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题名: 生物炭风险物质研究及可溶性有机碳 对有机污染物环境界面行为影响
作者: 陈自恩
学位类别: 硕士
答辩日期: 2016-05
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 罗磊
关键词: 生物炭,环境风险,可溶性有机碳,有机污染物,界面行为 ; Biochar, Environmental risk, Dissolved organic carbon, Organic contamitant, Interfacial behavior.
其他题名: Potentially Risky Substances in Biochars and Interfacial Behaviors of Organic Contaminants in the Presence of DOC in the Environment
学位专业: 环境科学
中文摘要:     生物炭以其在碳固定、污染土壤修复等方面的优越性能而在土壤环境科学领域受到越来越多的关注。然而最近研究表明,生物炭很可能是一把双刃剑,其中含有大量有害物质,具有不可忽视的环境风险。因此,系统深入地研究生物炭中的有害物质,阐明其环境行为及风险,对于更加安全合理地使用生物炭显得日益迫切。以此为出发点,本文以两类典型生物质材料(玉米秸秆和猪粪)为例,采用最常规的热解工艺,在 300℃或 500℃的无氧条件下制备得到生物炭,研究生物炭中几种潜在环境风险物质——重金属、持久性自由基和可溶性黑碳在热解过程中的形态转化、产生机制和影响因素;并利用分子表征技术对可溶性黑碳(DBC)在土壤界面的反应机制及对有机污染物界面过程的影响特征进行了探讨。
    结果表明,这两种生物质材料中都有重金属(As、Cd、Cu、Pb和  Zn)存在,尤其是猪粪中 Cu、Zn含量分别超过了0.1‰和 0.3‰,且这些重金属在生物炭制备过程中除 Cd外都发生了显著浓缩富集,富集系数随温度升高而增大;同时有超过 40%的 Cd和Pb在热解过程中挥发进入大气环境。同时,生物炭中有效态重金属含量却显著降低。运用X射线衍射(XRD)和扫描电镜-能谱(SEM-EDS)等技术进一步研究发现,生物炭中重金属有效态含量降低可能主要是被生物炭中 CaCO3和磷酸盐等无机组分吸附钝化所致。这些无机组分对  pH很敏感,在酸性条件下,钝化重金属存在再次活化的风险。电子顺磁共振(EPR)分析结果表明生物炭中存在大量持久性自由基(PFRs)。结合FT-IR分析,研究发现 PFRs的浓度与生物炭的芳香化程度密切相关。这些  PFRs稳定性很高,不受水、酸和有机溶剂洗提处理的影响;在土壤中老化培养 30天也无明显衰减。生物炭制备过程还伴随着另一种副产物的大量产生,即DBC。体积排阻色谱(HPSEC)、荧光(结合平行因子分析)和电喷雾电离傅里叶变换离子回旋共振质谱(ESI-FT-ICR-MS)分析结果表明,DBC与天然可溶性有机碳(DOC)分子组成存在明显差异,主要表现为相对较小的分子量和较高的芳香化程度;与之相伴的是活化、迁移污染物的风险。
    鉴于 DBC的潜在风险,本文进一步研究了DBC在土壤界面的吸附反应机制。除DBC外,还选取了泥炭DOC和草酸作为对照。运用       HPSEC和ESI-FT-ICR-MS等技术对不同   DOC吸附前后的分子组成进行分析发现,土壤对  DOC有明显的选择性吸附(即分馏)行为和配体交换反应,表现为优先吸附亲水性组分,如糖类、木质素类和单宁类等富含羟基的组分,而对不饱和烃或稠环芳香结构等疏水性组分则吸附较少。由于泥炭  DOC亲水性相对较高,羟基更为丰富,土壤对泥炭 DOC的吸附作用强于对  DBC的吸附作用。在此基础上,本文进一步考察了  DOC对污染老化土壤(黑龙江黑土和广州红壤)和污泥施用土壤(德州潮土)中菲的解吸释放的影响。结果表明:DBC可以显著促进黑土中菲的释放,但对红壤和潮土影响不明显;泥炭  DOC及草酸对土壤中菲的释放影响较弱。这种现象表明,DOC对有机污染物界面行为的影响与土壤性质以及 DOC的分子组成密切相关。
    此外,本文还研究了DOC影响生物炭吸附典型有机污染物的作用机制。实验选取了两种非极性有机化合物(萘和菲)及一种极性有机化合物(1,3-二硝基苯)作为目标污染物,比较了富里酸、胡敏酸和土壤老化处理对生物炭吸附三种有机污染物能力的影响特征。结果发现,胡敏酸、富里酸和土壤老化处理均能显著降低生物炭对有机污染物的吸附能力。通过 N2和CO2吸附比表面积分析,结合X射线光电子能谱(XPS)及近边X射线吸收精细结构(NEXAFS)分析,结果表明 DOC(胡敏酸/富里酸或土壤 DOC)能够通过微孔扩散或表面
覆盖等方式而改变生物炭表面的微孔分布以及官能团组成,从而减弱生物炭对有机污染物的吸附能力。

