CAS OpenIR
羟基自由基氧化黄铁矿及外场强化高硫铝土矿电解脱硫机理
胡英楠
Subtype硕士
Thesis Advisor王志
2018-07
Degree Grantor中国科学院研究生院
Degree Name硕士
Degree Discipline化学工程
Keyword高硫铝土矿,电解氧化脱硫,黄铁矿氧化机理,外场,羟基自由基
Abstract

我国氧化铝工业规模巨大,资源、能源、环境等约束日益凸显。铝土矿资源匮乏日益凸显,高铝硅比的高硫铝土矿具有重要的利用价值,脱硫处理获得低硫铝土矿可以缓解高品位铝土矿资源短缺的问题。本文主要研究了电解脱硫过程中黄铁矿的氧化机理,基于量子化学密度泛函理论计算出水电解产生羟基自由基对黄铁矿的氧化历程;通过超声、加压等外场强化电解水过程羟基自由基的形成,提高电解脱硫效率,并结合电化学表征,研究了超声和加压强化电解水产生羟基自由基机理;根据电极活性、耐腐蚀性、脱硫率等参数,研究了六种普通电极材料的电解脱硫特性和电化学腐蚀行为,确定了碱性体系的最佳电极材料,为电解脱硫的工业化应用提供了可能性。主要取得如下结果:(1)通过XPS和阴离子色谱分别研究了电解前后黄铁矿结构与电解液离子种类变化规律。结果表明电解后的黄铁矿表面被活化,出现孔道与褶皱。黄铁矿电解氧化后表面硫物种S2-丰度明显增加,同时表面形成Fe(OH)3。电解后溶液中出现硫代硫酸根离子(高达82ppm)和少量硫酸根离子(≤3ppm),同时在电解过程中发生耗碱反应。通过ESR研究羟基自由基形成规律,结果表明在碱性溶液中电解1h后,黄铁矿电解脱硫环境产生羟基自由基浓度为41.01μmol/L。随叔丁基醇添加量的增加,CV曲线上Fe和S的氧化峰峰强逐渐下降,证明羟基自由基是氧化黄铁矿的关键介质。因此,在电解脱硫过程中,主要氧化介质为羟基自由基,黄铁矿主要被氧化为S2O32-进入溶液,同时产生Fe(OH)3。(2)密度泛函(DFT)计算结果表明,当羟基自由基单独连续吸附在黄铁矿(100)面时,很难将矿物解离脱除;当羟基自由基连续吸附在黄铁矿(100)面时,羟基自由基首先吸附Fe原子,再吸附S原子,当第四个羟基自由基吸附S原子时,Fe-S键断裂,形成S2O32-,最终,S原子和Fe原子被氧化成SO42-和Fe(OH)3。羟基自由基中的氧参与含硫离子生成,氢原子生成氢离子。因此,羟基自由基氧化脱硫是耗碱过程。(3)研究了超声水电解过程阳极区羟自由基形成规律。结果表明超声电解不仅可以提高氧化反应前驱体的扩散系数,从而强化电解液中的物质传递,还可以强化氢氧根的电子得失。从Tafel、EIS曲线得知,超声使OER平衡电位正移,使平衡电流增加,表明超声波抑制了OER的热力学条件,改善了OER的动力学条件。超声使OER的Rct增加,Rs下降,证明了超声抑制了析氧过程,强化了离子扩散。通过模拟计算结果可知,超声促进其在电极上脱附过程,增加了活化空间,从而导致羟基自由基量的增加。超声增加了Pt和Ni电极电解铝土矿脱硫率,值得一提的是超声耦合镍电极电解脱硫可达到无超声铂电极电解脱硫效果。(4)研究了加压电解过程阳极/阴极羟基自由基形成规律。脱硫率与ESR结果表明,在加压电解脱硫过程中,HO·是阳极区的主要氧化介质,其含量随压力增加而增加,与脱硫率规律趋势一致。根据Tafel与EIS曲线可知,加压强化了水的解离、OH-的传质及其在阳极的电子得失,并抑制了HO·的猝灭,抑制氧气的析出,从而增加了阳极去羟基自由基的数量。采用电-芬顿方式实现阴极产生羟基自由基,根据脱硫率与ESR可知,加压增大了水溶液中氧气的浓度,强化了氧气在阴极的电子得失,强化形成O2-,再和H+结合生成H2O2,从而电-芬顿反应得到强化,羟基自由基的量增多。电-芬顿法将二维氧化升级为三维氧化,大大增加被氧化物质与羟基自由基的接触机会。(5)量化对比了电解脱硫过程阳极材料的电化学行为。通过考察六种电极材料的腐蚀行为、脱硫效果、电化学行为,确定了铝土矿电解脱硫技术的工业化阳极材料。用硫代硫酸钠溶液作为模拟电解液,利用Tafel和CV曲线研究了六中阳极材料的电化学行为。结果表明,它们的腐蚀电位依次为Ni> C> SS> Fe> Cu> Pb-Ag。铝土矿电解的脱硫率和电解槽电压顺序分别为Cu> Ni> Fe> SS> C> Pb-Ag和Ni> Fe> SS> Cu> C> Pb-Ag。最后,Ni被选作铝土矿电解脱硫的理想阳极材料,为电解脱硫工业化应用提供了可能性。;The high-sulfur bauxite with high ratio of aluminum to silicon has application potential, it can relieve the shortage of high-grade bauxite resources after desulfurization. In this paper, based on quantum chemical density functional theory, the mechanism of oxidation path of pyrite by hydroxyl radical produced in the process of electrolytic desulfurization was studied. Based on the improvement of the desulfurization efficiency of electrolysis and the electrochemical characterization, the mechanism of the electrolytically generation of hydroxyl radicals enhanced by ultrasonic water was studied. Finally, for the industrialization, according to three indicators of electrode activity, corrosion and resistance, nickel was selected as the best anode under alkaline conditions among 6 kinds of conventional electrode materials. A method of external field coupled with nickel electrolysis was proposed to provide possibilities for the industrial application. The main results are as follows:(1) The changes of pyrite and alkaline solution before and after electrolysis were studied. The electrolyzed pyrite surface was activated with the appearance of pores and wrinkles. XPS results showed that the surface valence S was oxidized to +4 or +6, and Fe(OH)3 was produced. In the solution after electrolysis, thiosulfate ions (up to 82 ppm) and small amounts of sulfate ions (≤3 