Knowledge Management System Of Institute of process engineering,CAS
|Thesis Advisor||曹宏斌, 孙峙|
废锂离子电池回收过程产生的废旧石墨负极由于含有重金属、有机物等而具有潜在的环境危害，其无害化处理及资源化利用近年来受到广泛关注。本论文总结了废旧石墨负极含有的杂质种类、性质和相应的除杂方法，通过系统表征、除杂以及机械力活化和原位负载实现了废旧石墨负极在重金属吸附过程中的应用，重点包括废旧石墨负极的杂质脱除、机械力活化提高吸附性能可行性的探究、机械力活化和原位负载协同提高吸附性能的机理以及复合吸附剂的吸附机理等研究。主要的研究内容与结论如下：（1）不同来源的废旧石墨负极所含杂质不同。将可能存在的杂质分为三类：第一类为电解液、粘结剂和导电剂，均可通过热解除去；第二类为固体电解质界面膜（SEI）、集流体铜箔（Cu）、集流体铝箔（Al）、铁的氧化物（FexOy）、镍钴锰的氧化物（Ni-Co-Mn-O）、Fe2TiO5和磷酸盐，均可用稀酸除去；第三类为α-Al2O3、TiO2和SiO2，不易被稀酸和稀碱除去。实验室拆解得到的废旧石墨负极（简称为石墨废料）的主要杂质为铜和有机物。工业再生流程产生的石墨浸出渣（简称为石墨浸出渣）的主要成分为层间轻微膨胀的缺陷石墨，所含杂质包括有机物、TiO2、α-Al2O3、SiO2、Fe2TiO5、铁的氧化物、磷酸盐、镍钴锰的氧化物。根据杂质种类和性质，选取了焙烧和酸浸结合的方法对两种废旧石墨负极进行除杂，得到了纯化石墨。（2）以纯化石墨废料为原料，通过机械力活化和原位负载二氧化锰（MnO2）成功制备得到了高效复合重金属吸附剂（AG@MnO2）。其对Cd(II)、Pb(II)、Cu(II)的吸附容量分别为135.81 mg/g、370.4 mg/g、105.2 mg/g，高于许多先前的吸附剂，验证了机械力活化提高吸附性能的可行性。复合吸附剂吸附性能的提升源于高能球磨和原位负载锰氧化物的协同作用。MnO2的负载可增加复合吸附剂表面官能团的数量和复合吸附剂的电负性，进而提高吸附性能。高能球磨通过提高石墨的比表面积和反应活性提高了MnO2的负载量，并通过增加表面官能团的数量和增强cation-Cπ相互作用增强了复合吸附剂对重金属离子的吸附能力。在石墨废料研究的基础上，初步将纯化石墨浸出渣再生为AIG@MnO2复合吸附剂，对Cd(II)的吸附量可达117.6 mg/g，优于先前研究中大部分吸附剂的吸附性能，为今后石墨浸出渣资源化再生的研究奠定了基础。（3）AG@MnO2复合吸附剂对Cd(II)的吸附过程符合准二级动力学和Redlich-Peterson热力学模型,∆Gθ的计算值为-5.628 kJ/mol，说明Cd(II)在AG@MnO2上的吸附为自发进行的多层吸附，吸附机理包括物理吸附。借助X射线电子能谱以及Zeta电位和pH值的变化，证实了AG@MnO2对Cd(II)的吸附机理包括物理吸附（静电吸附）和化学吸附（离子交换、表面络合）。AG@MnO2复合吸附剂可处理较宽pH范围（pH = 4-7）的含镉废水，在吸附过程中稳定存在，且循环使用四次后，AG@MnO2复合吸附剂对镉离子的去除率仍然较高，证明复合吸附剂有一定的实际应用价值。;Waste graphite anodes produced in the recycling process of waste lithium-ion batteries have potential environmental hazards due to the presence of heavy metals and organics. Its harmless treatment and resource utilization have drawn worldwide attention in recent years. This thesis summarized the types and properties of impurities contained in waste graphite anodes and the corresponding methods for impurity removal. The application of waste graphite anodes in heavy metal adsorption process was realized through systematic characterization, impurity removal, mechanical activation and in-situ loading. The focuses included the impurity removal of waste graphite anodes, feasibility of mechanical activation to improve the adsorption performance, mechanism of the synergistic improvement of adsorption capacity through mechanical activation and in-situ loading, adsorption mechanism of the composite adsorbent, etc. The main research contents are as follows:(1) The types of impurities contained in waste graphite anodes from different sources were different. The impurities were divided into three categories: the first category included electrolyte, binder and conductive agents, which could be removed by pyrolysis; the second category included solid electrolyte interface membrane (SEI), current collector copper foil (Cu) , current collector aluminum foil (Al), iron oxides (FexOy), Fe2TiO5, phosphate as well as oxides of nickel, cobalt and manganese (Ni-Co-Mn-O), which could be removed by dilute acid solutions; the third category included α-Al2O3, TiO2 and SiO2, which were difficult to be removed by dilute acid or dilute alkali solution. The main impurities of waste graphite anodes