英文摘要:     Biochars have been attracting increasing attention as agricultural/environmental amendments  because  of  their  excellent   capabilities  in  carbon  sequestration  and contaminated soil remediation. However,  recent studies have indicated that biochars contain   large   contents   of   substances   with  potential   risks,   which   can   be   a “double-edged  sword”  as  agricultural/environmental  amendments.  Clarifying  the possible environmental  risks derived  from biochars  is therefore needed  in order  to safely use the  biomass resources. To  this end, this  work examined the  behaviors of selected dark  sides-  including heavy  metals, persistent  free radicals  and  dissolved black carbon (DBC)-  of biochars made  from maize straw  and swine manure by  the most common pyrolysis processes, explored the possible factors influencing the dark sides, and then  investigated the interaction  of DBC with  soil/biochar interfaces and the consequent effects on the interfacial behaviors of typical organic contaminants in the environment.
    The  results  indicate  that   heavy  metals-  including  As,  Cu,  Pb,   Zn-  in  the biochars were  enriched significantly  during the pyrolysis  processes compared  with those in  the feedstocks,  and the  enrichment coefficients  were correlated  positively with  pyrolysis  temperature. Substantial  amounts  (over  40%)  of Cd  and  Pb  were emitted into  the  atmosphere during  the pyrolysis  processes, and  the trend  became increasingly obvious  at the  higher temperature.  Meanwhile, the biochars  showed a distinct decrease in  the concentrations of available  heavy metals compared with  the feedstocks,  which  can  be  attributed  mainly  to  the  immobilization  of  the  heavy metals by inorganics in  the biochars (e.g., CaCO3  and phosphate). The immobilized heavy metals were  vulnerable to remobilization at  low pH conditions and thus  their risks   should  be   monitored   carefully.  Electron   paramagnetic   resonance  (EPR)analysis indicated that persistent free radicals, emerging strongly as a function  of the aromatization  of  the  biochars,  were free  from  the  influence  of  water-,  acid-,  or organic-extraction treatment  and could remain  stable even after  being aged  in soils for 30  days. Dissolved  black carbon,  produced  largely during  pyrolysis processes,showed distinct properties from natural  DOC, such as fulvic acid and soil DOC.  For instance,  it  had lower  molecular  weights  as  demonstrated by  HPSEC  but  higher aromaticity  as revealed  by FT-IR,  fluorescence  (with parallel  factor  analysis) and electrospray ionization-Fourier transform-ion cyclotron resonance-massspectrometry (FT-MS) analyses. These results  provide important perspectives on the safe use of biochars as agricultural/environmental amendments.
    Considering the  potential risks  of DBC,  the interaction of  DBC with  soil and consequent  effects on  the  desorption  of phenanthrene  were  investigated.  Another two typical DOCs- peat  leachate and oxalic acid- were  included in this study. Three different  contaminated soils-  black  soil  (Heilongjiang), red  soil  (Guangzhou) and fluvo-aquic   soil   (Dezhou)-   were   applied.   The   results   demonstrate    that   the hydrophilic  fractions of  the  DOCs were  adsorbed  selectively in  the  soils through ligand  exchanging   reactions  based  on   HPSEC  and  FT-MS   analyses.  All   soils exhibited a higher affinity  for peat leachate than DBC,  which can be ascribed to the different molecular components  in the DOCs. The desorption  experiments indicated that DBC significantly facilitated  the release of phenanthrene from black  soil, while peat leachate  and oxalic  acid had relatively  weak effects.  This observation  implies that the effects of DOC on  the desorption of organic compounds depend on multiple factors, including soil properties and molecular components of DOC.
    Finally,  the effects  of  DOC  on the  adsorption  of  organic contaminants  onto biochars   were   investigated.   To   this   end,   two   nonpolar   organic   compounds (naphthalene and phenanthrene) and one polar organic compound(1,3-dinitrobenzene)   were   applied   as   adsorbates.   The   adsorption   of   organic contaminants onto  biochars was attenuated  greatly after being  aged in the  presence of either  fulvic  acid, humic  acid or  soil,  regardless of  contaminant types.  Surface area analysis  together with X-ray  photoelectron spectroscopy  (XPS) and near  edge X-ray  absorption  fine   structure  (NEXAFS)  analyses  revealed   that  parts  of  the nanopores  on  the  surfaces  of  the  aged  biochars  were  blocked,  and  that  surface functionality were modified significantly, owing to the DOC (fulvic acid, humic acid, or soil DOC) diffusing into the nanopores and coating the surface of the biochars.

内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/36783
Appears in Collections:环境化学与生态毒理学国家重点实验室_学位论文

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Recommended Citation:
陈自恩. 生物炭风险物质研究及可溶性有机碳 对有机污染物环境界面行为影响[D]. 北京. 中国科学院研究生院. 2016.
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