低温下氢气还原氧化铁的动力学研究

 用热重分析法研究了低温下不同粒度氧化铁的氢还原动力学,得出在同一温度下,铁矿粉粒度从107.5 μm降到2.0 μm后,由于粉体的表面积大幅度增加,提高了粉气接触面积,从而使得化学反应的速度提高了8倍左右,还原反应的表观活化能从78.3 kJ/mol降低到36.9 kJ/mol;当反应速度相同时, 粒度6.5 μm的粉体的反应温度比107.5 μm的降低了80 ℃左右。同时,通过理论推导和实验结果表明,当反应扩散层厚度相同时,铁矿粉粒度越小,反应扩散层厚度越薄,其还原率越高。     

Influence of size of hematite powder on its deoxidation kinetics with H2 at low temperature

 The deoxidation kinetics of hematite ore with various particle sizes with hydrogen at low temperature and reduction mechanisms were studied using the thermogravimetric analysis. Under the same temperature, after particle size of powder becomes thinner from 107.5μm to 2μm, the surface area of powder and the contact area between powder and gas increase, which makes the deoxidation process of hematite accelerate about 8 times, and the apparent activation energy of deoxidation reaction drops to 36.9 kJ/mol from 78.3 kJ/mol because of activity of ore powder improved with refining gradually. Under the same reaction rate, the reaction temperature of 6.5μm powder decreases about 80℃ than that of 107.5μm powder. Thinner diffusion layer also helps accelerate the reaction with powder refining. The higher the temperature, the greater peak of deoxidation rate is; under the same temperature, the greater the particle size, the smaller the peak of deoxidation rate is; both inner diffuse and interface chemical reaction play an important role in the whole reaction process.     

氧化物杂质对铁氧化物还原动力学的影响

系统分析了氧化物杂质对铁氧化物还原动力学的影响及其机理。发现：各种杂 特点与杂质浓度、存在开矿和／或加入方法,样品的初始化学组成和物理性状,还原剂的种类、反应温度、还原分数等多种因素有关。     

微纳米氧化铁粉低温还原特性的研究

研究了低温还原微纳米氧化铁粉的还原特性与机理。用高能球磨法获得的微纳米氧化铁粉在280～400 ℃内用氢气还原,并测定还原后粉末中氧、计算氧化铁粉末的还原率,通过扫描电子显微镜来观察还原铁粉的形貌;找出了氧化铁粒度、还原温度和还原时间等参数对氧化铁还原率、铁粉粒度和粒度分布、铁粉形貌等的影响。从动力学的角度,探讨了粉末细化对低温氢气还原氧化铁活化能的影响。研究结果指出,微纳米氧化铁粉的还原反应遵循吸附自动催化理论,反应动力学遵循界面化学反应理论,研究获得了反应所对应的反应机制函数和相应的动力学方程。     

微纳米氧化铁粉低温还原特性的研究

研究了低温还原微纳米氧化铁粉的还原特性与机理。用高能球磨法获得的微纳米氧化铁粉在280～400 ℃内用氢气还原,并测定还原后粉末中氧、计算氧化铁粉末的还原率,通过扫描电子显微镜来观察还原铁粉的形貌;找出了氧化铁粒度、还原温度和还原时间等参数对氧化铁还原率、铁粉粒度和粒度分布、铁粉形貌等的影响。从动力学的角度,探讨了粉末细化对低温氢气还原氧化铁活化能的影响。研究结果指出,微纳米氧化铁粉的还原反应遵循吸附自动催化理论,反应动力学遵循界面化学反应理论,研究获得了反应所对应的反应机制函数和相应的动力学方程。     

