【作者】 王春峰；

【导师】 王连军；

【作者基本信息】 南京理工大学 ， 环境工程， 2009， 博士

【摘要】 本论文目的是研究以粉煤灰为原料合成沸石,主要开展了从沸石制备工艺、材料品质表征、重金属及碱性染料吸附性能、吸附机理、沸石吸附剂再生这一较为系统的研究。论文探讨了由粉煤灰合成沸石的影响因素,从结构、性能和应用指标方面对比了采用两种方法（两步法和碱熔融—水热法）合成沸石的品质,并通过吸附等温线模型、动力学、热力学研究,深入解析了沸石吸附剂对重金属和染料的吸附机理。最后对粉煤灰合成沸石的新方法也进行了初步研究。首先,采用由粉煤灰制备沸石的两步法和碱熔融—水热法,重点探讨了NaOH溶液浓度、NaOH与粉煤灰质量比、Si/Al摩尔比和合成时间对沸石的种类和结晶度的影响,并从结构、性能及其应用指标三个方面对比研究了合成沸石的品质。结果表明,以除铁粉煤灰为原料,采用两步法分别合成了纯结构的NaA和八面沸石（NaX和NaY型沸石）,在3种NaOH溶液浓度(1.67 mol·L^-1,5 mol·L^-1和6.67 mol·L^-1)条件下,由粉煤灰制备的硅铝凝胶在100℃下分别经过5.5 h,4h和3 h晶化后可得到纯结构NaA型沸石。通过激光粒度仪和透射电镜表征,在5 mol·L^-1和6.67 mol·L^-1NaOH溶液浓度的条件下首次合成了纯结构的亚微米NaA型沸石,平均粒径分别为450 nm和250 nm,粒度分布范围分别为3.84和2.44。在3.33 mol·L^-1NaOH溶液浓度条件下,通过调节硅铝凝胶的SiO₂/Al₂O₃摩尔比为7.36,晶化合成24 h后获得纯结构的NaX型沸石。通过晶胞参数（α）和X射线荧光两种手段计算的SiO₂/Al₂O₃摩尔比值说明,由除铁粉煤灰合成纯结构的NaY型高硅八面沸石。对于碱熔融—水热合成法,在NaOH与粉煤灰的质量比为1.3,由粉煤灰制备的硅铝凝胶在100℃下经过24 h晶化后可由粉煤灰得到单一、结晶度完好的NaX型沸石;在此基础上,通过添加铝源调节硅铝凝胶的SiO₂/Al₂O₃摩尔比,晶化合成5 h后可获得单一、结晶度完好的NaA型沸石矿物种类。对采用两种方法（两步法和碱熔融—水热法）制备的NaA和NaX型沸石的品质（结构、性能及其应用指标）进行了详细表征,并与相应商品沸石作了对比。IR光谱分析表明合成产物具有相应的沸石骨架结构红外谱峰;DTA分析表明了合成产物中沸石水的存在,且产物稳定性较好;通过比较化学组成表明,大规模应用合成产物不会对环境造成危害;比表面积、孔容和CEC的比较说明,合成产物的性能和各项应用指标均接近于商品沸石,具有良好的工业潜在应用价值。此外,除铁前后合成产物的CEC表明:粉煤灰除铁有利于沸石产物的合成。静态吸附条件下,两步法合成NaA型沸石吸附三种重金属（Cu（Ⅱ）、Cr（Ⅵ）和Zn（Ⅱ））的动边界模型研究表明,Cu（Ⅱ）和Zn（Ⅱ）离子的吸附过程主要由液膜扩散控制,而Cr（Ⅵ）离子的吸附过程主要由颗粒扩散控制,三种重金属离子的吸附过程都符合二级动力学速率方程。NaA型沸石对三种重金属离子的吸附等温线更加符合Langmuir模型,静态饱和吸附量分别为82.30,65.96和47.78 mg·g^-1。解吸与再生实验表明,Cu（Ⅱ）和Zn（Ⅱ）离子的解吸效果较好,有利于重金属的回收及沸石吸附剂的再生重复利用。NaA型沸石对Cu（Ⅱ）和Zn（Ⅱ）离子的吸附机理主要是金属氢氧化物沉淀和离子交换吸附,而对Cr（Ⅵ）离子的吸附机理主要是氢键作用和沸石吸附。静态吸附条件下,对于碱熔融—水热法合成NaA和NaX型沸石矿物吸附MB染料而言,MB染料的吸附过程主要由膜扩散和颗粒内扩散联合控制,一级、二级动力学速率方程吸附速率方程拟合结果显示,两种沸石吸附剂对MB染料的吸附则更符合二级动力学速率方程。在Langmuir和Freundlich模型中,它们对MB染料吸附的更符合Langmuir等温线模型,且MB染料在NaX型沸石上的静态饱和吸附量均大于NaA型沸石,热力学参数（焓ΔH、熵ΔS和ΔG）表明,一方面,它们对染料的吸附主要为吸热过程;另一方面,染料的吸附是一种自发过程。本文以初始pH值、温度和沸石用量为考察因素,研究了原始和再生吸附剂对MB染料去除率的影响,发现随着初始pH值、沸石用量和吸附温度的增大,MB染料的去除率增大,焙烧再生后的沸石矿物吸附剂对MB染料的吸附性能略低于原始吸附剂。NaA和NaX型沸石矿物对MB染料的吸附机理为,通过静电引力、氢键、n-π作用及范德华力吸附MB染料分子,其中,静电引力与氢键作用起主要作用。本文提出了新工艺及新方法以补充和发展由粉煤灰合成沸石的研究领域。主要包括:一是基于传统一步合成法,以熔融粉煤灰和脱硅粉煤灰为原料,考察NaOH溶液浓度和晶化时间对合成沸石矿物种类和结晶度的影响。结果显示,合成产物以NaA、NaP和HS型三种沸石矿物类型为主,另外有少量菱沸石生成。二是在F^-离子体系下的同步抽取法,采用NaOH溶液同步抽取脱硅粉煤灰中硅铝成分;而后利用HF酸调节溶液的pH值;最后在F^-和OH^-离子共存的体系中水热合成沸石。实验结果表明,应用此新方法,可由脱硅粉煤灰合成了纯结构的NaA-NaX-HS型混合沸石相。更多还原

【Abstract】 The research objective of this dissertation is to investigate synthesis process of zeolites from fly ash（FA）.The systemic investigations are performed about zeolites synthesis method,materials quality characterization,heavy metal ions/dye adsorption mechanism and adsorbents regeneration.The influential factors on zeolites synthesis were discussed and the qualities of zeolites synthesized from FA by two-step and alkaline fusion methods were compared from structure,performance and application target points of view.Based on adsorption isotherms,kinetic and thermodynamic studies,the adsorption mechanism of heavy metal ions and dye on synthetic zeolites was analyzed.Finally,the pilot study was performed for new process and method of FA synthesized zeolites in this dissertation.In the