Adsorptive fractionation of dissolved organic matter (DOM) on minerals is an important geochemical process that affects the chemical compositions and properties of DOM. Phosphate, a widely occurring oxyanion in the natural environment, can compete with DOM for adsorption to iron (oxy)hydroxide surfaces, and thus, may change the compositions and reactivity of DOM during the adsorptive fractionation process. In this study, we investigated the effect of the adsorptive fractionation of fulvic acid (FA) at the ferrihydrite–water interfaces with or without phosphate on the optical compositions and the binding properties of FA by employing spectroscopic methods combined with two-dimensional correlation spectroscopy (2DCOS) analysis and potentiometric titration coupled with WHAM 7 model calculation. Our results showed that the presence of phosphate increased the concentrations of total organic carbon, aromatic components, chromophores, acidic groups, and fluorescent fractions in FA samples after adsorptive fractionation, indicating that phosphate would compete with these organic components for the binding sites of ferrihydrite and thus affect the partition of FA components at the ferrihydrite–water surfaces. The 2DCOS analysis revealed that phosphate competed with FA components in the order as follows: fulvic-like fractions (350 nm) > humic-like fractions (460 nm) or fulvic-like fractions (305 nm). Furthermore, the presence of phosphate during the adsorptive fractionation of FA enhanced the Cu binding ability of FA but did not change the binding sequence of Cu to FA components. Our results contribute to understanding the metal-binding characteristics of DOM under the influence of complex interactions among DOM, minerals, and inorganic constituents.

中文翻译：

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分馏前后富里酸对水铁矿的结合特性：磷酸盐的影响

矿物上溶解有机质（DOM）的吸附分馏是影响DOM化学成分和性质的重要地球化学过程。磷酸盐是一种在自然环境中广泛存在的氧阴离子，可以与 DOM 竞争吸附到铁（氧）氢氧化物表面，因此可能会在吸附分馏过程中改变 DOM 的组成和反应性。在这项研究中，我们通过光谱方法结合二维相关光谱研究了富里酸（FA）在有或没有磷酸盐的水铁矿-水界面处的吸附分馏对光学组成和 FA 结合特性的影响。 2DCOS) 分析和电位滴定加上 WHAM 7 模型计算。我们的结果表明，磷酸盐的存在增加了吸附分离后 FA 样品中总有机碳、芳香族成分、发色团、酸性基团和荧光部分的浓度，表明磷酸盐会与这些有机成分竞争水铁矿和水铁矿的结合位点。因此影响 FA 组分在水铁矿-水表面的分配。2DCOS 分析表明，磷酸盐与 FA 组分的竞争顺序如下：类富里酸组分 (350 nm) > 类腐殖质组分 (460 nm) 或类富里酸组分 (305 nm)。此外，在 FA 吸附分离过程中磷酸盐的存在增强了 FA 的 Cu 结合能力，但没有改变 Cu 与 FA 组分的结合顺序。