氢气还原氧化铁动力学的非等温热重方法研究

 用非等温热重分析法对氢气还原不同粒度细微氧化铁的动力学进行了研究。研究表明：铁矿粉粒度越小,起始反应温度越低,反应速度越快,反应达到平台期时所对应的还原率越高;平均粒度为3.5 mm的铁矿粉在400 ℃还原反应开始,700 ℃左右开始反应加快,达到平台期时的还原率为77%,而平均粒度为2 μm的铁矿粉在100 ℃已经开始反应,350 ℃反应加快,达到平台期时的还原率为98%,而且在600 ℃时还原率就达到了100%;铁矿粉粒度从3.5 mm降到2 μm后,还原反应的表观活化能从73.3 kJ/mol降低到30.46 kJ/mol;同时通过分析氢气还原氧化铁的反应机理得出,内扩散和界面化学反应均对整个反应过程起限制作用。     

低温非平衡条件下氧化铁还原顺序研究

研究了低温条件下(＜570℃)CO和H2还原氧化铁的动力学机理.结果表明:实际还原过程属于非平衡态过程,它的还原机理与还原气体的成分相关.当还原气体中CO(或H2)的含量不能满足Fe3O4 CO(H2)→3FeO CO2(H2O)反应进行的要求时,氧化铁的还原顺序为Fe2O3→Fe3O4→Fe;如果还原气体成分满足此要求,Fe2O3→Fe3O4→Fe和Fe2O3→Fe3O4→FeO→Fe两种还原顺序将同时存在.     

Reduction Kinetics of Fine Iron Ore Powder in Mixtures of H2-N2 and H2-H2O-N2 of Fluidized Bed

Reduction kinetics of fine iron ore powder in different gas mixtures were investigated in high-temperature fluidized bed at a scale of kilograms.Influence of processing parameters,such as particle size,gas flow velocity,height of charge,temperature,compositions of gas mixture,and percentage of inert components,on reduction kinetics was experimentally determined under the condition of fluidization.The equations for calculating instantaneous and average oxidation rates were deduced.It was found that an increasing H2 O percentage in the gas mixture could obviously decrease the reduction rate because the equilibrium partial pressure of H2 decreased with increasing content of H2 O in the gas mixture and then the driving force of reduction reaction was reduced.When the H2 content was high,the apparent reaction rate was so rapid when the average size of iron ore fines was less than 1mm that the reaction temperature can be as low as 750 ℃;when the average size of iron ore fines was more than 1mm,a high reaction temperature of 800 ℃ was required.In addition,it was also found that the content of H2 O should be less than 10%for efficient reduction.     

白云鄂博铁矿球团富氢还原动力学研究

针对气固直接还原工艺中存在着气体利用率低和还原供热不足等问题,利用恒温热重分析(TG)法,研究了氢/碳比率对白云鄂博铁精矿还原速度的影响。结果表明,在还原试验开始后40 min内,还原速率随wH2/wCO比增加而增大,使得Fe2O3→Fe3O4反应时间缩短。基于气相内扩散和界面反应的球团还原速度方程均能较好地处理本研究的数据,得到了反应速度常数与wH2/wCO的关系为:k界面=-0.1975+0.3 575wH2/wCO,k扩散=0.171 01+0.269 7wH2/wCO。根据Arrhenius方程计算出界面反应和气相内扩散活化能分别为26 k J/mol和44 k J/mol,因此本研究条件下限制性环节为气体内扩散控制。     

低温下碳还原氧化铁的催化机理研究

通过碳的气化反应、气体还原氧化铁以及碳粉还原氧化铁试验,探明了氧化铁的催化还原机理.加入催化剂后,碳的气化反应速率和铁矿的还原速率提高,并表现出相似的变化规律,K2CO3和Na2CO3的催化效果明显优于CaCO3的催化效果.对于气化反应和氧化铁的还原反应,催化剂的加入等同提高了碳的活性,由于碳活性的提高,加速了碳的气化反应进行,促进了氧化铁还原中的间接还原反应和直接还原反应,最终加速了氧化铁的还原反应.     

