Binding Properties of Fulvic Acid Before and After Fractionation on Ferrihydrite: Effects of Phosphate

Abstract

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.

Differential Adsorption of Dissolved Organic Matter and Phosphorus on Clay Mineral in Water-Sediment System

“…A competitive interplay occurs as P and DOM compete for adsorption onto or coprecipitation with FeO x , thereby directing the immobilization of OC or P, and influencing the distribution of OC between the liquid and solid phases. 13,14 The composition of the sourced DOM governs the extent of its inhibitory impact on P immobilization, while simultaneously mediating the elemental constitution of OC−P associations. 15,16 Moreover, changes in the OC to P (OC/P) ratio in the productive zone of a lake could quickly indicate phytoplankton response to decreasing bioavailable P, even with partial water quality restoration.…”

“…Similar to P, DOM compounds can adsorb onto metals by coordinating carboxylic/phenolic functional groups, leading to competition with P adsorption. , The modulation and reduction of metal–organic interactions also have implications for P dynamics, given the role of P as a key nutrient inducing eutrophication. A competitive interplay occurs as P and DOM compete for adsorption onto or coprecipitation with FeO x , thereby directing the immobilization of OC or P, and influencing the distribution of OC between the liquid and solid phases. , The composition of the sourced DOM governs the extent of its inhibitory impact on P immobilization, while simultaneously mediating the elemental constitution of OC–P associations. , Moreover, changes in the OC to P (OC/P) ratio in the productive zone of a lake could quickly indicate phytoplankton response to decreasing bioavailable P, even with partial water quality restoration . The OC/P ratio is highly variable due to complex environmental factors .…”

Physico-Chemical Aspects of Metal–Fulvic Complexation

“…However, metal ions are often dissolved as complex species such as with humic substances. Comparing the diffusion coefficients of metal complexes with fulvic acid and humic acid showed that the size of the ligand is of primary importance for the mobility of metal-humic complexes [5][6][7]. In contrast, the binding constants are usually higher for humic acids than for fulvic acids [4,[8][9][10][11].…”

Interactions of Metal Ions with Fulvic Acids: Particle Size Distribution, Colloidal Stability and Thermodynamic Aspects

“…However, metal ions are often dissolved as complexed species such as with humic substances. Comparing the diffusion coefficients of metal complexes with fulvic acid, and humic acid showed that the size of the ligand, is of primary importance for the mobility of metal-humic complexes [5][6][7]. In contrast, the binding constants are usually higher for the humic acids than for the fulvic acids [4,[8][9][10][11].…”