【作者】 林俊雄；

【导师】 杨辉； 詹树林；

【作者基本信息】 浙江大学 ， 材料学， 2007， 博士

【摘要】 纺织印染、造纸、塑料及皮革等工业每年都产生大量的染料废水，由于许多染料为含偶氮键、多聚芳香环的复杂有机物，可致畸、致癌、致突变，因此，这类废水中染料的去除非常重要。许多染料抗氧化、难降解，采用吸附剂去除废水中的染料具有较大优势。活性炭是一种有效的吸附剂，但价格昂贵，限制了它的广泛应用；而硅藻土资源丰富，多孔、比表面积大，有望成为一种高效廉价的吸附剂。然而，硅藻土原料吸附性能较差，需要进一步提高它的染料吸附性能，目前这方面的研究工作尚少，关于硅藻土染料吸附的应用、理论等方面的研究都有待完善。本文根据硅藻土矿物可有效改造的结构特征，通过活化、引入第二组分进行改性等方法，提出氢氧化镁改性及聚丙烯酰胺改性硅藻土基吸附剂制备技术，提高了硅藻土的染料吸附性能；由此，本论文率先开展了硅藻土基吸附剂的制备工艺、材料表征、染料吸附性能、染料吸附理论、染料废水处理应用这一较为系统的研究工作；在其中的理论研究中，本文对浓度比形式的准一级、准二级吸附动力学速率方程进行了修正，并在本文的染料吸附动力学研究中进行应用，验证了其可行性；而且，在染料吸附等温线模型、动力学、热力学研究的基础上，本文提出了硅藻土吸附剂的染料吸附机理。主要的研究成果如下：1、研究发现，硅藻土原料对染料溶液吸附时，杂质的存在使吸附后染液对480 nm以下的可见光吸收增强，并影响它的染料吸附性能；经450℃热活化后，杂质被去除，比表面积S_BET从67.17减小到52.56 m²·g^-1，平均孔径从8.847增大到10.29 nm，零电荷点pH_zpc由3.2提高到4.5左右，对染料溶液的脱色率增大。2、首次进行氢氧化镁改性硅藻土（MGMD）、聚丙烯酰胺改性硅藻土（HPMD）吸附剂的研究，并提出了它们的制备工艺。结果表明，MGMD中Mg（OH）₂的较佳含量在14％左右，HPMD中聚丙烯酰胺的较佳含量在0.8％左右；MGMD的材料表征结果显示，MGMD比表面积为57.84 m²·g^-1，平均孔径9.686 nm，ξ电位测定时其表面出现3次电荷反转，分别表示硅藻土等电点、Mg（OH）₂沉淀开始及Mg（OH）₂等电点；染料吸附结果显示，MGMD对阴离子染料的脱色率大于活性炭，HPMD对阳离子染料的脱色率接近于活性炭。3、研究了吸附剂浓度、盐的加入、吸附时间、pH值等因素对硅藻土吸附剂染料吸附的影响。发现了亚甲基蓝（MB）染液在较高pH条件下，因水解或形成二聚体对可见光的吸收强度随时间不断降低的现象。根据此现象，本文提出，pH值增大，硅藻土或其它矿物吸附剂对MB脱色率增大的原因有两个：一是pH值越大，吸附剂表面负电荷量越多，因此对阳离子染料MB的吸附增大；二是在高pH下，MB自身水解或形成二聚体导致脱色率增大。由于MB是表征吸附剂吸附性能最常用的染料之一，该发现对于其它吸附剂的研究也具有参考价值。4、修正了浓度比形式的准一级、准二级动力学速率方程。对动力学实验数据拟合时，它们能更直观地表现吸附质浓度随时间的变化过程，而且在平衡吸附容量q_e未测定的情况下，它们均可根据动力学数据直接预测吸附剂的q_e值；从而发展了准一级、准二级动力学模型新的应用模式。5、研究了热活化硅藻土与MGMD吸附剂的染料吸附等温线模型、动力学模型、热力学参数，并提出了它们的染料吸附机理。结果表明，在Langmuir、Freundlich及Redlich-Peterson模型中，它们对染料的吸附等温线最符合Redlich-Peterson模型；它们对染料的吸附过程则更符合准二级动力学模型；它们对染料的吸附机理为：通过静电引力、氢键、n-π作用及范德华力吸附染料分子，其中，静电引力和氢键吸附起主要作用。更多还原

