Biochars can remove potentially toxic elements, such as inorganic mercury [Hg(II)] from contaminated waters. However, their performance in complex water matrices is rarely investigated, and the combined roles of natural organic matter (NOM) and ionic composition in the removal of Hg(II) by biochar remain unclear. Here, we investigate the influence of NOM and major ions such as chloride (Cl^–), nitrate (NO₃^–), calcium (Ca²⁺), and sodium (Na⁺) on Hg(II) removal by a wood-based biochar (SWP700). Multiple sorption sites containing sulfur (S) were located within the porous SWP700. In the absence of NOM, Hg(II) removal was driven by these sites. Ca²⁺ bridging was important in enhancing removal of negatively charged Hg(II)-chloro complexes. In the presence of NOM, formation of soluble Hg-NOM complexes (as seen from speciation calculations), which have limited access to biochar pores, suppressed Hg(II) removal, but Cl^– and Ca²⁺ could still facilitate it. The ability of Ca²⁺ to aggregate NOM, including Hg-NOM complexes, promoted Hg(II) removal from the dissolved fraction (<0.45 μm). Hg(II) removal in the presence of Cl^– followed a stepwise mechanism. Weakly bound oxygen functional groups in NOM were outcompeted by Cl^–, forming smaller-sized Hg(II)-chloro complexes, which could access additional intraparticle sorption sites. Therein, Cl^– was outcompeted by S, which finally immobilized Hg(II) in SWP700 as confirmed by extended X-ray absorption fine structure spectroscopy. We conclude that in NOM containing oxic waters, with relatively high molar ratios of Cl^–: NOM and Ca²⁺: NOM, Hg(II) removal can still be effective with SWP700.

中文翻译：

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木基生物炭对受污染水中的汞去除取决于天然有机物和离子成分

生物炭可以从受污染的水中去除潜在的有毒元素，例如无机汞 [Hg(II)]。然而，它们在复杂水基质中的性能很少被研究，天然有机物 (NOM) 和离子组成在生物炭去除 Hg(II) 中的综合作用仍不清楚。在这里，我们研究了 NOM 和主要离子如氯离子 (Cl ^– )、硝酸根离子 (NO ₃ ^– )、钙离子 (Ca ²⁺ ) 和钠离子 (Na ⁺ ) 对木基去除 Hg(II) 的影响。生物炭 (SWP700)。多个含有硫 (S) 的吸附位点位于多孔 SWP700 内。在没有 NOM 的情况下，这些位点推动了 Hg(II) 的去除。钙²⁺桥接对于增强带负电荷的 Hg(II)-氯络合物的去除很重要。在 NOM 存在的情况下，可溶性 Hg-NOM 复合物的形成（从物种形成计算中可以看出）限制了进入生物炭孔隙，抑制了 Hg(II) 的去除，但 Cl ^-和 Ca ²⁺仍然可以促进它。Ca ²⁺聚集 NOM（包括 Hg-NOM 复合物）的能力促进了从溶解部分（<0.45 μm）中去除 Hg(II)。在 Cl 存在下去除 Hg(II) ^–遵循逐步机制。NOM 中的弱结合氧官能团被 Cl ^-竞争，形成更小尺寸的 Hg(II)-氯络合物，可以进入额外的颗粒内吸附位点。其中，Cl ^–被 S 击败，最终将 Hg(II) 固定在 SWP700 中，如扩展 X 射线吸收精细结构光谱所证实。^{我们得出结论，在含有 NOM 的含氧水中，Cl –} : NOM 和 Ca ²⁺ : NOM的摩尔比相对较高，使用 SWP700 仍然可以有效去除 Hg(II)。