Hardwood biochar (pyrolyzed at 700 °C), a potential candidate for Hg removal, has been proposed for use as reactive capping mats along groundwater discharge zones or riverbanks to control release of Hg from contaminated riverbank sediments. Frequent flooding and drainage in fluvial settings can influence the effectiveness of remediation systems in contaminated riverbank sediments and floodplain soils. This study evaluated the effectiveness of Hg removal using hardwood biochar under hydrogeochemical conditions representative of those present within a reactive capping mat installed in a fluvial setting. Two sets of treatment columns, containing 50% v.v biochar and quartz sand, were subjected to 100 weekly wetting/drying cycles that included dry air, water-saturated air, and drainage using leachate derived from two source columns as input solutions: 1. Passing simulated acid rain water through floodplain soil, 2. Passing river water through riverbank sediment. In both treatment columns, >80% of the Hg was retained on the biochar without promoting Hg methylation and the release of other unintended dissolved constituents (including N, P, DOC). Results from solidphase extraction analyses suggest that Hg accumulated near the air/biochar-sand interface (0–2 cm) in the treatment columns at low loadings but was present at greater depths at higher loadings. Results of micro X-ray fluorescence (μ-XRF) mapping and micro X-ray absorption near edge structure (μ-XANES) for the biochar collected at depths 0–2 cm in treatment columns suggest retention of Hg-bearing particles derived from riverbank sediment and floodplain soil within the pore structure of the biochar. Sulfur K-edge XANES analysis of the unused biochar and the biochar after treatment suggest formation of Hg complexes on the biochar surface. These results indicate that hardwood biochar is potentially an effective media for application in reactive mats for controlling Hg discharging from contaminated riverbank sediments.

有人提出将硬木生物炭（在700°C时热解）作为脱除汞的潜在方法，用作沿地下水排放区或河岸的反应性覆盖垫，以控制从受污染的河岸沉积物中释放汞。河流环境中频繁的洪水和排水会影响受污染的河岸沉积物和洪泛区土壤中修复系统的有效性。这项研究评估了在水力地球化学条件下使用硬木生物炭去除汞的有效性，这些条件代表了在河流环境中安装的活性覆盖垫中存在的那些条件。对两组处理柱（包含50％vv生物炭和石英砂）进行每周100次润湿/干燥循环，其中包括干燥空气，水饱和空气和使用源自两个来源柱的浸出液作为输入溶液的排水：1.使模拟酸雨水穿过洪泛区土壤，2.使河水穿过河岸沉积物。在两个处理柱中，> 80％的Hg保留在生物炭上，而没有促进Hg甲基化和释放其他意外的溶解成分（包括N，P，DOC）。固相萃取分析的结果表明，在低负荷下，处理柱中空气/生物炭-砂界面（0–2 cm）附近会积累汞，但在较高负荷下，汞的含量会更大。在处理柱中以0–2 cm深度收集的生物炭的微X射线荧光（μ-XRF）映射和靠近边缘结构（μ-XANES）的微X射线吸收的结果表明，保留了源自河岸的含汞颗粒生物炭孔隙结构内的沉积物和洪泛区土壤。未使用的生物炭和处理后的生物炭的硫K边XANES分析表明，在生物炭表面形成了Hg配合物。这些结果表明，硬木生物炭可能是一种有效的介质，可用于反应垫中，以控制从受污染的河岸沉积物中释放出的汞。