【作者】 胡途；

【导师】 白晨光；

【作者基本信息】 重庆大学 ， 冶金工程， 2013， 博士

【摘要】 我国四川攀西地区蕴藏着丰富的钒钛磁铁矿资源，其中铁、钒、钛为主要价值元素，除此之外，还共生有铬、钴、镍、钪等具有战略意义的金属，综合利用价值极高。该矿产资源经过复杂的选矿处理获得钒钛磁铁精矿和钛精矿。钒钛磁铁精矿主要通过高炉-转炉工艺加以利用，其中约95%的铁和46%的钒得以提取利用，钛元素则全部进入到高炉渣，其中TiO₂含量达到22²5%。目前，还没有一种合适的方法能够利用含钛高炉渣，只能大量堆弃，造成资源浪费、环境污染等问题。为了实现铁、钒、钛等资源高效分离及综合利用，近年来转底炉煤基直接还原-电炉熔分流程逐渐发展成为了处理钒钛磁铁精矿的可选工艺。此工艺无须使用焦炭，且可以进行全钒钛磁铁精矿冶炼。但是，由于矿物结构复杂、还原温度高等特点，钒钛磁铁精矿还原速率较慢，目前转底炉采用薄料层操作，转底炉生产效率低下、产能小。厚料层操作是提高转底炉生产效率及产能的重要途径，对我国钒钛磁铁矿转底炉直接还原工艺的发展与规模扩大化具有重要意义。本文针对攀枝花钒钛磁铁精矿，采用等温还原和非等温还原等实验方法对钒钛磁铁精矿碳热还原行为及其动力学以及钒钛磁铁精矿含碳球团多层球还原过程及强化等方面展开了系统研究。采用非等温还原和等温还原实验方法对钒钛磁铁精矿碳热还原行为进行了研究，并研究了温度和还原时间对钒钛磁铁精矿含碳球团还原过程中物相转变过程的影响。结果表明：（1）在本实验所涉及的温度范围内（T≤1350℃），钒钛磁铁精矿碳热还原过程可以分为五个阶段。第一阶段（T＜670℃）：主要发生的是煤粉中挥发分的去除与Fe₃O₄的还原；第二阶段（670℃≤T＜785℃）和第三阶段（785℃≤T＜885℃）：发生的主要是钛磁铁矿、磁铁矿和氧化亚铁的还原；第四阶段（985℃≤T＜1190℃）：主要是钛铁矿的还原；第五阶段（1190℃≤T）：发生的主要是假板钛矿的还原，部分TiO₂也在这一过程被还原。（2）得到了钒钛磁铁精矿碳热还原过程中物相转变规律。还原温度为900℃时，金属化球团中主要物相为金属铁、钛铁矿（FeTiO₃）和钛磁铁矿（Fe₃-xTi_xO₄）；1000℃下还原后，出现了TiO₂；当还原温度为1200℃时，还原产物中出现了碳化铁（Fe3C）和亚铁假板钛矿（FeTi₂O₅）。1350℃下还原足够长时间后，出现了碳化钛。在本研究条件下，没有发现氧化亚铁（FeO）和钛铁晶石（Fe₂TiO₄）。在1350℃下等温还原过程中，钛磁铁矿的还原顺序为：Fe_2.75Ti_0.25O₄→Fe_2.5Ti_0.5O₄→Fe_2.25Ti_0.75O₄→钛铁矿（FeTiO₃）。（3）在1300℃下还原后，球团中Fe与Ti实现分离，球团表面出现金属铁颗粒，且随温度升高，金属颗粒尺寸增大。利用等转化率法对钒钛磁铁精矿碳热还原过程等温还原动力学和非等温还原动力学进行了分析，得出以下结论：（1）在1250℃¹350℃范围内，钒钛磁铁精矿含碳球团等温还原动力学随着还原度的增加分为三个阶段：R≤0.3时，总反应速率受相边界反应速率控制，表观活化能约为68KJ mol-1；0.3＜R≤0.75时，总反应速率受相边界反应和三维扩散混合控制，表观活化能从69.5KJ mol-1增大到133.3KJ mol-1；R＞0.75后，总反应速率受三维扩散控制，表观活化能约为134.3KJmol-1。（2）钒钛磁铁精矿非等温碳热还原过程中表观活化能随着反应分数的增加不断变化，可大致分为一下几个阶段：T＜885℃时，碳气化反应速率为速率控制步骤，表观活化能随着反应的进行逐渐增大；885℃≤T＜985℃，速率控制步骤逐渐向为氧化亚铁还原反应控制，表观活化能随着反应进行逐渐减低；985℃≤T＜1190℃，钛铁矿还原反应和反应气体的扩散逐渐转变为速率控制步骤，表观活化能随反应分数的增加逐渐增大。T＞1190℃后，反应临近结束，表观活化能逐渐降低。采用等温还原和非等温还原实验方法研究了硅铁对钒钛磁铁精矿碳热还原过程的影响及其作用机理，得到以下研究结论：（1）硅铁的加入能加快钒钛磁铁精矿碳热还原反应速率，部分硅铁中的硅取代碳作为还原剂参与还原；（2）在还原过程中，硅铁中的铁作为形核粒子，且硅热还原反应放出热量，促进了新生金属铁的形核与长大聚集。（3）得出了硅铁作用下钒钛磁铁精矿碳热还原反应机理，整个还原过程可以分为三个阶段。在第一阶段（T＜1000℃），碳直接还原和硅热还原等固相还原反应为主要反应。硅热还原反应放出的热量在一定程度上促进了碳热还原反应的进行；在第二阶段（1000℃≤T＜1150℃），碳气化反应速率非常快，还原反应以CO作为还原剂的气固还原反应为主，固相还原反应速率比起其反应速率显得微不足道，硅铁对钒钛磁铁精矿碳热还原过程影响甚微；在第三阶段（1150℃≤T），硅热还原反应再次剧烈进行，其放出的热量进一步促进了碳热还原反应的进行和新生金属铁的聚集长大。采用实验室转底炉模拟设备对钒钛磁铁精矿含碳球团单层球及多层球还原过程进行了研究。结果表明：还原温度对含碳球团还原过程影响很大，温度越高，球团还原速率越快，反应所需时间越短；对于多料层还原，表层球团还原速率比其下部料层球团还原速率快，不同料层球团还原速率不同步，且表层球团在还原后期容易被二次氧化，金属化率降低。因此，各个料层球团的金属化率无法同时达到一个较高的水平，从而料层整体的总金属化率低。利用三段式加热炉模拟转底炉加热制度，对钒钛磁铁精矿含碳球团三层球还原过程进行了研究，并采用非等径布料方法和硅铁强化方法促进三层球同步还原。结果表明：在本实验条件下，单独采用增大表层球团尺寸的非等径布料方法以促进三层球团同步还原的效果不明显；单独采用硅铁强化方法能有效地提高下部球团还原速率，实现三层球团同步还原，当中层添加1%硅铁，下层添加3%硅铁后，还原时间大约为27min时，三层球团同时达到了一个较高的金属化率，大约88%。通过非等径布料和硅铁强化共同作用，即上层球团为直径30mm、无硅铁添加剂的圆球，中下两层球团分别为添加了1%和3%硅铁的椭球，三层球团在还原大约35min后共同达到一个更高的金属化率，约92%。根据实际生产情况以及经济性来确定合理的金属化率以及还原时间，调整不同料层球团尺寸和硅铁添加量，通过二者协同作用可以实现多层球同步还原，最终实现转底炉厚料层操作。更多还原

【Abstract】 There are huge amount of vanadium-titanium magnetite in Panxi area, China,containing iron, vanadium and titanium as main valuable elements and with thecoexistence of other strategic metal elements, such as chromium, cobalt, nickel andscandium, which has high value for comprehensive utilization. When these ore arebeneficiated, vanadium-titanium magnetite concentrates and ilmenite concentrates areproduced. Conventionally, titanomagnetite concentrates are treated by blast furnace.Most of iron and partly of vanadium can be extracted, however, almost all of titaniumgo into the slag containing22²5%TiO₂. There is no an appropriate and economicmethod so far to deal with the slag to recovery the titanium components from it,resulting in some issues such as resource waste and enviroment pullution. In recentyears, most of the studies focus on developing an alternative route to use thetitanomagnetite concentrates. One potential