dismantled in the laboratory (named as graphite scraps) were copper and organics. The main component of graphite leaching residues generated in the industrial regeneration process (named as graphite leaching residues) was defective graphite with slight expansion between layers, and the impurity components included organics, TiO2, α-Al2O3, SiO2, Fe2TiO5, FexOy, Ni-Co-Mn-O and phosphate. According to the type and properties of impurities, roast and acid leaching were selected to remove impurities in order to obtain purified graphite.(2) Taking purified graphite scraps as raw materials, the high-efficiency composite heavy metal adsorbent (AG@MnO2) was successfully prepared by mechanical activation and in-situ loading of manganese dioxide (MnO2). Its adsorption capacities for Cd(II), Pb(II) and Cu(II) were respectively 135.81 mg/g, 370.4 mg/g and 105.2 mg/g, higher than that of many previous adsorbents. This proved the feasibility of mechanical activation to improve the adsorption performance. The improvement of adsorption performance came from the synergy between high-energy ball milling and in-situ loading of MnO2. The loading of MnO2 improved the adsorption performance by increasing the number of surface functional groups and the electronegativity of composite adsorbents. High-energy ball milling increased the MnO2 loading content by increasing the specific surface area and reactivity of graphite. Besides, high-energy ball milling increased the number of surface functional groups and enhanced the cation-Cπ interaction, thereby enhancing the adsorption capacity of the composite adsorbent for heavy metal ions. Based on the study of graphite scraps, the purified graphite leaching residues were preliminarily regenerated into AIG@MnO2 composite adsorbent. The adsorption capacity for Cd(II) reached 117.6 mg/g, which was superior to the adsorption performance of most adsorbents in previous studies. This laid the foundation for the future research on the regeneration of graphite leaching residues.(3) The adsorption of Cd(II) onto AG@MnO2 conformed to the pseudo second-order kinetic model and Redlich-Peterson thermodynamic model, and the Gibbs free energy (∆Gθ) was -5.628 kJ/mol. These results indicated that the adsorption of Cd(II) onto AG@MnO2 was spontaneous multi-layer adsorption and physical adsorption was one of the adsorption mechanisms. According to X-ray photoelectron spectroscopy as well as the changes of the Zeta potential and pH value, it was confirmed that adsorption mechanisms of AG@MnO2 for Cd(II) included physical adsorption, i.e., electrostatic attraction, and chemical adsorption, i.e., ion exchange, surface complexation. AG@MnO2 composite adsorbent could treat cadmium-containing wastewater in a wide range of pH (pH = 4-7), the composite adsorbent was stable during the adsorption process, and the removal rate of Cd(II) by AG@MnO2 after four adsorption cycles was still high, indicating certain practical application potential.
|郝洁. 废旧石墨负极资源化利用研究及其在重金属吸附过程中的应用[D]. 中国科学院大学,2020.|
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