【作者】 李健；

【导师】 武建军；

【作者基本信息】 中国矿业大学 ， 化学工艺， 2023， 博士

【摘要】 煤气化渣（CGS）是煤气化工艺生产中产生的废弃物,组分富含残炭、非晶态硅铝酸盐、少量有机挥发物和重金属离子,年排放量高达6000～8000万吨,常规堆存易导致水源、土壤及空气的污染。煤气化废水是煤气化过程中洗涤、冷凝与分离阶段产生的废水,无组织排放的煤气化废水更易引发中毒、致癌、传染病及生态危害,二者叠加是造成区域环境污染和人体危害的重大环境问题。按照“以废治废”思路,本研究利用物理活化/化学改性方法对气化渣进行脱灰得到的残炭,负载Fe³⁺掺杂的纳米TiO₂制备了粒子电极(Fe³⁺-TiO₂@CGS)并填充于光电化学反应器中,进一步设计构筑了由高性能的涂层钛（DSA）阳极、钛阴极及Fe³⁺-TiO₂@CGS粒子电极组成的三维电极光电Fenton体系,并将其用于煤气化废水的降解,实现了光催化、三维电极电催化和Fenton三种技术耦合协同。详细考察了多因素对三维电极粒子材料设计过程的影响,验证了粒子电极具有多效性、可控性和实用性的特点,为三维粒子电极材料的微观结构与宏观反应动力学之间的关系等具体问题提供科学依据。主要完成了以下工作:（1）气化渣的特性分析及活化/改性法脱灰提炭研究:详细分析了GE水煤浆气化粗渣和细渣理化性质,采用物理活化/化学改性方法高效脱除气化细渣的灰分以获取多孔碳材料,通过响应曲面法获得较高比表面积的工艺条件,并进一步分析了炭灰分离机理及气化渣残炭作为粒子电极的优势。研究结果表明:气化细渣与粗渣相比,具有粗糙疏松的表面,较高的孔隙度、烧失量和固定碳含量,粒径分布均匀,比表面积(S_BET)达到335.08 m²/g,是制备功能炭材料的适宜前驱体。在煅烧温度为790℃,煅烧时间为2 h和碱渣质量比0.02:1的条件下,通过物理活化/化学改性方法可获得S_BET达624.94 m²/g的残炭,固定碳由41.03%提高到94.33%,细渣和残炭的平均粒径分别为120μm和100μm,残炭粒径分布更均匀且无较大颗粒。通过细渣和残炭的循环伏安（CV）曲线、线性扫描伏安（LSV）曲线、交流阻抗谱（EIS）等电化学性能测试,表明残炭具有较低的电阻和良好的导电性,是构筑新颖的环境友好型电催化电极材料的载体。（2）三维电极光电Fenton体系电极的制备、表征及性能研究:采用涂层法制备了DSA阳极并对其表面组成进行表征分析,利用不同方法制备了气化渣残炭负载Fe³⁺掺杂的TiO₂粒子(Fe³⁺-TiO₂@CGS),针对由DSA阳极、钛阴极及Fe³⁺-TiO₂@CGS粒子电极组成的三维电极光电Fenton体系,通过XRD、SEM及光电催化性能的研究考察煅烧温度、TiO₂负载量、Fe³⁺掺杂量对Fe³⁺-TiO₂@CGS粒子性能的影响,结果表明:采用溶胶凝胶法制备,在煅烧温度500℃、14.88%的TiO₂负载量和9.43%的Fe³⁺掺杂量时,Fe³⁺-TiO₂@CGS粒子表现出良好的光电催化性能和稳定性,这是因为TiO₂、Fe₂O₃纳米颗粒以较大附着力负载于残炭表面上,当Fe³⁺进入TiO₂晶格中强化了不可逆的电子捕获势阱,抑制了电子-空穴的复合,残炭孔结构表现出与TiO₂晶体间的协同作用,加之残炭本身在电化学过程的导电作用,这为构筑的Fe³⁺-TiO₂@CGS粒子在光电Fenton降解废水体系中的“吸附+光催化+电催化+Fenton”协同作用的实现提供理论依据。（3）三维电极光电Fenton体系降解模拟煤气化废水机制研究:分析了煤气化废水中有机化合物组成,确定了模型化合物,利用构建的三维电极光电Fenton体系考察影响降解模型废水的因素并建立了动力学方程,采用自由基捕获实验和电子顺磁共振技术（EPR）来验证自由基基团的种类和贡献能力,详细阐明降解路径过程和机理,考察Fe³⁺-TiO₂@CGS粒子在光电Fenton体系中对亚甲基蓝（MB）废水的降解和脱色效果。研究结果表明:煤气化废水中的有机物主要是酯类、醇类、醚类和烷烃类等,以乙酸乙酯和二氯乙烷作为萃取剂时,废水中乙二醇二乙醚（EGDE）的含量分别为50.79%和52.13%。利用三维电极光电Fenton处理EGDE模拟废水,在浓度为0.1 mol/L,电解电压25 V时、溶液p H=3、粒子投放量3 g、光照强度600 W时,具有良好的可降解性且符合一级动力学模型。自由基捕获实验表明在光电协同条件下产生羟基自由基（·OH）、超氧负离子自由基（·O₂^-）、过氧羟基自由基（HO₂·）和电子空穴（h⁺）,且·OH在降解过程中起主导作用。当EGDE的碱性基团与酸作用发生开裂反应和醚的自动氧化反应分解后的小分子有机物进一步矿化为CO₂和H₂O。分析发现EGDE的降解过程是由阳极直接氧化、阴极氧化性基团氧化、空穴氧化和粒子电极氧化的四种作用共同完成,其中Fe³⁺-TiO₂@CGS粒子的理化性能在降解废水时起到显著作用。研究还发现,在Na Cl为支持电解质、电解电压为20 V、溶液p H=3时,进行光电Fenton处理MB废水60 min后,去除率高达99.79%,降解和脱色效果明显。（4）三维电极光电Fenton体系对煤气化废水的降解工艺研究:在对比不同电解方法降解煤气化废水的基础上,研究三维电极光电Fenton降解煤气化废水中起始溶液p H、电解电压、粒子投放量对处理效果的影响,利用响应曲面法对单因素条件进行优化,最后考察处理前后的水质和光电Fenton体系的能耗。研究结果表明:煤气化废水中COD经不同电解条件在180 min处理后的去除率顺序为:三维电解+光照>三维电解>二维电解+光照>二维电解,其中三维电极+光照在调节溶液p H=5时废水的COD去除率可达58.38%。通过优化实验表明,当溶液p H=3,电解电压为25 V时,粒子投放量为4.9 g,该条件下废水的COD去除率可以达72.31%。改变粒子电极的种类(Fe³⁺-TiO₂@CGS+Zn、Fe³⁺-TiO₂@CGS+Ni、Fe³⁺-TiO₂@CGS)进行对比研究发现Fe³⁺-TiO₂@CGS粒子电极在煤气化废水处理中降解作用显著。在最佳条件下降解煤气化废水还可实现部分NH₃-N、Cl^-、BOD和TOC去除,而由DSA阳极和Fe³⁺-TiO₂@CGS粒子构成的电极体系在三维电极光电催化时能耗最低（0.1937 W·h/mg）,因此三维电极光电Fenton在废水处理中应用潜能显著。上述研究不仅为气化渣的资源化利用找到一种新途径,也为工业废水处理新方法提供理论指导与技术支撑。更多还原

