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题名: 饮用水中甲基砷的混凝和光催化氧化去除特性与机制研究
作者: 陈庆欣
学位类别: 硕士
答辩日期: 2015-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 胡承志
关键词: 甲基砷,混凝,絮体,光催化,氧化,Methylated arsenic, Coagulation, Flocs, Photocatalysis, Oxidation
其他题名: Removed characteristics and mechanisms of the coagulation and photocatalytic oxidation of methylated arsenic in drinking water
学位专业: 环境工程
中文摘要:     水中砷的去除方法和材料开发始终是饮用水安全保障的研究热点。环境中的砷元素主要以无机砷为主,但在自然界中有机砷也是砷元素的重要存在形式。一甲基砷(MMA)和二甲基砷(DMA)是最普遍的有机砷化合物,主要通过细菌对无机砷的甲基化作用和人类农业生产活动进入环境中。很多国家和地区的地表水以及地下水中都检测到了较高浓度的甲基砷。混凝是饮用水净化中最常用和最有效的除砷方法,但是迄今为止饮用水中甲基砷的混凝特性尚不清楚。本文研究了饮用水中 MMA和  DMA的混凝特性,重点考察了甲基取代对砷在絮体表面的凝聚吸附作用的影响机制,并进一步研究了光催化等高级氧化技术去除甲基砷的效能。
    混凝实验结果表明,与氯化铝和聚合氯化铝相比,铁盐混凝剂对甲基砷具有更好的去除效果。两种铝盐絮凝剂中,氯化铝去除甲基砷效能略高于聚合氯化铝。随着甲基取代程度的增加,砷的混凝去除效率逐渐降低。在初始砷浓度为200μg/L、絮凝剂投量为 0.2 mmol/L的条件下,氯化铝和氯化铁对  MMA的去除率分别为 63%和 95%,即使将絮凝剂投量增加到 0.6 mmol /L时,氯化铝和氯化铁对DMA的去除率分别仅达到  23%和 57%。絮体吸附是混凝去除甲基砷的主要作用机制,当混凝剂投量较低时,共沉淀可能也发挥了一定作用。
    对混凝后絮体进行了FTIR和XPS分析,结果表明As(V)、MMA和DMA中的As-O-基团取代了铁盐和铝盐氢氧化物中的-OH基团形成M-O-As(M为Fe/Al)形式的络合物。随着甲基取代程度的增加,甲基砷在水溶液中的形态所带的电荷量逐渐降低,甲基砷的分子尺寸逐渐增大,从而会阻碍甲基砷与 Fe/Al氢氧化物之间的表面络合。对于 DMA而言,由于只存在一个-OH基团,所以还需借助  As=O与    Fe/Al氢氧化物形成表面络合物,这种络合物的结构不稳定,对DMA的混凝去除产生不利影响。
    进一步探究了 DMA的去除方法,发现  NaClO和KMnO4等预氧化剂无法将DMA中甲基基团氧化脱除,不能提高饮用水中DMA的去除效能。为此,进一步开展了介孔 TiO2光催化氧化DMA的研究。采用溶剂挥发自组装法(EISA)制备出介孔TiO2,该材料呈现良好的锐钛矿晶型、具有均一的介孔孔径,比表面积达 140.1 cm/g。在光催化氧化过程中,DMA能有效地富集在介孔TiO2表面,模拟自然光能够有效地将 DMA氧化为  MMA或进一步氧化形成  As(V),随后氧化产物被吸附在介孔TiO2上,由此砷被完全去除。这种介孔TiO2光催化氧化DMA、吸附砷的能力明显强于普通 TiO2材料(P25)。初始  DMA浓度为200gAs/L、TiO2投量为0.8 g/L,经过 60分钟介孔TiO2光催化氧化-吸附处理后,水中砷浓度低于 10 μg /L。
    本研究表明铁盐混凝去除 MMA能够获得令人满意的效果,可以达到生活饮用水标准。对于饮用水中 DMA,采用介孔 TiO2光催化氧化是一种有效的处理方法。本研究为给水工程中甲基砷的去除提供了理论基础和技术支撑。
英文摘要: The removal methods and material development of arsenic is always a hot topic in the drinking water security research. Although arsenic in the environment mainly exists in  the  form   of  inorganic  arsenic,   organic  arsenic  can  also   be  found  in   nature.Monomethyl arsenic (MMA) and dimethyl arsenic (DMA) are common organic arsenic compounds. MMA and DMA can be introduced into the environment through bacterial methylation and agricultural  activities. MMA and DMA had been  detected in surface water  and  groundwater of  many  countries  and  regions.  Coagulation  is a  common method for arsenic removal in the water treatment. However, the removal of methylated arsenic from drinking  water by coagulation  has not been  studied and the coagulation performance of  methylated arsenic is  still unknown. We  investigated the coagulation behavior of  methylated arsenic in drinking water. We focused on the influence of methyl substitution  on the  mechanism of  coagulation removal.  Futhermore,  we studied  the removal efficiency of photocatalytic oxidation for methylated arsenic.
