【作者】 李密；

【导师】 彭兵；

【作者基本信息】 中南大学 ， 冶金工程， 2013， 博士

【摘要】 硫化锌精矿中常伴生有一定含量的铁,因而在传统的“沸腾焙烧-浸出-电解”锌湿法炼锌工艺中不可避免的生成铁酸锌(ZnFe2O4),导致大量的锌以铁酸锌的形式赋存于锌浸出渣中,由于铁酸锌性质稳定,使得铁锌的分离困难。现有的铁锌分离工艺流程复杂、能耗高、污染大,严重制约了锌冶炼的可持续发展。因此,铁酸锌中铁锌的高效分离是实现锌清洁冶炼的关键。本研究拟在弱还原气氛下将锌焙砂中的铁酸锌选择性分解为氧化锌及四氧化三铁,依据二者理化性质的差异,采用弱酸浸出-磁选组合工艺实现铁锌的分离。通过基础实验研究,查明了铁酸锌在弱还原气氛下的分解机制,掌握了铁酸锌在还原过程中的物相转变规律,实现了对铁酸锌还原过程的物相调控。通过对实际锌焙砂还原焙烧及铁锌分离工艺的研究,探明了铁锌分离的过程特征,实现了铁锌的高效分离。研究获得如下创新性结论：通过铁酸锌CO还原过程的热力学计算,确定了铁酸锌选择性还原的优势区域,查明了铁酸锌在弱还原气氛下的分解机制。铁酸锌在CO气氛下分解为氧化锌及四氧化三铁的反应可自发进行。铁酸锌选择性分解的优势区域与还原温度及CO/(CO+CO2)有关,当还原温度从700℃上升至900℃时,标准状态下获得氧化锌与四氧化三铁优势区域的CO/(CO+CO2)范围由3.1%-38.5%变为1.7%-30.7%。铁酸锌在弱还原气氛下的分解是通过连续析出氧化锌来实现的,铁酸锌的初始分解温度与其所处的气氛有较大的关系,惰性气氛下铁酸锌的初始分解温度为1020℃左右,CO气氛下铁酸锌的初始分解温度降至约400℃。通过对铁酸锌还原过程的失重行为、物相组成以及微观形貌的研究,掌握了铁酸锌在还原过程中的物相转变历程。铁酸锌的分解是一个连续的过程,在还原反应的初始阶段,铁酸锌快速失氧转变为铁锌缺氧体(ZnFe2O4-σ),随着还原反应的进行,铁锌缺氧体进一步失氧并析出氧化锌,铁酸锌的正尖晶石结构逐渐向四氧化三铁的反尖晶石结构转化,形成铁酸锌与四氧化三铁的连续固溶体。当温度达到750℃后,还原过程中容易生成铁锌固溶体(Fe0.85-xZnxO)新相,导致还原产物中氧化锌含量的显著降低。通过对铁酸锌还原过程的物相调控,实现了铁酸锌选择性分解为氧化锌及四氧化三铁,并建立了铁酸锌还原的动力学模型。铁酸锌还原过程物相调控的关键在于抑制四氧化三铁和氧化锌的还原以及铁锌固溶体的生成。四氧化三铁的还原可通过控制CO/(CO+CO2)低于30%来抑制,氧化锌的还原和铁锌固溶体的生成可通过控制温度低于750℃来抑制。铁酸锌选择性分解为氧化锌及四氧化三铁的过程符合未反应收缩核模型,反应过程受化学反应控制,表观活化能为29.26kJ/molo铁酸锌晶体内部锌铁离子的长程迁移是导致铁酸锌分解速率较慢的主要原因,铁酸锌还原产物中氧化锌富集于表面。研究了锌焙砂选择性还原焙烧工艺,确定了适宜的还原焙烧工艺参数,探明了锌焙砂还原焙烧过程中的工艺矿物学变化特征,显著提高了还原焙砂中可溶性锌的含量。锌焙砂选择性还原的适宜工艺参数如下：CO浓度8%,CO/(CO+CO2)为20%,还原温度750℃,还原时间75min,此条件下还原焙砂中可溶性锌含量达到92.8%,未经过还原焙烧的锌焙砂中可溶性锌含量仅为79%。还原焙砂的主要物相组成为氧化锌、四氧化三铁、硫化锌、单质铅、硅酸锌以及少量未反应的铁酸锌。还原焙砂颗粒呈中空结构,氧化锌处于颗粒的最外层,包裹着硫化锌、四氧化三铁以及未反应的铁酸锌,四氧化三铁颗粒呈球形,与其它物相有明显的界限。还原焙砂中的硫主要以硫化锌的形式存在,是导致可溶性锌含量不高的主要原因。锌焙砂还原焙烧之后,其磁性显著增强,为磁选铁锌分离创造了基本条件。开展了还原焙砂的弱酸浸出-磁选组合工艺研究,确定了适宜的铁锌分离工艺流程,实现了铁锌的高效分离。还原焙砂直接磁选铁锌分离结果表明,还原焙砂中由于存在铁、锌物相的机械夹杂及化学包裹,难以达到铁锌分离的效果。采用弱酸浸出处理还原焙砂,其铁锌分离效果较好。适宜酸浸条件为：硫酸酸度90g/L,浸出温度30℃,液固比10：1,浸出时间2min,锌的浸出率达到92.1%,铁的浸出率控制在7%以下,浸出液中铁的浓度仅1.03g/L。浸出渣的主要物相为四氧化三铁、硫化锌、硫酸铅及硫化铅,硫化锌的存在是导致浸出渣锌含量偏高的主要原因。浸出渣经过一次磁选后,铁精矿的品位达到51.3%,铅、铟、银等有价金属均富集于尾矿中。图87幅,表13个,参考文献216篇。更多还原

