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亚熔盐反应分离新过程的基础研究
其他题名Fundamental Research on the Reaction/separation Novel Process in Sub-molten Salt Media
金伟
学位类型博士
导师张懿
2012-05-22
学位授予单位中国科学院研究生院
学位专业化学工艺
关键词亚熔盐 活性氧 电化学方法 两性金属 Pitzer模型
摘要亚熔盐非常规介质液相氧化清洁集成技术可以在相对低温下实现难分解两性金属矿物的高效转化,资源能源利用率高,从源头上减少三废排放,是解决我国大宗难处理两性金属矿物的化学冶金新途径。针对亚熔盐工艺反应过程中热力学、动力学调控和多元复杂体系相分离设计这两个重要环节,以铬铁矿在亚熔盐中的反应分离新过程为切入点,采用电化学方法对亚熔盐非常规介质活化氧化两性金属矿物机理及过程调控机制展开了基础研究,揭示了活性氧的催化活化机理,获得了介质对活性氧组分赋存状态的调控规律,掌握了活性氧组分强化两性金属矿物分解的作用机制;建立了等压法测定渗透和活度系数的实验平台,完成了Na2CrO4-H2O 体系在80oC 下渗透和活度系数的等压法测定,并采用Pitzer 模型预测多元体系的相平衡,形成了多元复杂体系相平衡实验测定和理论计算集成的方法。研究成果为亚熔盐新化学冶金平台技术的发展提供了理论支撑。 论文取得以下创新性进展: (1) 证实了亚熔盐非常规介质为高活性氧负离子的理想载体,而大量赋存的氧负离子是介质化学场强化两性金属矿物分解的本质。通过电化学方法证明了高活性氧组分主要来源于OH-的分解和氧气的还原反应。对于非还原性两性金属矿物如铝土矿和铌钽矿,OH-分解产生的高活性O2-通过Lewis 酸碱反应,强化了矿物晶格结构的破坏,促进了矿物的分解;对于还原性两性金属矿物如铬铁矿和钒渣,氧气还原产生的高氧化性的O2-和O22-强化了低价两性金属氧化物的氧化,促进了矿物的氧化溶出。亚熔盐介质中不同种类活性氧负离子的协同作用可实现在相对低温下难分解两性金属矿物接近100%的高效清洁转化。 (2) 获得了不同种类氧负离子在亚熔盐介质中的赋存规律。研究表明,不同活性氧组分的赋存状态受控于介质的热力学及动力学环境,通过对介质的量化调控,可以获得不同氧负离子稳定存在的热力学优势区域,提高介质中OH-浓度,可为高活性的氧化性氧负离子如超氧离子O2-的稳定存在提供了理想的热力学环境;介质中存在的H2O 改善了体系流动和传质性能,增加了氧气的溶解度和扩散系数,在动力学强化活性氧组分的反应活性。亚熔盐介质优异反应活性的本质是通过量化调节介质的离子强度与传质,强化氧气的离子化过程,实现高效拟均相反应。 (3) 揭示了三价铬在碱性介质中的电化学氧化机制。研究表明CrO2-在碱介质中的电化学氧化行为受介质的离子强度和传质性质的调控,在低碱浓度下为电化学-歧化反应耦合过程,而高碱浓度下为直接电化学转化,反应更直接彻底,在热力学上更具优势;Cr2O3 在碱介质中呈现明显的电化学氧化行为,其反应过程受OH-浓度和温度的控制,提高OH-浓度可改善反应路径,强化反应热力学趋势,升高反应温度,可优化介质扩散传递性质,增加反应速率常数,加速反应过程。 (4) 掌握了介质对三价铬氧化反应热力学和动力学调控原则。研究表明,通过调控亚熔盐介质的物化性质,可以实现对三价铬化合物氧化过程热力学和动力学的调控。增加介质OH-浓度,可增加反应热力学趋势;而降低介质OH-浓度,可强化介质传质性能,加速反应动力学。因此,在给定反应温度下存在最佳的OH-浓度区间,可实现反应热力学和动力学的最优化。 (5) 证明了活性氧催化氧化三价铬化合物的作用,揭示了调控机理。研究结果表明氧气可以通过还原反应生成活性氧,高OH-浓度可以在热力学上促进高反应活性O2-的生成;活性氧O2-能间接氧化三价铬化合物,强化反应过程;通过量化调控介质的OH-离子强度和传质性质,可在热力学和动力学强化活性氧催化氧化两性金属矿物过程; (6) 建立了多元复杂体系相平衡实验测定与热力学计算结合的方法。采用等压法对Na2CrO4-H2O 在80oC 下的渗透和活度系数进行测定,并利用Pitzer 模型成功预测了Na2CrO4 在NaOH-H2O 中的溶解度,预测的结果满足了工业应用的需要,为亚熔盐分离过程的热力学设计提供理论支撑。
其他摘要The cleaner manufacturing process based upon sub-molten salt (SMS) liquid phaseoxidation technology can efficiently digest the referactory amphoteric mineral underrelatively mild condition. It provides a new strategy with high resource, engergy utilizationefficiency and low instrustrial waste discharge for treating the staple referactoryamphoteric mineral in China. In order to optimize the reaction kinetics andmulti-component separation in SMS technology, the novel reaction/separation process ofchromite extraction was investigated. The media-modulated formation of reactive oxygen species (ROS) in SMS media and its effect on transition metal oxidation were revealed.Besides, the osmotic and activity coeffcient of Na2CrO4-H2O system at 80oC weredetermined using self-designed isopiestic apparatus, and the data were correlated by Pitzermodel to sucessfully predict the solubility behavior in multi-component system. In this thesis, several achievements had been made to provide the fundamentalsupport for the SMS technology: (1) Sub-molten salt media was approved to be ideal carrier for the reactive oxygenspecies(ROS), which is the origin of chemical intensifying effect. The existence of ROS insub-molten salt media was confirmed using electrochemcial techniques, and it is mainlyconsists of O2- (from OH- decompostion), O2- and O22- (from oxygen reduction reaction(ORR)). The