choice is the rotary hearth furnace process,which involves the reduction step of composite briquette of titanomagnetiteconcentrates with noncoking coal and the smelting of the reduced sample in anelectric-arc furnace. This process has many features such as high temperature, coke freeand no other iron ores need to be added. However, the reduction rate ofvanadium-titanium magnetite concentrates is slow due to the complexity of mineralstructure and high reduction temperature. Moreover, the low bed height of agglomerates,about20²5mm, is prevailing in present RHF due to insufficient heat supply for a highbed height. These factors leading to the low productivity and low yeild for RHF process.It is a important way that increase the bed height to solve it. It is very significant toachieve the high bed height operation for the development and scale enlargement ofRHF process dealing with vanadium-titanium magnetite concentrates in China.The aim of present study is to achieve the reduction of multi-layer pellets madefrom vanadium-titanium magnetite concentrates and coal. The reduction behavior andkenitics of carbothermic reduction of vanadium-titanium magnetite concentrates andthat of multi-layer reduction were investigated by isothermal reduction andnon-isothermal reduction experimental methods.The carbothermic reduction behavior of vanadium-titanium magnetite concentrateswere investigated using isothermal reduction and non-isothermal reductionexperimental methods. The following conclusions are obtained: The carbothermal reduction behavior of vanadium-titanium magnetite concentratesand the effect of temperature and reduction time on the phase transformation duringreduction of vanadium-titanium magnetite concentrates were investigated bynon-isothermal reduction and isothermal reduction experimental methods. Followingconclusions are obtained:（1） Five stages were found in the carbothermic reduction ofvanadium-titanium magnetite concentrates briquette with coal. The devolatilization ofcoal occurred in the first stage, and reductions of iron oxides mainly in the second andthird stages. The reduction rate of iron oxide in the third stage was much higher thanthat in the second stage because of the high carbon gasification rate. The iron in theilmenite （FeTiO₃） was reduced in the fourth stage. In the final stage, TiO₂was partiallyreduced to lower valence oxides.（2） The phase transformation of the briquettes wasobtained. The main phases of sample reduced at900℃are metallic iron、ilmenite（FeTiO3） and titanomagnetite （Fe₃-xTi_xO₄）. The traces of rutile （TiO₂） were observed at1000℃. The iron carbide （Fe3C） and ferrous-pseudobrookite （FeTi2O5） appeared at1200℃. The titanium carbide was found in the sample reduced at1350℃. Wustite （FeO）and ulvospinel （Fe₂TiO₄） were not found in present study. The vanadium-titaniummagnetite concentrates was reduced to iron at1623K in argon along a stepwisesequence with Fe_2.75Ti_0.25O₄,Fe_2.5Ti_0.5O₄, Fe_2.25Ti_0.75O₄, ilmenite（FeTiO₃）, wustite（FeO）and ferrous-pseudobrookite （FeTi₂O₅） as intermediates.（3） Iron and titanium achievedseparation in the composite briquette reduced at1300℃. Nuggets were observedoutside of briquette reduced at1300℃and a higher temperature.The kenitics of carbothermic reduction of vanadium-titanium magnetiteconcentrates under isothermal and non-isothermal heating conditions were study bymodel-free isoconversional method. The following conclusions are obtained:（1）Forisothermal conditions, the reduction rate is controlled by phase boundary reaction for Rless than0.2with the apparent activation energy of about68KJ mol-1and bythree-dimensional diffusion for R greater than0.75with the apparent activation energyof about133.3KJ mol-1. For R in the range from0.2to0.75, the reaction rate is undermixed controlling and the apparent activation energy increases with increase inreduction degree.