Soil colloids significantly facilitate the transport of contaminants; however, little is known about the effects of highly reactive iron oxide and the most representative organic matter on the transport of soil colloids with different physicochemical properties. This study investigated the effects of goethite (GT) and humic acid (HA) on the sedimentation and transport of soil colloids using settling and column experiments. The stability of soil colloids was found to be related to their properties and decreased in the following order: black soil colloids (BSc) > yellow soil colloids (YSc) > fluvo-aquic soil colloids (FSc). Organic matter increased the stability of BSc, and ionic strength (Ca2+) promoted the deposition of FSc. Colloids in individual and GT colloids (GTc) coexistence systems tended to stabilize at high pH and showed a pH-dependence whereby the stability decreased with decreasing pH. The interaction of GTc and kaolinite led to a dramatic sedimentation of YSc at pH 4.0. HA enhanced the stability of soil colloids, especially at pH 4.0, and obscured the pH-dependent sedimentation of soil colloids. The transport ability of soil colloids was the same as their stability. The addition of GT retarded the transport of soil colloids, which was quite obvious at pH 7.0. This retardation effect was attributed to the transformation of the surface charge of sand from negative to positive, which increased the electrical double-layer attraction. Although sand coated with GT–HA provided more favorable conditions for the transport of soil colloids in comparison to pure sand, the corresponding transport was relatively slow. This suggests that the filtration effect, heterogeneity, and increased surface roughness may still influence the transport of soil colloids.

中文翻译：

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不同土壤胶体的沉积和运输：针铁矿和腐植酸的影响

土壤胶体显着促进污染物的迁移；然而，关于高活性氧化铁和最具代表性的有机物质对具有不同理化性质的土壤胶体运输的影响知之甚少。本研究通过沉降​​和柱状实验研究了针铁矿 (GT) 和腐植酸 (HA) 对土壤胶体沉积和迁移的影响。土壤胶体的稳定性与其性质有关，并按以下顺序下降：黑土胶体（BSc）>黄土胶体（YSc）>潮土胶体（FSc）。有机质增加了BSc的稳定性，离子强度（Ca2+）促进了FSc的沉积。单个胶体和 GT 胶体 (GTc) 共存系统中的胶体在高 pH 值下趋于稳定，并显示出 pH 依赖性，即稳定性随着 pH 值的降低而降低。GTc 和高岭石的相互作用导致 YSc 在 pH 值为 4.0 时发生剧烈沉降。HA 增强了土壤胶体的稳定性，尤其是在 pH 4.0 时，并掩盖了土壤胶体的 pH 依赖性沉降。土壤胶体的运输能力与其稳定性相同。GT 的加入延缓了土壤胶体的迁移，这在 pH 7.0 时非常明显。这种阻滞效应归因于沙子的表面电荷从负电荷转变为正电荷，从而增加了双电层吸引力。尽管与纯沙相比，涂有 GT-HA 的沙子为土壤胶体的运输提供了更有利的条件，但相应的运输速度相对较慢。这表明过滤效应、异质性和增加的表面粗糙度可能仍会影响土壤胶体的迁移。