Due to the potential negative impact of nano silica (nSiO₂) on human's health and living environments, it is important to investigate their transport in soil environments. Hydrochars has been widely used in agricultural soil and phosphate (P) is an important nutrient, thus the aggregation and transport of nSiO₂ in saturated sand columns were investigated in single and binary systems of hydrochars and P. The experimental results showed that the nSiO₂ aggregates can be restablized by the adsorption of P or the attachment of hydrochars at high IS (>100 mM) and low pH (<7.0). Accordingly, the transport of nSiO₂ in sand columns is enhanced due to the smaller particle size. However, the nSiO₂ presents the distinct surface characteristics at pH > 7.0 from that at pH < 7.0. Thus, nSiO₂ has a better dispersivity in 300 mM NaCl solution at high pH (9.0). Nevertheless, their deposition to sands becomes pronounced in the presence of hydrochars and/or P. In particular, the formation of nSiO₂-hydrochar-Phosphate clusters associated with the larger size mainly contributes to the enhancement of nSiO₂ retention in sand columns during the wide pH range, when hydrochars and P coexist in suspensions. The two-site dynamic model fitting results showed that the reversible retention is related to k₂ (First-order straining coefficient on site 2). The results in this study will provide the theoretical basis for assessing the retention of nSiO₂ in soil environment with the presence of hydrochars and phosphate.

中文翻译：

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碳氢化合物和磷酸盐增强纳米颗粒二氧化硅在饱和砂土中的运输

由于纳米二氧化硅（nSiO ₂）对人类健康和生活环境的潜在负面影响，因此研究其在土壤环境中的运输非常重要。碳氢化合物已被广泛用于农业土壤中，而磷酸盐（P）是一种重要的养分，因此，在碳氢化合物和P的单一和二元体系中研究了nSiO ₂在饱和砂柱中的聚集和迁移。实验结果表明，nSiO ₂可以通过在高IS（> 100 mM）和低pH（<7.0）下吸附P或附着碳氢化合物来重新稳定骨料。因此，由于较小的粒径，增强了nSiO ₂在砂柱中的传输。但是，nSiO ₂在pH> 7.0时表现出与pH <7.0时不同的表面特性。因此，nSiO ₂在高pH（9.0）下在300 mM NaCl溶液中具有更好的分散性。然而，在存在碳氢化合物和/或P的情况下，它们沉积在砂土上的现象尤为明显。特别是，与较大尺寸相伴的nSiO _2-碳氢化合物-磷酸盐簇的形成主要有助于提高nSiO ₂在砂柱中的保留率。悬浮液中同时存在炭和P时，pH范围宽。两点动力学模型拟合结果表明，可逆保持力与k _2有关。（站点2的一阶应变系数）。这项研究的结果将为评估存在碳氢化合物和磷酸盐的土壤中nSiO ₂的保留提供理论依据。