【作者】 何显达；

【导师】 叶红齐； 许开华；

【作者基本信息】 中南大学 ， 化学工艺， 2012， 博士

【摘要】 沉淀工艺在粉体制备、分离提纯等工业过程中应用广泛。围绕着沉淀工艺中优化操作参数、提升产品质量的要求,本文针对沉淀过程中的反应组分关联,提出了一种局部平衡模型。该模型认为：沉淀反应过程由液相反应和固相生成反应两个步骤组成,其中液相反应是快速步骤,液相反应体系处于局部平衡状态,可用离子平衡热力学描述。选择不同类型的沉淀体系,系统地考察了局部平衡模型的建模方法、预测性能和实际应用。对于M+-P-和M+-P--H+(M+指金属离子,P-指沉淀剂,H+指氢离子)两种类型的理想沉淀体系,考察了依据其反应机理所提出的局部平衡模型的预测性能。参照严格的动力学计算结果发现,局部平衡模型对反应组分浓度预测结果的准确性,受到反应速率常数和沉淀率的影响,随着液相反应速率常数的增大,局部平衡模型的准确性提高。对这两类沉淀体系,当液相反应速率常数为固相生成反应的100倍,沉淀率大于0.6%时,预测结果的偏差均小于1%。为了进一步考察局部平衡模型预测结果的准确性,选择两个便于检测的实际沉淀体系,进行了实验验证。对于Co(Ⅱ)-H2C204-K2C204体系,将pH和沉淀率引入局部平衡模型,建立了pH和沉淀率的关联。结果表明,模型预测结果与实验结果基本吻合。研究同时发现,将模型转化为半经验公式,或者进行Davies活度校正后,其预测的准确度可以得到提高。对于Ba(Ac)2-H2C204-HAc体系,将pH、Ba总浓度[Ba]T和电导率K同时引入局部平衡模型,模拟了pH-[Ba]T、 K-[Ba]T和pH-κ三种关系。结果表明,模型预测与实验结果吻合良好。在此基础上,选择五个实际沉淀体系,考察了局部平衡模型在粉体制备、分离提纯和过程在线监测三个方面的具体应用。首先,针对NiCl2-H2C204-K2C2O4单金属沉淀体系和Ni(Ⅱ)-Co(Ⅱ)-C2042--H2O双金属共沉淀体系,考察了局部平衡模型在粉体制备中的具体应用。为了获得粒度均匀、形貌一致的沉淀粉体,同时保证较高的金属回收率,通常要求沉淀过程的pH稳定、过饱和度适中、终点沉淀率高。针对这些工艺参数要求,通过所构建的局部平衡模型,模拟了沉淀过程原料溶液的组成、配比、操作方式和加料方式等工艺条件对pH值、过饱和度和沉淀率的影响,找到了满足粉体性能要求的沉淀工艺条件,并在模拟得到的工艺条件下通过沉淀实验研究,制备出了优质的草酸镍和镍钴草酸盐粉体。然后,考察了局部平衡模型在Ni(Ⅱ)-Mn(Ⅱ)-NH3-CO32--H2O选择性沉淀体系中镍锰分离提纯中的应用。为了从镍锰混合溶液中高效分离出锰,同时避免胶体氢氧化锰和细颗粒碳酸锰的生成,通常要求碳酸镍及氢氧化锰的过饱和度尽可能小,碳酸锰的过饱和度适中。以此工艺参数要求为目标,通过局部平衡模型的模拟,获得了合适的原料溶液浓度、配比和加料方式等工艺条件。在该工艺条件下通过实验最终实现了镍和锰的高效分离,镍的损失率可低至1.0%,锰的沉淀率高达99.7%。最后,对于CO(NO3)2-H2C2O4-K2C2O4和Ca(OH)2-CO2-H2O沉淀体系,考察了局部平衡模型在沉淀过程在线监测中的应用。对CO(NO3)2-H2C2O4-K2C2O4沉淀体系,依据其局部平衡模型中pH与沉淀率和过饱和度的关联,通过在线分析的pH的变化,就可获得沉淀率和过饱和度的演变。对更为复杂的气液两相Ca(OH)2-CO2-H2O沉淀体系,依据其局部平衡模型,可获得pH和电导率与过饱和度、钙离子浓度和总碳浓度的关联,从而通过pH和电导率的在线检测数据,就可得到过饱和度、钙离子浓度和总碳浓度。因此,局部平衡模型为采用简单实用的pH计和(或)电导率仪,为在线监控沉淀过程的主要组分和关键参数提供了可能。这对于掌握沉淀体系的内在演变规律及优化沉淀工艺,都具有重要的理论意义和实际应用价值。更多还原

