School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093, China.
School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China; Shanghai Engineering Research Center of Solid Waste Treatment and Recycling, Shanghai Jiao Tong University, Shanghai 200240, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, China.
Sci Total Environ. 2021 Jun 25;775:145824. doi: 10.1016/j.scitotenv.2021.145824. Epub 2021 Feb 13.
Biochar as a green amendment has been used to immobilize heavy metals in contaminated soil. Apart from the importance of the amendment itself, the interaction with soil components like clay minerals might also influence the immobilization behavior of biochar. Here, we examined the impact of a typical soil mineral, bentonite, on the immobilization of Pb by barley grass-derived biochar, and elucidated the underlying mechanisms by dividing biochar into dissolvable and undissolvable fractions. Results showed that biochar and bentonite could immobilize Pb through mechanism of electrostatic sorption, complexation, and precipitation. Compared to sole undissolvable biochar, coexistence of bentonite rapidly raised pH of the mixture over 7.0, leading the free Pb transformed into more stable PbCO(OH) (K = 1.3 × 10) instead of PbCO (K = 1.5 × 10), finally increased Pb removal rate by 1.47 times. As for the dissolvable biochar, the generation of dissolvable biochar-bentonite-Pb ternary complex raised the Pb removal rate by 59.6% with the presence of bentonite. Small angel XRD analysis showed that the free Pb and dissolvable biochar-associated Pb could enter the interlayer space of bentonite and thus expanded the d-spacing from 1.28 nm to 1.36-1.50 nm, which might favor the formation of ternary complex. Findings of this study not only provided a new insight into the immobilization of heavy metals by biochar in soil, but also emphasized the importance of interaction between biochar and soil minerals.
生物炭作为一种绿色改良剂，已被用于固定污染土壤中的重金属。除了改良剂本身的重要性外，与粘土矿物等土壤成分的相互作用也可能影响生物炭的固定行为。在这里，我们研究了一种典型的土壤矿物膨润土对大麦草衍生生物炭固定 Pb 的影响，并通过将生物炭分为可溶解和不可溶解两部分来阐明其背后的机制。结果表明，生物炭和膨润土可以通过静电吸附、络合和沉淀来固定 Pb。与单独的不可溶解生物炭相比，膨润土的共存会迅速将混合物的 pH 值提高到 7.0 以上，导致游离 Pb 转化为更稳定的 PbCO(OH)（K=1.3×10）而不是 PbCO（K=1.5×10），最终使 Pb 的去除率提高了 1.47 倍。对于可溶解生物炭，由于膨润土的存在，生成了可溶解生物炭-膨润土-Pb 三元配合物，使 Pb 的去除率提高了 59.6%。小角度 XRD 分析表明，游离 Pb 和可溶解生物炭结合的 Pb 可以进入膨润土的层间空间，从而将 d 间距从 1.28nm 扩展到 1.36-1.50nm，这可能有利于三元配合物的形成。本研究的结果不仅为生物炭在土壤中固定重金属提供了新的见解，而且强调了生物炭与土壤矿物质相互作用的重要性。
