科研之友
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摘要
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.
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