first,two-step and alkaline fusion methods were adopted to synthesize zeolites from fly ash.Emphasis was put on investigate the influential parameters such as concentrations of NaOH solution,NaOH/FA ration（g/g）,Si/Al molar ratio and synthesis time on the type and degree of synthetic zeolites and qualities of synthetic zeolites from structure,performance and application target points of view. Experimental results demonstrated,for two-step method,pure-form LTA（NaA zeolite） and FAU type zeolites（NaX and NaY zeolite） were syhtesized from pretreated-FA, respectively.Generally,pure-form NaA zeolite could be synthesized form FA prepared aluminosilicate gel when following conditions were used:NaOH concentrations,1.67,5 and 6.67 mol·L^-1;the synthesis temperature,100℃;the corresponding synthesis time,5.5,4 and 3 h.By analysis of particle size measurements and TEM,pure-form submicron-NaA zeolites are firstly synthesized at the condition of 5 and 6.67 mol·L^-1 NaOH solution,respectively.The average crystal size and size span of the products are 450 nm and 250 nm,3.84 and 2.44,respectively; pure-form NaX zeolite could be synthesized form FA prepared aluminosilicate gel when following conditions were used:NaOH concentrations,3.33 mol·L^-1; SiO₂/Al₂O₃ molar ratios,7.36;the synthesis temperature,100℃;the corresponding synthsis time,24 h.The SiO₂/Al₂O₃ molar ratios calculated using lattice parameters （a₀） and XRF explained pure-form NaY zeolite could be synthesized from pretreated-FA.For alkaline fusion method,single-phase and high-crystalline NaX zeolite could be synthesized form FA prepared aluminosilicate gel when following conditions were used:NaOH/FA ratio,1.3;the synthesis temperature,100℃;the corresponding synthesis time,24 h.Based on above studies,single-phase and high-crystalline NaA zeolite could be synthesized form FA after 5 h,and with the addition of Al source,to adjust SiO₂/Al₂O₃ molar ratios of prepared aluminosilicate gel.The qualities of NaA and NaX zeolites synthesized from FA by two-step and alkaline fusion methods were characterized detailedly from structure,performance and application target points of view.The corresponding commercial grade zeolites were also investigated for comparison.Analysis of IR spectra corresponds to peaks of corresponding zeolitic structural formation.DTA curves indicate the presence of zeolitic water in the products and the products have better stabilization.The elemental composition shows that the products do not pose any serious threat to the environment when compare with commercial zeolites.The data of the surface area,pore volume and CEC（CEC,Cation exchange capacity） values show that the qualities of synthetic zeolites are near to the corresponding commercial grade zeolites.FA synthesized zeolites have the potential value of industrial applications.In addition,CEC values clearly illustrated that acid-washing process demonstrated a benefit effect on synthesis.With the static method,the adsorption peoformance of NaA zeolite（two-step） to