生物炭的田间老化及其水溶性产物对重金属的络合与垂向共运移机制

Biochar plays an important role in decrease the bioavailability, and reduces its uptake by crop and alleviates the ecological risk of pollutants in soil, because of containing microporous structure, large specific surface area and abundant surface functional groups. Remediation of contaminated soils by biochar has been one of the hot topics in environmental science, but its aging process in the field and the long-term mechanism of the aging products impact on environmental is not well understand. Based on the existing biochar field amendment, together with the experiments on the complexation of heavy metals with water-soluble products in biochar aging and the vertical migration simulation of these complexes in soil column, the changes of components and structure of biochar in field within 10 year (2009-1019) will be investigated. Speciation of the heavy metals and its vertical distribution characteristics will also be analyzed. X-ray photoelectron spectroscopy (XPS), synchrotron radiation X-ray fluorescence spectrum (SRXRF) analysis and other modern analysis techniques will be used throughout this research. Key impact factors on the aging of biochar, chelating properties of water-soluble products and the vertical migration features of heavy metals will be discussed in detail, and then the long-term effects and potential mechanism of pollution stress on groundwater for biochar amendment in heavy metals contaminated soil will be clarified. Data obtained in this study is helpful in providing scientific basis for environmental risk assessment in the field application of biochar for soil amendment.

生物炭具有孔隙度好、比表面积大以及表面官能团结构丰富等特点，在降低土壤污染物生物有效性、减少作物吸收并其缓解生态风险方面有重要作用，已成为土壤污染修复技术领域研发热点，但田间环境中自身的老化过程及其产物的环境影响长效机制尚不明确。本研究以现有生物炭田间修复试验基地为依托，开展生物炭水溶性老化产物的重金属络合及垂向共运移的土柱模拟实验，并运用X射线光电子能谱技术 (XPS)、同步辐射X射线荧光光谱分析 (SRXRF) 等现代分析技术，考察10年周期内 (2009-2019) 生物炭在田间环境老化过程中组分与结构的变化，解析土壤重金属形态变化与垂向分布特征，探讨水溶性老化产物的重金属络合性能与垂向共迁移特性及其关键影响因子，阐明生物炭修复重金属污染土壤的长期效应及潜在地下水污染胁迫机制，为生物炭在土壤污染原位修复中的应用及其环境风险评估提供科学依据。

生物炭具有孔隙度好、比表面积大以及表面官能团结构丰富等特点，在降低土壤污染物生物有效性、减少作物吸收并其缓解生态风险方面有重要作用，已成为土壤污染修复技术领域研发热点，但田间环境中自身的老化过程及其产物的环境影响长效机制尚不明确。本研究以现有生物炭田间修复试验基地为依托，考察了生物炭在田间环境长期老化过程中的组分与结构变化，解析了水溶性老化产物(WSOC)的释放及其重金属络合性能与垂向共迁移特性，探讨其关键影响因子。结果表明，土壤复杂环境中，生物炭的老化受土壤类型(如矿物组成、有机质)以及气象条件(如光照、降雨)等多因素的影响。生物炭经矿化后，比表面积增大且表面老化层酸性官能团和含氧基团数目显著增强，电荷零点与pH值则有所降低；引入了荧光激发-发射矩阵(EEM)来分析WSOM特性的变化，特异性紫外吸收度(SUVA254)和腐殖质化指数(HIX)均表明，生物炭衍生的WSOM具有较高的芳香性。HNO3-H2SO4和NaOH-H2O2化学氧化中，生物炭表面碳损失和氧掺入贯穿整个过程，羧基为代表的含氧官能团显著增加，比表面积增加126-226%，镉的吸附能力增加了~21.2%；接种微生物生物炭培养液中则呈现对数函数增加，且与持水条件密切相关，100%持水下的WSOC浓度显著高于60%。三维荧光光谱 (EEM)、傅里叶变换红外光谱(FTIR)和X射线光电子能谱 (XPS)解析证实富里酸和腐殖酸类组分是生物炭的主要水溶性产物。40t ha-1生物炭修复8年的酸性水稻土和3年的盐碱土中，生物炭的施用降低了土壤表层土壤中镉的含量，但使土壤表层土壤中铅的含量增加，这是土壤表层土壤中交换态铅和碳酸盐铅转化成有机铅的结果，松散组合的腐殖质分别增加了30.1%和25.1%，但无机(铁氧化物)-有机复合物含量比酸性水稻土高30%，生物炭的添加可以减轻酸雨淋滤的影响，土壤有机质官能团结构、表面性质以及pH发生改变且长期维持，土壤脲酶、蔗糖酶和碱性磷酸酶等活性指标显著上升，土壤细菌等微生物群落结构更为丰富，SOM的提升减少铁铝结合物的垂直迁移，从而防止土壤灰化，提高土壤肥力。