Phosphate is added to Pb-contaminated soils to induce lead immobilization through lead phosphate precipitation. Organic coatings on soils, which may affect heterogeneous lead phosphate nucleation, can impact the effectiveness of lead immobilization. Here, SiO₂ surfaces were coated with silanol self-assembled thin films terminated with −COOH and −OH functional groups to act as model organic coatings on soil particles. Using grazing incidence small-angle X-ray scattering (GISAXS), heterogeneous lead phosphate nucleation on coatings was measured from mixed Pb(NO₃)₂ and Na₂HPO₄/NaH₂PO₄ solutions at pH 7 with varied ionic strengths (IS = 0.58, 4, and 11 mM). Raman spectroscopy identified the homogeneous precipitates in solution as hydroxylpyromorphite (Pb₅(PO₄)₃OH). The smallest lead phosphate nuclei (4.5 ± 0.5 nm) were observed on −COOH coatings, which resulted from the highest level of lead and phosphate ion adsorption on −COOH coatings. The IS of the solution also affected the sizes of the heterogeneous precipitates on −COOH coating, with smaller nuclei (1.3 ± 0.4 nm) forming under higher IS (4 and 11 mM). This study provided new findings that can improve our understanding of lead immobilization in contaminated soil environments.

中文翻译：

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磷酸盐在有机-水界面的异相成核：对铅固定化的影响

将磷酸盐添加到受Pb污染的土壤中，以通过磷酸盐铅沉淀诱导铅固定。土壤上的有机涂层可能会影响异质磷酸铅的成核作用，会影响铅固定的有效性。此处，SiO ₂表面涂有以-COOH和-OH官能团封端的硅烷醇自组装薄膜，以充当土壤颗粒上的模型有机涂层。使用掠入射小角X射线散射（GISAXS），从混合的Pb（NO ₃）₂和Na ₂ HPO ₄ / NaH ₂ PO _4中测量了涂层上的异磷酸铅成核pH值为7的溶液，具有不同的离子强度（IS = 0.58、4和11 mM）。拉曼光谱法鉴定出溶液中的均相沉淀为羟基焦晶石（Pb ₅（PO ₄）₃ OH）。在-COOH涂层上观察到最小的磷酸铅核（4.5±0.5 nm），这是由于-COOH涂层上铅和磷酸盐离子的吸附水平最高。溶液的IS也会影响-COOH涂层上非均相沉淀物的大小，在更高的IS（4和11 mM）下会形成较小的核（1.3±0.4 nm）。这项研究提供了新的发现，可以增进我们对污染土壤环境中铅固定的理解。