【作者】 钱林波；

【导师】 陈宝梁；

【作者基本信息】 浙江大学 ， 环境科学， 2014， 博士

【摘要】 生物碳(Biochar)是生物质在缺氧或无氧条件下低温裂解制备的富碳固体。生物碳具有特殊的结构和性质,在酸性土壤改良和污染土壤修复中具有巨大的应用潜力,引起了国际土壤和环境领域的极大关注。论文介绍了生物碳的制备及结构特征,重点评述了生物碳在退化土壤改良和重金属污染土壤修复中应用的研究进展。针对生物碳在酸性土壤改良中作用机理尚未阐明,生物碳对土壤中有毒金属Al和重金属毒性缓解和阻控作用的机理不清等问题,选择水稻秸秆、牛粪等为代表,制备了不同炭化温度的生物碳,通过元素分析、FTIR、XRD、SEM、Zeta电位等手段表征了生物碳的结构组成和表面性质；研究了生物碳对Al的吸附作用机理,探讨水培体系下对生物碳缓解植物Al毒的作用机理；在此基础上,揭示了生物碳对酸性土壤中Al毒缓解机制；并进一步采用酸氧化法模拟了生物碳老化过程,探明了其在增强Al和Cd吸附中的作用机理；最后对生物碳在土壤酸化和暖化效应耦合下重金属Cd阻控机理进行了探索。研究结果为酸性土壤改良和污染土壤修复提供理论基础与技术支撑。论文的主要结论及创新点如下：(1)揭示了生物碳与Al相互作用的机制及其构-效关系,发现生物碳上的有机组分和硅颗粒是吸附Al的两个主要区域。有机组分上的羟基和羧基对Al的表面络合作用、硅颗粒对Al的沉淀作用是生物碳吸附Al的两个重要途径。Al负载生物碳FTIR上的羧基非对称峰和对称峰的差值显著增加,表明羧基对A1产生了表面络合作用。同时,吸附Al之后,生物碳和灰分的表面负电荷在pH3-8之间出现了逆转,正电荷在pH4.5时达到最大,与硅的最大正电荷所在的pH一致,电荷转变主要是由羟基Al与硅表面的双电层氢键作用引起的。(2)发现生物碳能高效缓解Al的植物毒性,其作用机制包括生物碳的石灰效应(碱性)改变Al的存在形态、吸附作用降低Al的有效浓度、生物碳溶出硅在植物体内与A1形成铝硅化合物。水培实验表明,仅添加0.02%(极少量)生物碳到溶液中后,Al对植物生长的抑制作用得到显著的缓解,毒性阀值从3μmol/LA13+上升到95μmol/L Al3+。同时通过溶液pH的调整和生物碳碱性矿物水洗去除的方法,探明了石灰效应和吸附作用在生物碳缓解植物Al毒中的贡献,生物碳的石灰效应使Al的形态被转变成可被生物碳高效吸附的形态Al(OH)2+和Al(OH)2+的同时,从高毒性Al3+转化为低毒性的Al(OH)3和Al(OH)4-。然而,石灰效应是一个短暂的过程,吸附作用在植物Al毒缓解中具有更重要的作用。进一步将生物碳应用于酸性土壤中,探明了生物碳在酸性土壤Al毒的缓解中具有双重功能。土壤交换性Al、根尖Al浓度以及苏木精染色结果表明,生物碳在植物外部降低土壤交换性Al,减少Al向植物的迁移：同时,Morin荧光染色和SEM-EDS表征结果表明,生物碳溶出的硅可以进入植物体内,与Al在小麦根系的表皮中形成铝硅化合物,在植物体内缓解Al的毒害。(3)探明了酸化土壤中生物碳老化过程的结构演变以及对土壤有毒金属Al和Cd的吸附作用及阻控机理。模拟酸化土壤中生物碳老化过程,发现老化生物碳的盐基离子(Na+、K+、Ca2+、Mg2+)淋失,表面含氧官能团羧基和羟基增加。新增加的羧基和羟基为生物碳负载Al和Cd提供新的位点,从而促进了生物碳对Al和Cd的吸附固定,表明生物碳对酸性土壤有害金属有长期吸附固定作用。进一步研究发现土壤酸化和暖化效应对Cd植物毒性的增强具有协同效应,而生物碳在土壤酸化和暖化效应协同效应下对植物Cd毒性的具有很强的缓解作用。更多还原

