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|Na2O - ZnO - H2O体系溶液结晶动力学与氧化锌分离制备新方法|
氧化锌具有优良的催化、热电、压电和光电特性，在传感器、太阳能电池和压敏电阻等领域具有广阔的应用前景，是重要的基础工业材料。氧化锌材料制备方法可分为固相法、液相法和气相法，存在设备要求高、生产条件苛刻、产量小、能耗大、污染重和成本高等问题。而目前氧化锌资源的工业分离提取方法主要是硫酸浸出，产生大量的危险废弃物，资源利用率低、环境污染重。由于锌矿资源基本是经焙烧为氧化锌后浸出，同时二次锌资源也以氧化锌为主，因此，本论文提出采用氢氧化钠溶液直接浸出提取其中的氧化锌得到锌酸钠溶液，通过控制锌酸钠溶液水解结晶过程直接制备氧化锌或氢氧化锌产品，实现氧化锌资源分离及其产品制备一体化的新方法。该方法工艺简单、介质可循环使用、无副产物、无污染、流程短、能耗低、成本低、易于规模化生产。但是，关于Na2O - ZnO - H2O体系的溶液性质、结晶过程机理及其动力学研究的相关文献报道很少。因此，本论文系统地研究了Na2O - ZnO - H2O体系中锌酸钠溶液的水解结晶机理和动力学。获得的创新性结果如下：从锌酸钠溶液中水解结晶分别获得了制备氧化锌和氢氧化锌的工艺条件，并基于经典成核理论分析了氧化锌和氢氧化锌的成核和生长机理。同时计算了氧化锌和氢氧化锌在锌酸钠溶液中的界面张力。分析了温度对锌酸钠溶液结构的影响，温度大于等于50 ºC时，溶液中锌离子以Zn(OH)x2-x(x≥3)存在；当温度小于等于35 ºC时，溶液中锌离子主要以Zn(OH)+和少量的Zn(OH)x2-x(x≥3)存在；深化了对锌酸钠溶液结构的认识，并为锌酸钠溶液水解结晶提供了理论依据。 间歇动态法实验测定了锌酸钠溶液水解结晶过程中的动力学数据，并采用矩量变换法通过粒数衡算方程的粒度无关模型进行了动力学数据的研究，得出了氧化锌的成核速率、生长速率以及团聚速率方程。结果表明：锌酸钠溶液水解结晶过程中ZnO的生长机理属于扩散过程和表面反应共同控制；晶体悬浮密度对氧化锌团聚起到促进的作用；ZnO成核速率会随着悬浮密度的增加而减小，随着搅拌速率的增加而增加。研究还发现，研究还发现，温度小于60 ºC时，杂质硅既能促进锌酸钠溶液的结晶过程，又能抑制锌酸钠溶液的水解结晶过程。同时，杂质硅的存在影响结晶产品的物相。锌酸钠溶液结构分析表明：杂质硅的存在有利于锌元素以Zn(OH)+的形式存在锌酸钠溶液中，而温度大于50 ºC时该影响较小。锌酸钠溶液的水解结晶过程中，晶种、搅拌速率、过饱和度和温度等工艺参数对锌酸钠溶液结晶的转化率和粒度分布都有较大影响。实验研究结果表明，60 ºC时，氢氧化锌晶种对锌酸钠溶液水解结晶率的影响较大；35 ºC时，氧化锌晶种对锌酸钠溶液水解结晶率的影响较大。50 ºC时，水解结晶的氧化锌产品粒度分布最窄。实验条件下，搅拌速率小于300 rpm时，搅拌速率对锌酸钠溶液的结晶转化率具有显著的影响。在上述研究的基础上，本论文进一步进行了氢氧化钠溶液浸出湿法炼锌产生的二次资源镍钴渣中氧化锌的实验研究。获得浸出镍钴渣中氧化锌的最佳工艺条件是120 ºC、30 % NaOH（w/w）、1 h、L/S=10:1，锌元素的浸出率可达96%，而钴元素的浸出率仅4%，实现了锌、钴的高效分离。进一步将浸出的锌酸钠溶液水解结晶，制备了氢氧化锌产品。并阐明了氢氧化钠溶液浸出镍钴渣中氧化锌的动力学过程受化学反应和外扩散共同控制。;Zinc oxide has excellent catalytic, thermoelectric, piezoelectric and photoelectric characteristics. Zinc oxide has broad application prospects of the fields such as sensors, solar cells and varistor, and is an important basic industrial material. The preparation methods of zinc oxide materials can be divided into solid-phase method, liquid-phase method and gas-phase method, which have the problems of high equipment requirements, harsh production conditions, small output, large energy consumption, heavy pollution and high cost. At present, the main method of industrial separation and extraction of zinc oxide resources is sulfuric acid leaching, which produces a large number of hazardous wastes with low resource utilization rate and heavy environmental pollution. Zinc ores resources are basically leached after roasting to zinc oxide, and the secondary zinc resources are mainly zinc oxide. Therefore, this paper proposes a new method to use sodium hydroxide solution to extract zinc oxide directly and obtain sodium zincate solution, and zinc oxide and zinc hydroxide products were prepared by controlling the hydrolysis crystallization of sodium zincate solution to realize the integration of zinc oxide resource separation and product preparation. This method has the advantages of simple process, media can be recycled, no by-product, no pollution, short process, low energy consumption, low cost and easy to scale production. However, there is little research on the solution properties, crystallization process mechanism and kinetic of Na2O - ZnO - H2O system. Therefore, hydrolysis crystallization mechanism and kinetic of Na2O - ZnO - H2O system were studied in the paper. The innovative results obtained are as follows.Process conditions for the preparation of zinc oxide and zinc hydroxide were obtained by hydrolysis crystallization