Key Laboratory of Soil Environment and Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China.
Environ Sci Technol. 2013 May 21;47(10):5154-61. doi: 10.1021/es305337r. Epub 2013 May 7.
Biochar land application may result in multiple agronomic and environmental benefits (e.g., carbon sequestration, improving soil quality, and immobilizing environmental contaminants). However, our understanding of biochar particle transport is largely unknown in natural environments with significant heterogeneity in solid (e.g., patches of iron oxyhydroxide coating) and solution chemistry (e.g., the presence of natural organic matter), which represents a critical knowledge gap in assessing the environmental impact of biochar land application. Transport and retention kinetics of nanoparticles (NPs) from wheat straw biochars produced at two pyrolysis temperatures (i.e., 350 and 550 °C) were investigated in water-saturated sand columns at environmentally relevant concentrations of dissolved humic acid (HA, 0, 1, 5, and 10 mg L(-1)) and fractional surface coverage of iron oxyhydroxide coatings on sand grains (ω, 0.16, 0.28, and 0.40). Transport of biochar NPs increased with increasing HA concentration, largely because of enhanced repulsive interaction energy between biochar NPs and sand grains. Conversely, transport of biochar NPs decreased significantly with increasing ω due to enhanced electrostatic attraction between negatively charged biochar NPs and positively charged iron oxyhydroxides. At a given ω of 0.28, biochar NPs were less retained with increasing HA concentration due to increased electrosteric repulsion between biochar NPs and sand grains. Experimental breakthrough curves and retention profiles were well described using a two-site kinetic retention model that accounted for Langmuirian blocking or random sequential adsorption at one site. Consistent with the blocking effect, the often observed flat retention profiles stemmed from decreased retention rate and/or maximum retention capacity at a higher HA concentration or smaller ω. The antagonistic effects of HA and iron oxyhydroxide grain-coating imparted on the mobility of biochar NPs suggest that biochar colloid transport potential will be dependent on competitive influences exerted by a number of environmental factors (e.g., natural organic matter and metal oxides).
生物炭的土地应用可能会带来多种农业和环境效益（例如，碳封存、改善土壤质量和固定环境污染物）。然而，我们对生物炭颗粒在具有固相与溶液化学显著异质性的自然环境中的迁移行为知之甚少（例如，存在铁氢氧化物涂层的斑块和天然有机质的存在），这是评估生物炭土地应用的环境影响的一个关键知识空白。在环境相关浓度的溶解腐殖酸（HA，0、1、5 和 10mg/L）和沙粒表面铁氢氧化物涂层分数覆盖度（ω，0.16、0.28 和 0.40）下，研究了在水饱和砂柱中，由两种热解温度（即 350 和 550°C）制备的小麦秸秆生物炭的纳米颗粒（NPs）的迁移和保留动力学。在给定的 ω 为 0.28 时，由于生物炭 NPs 和砂粒之间的电排斥能增加，生物炭 NPs 的保留量随着 HA 浓度的增加而减少。相反，由于带负电荷的生物炭 NPs 和带正电荷的铁氢氧化物之间的静电引力增强，生物炭 NPs 的迁移显著减少。由于生物炭 NPs 和砂粒之间的电动排斥增加，随着 HA 浓度的增加，生物炭 NPs 的保留量减少。使用考虑到一个位点上的朗缪尔阻塞或随机顺序吸附的双位点动力学保留模型，很好地描述了实验突破曲线和保留曲线。与阻塞效应一致，由于在较高的 HA 浓度或较小的 ω 下，保留速率和/或最大保留容量降低，经常观察到平坦的保留曲线。HA 和铁氢氧化物粒状涂层对生物炭 NPs 迁移性的拮抗作用表明，生物炭胶体的迁移潜力将取决于许多环境因素（例如天然有机质和金属氧化物）施加的竞争影响。
