【作者】 张健；

【导师】 彭志伟；

【作者基本信息】 中南大学 ， 钢铁冶金， 2024， 博士

【摘要】 富铬电镀污泥（CRES）具有湿度大、粒度细、含铬高的特点,是一种回收利用价值极高的危险固废。目前,以CRES为主要原料冶炼高铬生铁是其利用的重要方向。然而,该固废由于含水量高、粒度小,难以直接造块用于传统高炉炼铁,同时因含铬高、含铁低,用于煤基直接还原则存在还原温度高、产品质量差等问题。本研究利用CRES微波吸收能力强、气基还原效率高、还原焙砂熔炼渣金易分离等优点,开发了基于微波脱水-气基预还原的CRES低温还原熔炼（≤1600℃）高铬生铁新工艺,通过微波加热实现CRES快速深度脱水,进而协同铁矿粉气基预还原调控焙砂金属化进程,抑制高熔点难还原铬铁尖晶石形成,降低熔炼还原剂耗量,促进铬、铁深度还原和熔融,获得了高附加值的高铬生铁产品。主要结论和创新点如下:查明了CRES的主要物理化学特征。CERS包含36.85 wt.%Cr、4.64 wt.%Fe、2.03 wt.%S、0.24 wt.%Zn、0.22 wt.%Pb、0.08 wt.%P,含水率高达45.72 wt.%,中位粒径小于0.3 mm;主要物相为Cr（OH）₃和少量的Cr₂O₃、Cr O（OH）、Fe（OH）₂、Fe（OH）₃、Ca SO₄和Ca SO₃;主要含铬物相热稳定性差,分解温度低,在室温下可以自发进行,当温度升高到393℃时,含铬物相完全转化为Cr₂O₃。明确了CRES的微波脱水行为与机理。CRES含水高,常温介电损耗大,微波穿透深度小,仅为34.72 mm,证实其具有很强的吸波能力。水分比（干基含水率与干基初始含水率的比值）对其吸波性能影响最大,随着水分比下降,微波穿透深度逐渐变大,吸波性能下降,微波脱水效率降低。此外,微波脱水效率还受到微波功率、装料量、污泥粒度等因素的影响,但三者的影响依次减弱。微波脱水动力学分析表明,CRES脱水过程受不同限制性环节控制,依次为外扩散控制（110 s内）、外扩散和化学反应共同控制（110～160 s）、化学反应控制（160 s后）,呈现出水蒸气回流的升温脱水特征。揭示了CRES的CO-H₂预还原行为与机理。为提升预还原效果,同时满足后续铬铁熔炼造渣要求,将CRES干样（水分比为0）、铁矿粉和助熔剂混合,控制铬铁质量比（Cr/（Cr+Fe）质量比）为0.25,助熔剂Ca O、Si O₂、Al₂O₃和Mg O纯试剂的添加量分别为5.00 wt.%、2.68 wt.%、0.79 wt.%和0.84 wt.%,以CO和H₂作为还原气体。预还原结果表明,随着H₂浓度在20～50 vol.%的范围内增加,预还原焙砂铁金属化速率先上升后下降。铁矿石中的铁氧化物在预还原过程被逐步还原为磁铁矿（10 min内完成）,浮氏体（20 min内完成）和金属铁。CRES中大部分的含铁组分在预还原过程中与Cr₂O₃反应生成铬铁尖晶石,仅30%左右的铁转化为金属铁,大部分（83%以上）的铬转化为Cr₂O₃。在CO/H₂体积比为7:3、温度为750℃、气体流量为140 m L/min的优化条件下还原60 min,获得的预还原焙砂铁金属化率达到78.79%,满足低温还原熔炼高铬生铁对于焙砂的成分要求。构建了CRES焙砂低温还原熔炼高铬生铁技术原型。低温还原熔炼热力学研究表明,Cr₂O₃还原难度较大。适当提高碱度和温度能够促进其熔化。熔炼试验研究结果表明,预还原焙砂铁金属化率、熔炼温度、铬铁质量比、熔炼时间、还原剂种类和配比等因素均能影响高铬生铁熔炼效果。特别是随着焙砂铁金属化率从48.32%提高到88.02%,高铬生铁中的铬品位、铬和铁回收率先上升后下降;随着铬铁质量比从0.2升高到0.35,铬品位不断上升,铬回收率先上升后下降。在熔炼过程中脉石组分转变为黄长石和硅酸钙进入渣相,降低了渣相粘度,促进了渣金分离。在焙砂铁金属化率为78.79%、温度为1600℃、铬铁质量比为0.25、时间为120 min、焦粉配比为1.5（C/O摩尔比）、碱度（Ca O/Si O₂质量比）为1.2、Al₂O₃和Mg O含量分别为13 wt.%和8 wt.%的优化条件下,高铬生铁中铬和铁的品位分别为21.49 wt.%、69.49 wt.%,回收率分别为86.14%和92.93%,S、P、Zn和Pb元素的脱除率分别为74.87%、20.38%、95.07%和89.92%。除硫通过炉外脱硫处理后达到Ⅱ级标准外,高铬生铁中有害元素的含量达到了不锈钢冶炼的I级标准。铬铁渣中Cr（Ⅵ）的浸出毒性降低到0.004 ppm的超低水平。上述研究结果表明通过富铬电镀污泥低温还原熔炼可获得高质量的高铬生铁,同时实现冶炼固废解毒,为富铬电镀污泥综合利用提供了新途径。图108幅,表29个,参考文献132篇更多还原

【Abstract】 Chromium-rich electroplating sludge（CRES）is a hazardous solid waste with high recovery value,featured by its high humidity,fine particle size,and high chromium content.At present,using CRES as the main raw material for smelting high-chromium pig iron is an important direction for its treatment.However,due to its high moisture content and small particle size,it is difficult to directly agglomerate this solid waste for traditional blast furnace ironmaking.Meanwhile,due to its high chromium content and low iron content,there are problems such as high reduction temperature and poor product quality when used for coal-based direct reduction.In this thesis,by taking the advantages of strong microwave absorption capability of CRES,high gas-based reduction efficiency,and easy separation performance of smelting slag and iron,a new process for CRES low-temperature reduction smelting（within1600℃）to produce high-chromium pig iron based on microwave