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废银催化剂清洁提银新工艺中银的浸出过程 及Ce(IV)再生反应研究
董旭龙
Subtype硕士
Thesis Advisor齐涛
2018-07
Degree Grantor中国科学院研究生院
Degree Name硕士
Degree Discipline化学工程
Keyword硝酸铈铵、银催化剂、浸出、清洁技术、电化学 
Abstract

银是一种重要的贵金属,具有优异的导热性、导电性及延展性,对可见光反射性优越,银及其相关产品在电子、感光材料、化工工业、医疗器材、航天材料、科研等众多领域有着广泛的应用。其中Ag/ɑ-Al2O3银催化剂广泛应用于聚酯工业中乙二醇的生产,以及乙烯氧化生产环氧乙烷及甲醇氧化制甲醛的生产过程中。银催化剂失去活性后必须更换,是非常重要的银二次资源,具有极高的回收利用价值。目前工业上主要采用硝酸浸出回收银的工艺路线,虽然工艺简单,但流程长、消耗大量硝酸和还原剂等药剂、NOx废气、硝酸盐废水量大,环境污染比较严重。因此,开发一种绿色环保的废银催化剂回收利用工艺显得尤为重要。作者所在课题组提出了以Ce(IV)溶液为浸出剂从Ag/ɑ-Al2O3废银催化剂中回收银的清洁环保新工艺。浸出过程中无NOx气体产生,且浸出剂可通过电化学反应实现循环再生,有望解决传统浸出工艺中产生NOx气体污染环境的问题。针对新工艺中的浸出、洗涤和电化学再生等关键问题,本文对Ce(IV)溶液浸出银过程、残渣洗涤过程、硝酸铈电化学氧化工艺进行了系统的研究,考察了不同反应条件对浸出过程、洗涤效果和电化学氧化效率的影响,为工业化生产奠定了基础。本论文主要结论如下:(1)对硝酸铈铵溶液浸出含银废催化剂工艺进行了系统研究,结果表明,提高反应温度、硝酸铈铵浓度、硝酸浓度和转速,有利于提高银浸出率。浸出过程没有气体产生,银的浸出率最高可达99.9%。由于硝酸浓度大幅度降低,对载体氧化铝的腐蚀降低,浸出液中未检出铝离子。含银浸出液电解后获得的金属银纯度达到99.999%以上。(2)对硝酸铈铵溶液浸出废银催化剂工艺的影响因素进行了正交试验,结果表明,影响银浸出率的显著性因素依次为:反应温度>硝酸铈铵浓度>硝酸浓度>转速。最优实验条件为1.6 mol/L硝酸铈铵、1.0 mol/L硝酸、反应温度70℃、转速60 r/min。在最优实验条件下,反应1h浸出率即达到99.8%,2 h银浸出率为99.9%。(3)对硝酸铈铵浸出银的反应进行了动力学研究,结果表明,该过程符合未反应缩核模型,受扩散控制,表观活化能为38.83 kJ/mol。(4)对Ce(IV)浸出银新工艺进行了扩大试验,重点对浸出渣洗涤过程进行了系统研究。结果表明,采用5%硝酸或去离子水,洗出液中的银含量在20 min即趋于稳定,而Ce含量则30 min时仍然还在升高。与纯水相比,采用稀硝酸洗涤有利于减少Ce在洗涤渣中的残余量,但对银残余量没有显著影响。提高洗水循环流量、洗涤温度均有益于残渣中铈离子的洗涤,对银的洗涤影响不大。使用体积分数5%的稀硝酸作为洗液,优化条件下洗涤8次后残渣铈含量123 g/t。银残余量在1000 g/t左右。按照原料含银17.2%计算,相对浸出率99.4%。(5)对Ce(NO3)3的电化学氧化工艺进行了研究,结果表明,阳极电流效率随阳极电流密度、硝酸浓度的升高而降低,随着硝酸铈浓度、电解温度的提高而提高。当阳极电流密度为1500 A/m2,电解液组成为1.5 mol/L硝酸铈和1.0 mol/L硝酸,50oC下电解时,反应3 h后阳极电流效率略有下降,但仍然在98.5%以上。;Silver is one of important precious metals, with excellent thermal conductivity, conductivity and ductility, and excellent visible light reflectivity. Silver and its related products are applied widely in many fields such as electronics, photosensitive materials, chemical industry, medical equipment, aerospace materials, and scientific research. The Ag/ɑ-Al2O3 catalysts are widely used in the production of ethylene glycol in the polyester industry, and in the production of ethylene oxide to produce ethylene oxide. After losing the activity the silver catalysts will need replace, so it is a very important silver secondary resource and has extremely high recycling value. At present, recovery of silver with nitric acid is mainly used in the industry. The process is simple, however there are still many disadvantages such as process is long, consumes large amounts of nitric acid and reducing agent, generates NOx waste gas, nitrate wastewater and neutralization slag, which has a large environmental impact. Therefore, it is particularly important to develop a green, waste-silver catalyst recycling process.The author's research group proposed a clean and environmentally friendly new technology that uses Ce(IV) solution as a leaching agent to recover silver from Ag/ɑ-Al2O3 spent silver catalyst. In the leaching process no NOx gas is generated, and the leaching agent could be recycled by electrochemical reaction, it is expected to solve the problem of NOx gas polluting environment in the traditional leaching process. Aiming at the key issues such as leaching process, washing process and electrochemical regeneration in the new technology, this thesis systematically studied the process of leaching silver by Ce(IV) solution, the washing process of residue, and the Ce(NO3)3 electrochemical oxidation process. The effects of different reaction conditions