【Abstract】 Coal gasification slag（CGS）,a waste generated by coal gasification,is rich in residual carbon and amorphous aluminosilicate,which also contains few organic volatiles and heavy metal ions.The annual emission of gasification slag is as high as60～80 million tons,and the conventional piling up and storage will cause the water sources,soil,and air.Generally,the coal gasification wastewater is produced during the processes of washing,condensation and separation stages of coal gasification,which will lead to poisoning,carcinogenesis,infectious diseases,ecological hazards,etc.after the unregulated and untreated discharge.These two pollution sources will cause major environmental problems that seriously affect the local ecological environment and threaten human health.According to the idea of treating the wastes with wastes,in this study,pulled out the residual carbon from gasification slag by physical activation/chemical modification method to remove the ash in gasification slag.Afterward,the extracted gasification slag residual carbon was used to prepare Fe³⁺-TiO₂@CGS particle electrode by loading Fe³⁺-doped nano-TiO₂on it,which was filled in a photoelectrochemical reactor.A three-dimensional（3D）electrode-based photoelectric-Fenton system composed of a high-performance DSA coating titanium anode,Ti cathode and Fe³⁺-TiO₂@CGS particle electrode was designed and constructed in order to realize the coupling and cooperation of photocatalysis,3D electrode-assisted electrocatalysis,and Fenton techniques to degrade the coal gasification wastewater.In addition,the effects of multiple factors on the design process of 3D particle electrode material were investigated in detail,and the particle electrode was verified to be multifunctional,controllable,and practical use.This study provides scientific guidance for evaluating the relationships between the microstructure and the macroscopic reaction kinetics of 3D particle electrode materials.The main contributions in this study are as follows:（1）Characteristic analysis of gasification slag and study on deashing and carbon extraction by activation/modification method.Physicochemical properties of coarse slag and fine slag obtained from GE coal-water slurry process were analyzed in detail.The ash in gasified fine slag was efficiently removed by a physical activation/chemical modification method to obtain porous-structured carbon material.Response surface methodology was adopted to obtain the relatively high specific surface area and optimum process conditions.Carbon-ash separation mechanisms and advantages of gasification slag residual carbon as particle electrode were further analyzed.Research results indicate that compared with coarse slag,fine gasified slag has a rough and loose surface,high porosity,high loss on ignition,fixed carbon content,a uniform particle size distribution,and a specific surface area(S_BET)reached at 335.08 m²/g.Therefore,fine slag is a suitable precursor for the preparation of functional carbon materials.Under the condition of the calcination temperature of790℃,calcination time of 2 h,and alkali residue mass ratio of 0.02:1,the S_BETof residual carbon obtained by physical activation/chemical modification method is as high as 624.94 m²/g.Moreover,the fixed carbon increased from 41.03%to 94.33%,and the average particle sizes of fine slag and residual carbon are 130μm and 100μm,respectively.The particle size distribution of residual carbon is more uniform,and no existence of larger particles.The electrochemical results from cyclic voltammetry（CV）,linear sweep voltammetry（LSV）,and AC impedance spectroscopy（EIS）indicate that the residual carbon has low resistance and excellent conductivity.Therefore,it is a reliable carrier for preparing novel environmental-friendly electrocatalytic electrode materials.