Metastable ferrihydrite is omnipresent in environments and can influence the fate of Pb(II) during ferrihydrite transformation. Ferrihydrite is rarely pure and often coexists with impurities, which may influence the mineralogical changes of ferrihydrite and Pb(II) behavior. In this work, we investigated the effect of malic acid or phosphate on Pb(II)-ferrihydrite coprecipitates (Fh-Pb) transformation and the subsequent fate of Pb(II) during the 10-day aging of Fh-Pb. Results showed that both malic acid and phosphate retarded Fh-Pb transformation and prevented the release of Pb(II) from Fh-Pb back into solutions. Pb(II) was beneficial to goethite formation by inhibiting hematite formation while both malic acid and phosphate inhibited goethite formation since they could act as templates of nucleation. Besides, malic acid and phosphate improved the proportion of non-extracted Pb(II) during Fh-Pb transformation, indicating that Pb(II) was incorporated into secondary minerals. Pb(II) could not replace Fe(III) within the crystal lattice due to its large radius but was occluded into pores and defect structures within the secondary mineral lattices. This work can advance our understanding of the influences of malic acid and phosphate on Pb(II) immobility during Fh-Pb aging.

亚稳态水铁矿在环境中无处不在，可以影响水铁矿转化过程中 Pb(II) 的命运。水铁矿很少是纯的，经常与杂质共存，这可能影响水铁矿的矿物学变化和 Pb(II) 行为。在这项工作中，我们研究了苹果酸或磷酸盐对 Pb(II)-水铁矿共沉淀物 (Fh-Pb) 转化的影响以及在 Fh-Pb 的 10 天老化过程中 Pb(II) 的后续命运。结果表明，苹果酸和磷酸盐都延缓了 Fh-Pb 的转化，并阻止了 Pb(II) 从 Fh-Pb 中释放回溶液中。Pb(II) 通过抑制赤铁矿的形成而有利于针铁矿的形成，而苹果酸和磷酸盐都可以抑制针铁矿的形成，因为它们可以作为成核模板。除了，苹果酸和磷酸盐提高了 Fh-Pb 转化过程中未提取的 Pb(II) 的比例，表明 Pb(II) 被纳入次生矿物。Pb(II) 由于半径大而不能取代晶格内的 Fe(III)，而是被吸藏在次生矿物晶格内的孔隙和缺陷结构中。这项工作可以促进我们对苹果酸和磷酸盐在 Fh-Pb 老化过程中对 Pb(II) 不动性的影响的理解。