（2）For non-isothermal conditions, it is found that the activationenergy changes with the reaction fraction increasing. T＜885℃，the overall reducitonrate is controlled by carbon gasification reaction, the activation energy increasegradually.885℃≤T＜985℃, the rate controlling step turns to the reduction of wustite, the activation energy decrease gradually.985℃≤T＜1190℃, reduction of ilmenite anddiffusion become the rate controlling step, the activation energy increase again.The effect of Fe-Si on the carbothermic reduction of vanadium-titanium magnetiteconcentrates was investigated by isothermal and non-isothermal experiment,respectively. The conclusion can be summarized as follows:（1） The addition of Fe-Siaccelerates the carbothermic reduction rate of vanadium-titanium magnetiteconcentrates. A part of silicon in the Fe-Si substitutes for carbon to participate thereduction of vanadium-titanium magnetite concentrates.（2） The addition of Fe-Sifacilitates the nucleation and coalescence of metallic iron formed by reduction. Thegreater the ferrosilicon dosage, the larger the metallic iron particle.（3） A reactionmechanism for the carbothermic reduction of vanadium-titanium magnetite concentrateswith Fe-Si addition was proposed. In the first stage （lower than1000℃）, the solid phasereactions with carbon and silicon as reductants are dominant. The exdothermicreduction by silicon, to certain extent, promotes the reduction of vanadium-titaniummagnetite concentrates. In the second stage （1000¹150℃）, the rate of reduction byCO is much faster than that of reduction by silicon, resulting in little influence of Fe-Sion the reduction of vanadium-titanium magnetite concentrates. Fe-Si has little influenceon the reduction of vanadium-titanium magnetite concentrates. In the final stage（1150℃≤T）, the reduction by silicon markedly occurs again, which further facilitates thereduction of vanadium-titanium magnetite concentrates and the coalescence of metalliciron.The reduction of composite pellet of vanadium-titanium magnetite concentratesand coal with one layer and multi-layer were investigated in a heating furnace usingnature gas as fuel. It is found that the reduction of composite pellets depend ontemperature greatly. For the multi-layer reduction, the reduction rate of top layer isfaster than other layers. In the later stage of reduction, reoxidation of iron occurs in toplayer. The metallizaiton degree for each layer can not reach to a high valuesimultaneouslyThe triple layer reduction of composite pellets and the enhencement of that wereinvestigated in a three-zone heating furnace. It is found that there are little effect on thesynchronous triple layer reduction by increase the pellet size of top layer alone.Ferrosilicon addition can significantly promote the reduction of composite pellet inlower layer. Under present experimental conditions, the synchronous triple layerreduction can be achieved with a metallizaiton degree of about88%. By the synergistic effect of non-equidimension distribution and ferrosilicon enhancement, themetallization degree of each layer can reach to about92%simultaneously. For specifymetallization degree and reduction time made according to the actual industrialproduction condition, the operation with high bed hegiht for RHF can be achieved bynon-equidimension distribution and ferrosilicon enhancement.更多还原