three heavy metal ions（Cu（Ⅱ）,Cr（Ⅵ）,Zn（Ⅱ）） and NaA and NaX zeolites（fusion） to MB dye in aqueous solution was studied and the adsorption mechanism was discussed, respectively.For two-step method,Moving Boundary Model analysis shows that the adsorption rate of Cu（Ⅱ） and Zn（Ⅱ） ions was mainly governed by liquid film diffusion, and intra-particle diffusion is important controlling factor for the adsorption rate of Cr（Ⅵ） ion.The adsorption processes of three heavy metal ions follow a pseudo-second-order kinetic model.The equilibrium adsorption data fitted to Langmuir isotherms and the greatest adsorption capacity of Cu（Ⅱ）,Cr（Ⅵ） and Zn（Ⅱ） is 82.30 mg/g,65.96 mg/g and 47.78 mg/g,respectively.The desorption and regeneration experiments showed that excellent desorption effect of Cu（Ⅱ） and Zn（Ⅱ） ions favor to recover heavy metal ions and regenerate adsorbents.The adsorption mechanisms of Cu（Ⅱ） and Zn（Ⅱ） ions were proposed as:metal hydrate precipitation and cation exchange reaction while the adsorption mechanisms of Cr（Ⅵ） ion were the common effect of hydrogen bond and adsorption.For alkaline fusion method,the step of MB dye adsorption was governed by liquid film diffusion with the experimental data mathematically described using liquid film diffusion,intraparticle diffusion and chemical reaction equations and the adsorption process followed pseudo-second-order model.The adsorption data correlated well with Langmuir equation.Thermodynamic parameters（ΔH,ΔS andΔG） revealed that the adsorption of MB dye is endothermic in nature and spontaneous process.It showed the removal performance of MB on original and regenerative adsorbents was dependent on these parameters such as initial pH value of the solution, temperature and adsorbent dosage.Generally,the removal efficiency of MB increased with a rise of initial pH value of the solution,temperature and adsorbent dosage. Regenerative adsorbents exhibited lower adsorption capacity compared to original adsorbents.And the adsorption mechanisms of MB dye were concluded as:adsorption by an electrostatic force,hydrogen bond,n-πinteraction and Van der Waals force,of which the electrostatic force and hydrogen bond were the main effects.In order to supplement and develop the fields of FA synthesized zeolites,the new synthesis process and method were studied in this dissertation.On the basis of this idea,we proposed two synthesis routes:one was the modified one-step method.The influential parameters such as concentrations of NaOH solution and synthesis time were investigated on the type and degree of synthetic zeolites from fusion FA and desilicated FA.The results showed that the products contain mainly NaA、NaX and HS zeolites with the trace of chabazite.The other was simultaneous extraction method in F^- ion.This method contains three steps:（1） NaOH solution simultaneous extraction Si and Al from desilicated FA;（2） adjust pH value of the solution by HF acid;（3） hydrothermal synthesis zeolites in concomitan F^- and OH^- ions system.更多还原