【作者】 姚金环；

【导师】 黎铉海；

【作者基本信息】 广西大学 ， 化学工艺， 2013， 博士

【摘要】 铟是一种典型的稀散金属,它具有十分独特的物化性能。铟大多数以含铁很高的锌精矿产出。锌精矿焙砂经中浸和酸浸两次浸出后,焙砂中的锌无法完全浸出,约有20%的锌残留于浸出渣中,而这部分锌主要以ZnFe2O4的形式存在,铟以替代阳离子的形式进入ZnFe2O4晶格中,由于铁酸锌很稳定,在通常情况下铟、锌很难被浸出。为了强化铟、锌的浸出,本文采用机械活化的方法对铟铁酸锌进行预处理,研究了从铟铁酸锌中用机械活化方法强化浸出铟、锌的机理。本文首先以人工合成的铟铁酸锌为研究对象,分别以滚筒磨和行星磨为活化设备,利用X射线衍射(XRD)分析、粒度分析、BET比表面积分析、傅立叶红外光谱(FT-IR)分析、穆斯堡尔谱分析和浸出实验研究了机械活化条件(磨筒转速、活化时间、介质填充率、球料比和介质种类)对铟铁酸锌物化性质和铟、锌浸出性的影响,在此基础上研究了滚筒磨活化和行星磨活化对铟铁酸锌中铟、锌浸出反应动力学的影响。研究表明,滚筒磨和行星磨活化均导致了铟铁酸锌颗粒细化,比表面积增加,晶格缺陷增加,晶格中部分Zn2+和Fe3+发生了转置,机械活化能有效地强化铟铁酸锌中铟、锌在硫酸体系中的浸出。以滚筒磨为活化设备时,由于存在临界转速,铟铁酸锌的物化性质和浸出性的改善随转速增加先越来越明显然后越来越不明显；活化时间对铟铁酸锌粒度的影响主要发生在最初的30min,延长活化时间铟铁酸锌的晶体结构破坏程度加大、浸出性增强；当介质填充率为30%～50%时,活化对铟铁酸锌物化性质和浸出性的改善基本一致,当介质填充率大于50%时,随着介质填充率的增大铟铁酸锌物化性质和浸出性的改善变差；球料比越大,铟铁酸锌物化性质变化越显著,铟、锌浸出率越高；磨球介质对铟铁酸锌物化性质和铟铁酸锌浸出行为影响程度大小顺序为氧化锆球>不锈钢球>刚玉球。以行星磨为活化设备时,行星磨转速越大、活化时间越长、介质填充率越少、球料比越大,铟铁酸锌物化性质的改善和浸出性的提高越显著；磨球介质种类对铟铁酸锌物化性质和浸出行为影响程度大小顺序为不锈钢球>氧化锆球>刚玉球。动力学研究发现,机械活化使铟铁酸锌的浸出过程对反应温度和硫酸浓度的依赖性降低。根据动力学数据确定的未活化、滚筒磨活化30min和行星磨活化15main的铟铁酸锌与硫酸反应时铟浸出反应的表观活化能分别为78.1kJ/mol、73.5kJ/mol和49.1kJ/mol,锌浸出反应的表观活化能分别为73.9kJ/mol、70.3kJ/mol和57.2kJ/mol;铟浸出反应的表观反应级数分别为0.82、0.69和0.57,锌浸出反应的表观反应级数分别从为0.72、0.70和0.61。实验确立的动力学模型能够较好地描述铟铁酸锌在硫酸溶液中的浸出过程。在上述研究的基础上,以行星磨活化15min的铟铁酸锌为研究对象,通过高温退火处理研究活化的铟铁酸锌的失活条件和失活机理。研究结果表明,活化的铟铁酸锌在不同温度下退火处理时有两次明显的失活现象。一是在450℃的条件下退火处理4h,此时活性的降低主要是颗粒发生团聚导致的,对比未活化、活化和退火处理样品的浸出数据可知,机械活化引起的颗粒细化并不是改善铟铁酸锌浸出的主要原因,颗粒细化的作用不足25%。二是在1000℃的条件下退火处理4h,此时活性的降低主要是晶格缺陷恢复引起的,但活化的铟铁酸锌仍无法达到完全失活。450℃退火处理样品的浸出反应动力学研究结果表明,行星磨活化引发的颗粒细化在改善铟铁酸锌浸出动力学方面具有一定的作用,但不及晶格破坏对其的影响程度大。机械活化使铁酸锌的晶格结构受到破坏,产生各种晶格缺陷。晶格缺陷对晶体材料的几何和电子结构都有较大的影响,因此会影响到材料的反应活性。为了进一步分析机械活化引起的晶格缺陷对铁酸锌微观结构和反应活性影响的本质原因,本文采用基于密度泛函理论(DFT)的第一性原理计算,研究了空位缺陷和锌铁转置缺陷对铁酸锌的几何结构和电子结构的影响。结果发现：铁酸锌是直接带隙的半导体；铁酸锌晶体中Zn-O键是由所谓的sp3杂化轨道互成109°28’的角度成键；铁酸锌具有高稳定性的原因是其四面体内部存在百分率较高的Zn-O配价键。锌空位和铁空位使铁酸锌的晶格常数变大,晶胞变形,氧空位和锌铁转置使铁酸锌的晶格常数变小,晶胞也发生变形。各种缺陷形成的难易程度为：锌铁转置缺陷最容易形成,其次是锌空位、铁空位,最难形成的是氧空位。空位缺陷和锌铁转置缺陷使铁酸锌由半导体属性变为金属属性。锌空位、铁空位、氧空位均使空位周围原子所带的电荷降低。锌空位和铁空位使其相邻的键的作用略微增强；氧空位使其相邻的Fe-O键的强度略微增强、Zn-O键的强度明显减弱。含锌铁转置缺陷的铁酸锌中与四面体(A)位铁原子相连的氧原子所带的电荷数降低,与其相连的Fe-O键的强度增强,键长变短；与八面体[B]位锌原子相连的氧原子所带的电荷数增加,与其相连的Zn-O键的强度减弱,键长变长。另外,本文分别对铟取代锌和铟取代铁的铁酸锌的几何结构和电子结构进行了理论计算。结果发现：铟取代导致铁酸锌晶胞膨胀变形；铟在铁酸锌晶胞中以取代锌的形式存在时具有更高的稳定性；铟取代锌的铁酸锌中,In-O键的强度与Zn-O键的强度接近,均表现出共价键性质,In原子周围Fe-O键的强度被削弱；铟取代铁的铁酸锌中,In-O键的强度低于Zn-O键和Fe-O键的强度,In原子周围Zn-O键的强度被削弱,Fe-O键的强度略微增强。本论文的研究工作可完善从铟铁酸锌中用机械活化方法强化浸出铟、锌的机理及动力学理论,为高效提取含铟铁酸锌的湿法炼锌渣中的铟、锌提供理论依据和设计模型,具有较高的学术价值和实际指导意义。更多还原

【Abstract】 Indium is a representative rare scattered metal with many unique physicochemical properties. Indium is produced mainly from zinc concentrate with the presence of iron. After zinc calcine is leached using neutral solution and acid solution, about20%of zinc remains in the leaching residue, and exists in the form of zinc ferrite (ZnFe2O4). The indium enters the crystal lattice of ZnFe2O4through substituting cation ion to form indium-bearing zinc ferrite. Because zinc ferrite is very stable, it is difficult to leach indium and zinc from zinc ferrite under normal conditions. In order to improve the leaching efficiency of indium and zinc, mechanical activation was used to pretreat indium-bearing zinc ferrite, and the mechanism of indium and zinc leaching from indium-bearing zinc ferrite enhanced by mechanical activation was studied.In this paper, the effect of mechanical activation conditions (rotation speed, activation time, media filling, ball to material ratio and species of media) on the physicochemical properties and leaching behavior of synthetic indium-bearing zinc ferrite activated by tumbling mill and planetary mill were studied by means of X-ray diffraction (XRD) analysis, particle size analysis, BET specific surface area analysis, scanning electron microscopy (SEM) analysis, Fourier transform infrared spectra (FT-IR) analysis, Mossbauer spectrometry analysis, and leaching tests. The results showed that mechanical activation by tumbing mill and planetary mill led to the decrease of particle size, the increase of specific surface area and lattice defect, and the inversion between Zn2+and Fe3+. Mechanical activation improved efficiently the leaching of indium-bearing zinc ferrite in sulfuric acid solutions.For indium-bearing zinc ferrite activated by tumbling mill, the improvement of physicochemical properties and leaching behavior became more obvious with the increase of rotation speed, then was not obvious due to the critical rotation speed. The effect of activation time on particle size mainly ocurred in the initial30min of tumbing mill activtion. Prolonging activation time, the damages of crystal structure aggravated and the leaching efficiencies were improved. When the media filling was30%-50%, the changes of physicochemical properties and leaching behavior were very similar. When the media filling was bigger than50%, the improvement of physicochemical properties and leaching behavior decreased with the increase of media filling. The improvement of physicochemical properties and leaching behavior became more significient with the increase of ball to material ratio. The effect of species of media on physicochemical properties and leaching behavior was determined as zirconium oxide> stainless steel> corundum.For indium-bearing zinc ferrite activated by planetary mill, the changes of physicochemical properties and leaching behavior became more notable with the increase of rotation speed, activation time and ball to material ratio, and the decrease of media filling. The effect of species of media on physicochemical properties and leaching behavior was determined as stainless steel> zirconium oxide> corundum.Kinetic study showed that mechanical activation decreased the dependency of leaching process of indium-bearing zinc ferrite on reaction temperature and H2SO4concentration. The apparent activation energies of indium leaching from the unmilled, activated for30min by tumbling mill and activated for15min by planetary mill indium-bearing zinc ferrite were determined as78.1kJ/mol,73.5kJ/mol and49.1kJ/mol, respectively; the apparent activation energies of zinc leaching were73.9kJ/mol,70.3kJ/mol and57.2kJ/mol, respectively. The apparent reaction orders of indium leaching were0.82,0.69and0.57, respectively; the apparent reaction orders of zinc leaching were0.72,0.70and0.61, respectively. The determined kinetics models can describe the leaching process of indium-bearing zinc ferrite well.Base on the above study, the deactivation conditions and deactivation mechanism of indium-bearing zinc ferrite activated for15min by planetary mill were investigated using the method of annealing treatment. The results showed that there were two obvious deactivation phenomenon when the activated sample was treated under different anealing temperatures. The fist one occurred in anealing treatment at450℃for4h. In this deactivation stage, the decrease of activity was mainly caused by particles agglomeration. Comparing the leaching data of annealed sample to those of unilled and activated samples, it can be concluded that the decrease of particle size was not the most important cause in the improvement of leaching process of indium-bearing zinc ferrite. The effect of the decrease of particle size was less than25%. The second one occurred in anealing treatment at1000℃for4h. In this stage, the decrease of activity was mainly caused by lattice defect restoration, but the activated indium-bearing zinc ferrite can not lose activity fully. The study on the leaching kinetics of the sampe treated by anealing at450℃showed that