【Abstract】 Precipitation is widely used in the industry of powder production, metal ions separation and purification. In order to optimize the operating parameters and improve the product quality, a partial equilibrium model was proposed in the thesis for describing the relationships among the reaction components in the precipitation reaction process. The new model assumes that the precipitation reactions should consist of two steps including a liquid-phase reaction step followed by a solid-formation step, in which the first step is considered fast enough to make the liquid phase reaction system in a partial equilibrium state which can be described by ionic equilibrium thermodynamics. Various precipitation systems were chosen for systematic research on the model construction, prediction verification, and practical application.For the ideal precipitation systems of M+-P-and M+-P--H+(M+metal ion, P-precipitant, H+hydrogen ion), partical equilibrium models based on their reaction mechanisms were investigated. Compared with the calculation results of the rigorous kinetic models, the prediction results of the reactant component concentrations by the partial equilibrium models were found to be affected by the reaction rate constants and yield of precipitation. The prediction was found to be more accurate with higher reaction rate constants. For both of the ideal systems, the prediction deviation from the kinetic model was found to be less than1%under the condition that the liquid-phase reactant constants are100times of the solid-formation reaction constant and the yield of precipitation is more than0.6%at the same time.To further study the prediction accuracy of the partial equilibrium models, two convenient-for-detection practical systems were chosen and experiments were performed. For the system of Co(II)-H2C2O4-K2C2O4, pH and the yield of precipitation were both introduced into the partial equilibrium model for simulation of the relationship between them. The simulation results correspond well to the experimental results. Research results also indicate that the accuracy of the partial equilibrium model is improved after the transformation into a semi-empirical equation or the introduction of Davies activity correction. For the system of Ba(Ac)2-H2C2O4-HAc, parameters including pH, Ba total concentration [Ba]1and conductivity k were all introduced into the partial equilibrium model to model the three relationships of pH-[Ba]T, K-[Ba]T, and pH-K. The simulation results are in good agreement with the experimental results.Based on the above verifications, five practical precipitation systems were adopted to investigate the application of the partial equilibrium model in powder manufacturing, separation and purification, and online process monitoring.Firstly, the monometallic precipitation system of NiCl2-H2C2O4-K2C2O4and the co-precipitation system of Ni(II)-Co(II)-C2O42--H2O were studied to investigate the practical application of partial equilibrium models in the preparation of powders. Normally stable pH, appropriate supersaturation, and high metallic recovery rate are required to obtain narrowly distributed and monoshaped powders economically. To achieve such requirements, corresponding partial equilibrium models were constructed to simulate the effects of process operation conditions such as feed solution composition, proportion, operating mode and feeding mode on process pH, supersaturation and yield of precipitation with the goal of finding proper operating conditions for producing narrowly distributed and monoshaped powders with high yield of precipitation. Under such optimized operating conditions, experiments were carried out to prepare high quality nickel oxalate powders and nickel-cobalt oxalate powders.Afterwards, the system of Ni(II)-Mn(II)-NH3-CO32--H2O was employed to investigate the practical application of partial equilibrium model in separation and purification of metal ions. To achieve effective separation of manganese by selective precipitation from the nickel manganese mixture solution in the absence of the formation and colloidal manganese hydroxide and fine-sized manganese carbonate, a low supersturation level of nickel carbonate and manganese hydroxide with a suitable supersaturation level of manganese supersaturation are commonly desirable. To satisfy such a requirement, partial equilibrium models were established and simulations were carried out to determine the optimum process conditions such as feed solution concentration, proportion, and feeding modes for separation. Under such optimized conditions, experiments were performed to achieve the effective separation of nickel and manganese with the loss percentage for nickel as low as1.0%and the yield of precipitation for manganese as high as99.7%.Lastly, the precipitation systems of Co(NO3)2-H2C2O4-K2C2O4and Ca(OH)2-CO2-H2O were adopted to investigate the practical application of partial equilibrium model in the online monitoring of the precipitation processes. It was shown that by the input of the online monitored pH data, the evolution of yield of precipitation and supersaturation for the system of Co(N03)2-H2C204-K2C204can be calculated by a partial equilibrium model. And by the input of the both online monitored pH and conductivity data, the evolution of yield of precipitation and supersaturation of the more complicated system of Ca(OH)2-CO2-H2O can also be calculated by a partial equilibrium model. It can be therefore considered that the partial equilibrium models provide possible opportunity for the application of simple and practical devices including the pH meter and (or) conductivity meter for online inspection of the main components and key process parameters in precipitation. Such applications show great theoretical and practical significance in obtaining information on evolution of the precipitation system and in optimization of the precipitation processes.更多还原