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题名: 纳米颗粒物混凝过程的影响机制与絮体调控
作者: 徐慧
学位类别: 博士
答辩日期: 2015-07
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 王东升
关键词: 纳米材料,混凝过程,破碎再絮凝,强度因子,恢复因子,Nano materials, Coagulation process, Breakage and regrowth, Strength factor, Recovery factor
其他题名: The mechanisms on the coagulation process and regulation of flocs in nano particles system
学位专业: 环境科学
中文摘要:       混凝池中由于各处流场的速度梯度存在分布不均匀的现象,絮体会发生一定程度的破碎。因此,研究混凝过程中絮体的絮凝、破碎以及再生长过程对于保证混凝效果、保障供水安全具有重要的意义。目前针对混凝过程中絮体的形态以及破碎再生长过程的研究主要集中在高岭土-腐殖酸体系中,对于纳米颗粒物混凝过程的影响机制与絮体调控的研究还没有进行的很充分。本研究主要采用马尔文激光粒度仪对混凝过程中形成的絮体进行监测和分析,并且应用动态红外技术对混凝过程中的官能团变化进行了表征,探讨纳米材料(纳米TiO2 与纳米Al2O3)对混凝过程的影响以及不同混凝条件(不同pH 值、不同阴阳离子浓度、有机物的浓度)对纳米TiO2 体系中形成絮体形态的影响,得出了一系列的结论:
    1. 通过研究纳米颗粒物对混凝过程的影响可以发现,体系中存在的纳米颗粒对混凝过程的影响主要体现在纳米颗粒对体系Zeta 电位的影响上。在实验pH值范围内,纳米TiO2 颗粒均带负电,过高浓度的纳米TiO2 颗粒使得平衡时絮体粒径下降。当纳米颗粒不带电荷时,其对混凝过程中形成的絮体粒径无明显影响。体系中有腐殖酸(HA)分子存在时,纳米颗粒对混凝过程的影响除了对体系Zeta电位的影响外,还包括对体系中HA 分子的吸附。纳米颗粒对体系中HA 分子的吸附使得体系中HA 分子数量下降,絮体分形维数上升,但是当纳米TiO2 浓度
过高时,体系Zeta 电位由于含有过多的纳米TiO2 颗粒而下降,颗粒之间的相互排斥使得絮体分形维数下降。通过监测、对比混凝过程中的原位红外变化,揭示了纳米颗粒物表面官能团在混凝过程中的作用。
      2. 研究了具有不同铝形态的混凝剂对纳米TiO2 体系混凝过程的影响,表明了提纯Al13 其混凝过程受pH 值影响较小,在较宽的pH 范围内均能保证一定的混凝效果。提纯Al13 在相同投加量下形成的絮体具有最大的粒径,且酸性条件下絮体粒径大于中性和碱性条件下形成的絮体粒径。当硫酸铝(AS) 溶液中存在纳米Al2O3 时,形成的絮体具有较使用AS 形成絮体更大的分形维数和粒径,且纳米Al2O3 的加入会增加混凝剂对pH 值的适应性和混凝剂的电中和能力。使用AS作混凝剂时,强度因子随投加量的增加而增加,在酸性条件下形成的絮体具有较大的强度因子,且絮体恢复因子受体系中HA 浓度的影响。
      3. 通过研究阳离子或者具有正电荷的纳米颗粒对混凝过程的影响可以发现,在最优投加量下体系中存在的正电荷物质会降低絮体的粒径,但絮体恢复因子会由于正电荷物质的“架桥作用”而升高(Ca2+的架桥作用明显大于Na+)。当破碎强度较高时,吸附在纳米TiO2 表面的HA 分子会解吸到水溶液中,造成絮体分形维数下降。在纳米TiO2 体系中使用AS 和PACl 作混凝剂时,絮体破碎后Zeta电位下降,当体系中有HA 存在时,再生长结束后体系Zeta 电位由于HA 分子阻止纳米TiO2 颗粒的团聚而继续下降。
      4. 研究了阴离子对纳米TiO2 体系混凝过程的影响,表明SO42-对于纳米TiO2体系的强度因子无明显影响,但是能够明显降低AlCl3 作混凝剂时再生长后絮体的粒径。HA 分子在絮体恢复阶段具有重要的作用,当体系中HA 分子数量降低时,体系恢复因子下降。体系中存在的CO32-会与混凝剂反应形成沉淀,所以对絮体粒径的影响比SO42-大,当混凝剂投加量较小,体系中较低浓度的CO32-就会使得混凝过程中无明显絮体形成。
英文摘要:       Coagulation is one of the most important technologies in drinking water and waste water treatment processes. It is inevitable that the breakage and re-growth for flocs will occur at the same time due to the asymmetry of liquid filed in the coagulation processes. So it is important to investigate the mechanisms for the floc growth, breakage and re-growth. The characteristics of flocs were studied for many years, but the effects of nano particles on the coagulation performances were not investigated well. In order to investigate the mechanism, the flocs formed in the coagulation process were continuously measured by Msatersizer 2000, and the the effects of nano particles on the coagulation performances were also carried out.
      The results for the effects of nano particles on the coagulation performances indicated that Zeta potential had significant effects on the strength factors and recovery factors in kaolin suspension. The strength factors in the presence of TiO2 particles increased with increasing the concentration of nano TiO2, but when the concentration of nano TiO2 was large enough, the strength factors decreased. The concentration of nano Al2O3 particles had no significant effects on the floc size formed in the coagulation process when the solution pH was adjusted to 8.5. The HA molecules could decrease the floc size through decreasing the Zeta potential, and the removal efficiencies for nano TiO2 and Al2O3 particles decreased with increasing concentration of DOC due to two mechanisms.
      The coagulation performances using different coagulants indicated that Al13 had largest charge neutralization ability, and the removal efficiency for DOC decreased with increasing the solution pH. The recovery factors for flocs using Al2O3+AS as coagulant were smaller, and this may be caused by the adsorption of HA molecules on nano Al2O3 particles. The strength factors for flocs formed by AS increased with increasing the dosages of AS.
      Polyacrylamide (PAM) could significantly increase the floc size, and the fractal dimension decreased with increasing the concentration of N-PAM (non ionic PAM). Zeta potentials of flocs formed without N-PAM as flocculant decreased when the flocs were broken at 400 rpm. Zeta potential using N-PAM as flocculant did not significantly decrease during breakage period, and this may be caused by the adsorption of N-PAM molecules on the new exposed TiO2 surfaces which had negative charges. The Al2O3 particles existed in the coagulants could increase the floc size and fractal dimension, and the recovery factors for flocs were larger due to the bridging effects. When the coagulant dosages were increased to 1.0 mmol/L, PACl could produce larger flocs due to electrostatic patch effects.
      4. The amount of SO42- had no significant effects on the strength factors, and it could significantly decrease the floc size after growth period using AlCl3 as coagulant. The flocs formed by PACl10 had larger size due to the electric patch effects. When the Zeta potential was large enough, there were no flocs formed in the coagulation process in TiO2 system using Al13 as coagulant. Different anions had different effects on the coagulation performances. CO32- may react with the coagulant, so it had more effects on the coagulation performances than SO4 2-. This mechanism was also proved in the second addition experiments. HA molecules played an important role in the recovery period due to bridging effects.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34453
Appears in Collections:环境水质学国家重点实验室_学位论文

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Recommended Citation:
徐慧. 纳米颗粒物混凝过程的影响机制与絮体调控[D]. 北京. 中国科学院研究生院. 2015.
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