Abstract：
Biochar pyrolyzed by biomass shows excellent application prospects for heavy metal (HM) remediation, but a part of biochar can be inevitably broken into micro- and nano-sized biochar colloids (BCs) under biological and physicochemical actions in soil. BCs derived in the process of remediation have rough surface, rich elemental species and contents, and multiple functional groups, which are similar to biochar. However, BCs have some unique colloidal properties because of their micro and nano scale size. Due to these properties, BCs exhibit strong mobilities in the soil environment, and the mobilities may be influenced by a combination of colloidal properties of BCs and environmental factors including soil colloids and other soil environmental conditions. In addition, BCs may have affinity effects on HMs through electrostatic adsorption, ion exchange, surface complexation, precipitation/co-precipitation, and redox because of the properties such as large specific surface area, and rich oxygen-containing functional groups and minerals on the surface. This review summarizes the physicochemical and migratory properties of BCs, and the internal and external factors affecting the migration of BCs in the soil environment, and the possible effects of BCs on HMs are high-lighted. This review provides a theoretical basis for the optimization of soil contaminated with HMs after remediation using biochar. Notably, the innovative idea that BCs may influence the presence of HMs in soil needs to be further confirmed by more targeted detection and analysis methods in future studies to prevent the possible environmental toxicities of the lateral and vertical diffusion of HM caused by BCs in soil.
摘要：
生物质热解的生物炭在重金属修复中显示出良好的应用前景,但是，在土壤中的生物和物理化学作用下，一部分生物炭不可避免地会分解成微米和纳米大小的生物炭胶体（BCs）。修复过程中产生的BCs表面粗糙，丰富的元素种类和含量，和多个功能组，类似于生物炭。然而,BCs由于其微观和纳米尺度尺寸而具有一些独特的胶体性质。由于这些属性，BCs在土壤环境中表现出很强的迁移率，并且迁移率可能受BCs的胶体特性和环境因素（包括土壤胶体和其他土壤环境条件）的组合影响。此外,BCs可能通过静电吸附对HMs具有亲和力，离子交换,表面络合,沉淀/共沉淀，和氧化还原，因为其特性，如大的比表面积，表面富含含氧官能团和矿物质。本文综述了BCs的物理化学和迁移特性，以及影响BCs在土壤环境中迁移的内部和外部因素，BCs对HMs的可能影响是很高的。该综述为生物炭修复后HMs污染土壤的优化提供了理论依据。值得注意的是,BCs可能影响HMs在土壤中的存在的创新观点需要在未来的研究中通过更有针对性的检测和分析方法进一步证实，以防止BCs在土壤中引起的HMs横向和纵向扩散的可能的环境毒性。