硅铁配比对氧化镍矿低温金属化还原的影响

以三氧化二铁、氧化亚镍和硅酸镁为原料,依照云南代表性氧化镍矿原矿中铁、镍和硅质量比进行配矿,研究硅铁比对镍铁金属化以及镍铁合金聚合行为的影响。结果表明,当Fe/Ni=13/1,Si/Fe=1.2/1,煤粉加入理论量2倍,1 280℃反应60 min后,经磁选分离获得的精矿中镍、铁品位分别为4.95%、50.93%,镍、铁回收率分别为99.32%、80.12%。还原产物主要相为MgSiO_3和[Fe,Ni],镍铁合金聚集状态良好,精矿主要相为[Fe,Ni],仅有少量SiO_2残留,分离效果较好。云南代表性氧化镍矿原矿的验证试验取得了相似结果。     

Volume Changes of Iron Oxide Compacts under Isothermal Reduction Conditions

Compacts made from chemically grade Fe₂O₃ were fired at 1473K for 6 hrs. The fired compacts were isothermally reduced either by hydrogen or carbon monoxide at 1073–1373K. The O₂ weight‐loss resulting from the reduction process was continuously recorded as a function of time using TGA technique, whereas the volume change at different reduction conditions was measured by displacement method. Porosity measurements, microscopic examination and X‐ray diffraction analysis were used to characterize the fired and reduced products. The rate of reduction at both the initial and final stages was increased with temperature. The reduction mechanism deduced from the correlations between apparent activation energy values, structure of partially reduced compacts and application of gas‐solid reaction models revealed the reduction rate (dr/dt) at both the initial and final stages. At early stages, the reduction was controlled by a combined effect of gaseous diffusion and interfacial chemical reaction mechanism, while at the final stages the interfacial chemical reaction was the rate determining step. In H₂ reduction, maximum swelling (80%) was obtained at 1373K, which was attributed to the formation of metallic iron plates. In CO reduction, catastrophic swelling (255%) was obtained at 1198K due to the formation of metallic iron plates and whiskers.     

氧化物型杂质或添加剂对铁氧化物还原动力学的影响

系统地评估了铁氧化物还原动力学中氧化物型杂质或添加剂的影响,进行了必要的量化分析.其影响的特点与杂质含量,杂质存在形式和加入方法,样品的初始化学组成和物理性状,还原剂的种类,反应温度,还原分数等多种因素有关.     

A Kinetic Study on Carbothermic Reduction of Hematite with Graphite Employing Thermogravimetry and Quadruple Mass Spectrometry

The reduction of hematite–graphite pellet was investigated from a kinetic viewpoint in the temperature range of 1173–1473 K (900–1200°C). The experimental procedure included thermogravimetric analysis (TGA) for measuring the weight change of the pellet and quadruple mass spectrometry (QMS) for monitoring the compositional change of the product gases. By applying a uniform internal reduction model to the current system, the activation energies for the reduction of Fe₃O₄ to wustite and for that of wustite to Fe were evaluated to be 91.0 and 25.9 kJ mol^?1, respectively. Due to the product gas analyses by QMS, it was observed that the reduction rate of hematite–graphite pellet was accelerated up to the equilibrium concentration of CO determined by the carbon gasification curve. Changeover of reduction mechanism with increasing reduction degree was explained in terms of a schematic diagram based on the results obtained in the current study.     