【Abstract】 Biochar is a carbon-rich material that is produced during the pyrolysis of biomass, and it has received increasing attention as an effective approach to acidic soil amelioration and contaminated soil remediation. This paper introduced the structure and composition of biochar, and focused on the progress of acidic soil improvement and heavy metal contaminated soil remediation. Until now, the mechanism of acidic soil amelioration by biochar amendment was not well understood, and the adsorption and phytotoxicity alleviation mechanism of aluminum and heavy metal by biochars has not been systematically elucidated. In this dissertation, biochars derived from rice straw and cattle manure were prepared under different pyrolytic temperatures. Through the structural characterization of biochar by element analysis, FTIR, XRD, SEM and Zeta potential, the Al binding mechanisms by biochars were discovered, and then the Al phytotoxicity alleviation mechanisms by biochar in hydroponic system were investigated. Furthermore, the mechanisms of Al phytotoxicity alleviation in acidic soil were revealed. Simulating aging process of biochar by oxidation, the Al and Cd binding mechanisms by aging biochar were illustrated, and the Cd phytotoxicity mitigation mechanisms by biochar were clarified when response to the coupling of greenhouse effect and soil acidification. These results provide a theoretical basis for acid soil improvement and contaminated soil remediation. The main original conclusions of this work are drawn as follows:(1) Revealed the mechanism and structure-effect relationship of biochar and Al interaction, and found that the oxygen-containing organic components and the scattering silicon particles of biochar are two main regions of Al adsorption. The complexation of Al with organic hydroxyl and carboxyl groups and the surface adsorption and coprecipitation of Al with silicate particles both contributed to the Al adsorption of the biochars. According to the FTIR of biochar, the difference peak of carboxyl asymmetric and symmetric showed a significant increase after Al loaded, indicating the surface complexation of carboxyl group and Al. After the biochars were loaded with Al, the zeta potentials of the biochars and ashes increased as a function of pH. The charge reversal was caused by the Stern-layer adsorption of hydrolyzed aluminum species on the silicate surfaces via hydrogen bonds.(2) Effective alleviation of Al phytotoxicity by biochar was found, and its mechanism included the liming effect of biochar (alkaline) to change form of Al, the adsorption by biochar to reduced the available Al and the alleviation was the formation of aluminosilicate by dissolution silicon and Al. Hydroponic experiments showed that upon addition of0.02%biochar to the exposure solution, the inhibition of plant growth by Al was significantly reduced while the toxic threshold was extended from3to95μmol/L Al3+. Due to the biochar liming effect, the aluminum species were converted to Al(OH)2+and Al(OH)2+monomers, which were strongly adsorbed by biochar; furthermore, the highly toxic Al3+evolved to less toxic Al(OH)3and Al(OH)4-species. Further used biochar in acidic soil, it has proven a dual function in Al phytotoxicity alleviation. Soil exchangeable Al, Al concentration and hematoxylin stai ning showed that the biochar reduced soil exchangeable Al, thus reduce the migration to plants. Meanwhile, Morin staining and SEM-EDS showed silicon dissolution from biochar can enter in plants, then form Al-Si compounds with Al in the epidermis of wheat roots, alleviating the Al phytotoxicity in plants.(3) Elucidated the biochar structural evolution by aging process as well as the adsorption and resistance mechanisms controlling of soil toxic metals Al and Cd during soil acidification. Simulated biochar aging process in acidic soil and found that biochar aging process lead to the leaching of base cations and the increase of surface carboxyl and hydroxyl functional groups. Additional carboxyl and hydroxyl groups provided new adsorption sites of Al and Cd, thus promoting the adsorption of Al and Cd biochar, indicating that biochar had long-term effect on harmful metals immobilization in acidic soil. Further studies showed that soil acidification and warming effect have a synergistic effect on the phytotoxicity of Cd. Under the coupling of the soil acidification and warming effects, biochar showed effective alleviation of Cd phytotoxicity.更多还原