【Abstract】 Formation of zinc ferrite (ZnFe2O4) is unavoidable in traditional zinc hydrometallurgical of "roast-leach-electrowin" process due to the presence of iron in zinc sulfide concentrate, which leads to the enrichment of zinc in leaching residue. It’s hard to separate zinc and iron because the stable of zinc ferrite. The existing technology for zinc and iron separation is characterized by complex process, high energy consumption and serious environmental pollution, which significantly hampered the sustainable development of zinc production. Thus, the efficient separation of zinc and iron from zinc ferrite is critical for cleaner zinc production. Decomposing zinc ferrite to zinc oxide and ferroferric oxide selectively under reduction atmosphere was proposed, and acid leaching and magnetic separation processes were carried out to separate zinc and iron from reduced zinc calcine according to their characteristic difference. The decomposition mechanism, phase transformation and phase composition during zinc ferrite reduction process were detected. Besides, selective reduction of zinc calcine was carried out and the process features was identified. The main conclusions obtained are as follows:The thermodynamic predominace area for selective reduction of zinc ferrite under CO atmosphere was determined after the thermodynamic calculation and study of the decomposition mechanism. Thermodynamics analysis results show that the decomposition of zinc ferrite to zinc oxide and ferroferric oxide occurred spontaneously. The predominace area of CO/(CO+CO2) reduced from3.1%-38.5%to1.7%-30.7%at equilibrium when temperature increased from700to900℃. Zinc ferrite decompostion was a continuous zinc oxide precipitation process. Atmosphere have a great impact on the initial decomposition temperature of zinc ferrite. The zinc ferrite begins to decompose at1020℃and400℃under inert atmosphere and reduction atmosphere, respectively.The phase transformation behavior of zinc ferrite was conformed according to the weight loss, change of phase composition and microstructure in reduction process. At the initial stage of the reduction process, the zinc ferrite transformed to oxygen-deficient zinc ferrite by fast lossing oxygen at the crystal surface. As the reaction proceeds, the oxygen-deficient zinc ferrite began to precipitate zinc oxide by further lossing oxygen. The normal spinel structure of zinc ferrite gradually converted to inverse spinel structure of ferroferric oxide, and the continuous solid solution between zinc ferrite and ferroferric oxide was formed. The formation of zinc iron solid solution at750℃lead to the decrease of zinc oxide content in reduced products.The zinc ferrite was selectively decomposed to zinc oxide and ferroferric oxide by control of reduction conditions and the kinetic model of zinc ferrite decomposition was established. The key points for selective decomposition of zinc ferrite is to restrain the over reduction of zinc oxide and ferroferric oxide and the formation of zinc iron solid solution. Reduction of ferroferric oxide was restrained by controlling the CO/(CO+CO2) below30%, and the reduction of zinc oxide and the formation of zinc iron solid solution were restrained by controlling temperature below750℃. The unreacted shrinking core model was used to study the reduction kinetics of zinc ferrite, and the results showed that decomposition of zinc ferrite to zinc oxide and ferroferric oxide is controlled by chemical reaction, and the apparent activation energy is29.26kJ/mol. The long-range migration of zinc and iron ions in zinc ferrite crystal during reduction process is the main cause that contributes to the lower decomposition rate, The zinc oxide in reduced zinc ferrite mainly enriches at the surface of the particles.The parameters for selective reduction of zinc calcine were optimized, and the mineralogical properties of zinc calcine in reduction process were studied. The soluable zinc content in roasted product reached92.8%after roasting zinc calcine at8%CO with20%CO/(CO+CO2) under750℃for75min. However, the soluable zinc content in unroasted zinc calcine is only79%. The roasted zinc calcine mainly contains zinc oxide, ferroferric oxide, zinc sulfide, lead, zinc silicate and few unreduced zinc ferrite. The roasted zinc calcine particles have hollow structure with zinc oxide exists in the outmost layer, while zinc sulfide, ferroferric oxide and unreacted zinc ferrite particles form a hollow skeleton. The ferroferric oxide particles have clear baundaries with other phases are basically spherical in shape. The sulfur exists in zinc sulfide contributes to the lower soluable zinc content in roasted zinc calcine. The magnetic properties of zinc calcine incresed significantly after reduction roasting, which provide the basic condition for magnetic separation.The routes of magnetic separation and acid leaching were proposed to separate zinc and iron on the basis of mineralogical properties of roasted zinc calcine. The study of direct magnetic separation of roasted zinc calcine indicates that the separation efficiency of zinc and iron were limited due to the phase inclusions in the form of chemical and physical states. The acid leaching showed better effect on the separation efficiency of zinc and iron. The appropriate conditions were determined after leaching roasted zinc calcine in90g/L H2SO4at30℃with L/S of10:1for2min. Under these conditions, the zinc leaching rate achieved92%, while iron leaching rate was below7%and the iron concentration in leaching solution was only1.03g/L. The study results of mineralogical properties of leaching residue show that the main phase composition of leaching residue were ferroferric oxide, zinc sulfide, lead sulfate and lead sulfide. The presence of zinc sulfide was the main cause that lead to the high content of zinc in leaching residue. An iron grade of51.3%have been obtained after leaching residue treated by magnetic separation, and the valuable metals such as lead、indium and silver were enriched in magnetic separation tailings. The figures, tables and references are87,13and216, respectively.更多还原