from sodium zincate solution. Based on the classic nucleation theory, nucleation and growth mechanisms of ZnO and Zn(OH)2 were analyzed. The interfacial free energies of Zn(OH)2 and ZnO were calculated respectively. The effect of temperature on the sodium zincate solution structure was investigated. When temperature is equal or greater than 50 ºC, Zn element exists as Zn(OH)x2−x (x ≥ 3), and Zn element mainly exists as Zn(OH)+ and a little as Zn(OH)x2−x (x ≥ 3) is less than or equal to 35 ºC. It deepens the understanding of the structure of sodium zincate solution and provides a theoretical basis for the hydrolysis crystallization of sodium zincate solution.Batch dynamic method was used to research the hydrolysis crystallization of sodium zincate solution, and kinetic data was obtained. Based on the population balance model, kinetic data was treated by size independent model and moment transformation, and nucleation rate, growth rate and agglomeration rate equations of ZnO were obtained at last. It founds that the growth mechanism of ZnO during the hydrolysis crystallization of sodium zincate solution is controlled by diffusion process and surface reaction. Suspension density of crystals promotes the agglomeration of ZnO. Nucleation rate of ZnO decreases with increasing suspension density, and increases with increasing agitation speed.When the temperature is below 60 ºC, impurity silicon can not only promote the crystallization process of sodium zincate solution, but also inhibit the hydrolysis crystallization process of sodium zincate solution. Impurity silicon affects the phase of the crystalline products also. The structure analysis of sodium zincate solution showed that impurity silica was beneficial to Zn2+ existed as Zn(OH)+ in the sodium zincate solution, but the effect is small when temperature is above 50 ºC.Hydrolysis crystallization of sodium zincate solution was investigated systematically. Parameters such as seed, agitation speed, supersaturation and temperature had obviously influence on the conversion and particle size distribution of crystallization. It founds that Zn(OH)2 seed had effect on the hydrolysis crystallization ratio of sodium zincate solution at 60 ºC, and ZnO seed had effect on the hydrolysis crystallization ratio of sodium zincate solution at 35 ºC. The narrowest particle size distribution of hydrolyzed zinc oxide products is at 50 ºC. Under experimental conditions, the conversion of sodium zincate solution was affected by agitation speed below 300 rpm. On the basis of the above research, this paper further carried out the experimental study of zinc oxide in the secondary resource nickel cobalt residue produced by the wet process of zinc smelting with sodium hydroxide solution. The optimal leaching condition was 120 ºC, 30 % NaOH（w/w），1 h，L/S=10:1. The leaching rate of zinc and cobalt were 96 % and 4 % in the optimal leaching condition. Effective separation of zinc and cobalt was achieved. The sodium zincate solution was further hydrolyzed and crystallized to prepare zinc hydroxide. The kinetic process of leaching zinc oxide from nickel cobalt residue with sodium hydroxide solution is controlled by chemical reaction and external diffusion.
|刘鹏飞. Na2O - ZnO - H2O体系溶液结晶动力学与氧化锌分离制备新方法[D]. 中国科学院大学,2020.|
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