（2）Preparation,characterization and properties of electrodes in three-dimensional photoelectro-Fenton system.DSA anode was prepared using a coating method.The surface composition of this anode was characterized and analyzed.Different methods were used to prepare Fe³⁺-doped TiO₂particles,which were further loaded on residual carbon to obtain Fe³⁺-TiO₂@CGS.A three-dimensional（3D）electrode-based photoelectric-Fenton system composed of DSA anode,Ti cathode and Fe³⁺-TiO₂@CGS particle electrode was designed and constructed.XRD,SEM,and photoelectrocatalytic performance tests were carried out in order to evaluate the effects of calcination temperature,TiO₂loading,and Fe³⁺doping content on the performance of Fe³⁺-TiO₂@CGS particles.The results indicate that Fe³⁺-TiO₂@CGS exhibit good photoelectrocatalytic performance and stability when it was prepared by sol-gel method with a calcination temperature of 500℃,a TiO₂loading of 14.88%,and Fe³⁺doping content of 9.43%.This is attributed to that TiO₂and Fe₂O₃nanoparticles are strongly adhered to the surface of residual carbon.When Fe³⁺ions entered the TiO₂crystal lattice,the irreversible electron-capturing potential well was strengthened and the electron-hole recombination was reduced,resulting in the enhancement of the cooperative effect between the residual carbon pore structure and TiO₂crystals.In addition,the residual carbon itself has good conductivity that is beneficial to the electrochemical process.These findings will provide theoretical basis for employing Fe³⁺-TiO₂@CGS as particle electrode for achieving the"adsorption+photocatalysis+electrocatalysis+Fenton"synergistic effect in a photoelectrically-coupled wastewater degradation system.（3）Study on the mechanism of simulated coal gasification wastewater degradation by three-dimensional electrode photoelectric-Fenton system.The composition of organic compounds in coal gasification wastewater were investigated in detail,and a model compound was determined.The constructed three-dimensional electrode photoelectric-Fenton system was used to examine the factors that affect the degradation of simulated wastewater,and a kinetic equation was established.We employed free radical capture experiments and electron paramagnetic resonance（EPR）technology to clarify the degradation process and pathways,and degradation and decolorization effects of Fe³⁺-TiO₂@CGS on methylene blue（MB）-containing organic wastewater in the photoelectric-Fenton system were examined.The results indicate that the organic matter in coal gasification wastewater mainly consists of esters,alcohols,ethers,and alkanes.When ethyl acetate and dichloroethane were used as extractants,ethylene glycol diethyl ether（EGDE）contents in wastewater are determined to be 50.79%and 52.13%,respectively.The 3D electrode-based photoelectric-Fenton system was used to treat the simulated EGDE wastewater.At a concentration of 0.1 mol/L,an electrolysis voltage of 25 V,a solution p H of 3,a particle dosage 3 g and a light intensity of 600 W,the simulated wastewater was well degradable,and the degradation process conforms to a first-order kinetic