Six-membered ring heterocyclic compounds are widely present in the Earth's surface environments as biological organic molecules composed of soil organic matter including plant and microbial residues, while little is known about their effect on the dissolution of silicate minerals including amorphous silica. To evaluate the effect of these biological molecules on amorphous silica dissolution, dissolution experiments were carried out by the flow-through method using 0.1 g of amorphous silica and 0.1 mM NaCl electrolyte solutions containing 0.0, 0.1, 1.0, or 10.0 mM of the heterocyclic compounds, piperidine (pK = 11.12), pyridine (pK = 5.25), or pyridazine (pK = 2.33), at a pH of 6, 5, or 4. Additionally, adsorption experiments of the compounds on the amorphous silica surface were performed to confirm the adsorption affinity for the amorphous silica surface. The results demonstrated that these heterocyclic compounds enhance the dissolution rate of amorphous silica in the following order: piperidine > pyridine > pyridazine. When 10.0 mM solutions were used, the heterocyclic compounds enhanced greatly the dissolution rate up to enhancement factors of 6.0 to ~14.8, 5.0 to ~14.0, and 1.0 to ~2.6 through an interaction of piperidine, pyridine, and pyridazine, respectively, in the pH range of approximately 6 to ~ 4. The adsorption experiments indicated that the heterocyclic compounds exhibited significant adsorption affinity for the amorphous silica surface as follows: piperidine > pyridine > pyridazine, which was consistent with the order of their effects on the dissolution enhancement. The geochemical calculation revealed that this order of enhancement was in good agreement with the concentrations of cationic species of heterocyclic compounds at corresponding pH conditions. Consequently, the enhancement of amorphous silica dissolution is likely to be influenced by the electrostatic complexation of the cationic species of the heterocyclic compounds with the negative >SiO– sites on the amorphous silica surface.

中文翻译：

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通过与六元环杂环化合物的相互作用增强无定形二氧化硅的溶解

六元环杂环化合物作为由土壤有机质（包括植物和微生物残留物）组成的生物有机分子广泛存在于地球表面环境中，而关于它们对包括无定形二氧化硅在内的硅酸盐矿物溶解的影响知之甚少。为了评估这些生物分子对无定形二氧化硅溶解的影响，使用 0.1 g 无定形二氧化硅和 0.1 mM NaCl 电解质溶液（含有 0.0、0.1、1.0 或 10.0 mM 杂环化合物）通过流通法进行溶解实验、哌啶 (pK = 11.12)、吡啶 (pK = 5.25) 或哒嗪 (pK = 2.33)，pH 为 6、5 或 4。此外，进行化合物在无定形二氧化硅表面上的吸附实验以确认对无定形二氧化硅表面的吸附亲和力。结果表明，这些杂环化合物按以下顺序提高了无定形二氧化硅的溶解速率：哌啶>吡啶>哒嗪。当使用 10.0 mM 溶液时，杂环化合物分别通过哌啶、吡啶和哒嗪的相互作用大大提高了溶解速率，提高因子分别为 6.0 至 ~14.8、5.0 至 ~14.0 和 1.0 至 ~2.6。 pH范围约为6~4。吸附实验表明杂环化合物对无定形二氧化硅表面表现出显着的吸附亲和力如下：哌啶>吡啶>哒嗪，这与它们对溶解增强的影响顺序一致。地球化学计算表明，在相应的 pH 条件下，这种增强顺序与杂环化合物的阳离子物质浓度非常吻合。因此，无定形二氧化硅溶解的增强很可能受到杂环化合物的阳离子物质与无定形二氧化硅表面上的负 >SiO– 位点的静电络合的影响。