on the leaching process, washing and electrochemical oxidation efficiency were investigated, providing the foundamental data for commercial practices. The main conclusions of this paper are as follows: (1) The leaching silver process from spent Ag/ɑ-Al2O3 catalysts by ceric ammonium nitrate (CAN) solution was systematically studied. The results showed that increasing the reaction temperature, ceric ammonium nitrate concentration, nitric acid concentration and rotation speed were beneficial to improve the silver leaching rate. No gas was produced in the leaching process. As the concentration of nitric acid was greatly reduced, the corrosion of alumina carriers was reduced, no aluminum ions were detected in the leachate, which reduced the amount of impurities. The best leaching rate of silver is up to 99.9%. (2) The orthogonal studies were carried out, the results indicated that the main factors affecting the leaching of silver by CAN are: temperature > CAN concentration > HNO3 concentration > stirring speed. The optimal experiment conditions were obtained, the experiment was performed at 70℃, with a lixiviant solution of 1.6 mol?L-1 CAN and 0.1 mol?L-1 HNO3 and under stirring (60 r/min), the leaching rate was 99.8% after 1 h reaction and 99.9% after 2 h reaction.(3) The kinetic analysis of the leaching silver process was studied. The results showed that the leaching reaction can be described by an internal diffusion-controlled model, and the activation energy was calculated to be 38.83 kJ/mol. (4) The expansion experiment of new silver leaching process for Ce(IV) has been carried out, the residue washing process was systematicly studied. The results showed that, whether 5% nitric acid or deionized water was used, the silver content in the eluate was stable at 20 min, while the Ce content was still elevated at 30 min. Compared with pure water, washing with dilute nitric acid is beneficial to reduce the residual amount of Ce in the residue solid, but has no significant effect on the residual amount of silver. Increasing the flow rate of the washing solution and the washing temperature are beneficial to the washing of the Ce ions in the residual, and have little effect on the washing of silver. Dilute nitric acid with a volume fraction of 5% was used as a lotion, and after the washing 8 times under optimized conditions, the Ce content of residue was 123 g/t, the silver content was about 1000 g/t, and the relative leaching rate is about 99.4%.(5) A systematic study of the electrolysis oxidation Ce(NO3)3 has been carried out. The results showed that the anode current efficiency decreased with increasing anode current density and nitric acid concentration, while increasing the Ce(NO3)3 concentration and the electrolysis temperature were beneficial to increase the anode current efficiency. When the anode current density is 1500 A/m2, the electrolyte composition is 1.5 mol/L niobium nitrate and 1.0 mol/L nitric acid. The electrolysis were performed at 50℃, the anode current efficiency can reach 98.5% after 3 h reaction. Key Words: Ceric ammonium nitrate (CAN); Silver catalyst; Leaching; Cleaning technology; Electrolysis oxidation 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26849
Collection中国科学院过程工程研究所
研究所(批量导入)
Recommended Citation
GB/T 7714
董旭龙. 废银催化剂清洁提银新工艺中银的浸出过程 及Ce(IV)再生反应研究[D]. 中国科学院研究生院,2018.
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