Struvite precipitated from wastewaters is an important fertilizer. However, struvite derived from wastewater usually contains toxic Pb, which can bring contamination to soil and even plants. Thus, understanding the incorporation mechanisms of Pb2+ during struvite precipitation is critical to its safe application. Here the influence of Pb concentration on struvite precipitation was assessed. When the initial Pb concentrations were at the range of 0.1-1 mg/L, the formation of pitting and roughening on struvite crystal surfaces was observed by scanning electron microscopy (SEM), indicating a surface interaction between Pb and struvite. Combined with X-ray photoelectron spectra (XPS), the results confirmed that the formed Pb-enriched layer with Pb-OH and Pb-PO4 bonds was absorbed on struvite surface during precipitation. When Pb concentrations were increased to 10-100 mg/L, the precipitation of dominating Pb phase, crystalline Pb10(PO4)6(OH)2, was confirmed by X-ray diffraction (XRD). Combined with XPS, the amorphous Pb hydroxide/phosphate and Mg phosphate were also detected in struvite solids. Our findings revealed that at low concentrations (0.1-1 mg/L), Pb can affect the mineral surface by surface absorption, whereas Pb precipitated as separated phase(s) (e.g. Pb10(PO4)6(OH)2, Pb hydroxide and/or phosphate) at high Pb concentrations (10-100 mg/L). Thus, the initial Pb2+ concentrations in wastewater will dictate final struvite contents and Pb-bearing phases in recovered solids.

中文翻译：

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鸟粪石沉淀过程中Pb2 +的掺入：定量，形态和结构分析。

从废水中沉淀出来的鸟粪石是一种重要的肥料。但是，废水中的鸟粪石通常含有有毒的Pb，会污染土壤甚至植物。因此，了解鸟粪石沉淀过程中Pb2 +的掺入机制对于其安全应用至关重要。在此评估了铅浓度对鸟粪石沉淀的影响。当初始Pb浓度在0.1-1 mg / L范围内时，通过扫描电子显微镜（SEM）观察到鸟粪石晶体表面出现点蚀和粗糙化现象，表明Pb和鸟粪石之间存在表面相互作用。结合X射线光电子能谱（XPS），结果证实形成的具有Pb-OH和Pb-PO4键的Pb富集层在沉淀过程中被吸收在鸟粪石表面。当Pb浓度增加到10-100 mg / L时，通过X射线衍射（XRD）证实了主要的Pb相的沉淀，即结晶Pb10（PO4）6（OH）2。结合XPS，在鸟粪石固体中也检测到无定形的Pb氢氧化物/磷酸盐和Mg磷酸盐。我们的发现表明，在低浓度（0.1-1 mg / L）下，Pb可以通过表面吸收影响矿物表面，而Pb则以分离相的形式沉淀（例如Pb10（PO4）6（OH）2，氢氧化铅和/或磷酸盐）在高Pb浓度（10-100 mg / L）下进行。因此，废水中的初始Pb2 +浓度将决定回收固体中最终鸟粪石含量和含Pb相。在鸟粪石固体中也检测到无定形的Pb氢氧化物/磷酸盐和Mg磷酸盐。我们的发现表明，在低浓度（0.1-1 mg / L）下，Pb可以通过表面吸收影响矿物表面，而Pb则以分离相的形式沉淀（例如Pb10（PO4）6（OH）2，氢氧化铅和/或磷酸盐）在高Pb浓度（10-100 mg / L）下进行。因此，废水中的初始Pb2 +浓度将决定回收固体中最终鸟粪石含量和含Pb相。在鸟粪石固体中也检测到无定形的Pb氢氧化物/磷酸盐和Mg磷酸盐。我们的发现表明，在低浓度（0.1-1 mg / L）下，Pb可以通过表面吸收影响矿物表面，而Pb则以分离相的形式沉淀（例如Pb10（PO4）6（OH）2，氢氧化铅和/或磷酸盐）在高Pb浓度（10-100 mg / L）下进行。因此，废水中的初始Pb2 +浓度将决定回收固体中最终鸟粪石含量和含Pb相。