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二氧化钛（钛白）是性能最好的白色颜料，应用广泛且前景广阔。基于我国大量赋存的重大特色钒钛磁铁矿资源，本课题组提出钠化冶炼新工艺以实现高效清洁分离钛、钒和铁。新工艺提取钒和铁后，大量钛组分仍以钙钛矿形式赋存于钛渣中，现有钛白生产工艺难以实现该钛渣的高值化利用。而采用硫酸-盐酸混合酸体系在低温低酸度下即可高效溶解该钛渣并获得钛液，后经水解过程制备合格偏钛酸。其中水解反应是决定偏钛酸与钛白性能的关键控制步骤，目前尚无混酸体系钛液水解研究报道。因此，本论文对硫酸-盐酸混酸体系钛液水解过程进行重点研究，明晰混酸体系钛水解机理，并将其应用于含钙钛矿钛渣的处理过程中，为混酸体系进一步应用制备钛白产品奠定理论和实践基础。主要研究成果和创新如下：（1）对混酸体系钛液水解过程进行系统调控：（I）升高反应温度及钛液浓度可以提高水解率、减小偏钛酸团聚粒径和增大晶粒尺寸；水解温度的促进作用明显，当水解温度达到150~160 ºC时，水解率 ＞ 95%，且偏钛酸团聚粒径降至2 mm。（II）Cl- : SO42-摩尔比例对水解率影响较小，但对水解团聚粒径及其形貌影响明显。当Cl- : SO42- = 1:1时，水解粒径达到2 mm左右且呈均匀球型。当Cl- : SO42- > 2:1时，水解粒径大且团聚。（III）Al3+在水解温度较低时浓度过高抑制水解，Al3+的加入有利于促使偏钛酸形成片层结构，对晶粒尺寸影响较小。Na+对水解过程影响较小。（IV）当添加PEG 1000分散剂后，常压水解可提高水解率，有效避免偏钛酸粒子的团聚；当Cl-比例较低时，有助于降低偏钛酸团聚粒径并促使其呈均匀球型堆积。（2）对混酸体系钛液水解机理进行探讨。对比实验及理论计算得到的Raman图谱，确定硫酸-盐酸体系钛液中可能存在的钛络合物结构；利用阿伦尼乌兹公式及玻尔兹曼分布模型通过钛处于不同化学环境的粒子数量与能量之间的关系拟合得到水解参数与晶粒尺寸的关系式，进而实现对晶粒尺寸的预测；并根据混酸体系中钛络合物和偏钛酸的结构结合DFT计算，推测钛水解过程中间体微观结构-能量变化规律及相应的反应路径。（3）以水解调控和机理研究结果为基础，将硫酸-盐酸混酸体系应用到钠化冶炼得到的含钙钛矿钛渣处理中。对混酸分解钛渣过程的热力学和动力学进行系统研究，经过4次循环实验，浸出率均达80%；水热水解后，水解率均达90%，偏钛酸团聚粒径维持在2~3 µm，得到合格偏钛酸产品。将混酸新工艺与传统硫酸法工艺进行对比，发现混酸法是实现钛高效回收和酸循环利用的一种有效途径。（4）研究混酸体系偏钛酸盐处理及煅烧工艺对钛白产品性能的影响。结果表明，适当盐处理剂含量、提高煅烧温度以及延长保温时间，均有利于提高颜料性能。经过K2SO4和H3PO4盐处理剂处理后，在850~890 ºC不同升温参数调控下得到的最佳产品可接近市售AO101锐钛型TiO2的颜料性能。此外，水解时添加Al3+及Na+制备偏钛酸，在煅烧过程中对煅烧产物起到防止其烧结的作用。;Titanium dioxide (TiO2) is the best white pigment with widely applications and bright prospects in many industries. Among the rich titanium mineral resources existed in China, most of them are hosted in vanadium-titanium magnetite. Therefore, the novel metallurgical process using Sodium Oxide molten salt was proposed by our research group for comprehensive utilization of Ti, V and Fe from them. However, after extraction of Fe and V resources, large amount of Ti component was still remained in the titanium slag with perovskite structure (CaTiO3), leading to difficulties to realize high value utilization of this titanium slags. In order to decompose this perovskite titanium slags efficiently, therefore, a promising approache of Sulfuric-Chloric Mixture Acid (SCMA) method has been proposed for preparation of anatase-type metatitanic acid particles. This SCMA method mainly contained the decomposition of titanium slag by low concentration of mixture acid, followed by the thermal hydrolysis of low titanyl SCMA solutions. Among the process, the hydrolysis process played an important role to decide the properties and qualities of the TiO2 products. But the controlling of this hydrolysis process and corresponding mechanisms in this SCMA system should be future studied. Then, the SCMA method was applied to perovskite-containing titanium slag to realize the efficient reuse of titanium components and the recovery of waste acid. This laid a theoretical and practical foundation of the further application of the SCMA method to prepare titanium dioxide products. Therefore, the main contents and achievements of this paper were as follows:(1) The systematic regulations of the hydrolysis process of the SCMA titanium solution were investigated. (I) Increasing the reaction temperature and the concentration of titanium solution increased the hydrolysis ratio, reduced the agglomerated particle size and increased the grain size of metatitanic acid. Especially, the promoting effect of hydrolysis temperature was relatively