occur during the leaching process, e.g. low leaching rate and serious pulverization of leaching product, has been a necessitated problem for the development of hydrochloric acid leaching process. Based on the research findings of predecessors, we cannot fully understand the effects of phase and the microstructure changes during roasting pretreatments on the hydrochloric acid leaching or systematically optimize the roasting-leaching process. Therefore, this paper systematically studied the phase and microstructure changes during the oxidation and reduction roasting and their influence mechanisms on the following leaching process. The main obtained innovative conclusions are described as following: (1) The results of study on the oxidation roasting process for Panzhihua ilmenite at 600-1000 ℃ show that there are two different reaction paths for the oxidation process of ilmenite. At temperatures below 800 ℃(low and moderate temperature ranges), only oxidation reaction of ilmenite happens and the main products are Fe2O3 and TiO2. In the initial stage, ferrous irons of ilmenite are oxidized through the out-diffusion of Fe cations. A Fe2O3 layer is therefore formed on the particle surface (another product is Fe2Ti3O9). However, when the thickness of Fe2O3 layer grows to 1-2 μm, the in-diffusion of O anions replaces the Fe diffusion to lead to the oxidation of residual ferrous irons. Needlelike TiO2 grains intermingled with Fe2O3 grains are therefore formed inside of particle. The oxidation products constantly form and grow during the roasting process. Finally TiO2 grains become conterminous and form a network structure intermingle with Fe2O3 grains. While when the temperature is increased to 800 ℃ or greater (high temperature range), ilmenite undergoes the same oxidation reaction first and a TiO2 network is formed inside of particle. However, due to thermodynamic instability, Fe2O3 and TiO2 combine with each other to form Fe2TiO5, which becomes the main phase finally. Residual TiO2 and Fe2O3 grains disperse in the Fe2TiO5 matrix with island and spot shapes respectively. At the two temperature ranges, oxidation temperature only affects rates of reaction and crystal growth. (2) The results of study on the weak reduction roasting process at 600-800 ℃ for two typical thermodynamic stable (oxidation temperatures: T<800 ℃ and T≥800 ℃) pre-oxidized ilmenites show that the weak reduction roasting of pre-oxidized ilmenite has two competitive reaction paths. At high reduction temperatures e.g. 750 and 800 ℃, TiO2 grains formed by the pre-oxidation take part in reduction reactions and are consumed. Ilmenites pre-oxidized at T <800 ℃ and T≥800 ℃ are both reduced to FeTiO3. The former obtains FeTiO3 with network structure, while the latter obtains micron sized FeTiO3 grains scattered by micro-pores. At low reduction temperature, e.g. 600 ℃, TiO2 grains do not participate in the reduction reactions. For ilmenite pre-oxidized at T<800 ℃, Fe2O3 is reduced to metallic iron; and the TiO2 network is reserved well; while for ilmenite pre-oxidized at T≥800 ℃, Fe2TiO5 is reduced independently to FeTiO3, and a little island-like TiO2 grains inside of particle are also reserved. (3) The results of investigation on influence mechanisms for pre-oxidation and oxidation-high temperature weak reduction on the leaching process show that the leaching rate is controlled by both the phase and the microstructure of ilmenite. Leaching kinetics of pure FeTiO3、Fe2O3 and Fe2TiO5 has been characterized to clarify the phase effect on the rate of iron leaching and it is found that the rate of iron leaching is in the orde
Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/15523
Collection研究所(批量导入)
Recommended Citation
GB/T 7714
张溅波. 攀枝花钛铁矿氧化还原中的物相和形貌变化及其对盐酸浸出的影响机理[D]. 中国科学院研究生院,2014.
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