model.The free radical capture experiments demonstrate that hydroxyl radicals（·OH）,superoxide anion radicals（·O₂^-）,peroxyhydroxyl radicals（HO₂·）,and electron holes（h⁺）were generated under the coupled photoelectrical conditions,and·OH plays a key role in the degradation process.When the alkaline group of EGDE interacts with acid,both the spontaneous oxidation and cracking reaction of ether take place,which can promote the mineralization of the generated low molecular weight organic matter after the decomposition into CO₂and H₂O.The degradation process of EGDE occurred via multiple oxidation processes,including the direct oxidation of anode,the oxidation of cathodic oxidizing group,hole oxidation,and particle electrode oxidation.The physico-chemical properties of Fe³⁺-TiO₂@CGS further enhance the degradation efficiency of simulated EGDE wastewater.The removal efficiency of up to 99.79%can be achieved in Na Cl supporting electrolyte with a p H of 3,when the photoelectric-Fenton treatment of MB wastewater at the voltage of 20 V was carried out for 60 min Thus,the effect of degradation and decolorization is obvious.（4）Study on the degradation conditions of coal gasification wastewater by three-dimensional electrode photoelectric-Fenton system.Based on the comparation of coal gasification wastewater degradation by electrolysis method,the effects of solution initial p H,electrolysis voltage,and particle dosage on the treatment and degradation performance of 3D electrode-based photoelectric-Fenton system were investigated respectively.Additionally,the response surface methodology was used to optimize single factor condition,examine the water quality before and after treatment,and evaluate the energy consumption of the constructed photoelectric-Fenton system.When the time of coal gasification wastewater treatment via various electrolysis conditions reaches 180 min,The order of COD removal rates are listed as follows:3D electrolysis+light>3D electrolysis>2D electrolysis+light>2D electrolysis.The combination of 3D electrolysis+light can achieve a COD removal rate of 58.38%in the solution with a p H of 5.The optimization experiments show that the COD removal rate can be achieved as high as 72.31%in the solution with a p H of 3 at the electrolysis voltage of 25 V when a particle dosage of 4.9 g was used.Different particle electrodes(Fe³⁺-TiO₂@CGS+Zn,Fe³⁺-TiO₂@CGS+Ni,Fe³⁺-TiO₂@CGS)were evaluated,and the results indicate that Fe³⁺-TiO₂@CGS particle electrode has an efficient degradation effect for the treatment of coal gasification wastewater.Moreover,NH₃-N,Cl^-,BOD,and TOC can also be partially removed during the degradation process of coal gasification wastewater under the optimal conditions.The electrode system composed of a DSA anode and Fe³⁺-TiO₂@CGS particle electrode has the lowest energy consumption（0.1937 W·h/mg）for the 3D electrode-assisted photoelectrocatalysis process.Therefore,this photoelectric-Fenton system has significant application potential in wastewater treatment.This work not only discovers a new approach for the resource utilization of gasification slag,but also provides theoretical guidance and technical support for new methods of industrial wastewater treatment.更多还原