the decrease of particle size induced by planetary mill activation had a positive effect on the improvement of the leaching kinetics of indium-bearing zinc ferrite, but it was less than the effect of the damages of crystal structure. Mechanical activation led to the damages of crystal stucture and caused various lattice defects. However, lattice defects have an important effect on the geometric stucture and electronic structure of crystal materials so that it will affect the reaction activity. In order to analysis the essential effect of the lattice defects induced by mechanical activation on the microstructure and reaction activity of zinc ferrite, the effect of the vacancy defects and the inversion defect between Zn2+and Fe3+on the geometric stucture and electronic structure of zinc ferrite was investigated using the first principle calculation based on density function theory (DFT) in this study. The results showed that zinc ferrite was a semiconductor with direct band gap; the Zn-O bonds in ZnFe2O4had sp3covalent bond character with the Zn at the center and the agnle between any two Zn-O valencies was109°28’; the high chemical stability of ZnFe2O4could be attributed to the existence of high percent Zn-O covalent bonds. Both Zn-vacancy and Fe-vacancy increased the lattice parameters and caused lattice deformation; both O-vacancy and inversion defect decreased lattice parameters and also caused lattice deformation. The formation of different lattice defects had different difficult levels. Among them, the inversion defect was the easiest one to form, then Zn-vacancy, Fe-vacancy and O-vacancy. The vacancy defects and inversion defect changed the spinel zinc ferrite from semiconductor properties into metallic properties. Zn-vacancy, Fe-vacancy and O-vacancy decreased the charge of atoms around vacancy defect. Zn-vacancy and Fe-vacancy increased slightly the bond strength around vacancy defect, and O-vacancy increased slightly the strength of Fe-O bonds and decreased significantly the strength of Zn-O bonds around vacancy defect. For zinc ferrite with inversion defect, the charge of O atoms attated with Fe atom located at the tetrahedral (A) site decreased, the strength of Fe-O bonds increased and the bond lengths became short; the charge of O atoms attated with Zn atom located at the octahedral [B] site increased, the strength of Zn-O bonds decreased and the bond lengths became long. In addition, the results of theoretical calculation have confirmed that indium entered into the crystal lattice of zinc ferrite through substituting zinc ions for the industrial indium-bearing zinc ferrite due to the lower indium concentration.In addition, the geometric and electronic structures of In-substituting ZnFe2O4were also studied by first-priciples DFT calculations. The results showed that In substitution induced the increase of lattice parameters and slight deformation of lattice cell.In substituting Zn in the ZnFe2O4had high stability. For ZnFe2O4with In substituting Zn, the bond strengths of In-O and Zn-O were similar and showed covalent character. Moreover, the strength of Fe-O around In-atom decreased. For ZnFe2O4with In substituting Fe, the bond strength of In-O was lower than those of Zn-O and Fe-O. In addition, the bond strength of Zn-O around In-atom decreased and the bond strength of Fe-O around In-atom increased.This study can perfect the mechanism of enhancing leaching indium and zinc from indium-bearing zinc ferrite by mechanical activation and kinetics theory. It can provide theoretical basis and design model for the indium and zinc recovery from hydrometallurgical zinc residue contains indium-bearing zinc ferrite. It owns high academic value and practical guiding significance.更多还原