dehydration and gas-based prereduction was developed.Through microwave heating,CRES was rapidly and largely dehydrated.It was then synergically used with iron ore powder to regulate the metallization process of calcine during the gas-based prereduction stage,inhibiting the formation of high melting point refractory chromite spinel to reduce the consumption of reducing agent during smelting,eventually promoting reduction and melting of chromium and iron to obtain value-added high chromium pig iron product.The main conclusions and innovative points are as follows.The primary physicochemical characteristics of CRES were identified.CERS contained 36.85 wt.%Cr,4.64 wt.%Fe,2.03 wt.%S,0.24 wt.%Zn,0.22 wt.%Pb,0.08 wt.%P,with the moisture content of45.72 wt.%and mean particle size smaller than 0.3 mm.The main phase was Cr（OH）₃with small amounts of Cr₂O₃,Cr O（OH）,Fe（OH）₂,Fe（OH）₃,Ca SO₄,and Ca SO₃.The main chromium-containing phase had poor thermal stability and low decomposition temperature,which could spontaneously occur at room temperature.When the temperature rose to393℃,the chromium-containing phases were completely transformed into Cr₂O₃.The microwave dehydration behavior and mechanism of CRES were clarified.It was shown that CRES had high moisture content,large dielectric loss at room temperature,and small microwave penetration depth of only 34.72 mm,confirming its strong microwave absorption capability.The moisture ratio（ratio of moisture content to initial moisture content on the dry basis）had the greatest impact on its microwave absorption capability.As the moisture ratio decreased,the microwave penetration depth increased gradually.Consequently,the microwave absorption capability and microwave dehydration efficiency decreased.In addition,the microwave dehydration rate was also affected by factors such as microwave power,load mass and particle size,with the corresponding effects decreased in order.The kinetics analysis of microwave dehydration showed that the dehydration process of CRES was controlled by three different steps successively,namely external diffusion control（within 110 s）,external diffusion and chemical reaction common control（110–160 s）,and chemical reaction control（after 160 s）,exhibiting a temperature-rise dehydration characteristic of water vapor reflux.The CO-H₂prereduction behavior and mechanism of CRES were revealed.In order to improve the prereduction performance and to meet the requirements of subsequent smelting and slagging,dried CRES with a moisture ratio of 0,iron ore powder,and fluxes were mixed.The chromium-iron mass ratio（Cr/（Cr+Fe）mass ratio）was controlled to be0.25,and the additions of pure reagents Ca O,Si O₂,Al₂O₃,and Mg O were5.00 wt.%,2.68 wt.%,0.79 wt.%,and 0.84 wt.%,respectively,with CO and H₂as reducing gases.The prereduction results showed that as the concentration of H₂increased within the range 20–50 vol.