activation mechnism of ROS on mineral digestion was proposed, the O2-facilitated the non-reductive mineral decomposition, such as bauxite andNiobium-Tantalum ore, in oxygen-free SMS media via Lewis acid-base reaction, while theO2- and O22- significantly improve the oxidative dissolution of reductive mineral, such aschromite and vanadium slag, in oxygen-containing SMS meida. The synergistic interactionof various ROS is the origin of efficient conversion of referactory amphoteric mineral in sub-molten salt; (2) The media-modulated scheme on the ROS formation was obtained. The existenceof different ROS can be thermodynamically and kinetically modulated by the mediacondition. As the OH- concentration in electrolyte increases, the oxygen reduction reactionto highly active superoxide (O2-) was faciliteted; the H2O content can increase the oxygensolubility and diffusion coefficient in electrolyte by improving the mass transport, leading to the increasing ROS formation. In order to obtain the pseudo-homogeneous process withhigh reactivity, the ionic intensity and mass transport were adjusted to improve the O2ionization; (3) The media effect on the trivalent chromium oxidation in alkaline solution wasdiscovered. It is observed that the electro-oxidation of CrO2- was determined by the ionicintensity and mass tranport in electrolyte, there is a concentration-dependent mechanismtransition from electrochemical-disproportionation coupled reaction to directelectrochemical reaction. Similarly, in the oxidative dissolution of Cr2O3, the OH- canimprove mechanism, and the temperature can enhance the mass transport and rateconstant; (4) The thermodynamical and kinetic optimization scheme on the trivalent chromiumoxidation was obtained. The increasing OH- can thermodynamically facilitate the oxidation,whild the decreasing OH- can kinetically improve the oxdiation. Consequently, the properratio between OH- and H2O in alkaline meida can provide optimized electrolyte conditionfor trivalent Cr oxidation; (5) The electrolyte-dependent effect on the oxidation stress of reactive oxygen speciestoward trivalent chromium oxidation was investigated. It is observed oxygen couldindirectly oxidize the trivalent Cr via reactive oxygen species in-situ generated from ORR;the high OH- contration can thermodynamically facilitate the O2- formation, and the properamount of H2O could improve the mass tranport, kinetically increase the ROS formation. Asa result, the indirect oxidation on Cr(III) was improved (6) The combination of experimental measurement and theoretical calculation wasemployed to thermodynamically predict the solid-liquid equilibrium in multi-componentsub-molten salt system. The osmotic and activity coefficient for the Na2CrO4-H2O systemat 80oC were determined using self-constructed isopiestic apparatus, the experimental datawere correlated to predict the solubility of Na2CrO4 in NaOH-H2O and satisfied the requirement of industrial process, providing a new strategy for the optimization of separation process in sub-molten salt technology.
语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/1841
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金伟. 亚熔盐反应分离新过程的基础研究[D]. 中国科学院研究生院,2012.
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