【作者】 王强；

【导师】 黄小卫； 薛向欣；

【作者基本信息】 东北大学 ， 冶金工程， 2024， 博士

【摘要】 稀土是重要战略资源,所以发展其冶炼分离技术格外关键。目前,稀土分离一般采用P507作为萃取剂,对混合氯化稀土料液进行萃取分离。但是,在萃取分离工序会产生氨氮废水和高盐废水。这些废水处理难度大且循环利用率低,因此,亟待开发稀土冶炼废水绿色处理技术。为进一步推动稀土行业的绿色发展,中国有研集团研发团队以物料循环为出发点,提出稀土萃取分离氯化镁溶液喷雾热解-酸碱循环利用新工艺。本文对该新工艺的关键工序开展研究,包括对高浓度氯化镁溶液除杂机制,氯化镁喷雾热解动力学机制和产物氧化镁活性影响机制、辅助强化热解作用机制以及产物应用开展基础理论研究。为该新工艺的工业化应用提供基础数据和理论支撑。本论文主要研究内容及结论如下:1、确定了氯化镁溶液深度除杂的工艺和参数,阐明了除杂机理。萃取分离工序产生的氯化镁溶液含铝离子、钙离子、镧离子和痕量P507杂质。此时通过添加液碱调节溶液pH,使铝离子原位沉淀可吸附除杂。研究结果表明,在pH值2～4时,P507会形成Alx(OH)yz+-P507有机配合物;在pH值4～5时,铝离子沉淀为具有较多表面活性位点的蓬松絮状非晶氢氧化铝,使得P507吸附去除效果较好;但是因沉淀物的比表面积较小,镧离子吸附量极少,此时其去除率较低。在pH值6～6.5时,铝离子和镁离子形成层状晶体氢氧化铝和镁铝层状氢氧化物,表面活性位点较少,使得P507吸附去除效果变差;然而此时沉淀物的比表面积较大,镧离子可以进入沉淀物的内部孔道被吸附,此时其去除率显著增加。调节溶液pH值为4.5～6.5之间,铝离子浓度大于300 mg/L时,氯化镁溶液中的P507、铝离子、镧离子的去除率分别可达94%以上、100%和95%以上。此外,在此条件下,溶液中的镁离子保留率在99%以上,可达到深度除杂的目的。2、构建了氯化镁喷雾热解的平衡常数、反应热、平衡组分、气体分压、热力学产量和优势区图理论计算体系,为热解实验的工艺研究和喷雾热解炉的设计具有较大的指导意义。热力学研究表明热解温度和炉内气体分压对氯化镁的热解具有影响,热解实验需要重点关注温度、氯化镁料液浓度和氮气流速三个主要影响因素。氯化镁喷雾热解的吉布斯自由能变、平衡常数、反应热以及优势区图的研究表明,当热解温度超过700℃时,氯化镁热解正向反应速率急剧增加;为了防止逆反应的发生,热解产生的粉体和气体通路需要分开。平衡组分、气体分压、热力学产量和优势区图的研究表明,炉内气体分压会影响氯化镁热解率和分解温度,热解炉内气压增大,氯化镁的热分解率降低,为使得热解反应顺利进行,需要将气体产物及时排出。3、阐明了氯化镁喷雾热解动力学机理、工艺参数和热解产物的基础应用。氯化镁喷雾热解的实验结果表明,在热解温度900℃、氯化镁料液浓度300g/L、氮气流量40L/min时,氯化镁的热分解率达到99.54%,粉体碱度达到0.0447mol/g,碘吸收值达到102.72 mg I2/g MgO,同时,还得到了浓度为6.70mol/L的高纯盐酸。喷雾热解的动力学研究表明,在600～800℃,氯化镁喷雾热解的表观活化能Ea为53.55kJ/mol,喷雾热解受化学反应控制;在800～900℃和900～1000℃,氯化镁喷雾热解的表观活化能Ea分别为9.57 kJ/mol和1.16 kJ/mol,喷雾热解受扩散过程控制。喷雾热解获得高活性氧化镁粉体,可以与酸性较弱的P507萃取剂反应完全,皂化后分相快速,无三相物出现,可达到粉体回收利用的工艺指标。喷雾热解所得的高纯盐酸,可用于反萃。因此,喷雾热解制备的高活性氧化镁和高纯盐酸满足使用需求,可循环用于稀土萃取分离工序,实现氯化镁全循环利用。4、揭示了喷雾热解所得氧化镁粉体产物的活性影响机制。喷雾热解可制备比表面积介于16～50 m2/g,疏松多孔的粉体颗粒,但是上述两点不是影响粉体活性的主要因素。影响粉体活性的主要因素是缺陷,喷雾热解的速度快、时间短,导致氯根未完全脱除。氯根的存在导致氧化镁晶粒在生长过程中出现严重的晶格畸变,产生较多的活性吸附位点;同时,粉体中残留的碱式氯化镁为多晶,缺陷也较多,活性吸附位点较多。因此,喷雾热解粉体产物的缺陷较多,活性较高。5、阐明了氯化镁喷雾热解的强化作用机制。在使用双氧水强化热解时,双氧水或其分解产生的氧气具有强氧化性,其参与反应后,改变了喷雾热解过程中部分化学反应的进程,起到脱氯作用,促进氯化镁的分解,从而降低热解温度。温场强化的作用机理是高温增加氯化镁液滴的传质与传热速率,提高氯化镁的热解反应速率,强化氯化镁热解。使用双氧水可以起到强化氯化镁热解的效果,在得到的粉体碱度相似的情况下,热解温度可以降低约100℃。但是添加双氧水会导致氯气的生成,从而减小氯根的回收率。为避免氯气的产生,使用二流体喷枪深入炉内进行温场强化热解,可以提高热解效率,在得到的粉体碱度相似的情况下,热解温度可以降低约100℃,且不会影响氯根的回收,为工业生产提供技术指导。更多还原

【Abstract】 Rare earths are important strategic resources,therefore,the development of their smelting and separation technology is particularly critical.Currently,in industry,P507 is generally used as the extractant to extract and separate the mixed chloride rare earth solution.High salt wastewater,such as ammonia nitrogen and sodium chloride wastewater,would be generated in the rare earth extraction and separation process.These wastewaters are difficult to treat and have a low recycling rate,so there is an urgent need to develop green treatment technologies for rare earth smelting wastewater.In order to further promote the green development of the rare earth industry,the research and development team of China GRINM taking the material circulation as the starting point,proposed a new process of rare earth extraction and separation of MgCl2 solution spray pyrolysis acid-alkali recycling.In this paper,the key processes of the new process are studied,including the impurity removal mechanism of high concentration MgCl2 solution,the kinetic mechanism of MgCl2 spray pyrolysis and the effect mechanism of MgO activity,the enhancement mechanism of H2O2 additive and the basic theoretical research of product application.Provide basic data and theoretical support for the industrial application of this new process.The main research contents and conclusions of this thesis are as follows:1.The process and parameters