%,the iron metallization rate of the prereduction product,namely calcine,increased firstly and then decreased.The iron oxides in iron ore powder were gradually reduced to magnetite（completed within 10 min）,wüstite（completed within 20 min）,and metallic iron during the prereduction process.Most of the iron-containing components in CRES reacted with Cr₂O₃during the prereduction process to form chromite spinel.Only about 30%of the iron was converted to metallic iron,and most（>83%）of the chromium was converted to Cr₂O₃.Under the optimized conditions of CO/H₂volume ratio of 7/3,temperature of 750℃,gas flow rate of 140m L/min,the iron metallization degree of the calcine reached 78.79%after reduction for 60 min,meeting the requirement of low-temperature reduction smelting to produce high-chromium pig iron.The technology prototype of preparation of high-chromium pig iron by low-temperature reduction smelting of CRES calcine has been constructed.The thermodynamic study of the low-temperature reduction smelting process indicated that the reduction of Cr₂O₃was relatively difficult.Properly increasing the basicity and temperature could promote its melting process.The research on smelting test showed that the factors such as iron metallization degree of calcine,smelting temperature,chromium-iron mass ratio,smelting time,and type and ratio of reducing agent could affect the preparation of high-chromium pig iron.In particular,as the iron metallization degree of calcine increased from48.32%to 88.02%,the chromium grade,chromium and iron recoveries in high-chromium pig iron increased firstly and then decreased.when the chromium-iron mass ratio increased from 0.2 to 0.35,the chromium grade increased continuously and the chromium recovery increased initially and then decreased.During the smelting process,the gangue components were transformed into feldspar and calcium silicate,which could reduce the viscosity of slag and promote the separation of slag and metal.Under the optimized conditions of iron metallization degree of calcine of 78.79%,smelting temperature of 1600℃,chromium-iron mass ratio of 0.25,smelting time of 120 min,coke powder ratio of 1.5（C/O molar ratio）,basicity（Ca O/Si O₂mass ratio）of 1.2,Al₂O₃of 13 wt.%and Mg O content of 8 wt.%,the grades of chromium and iron in high-chromium pig iron reached 21.49 wt.%and 69.49 wt.%,with the recoveries of 86.14%and 92.93%,respectively.The removal percentages of S,P,Zn,and Pb were 74.87%,20.38%,95.07%,and 89.92%,respectively.The content of harmful elements in high-chromium pig iron met the Level I standard for stainless steel smelting,except for S element that met the Level II standard after external desulfurization.The leaching toxicity of Cr（VI）in the chromium-iron slag reduced to an ultra-low level of 0.004 ppm.The above research results indicated that high value-added high-chromium pig iron could be obtained through low-temperature reduction smelting of CRES,with simultaneous detoxification of smelting solid waste,providing a new way for comprehensive utilization of CRES.更多还原