Department of Environmental Science, Zhejiang University , Hangzhou, Zhejiang 310058, China.
Environ Sci Technol. 2014 Mar 18;48(6):3411-9. doi: 10.1021/es405676h. Epub 2014 Mar 6.
Biochars are increasingly recognized as environmentally friendly and cheap remediation agents for soil pollution. The roles of silicon in biochars and interactions between silicon and carbon have been neglected in the literature to date, while the transformation, morphology, and dissolution of silicon in Si-rich biochars remain largely unaddressed. In this study, Si-rich biochars derived from rice straw were prepared under 150-700 °C (named RS150-RS700). The transformation and morphology of carbon and silicon in biochar particles were monitored by FTIR, XRD, and SEM-EDX. With increasing pyrolytic temperature, silicon accumulated, and its speciation changed from amorphous to crystalline matter, while the organic matter evolved from aliphatic to aromatic. For rice straw biomass containing amorphous carbon and amorphous silicon, dehydration (<250 °C) made silicic acid polymerize, resulting in a closer integration of carbon and silicon. At medium pyrolysis temperatures (250-350 °C), an intense cracking of carbon components occurred, and, thus, the silicon located in the inside tissue was exposed. At high pyrolysis temperatures (500-700 °C), the biochar became condensed due to the aromatization of carbon and crystallization of silicon. Correspondingly, the carbon release in water significantly decreased, while the silicon release somewhat decreased and then sharply increased with pyrolytic temperature. Along with SEM-EDX images of biochars before and after water washing, we proposed a structural relationship between carbon and silicon in biochars to explain the mutual protection between carbon and silicon under different pyrolysis temperatures, which contribute to the broader understanding of biochar chemistry and structure. The silicon dissolution kinetics suggests that high Si biochars could serve as a novel slow release source of biologically available Si in low Si agricultural soils.
生物炭作为一种环境友好且廉价的土壤污染修复剂，其作用正受到越来越多的关注。目前，文献中忽视了硅在生物炭中的作用以及硅与碳之间的相互作用，而富硅生物炭中硅的转化、形态和溶解仍未得到充分研究。本研究以水稻秸秆为原料，在 150-700℃下制备了富硅生物炭（命名为 RS150-RS700）。通过傅里叶变换红外光谱（FTIR）、X 射线衍射（XRD）和扫描电子显微镜-能谱仪（SEM-EDX）监测生物炭颗粒中碳和硅的转化和形态。随着热解温度的升高，硅不断积累，其形态从无定形转变为结晶态，而有机质则从脂肪族转变为芳香族。对于含有无定形碳和无定形硅的水稻秸秆生物质，脱水（<250℃）会使硅酸聚合，从而使碳和硅更紧密地结合在一起。在中等热解温度（250-350℃）下，碳组分发生强烈裂解，因此内部组织中的硅暴露出来。在较高热解温度（500-700℃）下，由于碳的芳构化和硅的结晶，生物炭变得致密。相应地，生物炭在水中的碳释放显著减少，而硅释放先略有减少，然后随热解温度升高而急剧增加。结合生物炭水洗前后的 SEM-EDX 图像，我们提出了生物炭中碳和硅的结构关系，以解释不同热解温度下碳和硅之间的相互保护，这有助于更深入地了解生物炭的化学和结构。硅的溶解动力学表明，高硅生物炭可以作为一种新型的低硅农业土壤中生物有效硅的缓释源。
