Department of Earth Sciences, National Cheng Kung University, Tainan, Taiwan.
X-ray Imaging Group, National Synchrotron Radiation Center, Hsinchu, Taiwan.
Sci Total Environ. 2020 Jul 10;725:138195. doi: 10.1016/j.scitotenv.2020.138195. Epub 2020 Mar 24.
Our study underpins the mechanism of organo-mineral interaction between black carbon (BC, biochar) and associated minerals in the historical BC-rich Amazonian Dark Earth (ADE) by using synchrotron-based microscopic (TXM), microspectroscopic (μFTIR) and spectroscopic (XAS and μ-diffraction) approaches. The BC-rich ADE contained over 100% more poorly crystalline minerals than the adjacent tropical soil. Linear combination fitting of k-spacing in the X-ray Absorption Spectra (XAS) revealed that ferrihydrite contributed to 81.1% of the Fe-minerals in BC. A small but distinct peak was observed at 5.7 Å in the extended X-ray absorption fine structure k oscillation of BC, revealing the presence of FeC (including Fe-O-C) covalent bonds. No FeC path was yielded by the XAS fitting when an obvious peak downshift of the first (FeFe) shell was observed, suggesting that the availability of inner-sphere FeC complexation was limited to the BC surface and interphase region. The main minerals for organo-mineral complexation were short-range-order (SRO) ferrihydrite on BC instead of corner-sharing FeO octahedra. Compared to ADE, the coordination number of the first (FeFe) and second (FeFe) shell was higher in BC, revealing a higher degree of order in coordination between the neighboring Fe mineral crystals. Black C limited the progressive aging of amorphous Fe phases and greatly enriched SRO ferrihydrite in the redox-fluctuating and high-leaching environment. The transformation of SRO ferrihydrite into the more crystalline Fe oxides was controlled by the local pH environment. A strong signal from the complexed phenolic group (aryl-OH, 1241 cm) and a distinct band of inner-sphere complexation (Fe-aryl C, 1380-1384 cm) were identified in the FTIR spectra. The enrichment of poorly crystalline minerals can have positive feedback on the long-term stabilization of BC. The scale-up application of biochar to agricultural and ecological systems may have a long-lasting impact on the enrichment and transformation of the SRO minerals in the soil.
我们使用基于同步加速器的微观（TXM）、微光谱（μFTIR）和光谱（XAS 和 μ 衍射）方法，研究了黑碳（BC，生物炭）与历史上富含 BC 的亚马逊黑土（ADE）中相关矿物质之间的有机-矿物相互作用的机制。富含 BC 的 ADE 比相邻的热带土壤含有超过 100%的非晶质矿物。X 射线吸收光谱（XAS）中 k 间距的线性组合拟合表明，水铁矿对 BC 中的 Fe 矿物的贡献为 81.1%。在 BC 的扩展 X 射线吸收精细结构 k 振荡中观察到一个小但明显的 5.7 Å 峰，表明存在 FeC（包括 Fe-O-C）共价键。当观察到第一（FeFe）壳明显的向下峰移时，XAS 拟合没有产生 FeC 途径，这表明内球 FeC 络合的可用性仅限于 BC 表面和相间区域。有机-矿物络合的主要矿物是短程有序（SRO）水铁矿而不是共用角 FeO 八面体。与 ADE 相比，BC 中第一（FeFe）和第二（FeFe）壳的配位数更高，这表明相邻 Fe 矿物晶体之间的配位具有更高的有序度。黑碳限制了非晶态 Fe 相的渐进老化，并在氧化还原波动和高浸出环境中极大地富集了 SRO 水铁矿。SRO 水铁矿向更结晶的 Fe 氧化物的转化受局部 pH 环境的控制。FTIR 光谱中鉴定到复杂酚基（芳基-OH，1241 cm）的强信号和内球络合（Fe-芳基 C，1380-1384 cm）的明显带。非晶质矿物的富集对 BC 的长期稳定具有正反馈作用。生物炭在农业和生态系统中的规模化应用可能对土壤中 SRO 矿物的富集和转化产生持久影响。