二氧化锰低温分解动力学研究

采用热重分析仪在5种升温速率下对二氧化锰矿进行热重试验,研究预处理过程中二氧化锰的低温分解行为,并通过物相分析验证热重试验结果及反应推论,应用非模型等转化率法及Popscu法对两步反应动力学求解,得到各自的反应机理函数。结果表明,二氧化锰升温过程发生了两步反应,第一步反应产物为Mn2O3,反应机理为dα/dt=(3.96×109/β)(1-α)e-1.86×105/RT,为一级简单反应,符合Mample单行法则动力学机理特征;第二步产物为Mn3O4,反应机理为dα/dt=(3.28×1024/β)e-2.81×105/RT×(3/2)(1-α)[-ln(1-α)]1/3,符合Avarami-Erofeev方程动力学机理特征。两步反应的反应机理均为随机成核和随后生长。     

还原工艺对钴粉粒度的影响

对钴粉还原生产过程中，原料、还原温度、氢气流量及纯度、推舟速度和装舟量等因素对钴粉粒度的影响进行了试验研究，并总结了还原钴粉粒度的控制方法。     

Dephosphorization Kinetics of Hot Metal at Low Slag Basicity and Low Temperature under the Different Fe2O3 Addition Amounts

In this article, the influence of the Fe₂O₃ addition amount on the dephosphorization kinetics of hot metal at the low slag basicity (CaO/SiO₂) of about 1.6 and low temperature of 1623 K is investigated with laboratorial experiments and the kinetic model. Si and P contents in the hot metal during the whole dephosphorization process, and the endpoint FeO content in the slag, show good agreements between the calculated results with the kinetic model and experimental results. The peak value of dephosphorization rate linearly increases from 8.35 × 10⁻⁵ to 4.52 × 10⁻⁴ mass% s⁻¹ when the weight ratio of Fe₂O₃ is increased from 5 to 10/100 g hot metal. With the increase in Fe₂O₃ addition amount, the mass transfer coefficient in the hot metal phase (k_m) and that in the slag phase (k_s) and dephosphorization rate constant (k) all increase. The value of k_m is found to be 4.34 times that of k_s. During the dephosphorization process, the rate-controlling step converts from the mass transfer in slag phase to the mass transfer in hot metal phase in less than 10 min. With the increase in Fe₂O₃ addition amount, the value of interfacial oxygen activity of $a_{\mathrm{O}}^{*}$ increases from 0.0102 to 0.0201.     

Kinetics of hexavalent chromium reduction by grey cast iron powder

The kinetics of Cr (VI) reduction by grey cast iron powder (HT250 as per Chinese standard GBT 9439-2010) was investigated in this paper. Factors such as pH, initial Cr (VI) concentration, particle size, stirring speed and temperature on Cr (VI) reduction were first examined at a moderate reducing agent dosage. It was found that Cr (VI) reduction could only occur at an initial pH of 2.0 and above this value, the reaction nearly stopped. Additionally, the obvious dependence of Cr (VI) reducibility on other parameters was also revealed. The changes of pH, ORP and the concentration of Fe ions during the reaction were investigated. The correlations between the experimental data and reaction models involving homogeneous and heterogeneous reactions were studied. The results indicated first-order kinetics for the Cr (VI) reduction, which was a homogeneous reaction with an apparent activation energy of 20.718 kJ/mol. A semi-empirical equation was proposed to describe the kinetics of Cr (VI) reduction by HT250 powder. It was concluded that HT250 powder was a promising zero-valency iron (ZVI) material offering excellent reducibility and its use can be extended to the pre-treatment of wastewater containing other heavy metal ions such as Cu(II) and Pb(II).     

废旧锂电池正极材料低温碳还原熟化过程动力学研究

采用低温碳还原硫酸熟化工艺处理废弃锂离子电池正极材料,综合回收有价金属Ni、Co、Mn。考察了熟化反应温度、熟化时间和硫酸用量对金属回收率的影响。结果表明,在反应温度250℃、反应时间30min、硫酸和正极黑粉的用量比为0.97mL/g时,有价金属的回收率均超过了96%。进一步对硫酸熟化过程中金属氧化物转变为金属硫酸盐的过程进行动力学研究,确认了废弃锂离子电池正极材料中有价金属硫酸熟化过程的动力学模型为收缩核模型,反应表观活化能在固膜扩散控制的范围内,浓硫酸低温熟化过程受内扩散控制。