for the deep impurities removal from MgCl2 solution are determined,and the impurities removal mechanism has been elucidated.The aluminum ions,calcium ions,lanthanum ions,and trace amounts of P507 impurities are contained in MgCl2 solution in rare earth extraction and separation process.The pH of the solution is adjusted by adding liquid alkali to enable aluminum ions in-situ precipitation which can be removed impurities by adsorption.The results indicate that P507 forms Alx(OH)yz+-P507 organic complexes at pH 2 to 4.At pH 4 to 5,aluminum ions precipitate into fluffy and flocculent amorphous aluminum hydroxide with more surface active sites,resulting in better adsorption and removal efficiency of P507.However,due to the small specific surface area of the precipitate,the adsorption amount of lanthanum ions is small,resulting in lower removal rate low at this time.At pH 6 to 6.5,aluminum ions and magnesium ions form layered crystal aluminum hydroxide and magnesium aluminum layered hydroxide,with fewer surface active sites,resulting in poor adsorption and removal efficiency of P507.However,the specific surface area of the precipitate is relatively large,and lanthanum ions can enter the internal pores of the precipitate for adsorption,resulting in a significant increase in its removal rate.When the pH value of the solution is adjusted between 4.5 and 6.5,and the concentration of aluminum ions is greater than 300 mg/L,the removal rates of P507,aluminum ions,and lanthanum ions in magnesium chloride solution can reach over 94%,100%,and 95%,respectively.Meanwhile,the retention rate of magnesium ions in the solution is above 99%,which can achieve the goal of deep impurities removal.2.The theoretical calculation system of equilibrium constant,reaction heat,equilibrium components,gas partial pressure,thermodynamic yield and dominant zone diagram of spray pyrolysis of magnesium chloride is constructed,which has a good guiding significance for the development of pyrolysis experiments and the design of spray pyrolysis furnace.Thermodynamic research indicates that the pyrolysis temperature and partial pressure of gas in the furnace can affect the pyrolysis process of magnesium chloride.The experiment needs to focus on three main influencing factors:temperature,concentration of magnesium chloride solution,and nitrogen flow rate.The Gibbs free energy change,equilibrium constant,heat of reaction,and dominant zone diagram of spray pyrolysis of magnesium chloride indicate that the positive direction of the pyrolysis reaction will be sharply promoted at temperatures greater than 700℃.In order to prevent the occurrence of the reverse reaction,the powder and the gas pathway produced by pyrolysis need to be separated.The study of equilibrium components,gas partial pressure,thermodynamic yield and dominant zone diagram suggest that the gas partial pressure in the furnace affects the decomposition rate and temperature of magnesium chloride;the higher the gas pressure in the furnace,the lower the decomposition rate of magnesium chloride.Therefore,to ensure the normal progress of pyrolysis reaction,gas products need to be discharged in time.3.The kinetic and process parameters of spray pyrolysis of magnesium chloride are elucidated.The results of spray pyrolysis of magnesium chloride show that at a temperature of 900℃,magnesium chloride concentration of 300 g/L and N2 flow rate of 40 L/min,the thermal decomposition rate of magnesium chloride reach 99.54%,the alkalinity of the powder reached 0.0447 mol/g,and the