锗在锌电积中的行为及添加剂作用的研究

【作者】 刘春侠；

【导师】 王吉坤；

【作者基本信息】 昆明理工大学 ， 冶金物理化学， 2008， 博士

【摘要】 锌电积是湿法炼锌工艺的一个重要工序,而电解液中杂质的存在直接关系到阴极锌的质量。为此,国内外工作者做了大量的研究工作,一方面对杂质在电积过程中的行为进行探讨,另一方面寻求合适的添加剂抑制杂质的影响,以利于电积的顺利进行。本文针对驰宏公司铅锌矿锗含量高等特点,根据长周期锌电积作业的生产实践,结合生产中遇到的锗烧板问题,采用线性扫描伏安技术、计时电流和交流阻抗技术等现代电化学方法和激光拉曼光谱和电子探针等分析技术,对电解液中存在的微量锗及所添加的有机添加剂之间的作用机理进行了研究,为生产实践提供理论依据,并具有指导意义论文应用多种电化学方法及现代分析技术对锗在锌电积过程中的行为进行了研究。电解液含不同浓度锗条件下的阴极极化曲线表明锗的存在会削弱锌电积阴极极化,且随着电解液中锗浓度从0.04 mg·L-1增加到0.8 mg·L-1,去极化作用增强。通过对阴极极化曲线进行Tafel拟合发现：电解液中存在锗会增大锌电沉积过程中的交换电流密度和传质系数,且随锗浓度的增加而增大,由此可知锗的存在会改变锌电沉积机理,增大电极反应的可逆程度和反应速率。相同条件下测得的交流阻抗图表明：锌沉积是一个多步反应过程,锗的存在不但加剧氢还原反应的发生,且影响锌沉积的电荷传递步骤。计时电流曲线进一步证实了锗会加剧氢还原反应的发生。结合电解液中存在锗时电积阴极锌的激光拉曼光谱图和电子探针图可知：锌电积过程中伴随单质锗的析出,同时由于金属锗的沉积,加剧了氢还原反应的发生,使阴极锌表面出现了不同程度和深度的孔洞。提出含锗硫酸锌电解液电积锌的反应动力学模型,并首次采用基于第一原理的密度泛函理论,应用CASTEP量化软件对提出的含锗硫酸锌电解液电极反应动力学模型进行理论验证。结构优化结果表明H+在Zn(101)面吸附使整个Zn(101)面结构变疏松,而Ge4+(Ge)的吸附则使Zn(101)面局部结构疏松以致出现缺陷；能量优化结果表明锗在Zn,ZnHad,Znad+,Zn*上吸附反应较电极表面发生的其他反应容易,且氢在Gead表面上还原比在Zn上更容易发生配制了一种适合长周期锌电积的复合添加剂(A),并与明胶、硫脲和甲酚进行对比研究,发现复合添加剂A在提高电流效率、改善阴极锌表面质量和降低能耗方面都优于其他添加剂。对电解液添加不同浓度复合添加剂A时的阴极极化曲线分析可知：添加剂A有利于锌电积阴极极化,且随着电解液中添加剂A浓度从5 mg·L-1增加到25 mg·L-1,极化作用增强。通过对阴极极化曲线进行Tafel拟合发现：电解液中存在添加剂A会降低锌电沉积过程中的交换电流密度和传质系数,且随复合添加剂A浓度的增加而逐渐减小,但变化幅度较小。相同条件下测得的交流阻抗图表明添加剂A的吸附影响了锌沉积的电荷传递步骤,抑制了氢的析出。采用多种电化学方法及现代分析技术对复合添加剂A与锗在锌电积过程中的相互作用进行了探讨。添加适量添加剂A可以提高因锗存在引起下降的锌电沉积电流效率,且能有效改善因锗引起的恶化的沉积锌表面质量。通过对含0.12mg·L-1Ge的基液添加不同浓度添加剂。A进行线性极化曲线、交流阻抗和计时电流曲线测量发现：添加剂A可以抑制锗对锌电积的去极化作用和因锗引起的强烈氢还原反应的发生；由计时电流曲线可以看出锗的影响在沉积初始时作用较大,随着时间的延长,添加剂A的作用占主导地位。更多还原