obvious. When the hydrolysis temperature was up to 150~160 ºC, the hydrolysis rate was above 95% and the aggregated particle size of metatitanic acid reached about 2 µm. (II) The molar ratio of Cl- : SO42- had little effect on the hydrolysis rate, but a significant influence on the particle size and morphology of the metatitanic acid. When the molar ratio of Cl- : SO42- was 1:1, the hydrolyzed particle size was about 2 µm with the metatitanic acid in a uniform spherical shape. But when the molar ratio of Cl- : SO42- was more than 2:1, the hydrolyzed particle size was larger to 8 µm with agglomeration. (III) The Al3+ had a negative effect on the hydrolysis ratio at a lower hydrolysis temperature (130 ºC). But the Al3+ admixture was beneficial to promote the formation of lamellar structure of metatitanic acid, which had a slight influence on the grain size. The effect of Na+ was not obvious on the whole hydrolysis process. (IV) After PEG 1000 dispersant addition, the hydrolysis ratio under normal pressure increased and the distribution of metatitanic acid particles was facilitated. If the molar ratio of Cl- was low, the PEG addition also helped reducing the particle size of metatitanic acid with a uniform spherical distribution.(2) The titanium hydrolysis mechanisms of SCMA system were deduced. By comparing the Raman spectra obtained from experiments and theoretical calculations (DFT), the possible titanium cluster structures in the titanium SCMA solutions were determined. Besides, the Arrhenius formulas and the Boltzmann distribution models were used to fit the relationship between the hydrolysis parameters and the grain size, thus the grain size was predicted successfully. And based on the microstructure and the corresponding energy change of the intermediates, the hydrolysis mechanisms were speculated in this SCMA system.(3) Based on the hydrolysis results and the corresponding mechanisms, the SCMA method was furthermore introduced to decompose perovskite titanium slags to prepare qualified metatitanic acid. The thermodynamics and kinetics of the mixed acid decomposition of titanium slags were systematically studied. After 4 cycles of experiments, the leaching ratio could reach 80%. By thermal hydrolysis, the hydrolysis ratio reached 90% and the metatitanic acid showed a uniform particle size distribution with the size of 2~3 mm. Moreover, the method had good economic and environmental advantages compared with the traditional sulfate process. This SCMA method realized recycle of waste acid and reuse of titanium components, thereby achieving cleaner production.(4) The effects of doping and calcination of metatitanic acid on the properties of titanium dioxide pigments were studied. The results showed that the proper doping, the calcination temperature and the holding time were conducive to improving pigment performances. After treatment with K2SO4 and H3PO4, the best samples obtained under different temperature of 850~890 ºC could approach the pigment performance of AO101 TiO2 product on the market. Besides, the metatitanic acid hydrolyzed by the addition of Al3+ and Na+ were calcinated. The Al3+ and Na+ could prevent the calcined products from sintering during the calcination process.
|田铭. 硫酸-盐酸体系中钛液水解行为基础研究[D]. 中国科学院大学,2020.|
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