【Abstract】 A huge quantity of dye wastewater is discharged by textile, paper, plastic and leather industries every year. As many dyes are complex organic contained azo and poly aromatic ring, which may cause people abnormal, cancerous and mutagenic, the removal of dyes from these wastewaters is a very important subject. Lots of dyes are resistant to oxidation and degradation, so adopting adsorbent to remove the dyes may be superior to other methods. The activated carbon is a very effective adsorbent, but its high price limits its extensive use. The diatomite is abundant, porous and has high specific surface area, which make it hopeful to be one effective and low-cost adsorbent. However, the adsorption capability of raw diatomite still needs to be improved and the studies on its application and theory on dyes adsorption are still expected to be carried out further.In this paper, basing on the structure characteristics of diatomite, the preparation technique of adsorbent of Mg（OH）₂-modified diatomite and polyacrylamide-modified diatomite were developed with the method of activated and combined the second composition, which improved the adsorption capability for dyes. Hence, the system study from preparation process, materials characterization and dye-adsorption property to the dye-adsorption theory and application of diatomite-based adsorbent was carried out. On the study of adsorption theory, the traditional pseudo-first-order and pseudo-second-order kinetics equations were rearranged to be concentration form in the paper, and then they were applied to study the kinetics of dyes adsorption onto diatomite, which verified their practicability. Moreover, the adsorption mechanisms of dyes onto diatomite-based adsorbent were presented in this paper after the study of adsorption isotherms, kinetics and thermodynamics. The main achievements are as follows:（1） It was found that when the dye solution was adsorbed by the raw diatomite, the impurity on the raw diatomite made the dye solution after adsorbed increase the absorbance of visible light under the wavelength of 480 nm, which impacted the adsorption capability of diatomite. The impurity was removed when the diatomite was calcined at 450 ℃, with the specific surface area (S_BET) decreasing from 67.17 to 52.56m²·g^-1, the average pore diameter increasing from 8.847 to 10.29 run, the zero charge point (pH_zpc) increasing from 3.2 to 4.5, and the removal of dye solution improving.（2） The preparation processes of adsorbents of Mg（OH）₂-modified diatomite （MGMD） and polyacrylamide-modified diatomite （HPMD） were developed first time. It was found that the optimum content of Mg（OH）₂ in MGMD was about 14% and that of polyacrylamide in HPMD was about 0.8%. The characterization study of MGMD showed that the S_BET of MGMD was 57.84 m²·g^-1 and the average pore diameter was 9.686 nm, and there were three times of charge reverse during the determination of zeta potential, which denoted the isoelectric point of diatomite, the precipitation start of Mg（OH）₂ and the isoelectric point of Mg（OH）₂. Moreover, the dye removal of anionic dyes onto MGMD was higher than that onto activated carbon while the removal of cationic dyes onto HPMD was close to that onto activated carbon.（3） The effects of adsorbent concentration, salt, adsorption time and pH value on the dyes adsorption of diatomite adsorbent were analyzed. It was found that the absorbance of visible light of Methylene blue （MB） solution decreased at high pH because of hydrolysis or forming dimer of MB. On the basis of this find, we proposed that there were two reasons for the increasing removal of MB onto diatomite or other mineral adsorbents with the increasing pH value: one was the increasing negative charge on the adsorbents surface with pH increasing and the other was the hydrolysis or dimer forming of MB which causing the removal increase. As MB is one of the most popular dyes for characterization of various adsorbents, this find may be also taken as reference to other adsorbent studies.（4） The concentration forms of pseudo-first-order and pseudo-second-order kinetics equations were rearranged in the paper. When they are applied to fit the kinetic data, they can describe the variation process of the dye concentration with time more visually, and under the condition of without equilibrium adsorption capacity （q_e） determination, both of them can be used to predict the q_e value directly after the fitting.（5） The adsorption isotherms model, kinetics model and thermodynamic parameters of dyes onto heat activated diatomite and MGMD were firstly studied and their dyes adsorption mechanisms were then proposed in the paper. The adsorption isotherms were studied using Langmuir, Freundlich and Redlich-Peterson models. It showed that theRedlich-Peterson model was the best one. The adsorption process of dyes can be better described by the pseudo-second-order model than the pseudo-first-order model. And the adsorption mechanisms of dyes were proposed as: adsorption by an electrostatic force, hydrogen bond, n-π interaction and Van der Waals force, of which the electrostatic force and hydrogen bond were the main effects.更多还原