    The coagulation  results indicated  that FeCl3  was more  efficient than  AlCl3  and PACl on methylated arsenic removal. The removal efficiency of methylated arsenic by AlCl3  coagulation was  slightly higher  than  that by  PACl.  The coagulation  removal efficiency of arsenic decreased  with the increase of the degree  of methyl substitution.For the initial arsenic concentration of 200 μg/L and a coagulant dosage of 0.2 mmol/L,the removal efficiency of MMA achieved by  FeCl3 coagulation and AlCl3  coagulation were 63% and  95%, respectively. However,  for the coagulant dosage  of 0.6 mmol/L,DMA removal efficiency  achieved by FeCl3  coagulation and  AlCl3 coagulation were 23% and 57%, respectively.  Adsorption on the flocs was the  predominant mechanism during   the   methylated   arsenic  removal   by   coagulation.   Precipitation   and   co-precipitation might also play a specific role at low coagulant doses.
        The results  of the  flocs characterized  by FTIR  and XPS  showed that  the As-O group of As(V), MMA and DMA substituted the O-H group of Fe/Al hydroxide to form a Fe/Al -O-As complex during the coagulation process. With the increase of the degree of methyl substitution, the quantity of negatively charged species of methylated arenic decreased and the molecular  size of arsenic increased. These  factors might hinder the sufurace complexation  between methylated arsenic  and Fe/Al hydroxide.  In terms of DMA, the formation of a bidentate binuclear complex  between DMA and Fe/Al oxide requires that both As=O and  the As-OH group are involved in the  complexation. This kind of  complex structure between  DMA and Fe/Al  oxide could  be less stable.  This would be a detrimental effect on the removal of DMA.
        Futhermore, we investigated  other removal methods of  DMA. We found NaClO and KMnO4 could not destroy the methyl group of DMA. Thus, we could not enhance the  removal efficiency  of  DMA  by these  methods.  Therefore,  we  investigated the photocatalytic oxidation  of DMA by mesoporous TiO2.  We prepared the  mesoporous TiO2 by  the method of  EISA. The material  was mainly composed  by anatase.  It had uniform meoporous  size  and the  specific surface  area was  140.1  cm2 /g.  During the photocatalytic   oxidation   process,  DMA   could   be   effectively   adsorbed  on   the mesoporous TiO2. DMA could be oxidized to MMA or As(V) under simulated  natural light  irradiation. These  oxidation  products  could  be removed  by  the  adsorption of mesoporous TiO2. The ability of adsorption and photocatalytic oxidation of mesoporous TiO2  was  much  stronger  than  the  common  TiO2  (P25).  For  the  the  initial  DMA concentration of 200 μg As/L and the mesoporous  TiO2 dosage of 0.8 g/L, the arsenic concentration in the treated water  was less than 10 μg /L after natural  light irradiation of 60 min.
        The  study of  methylated  arsenic removal  by  coagulation indicated  that  MMA could be effectively removed by FeCl3 coagulation and the arsenic concentration in the treated water could meet the drinking water standard. In terms of DMA in the drinking water, the photocatalytic oxidation by mesoporous TiO2 was an effective approach. This study provides a theoretical basis and  technical support for the removal of methylated arsenic in water supply project.





内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/34118
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:
陈庆欣. 饮用水中甲基砷的混凝和光催化氧化去除特性与机制研究[D]. 北京. 中国科学院研究生院. 2015.
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