【Abstract】 Zinc electrowinning is an important procedure in zinc hydrometallurdry, and zinc deposit quality is affected by metal impurities directly. A great deal of research had been done about the effects of impurities on zinc electrowinning and exploring suitable additives to inhibit influences of impurities to make electrowinning carry out smoothly. Therefore, in this paper, the behaviors of trace germanium and additives in zinc electrowinning from sulfate zinc electrolyte were studied on the basis of three main ideas:high germanium content of lead-zinc mine from Chihong Zinc & Germanium Stock Company, production practice of long period zinc electrowinning, especially, redissolution of zinc deposit in zinc electrowinning from sulfate zinc electrolyte in presence of germanium, some electrochemical techniques such as linear scanning voltammetry, Chronoamperometry, and impedance technique and analysis methods of laser Raman spectra and electron probe X-Ray microanalysis (EMPA) were used. The study may provide theoretical basis for guiding production.The behavior of trace germanium in zinc electrowinning from sulfate zinc electrolyte was studied by many electrochemical and modern analysis methods. Polarization curves of zinc deposition from base electrolyte in presence of various concentrations Ge demonstrates that germanium has an action of depolarization on the zinc deposition, and depolarization heightens with germanium concentration increases from 0.04 mg·L-1 to 0.8 mg·L-1. Moreover, Tafel fitting results of the polarization curves indicate that exchanging current density and transfer coefficient increase with germanium concentration increasing, which prove the presence of germanium in the electrolyte will change zinc electrodeposition mechanism, and increase degree of reversibility and rate of electrode reactions. Impedance diagraphs obtained at the same conditions reveals that zinc deposition is a many steps process, the presence of germanium in the electrolyte not only strongly stimulates hydrogen evolution, but also affects charge transfer step of zinc deposition. In addition, chronoamperometry curves also prove that hydrogen evolution is stimulated by germanium. Both laser Raman spectra and EPMA photographs reveal zinc deposition associating with germanium deposition, therefore, hydrogen evolution is stimulated with simultaneous zinc redissolution.A reaction kinetics model of zinc deposition in sulfate zinc electrolyte in presence of germanium was put forward. Moreover, this model was firstly verified through quantum chemistry calculation based on density functional theory. In this calculation, CASTEP software was used to carry out structure optimization and energy optimization of adsorption species on electrode surface. The results of structure optimization show that H+ adsorption makes structure of Zn(101) surface loosen, and Ge4+(Ge) adsorption actions are more serious than that of H+, which make part of Zn (101) surface loosen, and even appear defect. In addition, from energy optimization calculation, it is shown that germanium adsorption reactions on Zn, ZnHad, Znad+ and Zn* are more easily than the other reactions and hydrogen evolution on Gead is more easily than on Zn.Compound additive A was prepared using for long period zinc electrowinning, and the effects of additive A, gelatin, thiourea and cresol on zinc electrowinning were investigated. In comparison with the results, additive A is superior to other additives in aspects of increasing current efficiency, improving surface quality of zinc deposit and reducing consumption of power. Polarization curves of zinc deposition from base electrolyte in presence of various concentrations additive A demonstrates additive A has an action of polarization on the zinc deposition, and polarization heightens with additive A concentration increases from 5 mg·L-1 to 25 mg·L-1. Moreover, Tafel fitting results of the polarization curves indicate that exchanging current density and transfer coefficient faintly decrease with additive A concentration increasing. Impedance diagraphs obtained at the same conditions reveals that the presence of additive A in the electrolyte not only inhibits hydrogen evolution, but also affects charge transfer step of zinc deposition.The interaction of trace germanium and additive A in zinc electrowinning from sulfate zinc electrolyte was firstly studied by many electrochemical and modern analysis methods. Proper additive A may inhibit the effect of germanium on zinc deposition in terms of current efficiency and deposit morphology, on the other hand, from polarization curves, impedance diagraphs and chronoamperometry curves obtained from the base electrolyte in presence of 0.12 mg·L-1 Ge and various concentrations additive A, it is found that additive A may inhibit the depolarization and stimulating hydrogen evolution effects of germanium on zinc deposition, chronoamperometry curves also indicate that germanium dominate the reaction during the first second, additive A become more evident with prolonging of time.更多还原