ppm) were detected in the solution. Simultaneously, the pH of the electrolyte is reduced of 0.8 in one hour. ESR results showed that the hydroxyl radical concentration was 41.010 μmol/L after electrolysis in alkaline solution for 1 h. Electrochemical characterization results showed that the iron metamorphic potential of the pyrite electrode in alkaline solution was -0.79V, and the sulfur valence potential was -0.32V. Ultrasonic electrolysis can increase the diffusion coefficient of the oxidation reaction precursor, thereby strengthening the mass transfer in the electrolyte. (2) The result of density functional theory (DFT) calculation shows that when oxygen radicals are continuously adsorbed on the 100 surface of pyrite alone, it is difficult to dissociate the minerals; when hydroxyl radicals are continuously adsorbed on the 100 surface of pyrite, oxygen radicals combine with S and Fe continuously, which lead to disconnection of S-S bond. Finally, iron hydroxide, SO2, SO32-, SO42-, S2O32-, etc. are generated, and the chemical reaction equation is given. The oxygen element in the final hydroxyl radical participates in the formation of sulfur-containing ions, and hydrogen generates hydrogen ions. Therefore, the pyrite oxidation of hydroxyl radicals is an alkali-consuming process. (3) The effect of ultrasound on the formation of hydroxyl radicals by electrolysis of water was studied. The results show that the ultrasonic can not only enhance the mass transfer in the liquid phase, but also enhance the electron gain and loss. Ultrasound suppresses the release of oxygen, strengthens the dispersion of hydroxyl radicals, promotes the desorption process on the electrodes, and increases the activation space, resulting in an increase in the amount of hydroxyl radicals. By analyzing the Tafel and EIS curves, it is known that ultrasound makes a positive shift in the equilibrium potential of the OER and increase the equilibrium current, which indicates that the ultrasound suppresses the thermodynamic conditions of the OER and improves the dynamic conditions of the OER. Ultrasound increases the Rct of OER and decreases Rs. Regardless of Pt or Ni electrode, the desulphurization of bauxite can be improved by ultrasonic. Electrolysis desulphurization with ultrasonic coupled nickel electrode can achieve the effect of platinum electrode without ultrasonic. (4) By examining the corrosion behavior, desulfurization effect, and electrochemical behavior of the six electrode materials, the ideal anode material was optimized. Sodium thiosulfate solution was used as a simulated electrolyte, Tafel and CV curves show that corrosion potentials of six electrode materials are Ni> C> SS> Fe> Cu> Pb-Ag. The desulphurization rate and cell voltage of the bauxite electrolysis are Cu> Ni> Fe> SS> C> Pb-Ag and Ni> Fe> SS> Cu> C> Pb-Ag respectively. Finally, Ni was selected as the ideal anode material for the desulphurization of bauxite, which provided the possibility for industrial application of electrolytic desulfurization.

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26867
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
胡英楠. 羟基自由基氧化黄铁矿及外场强化高硫铝土矿电解脱硫机理[D]. 中国科学院研究生院,2018.
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