iodine absorption value reached 102.72 mg I2/g MgO.Meanwhile,the superior pure hydrochloric acid with a concentration of 6.70 mol/L was obtained.The kinetic study on the spray pyrolysis of magnesium chloride show that the apparent activation energy Ea of magnesium chloride spray pyrolysis is 53.55 kJ/mol at 600 to 800℃,and the ratedetermining step is chemical reaction.At 800 to 900℃ and 900 to 1000℃,the apparent activation energies Ea of magnesium chloride spray pyrolysis are 9.57 kJ/mol and 1.16 kJ/mol respectively,and the rate-determining step is diffusion process.The highly active magnesium oxide powder obtained by spray pyrolysis can completely react with P507 with weak acidity.After saponification,the phase separation is fast,and there is no three-phase substance,which can reach the process index of powder recycling.The high-purity hydrochloric acid obtained from spray pyrolysis can be used for stripping.Therefore,the highly active magnesium oxide and high-purity hydrochloric acid prepared by spray pyrolysis can meet the demand for recycling in the rare earth extraction and separation process to realize the full recycling of magnesium chloride.4.The mechanism of affecting activity of magnesium oxide powder obtained by spray pyrolysis is revealed.Spray pyrolysis can produce loose and porous powder particles with specific surface area between 16 to 50 m2/g,but the above two points are not the main factors affecting the activity of the powder.The main factor affecting the activity of the powder is the defect.The spray pyrolysis is fast and short,resulting in incomplete removal of chloride.The presence of chloride ions leads to severe lattice distortion in the growth process of magnesium oxide grains,resulting in more active adsorption sites.At the same time,the residual basic magnesium chloride in the powder is polycrystalline,with many defects and active adsorption sites.Therefore,the defect density of magnesium oxide powder is higher,causing higher activity.5.The mechanism of the reinforcement of spray pyrolysis of magnesium chloride,the process parameters of the spray pyrolysis of magnesium chloride,and the kinetic of spray pyrolysis are revealed.When using hydrogen peroxide to enhance pyrolysis,H2O2 or O2 produced by its own decomposition change the course of some chemical reactions in the spray pyrolysis process.Its oxidizing properties act as a dechlorinating agent,which promotes the decomposition of magnesium chloride,thus reducing the pyrolysis temperature and energy consumption.The mechanism of temperature field enhancement is to increase the mass and heat transfer rate of magnesium chloride droplets,increase the pyrolysis reaction rate of magnesium chloride,and enhance the pyrolysis of magnesium chloride.The use of hydrogen peroxide can enhance the pyrolysis of magnesium chloride.When the obtained powder has similar alkalinity,the pyrolysis temperature can be reduced by about 100℃.However,while strengthening with hydrogen peroxide,it also produces chlorine gas,reducing the concentration of hydrochloric acid.Therefore,it is necessary to strictly control the amount of hydrogen peroxide added.To avoid the generation of chlorine gas,a two fluid spray gun is used to conduct temperature field enhanced pyrolysis deep into the furnace,which can improve pyrolysis efficiency.When the obtained powder has similar alkalinity,the pyrolysis temperature can be reduced by about 100℃ without affecting the recovery of chloride ions,providing technical guidance for industrial production.更多还原