Influence of divalent heavy metals on the aggregation of humic acids: Hofmeister effects

Stoichiometry between Humate Unit Molecules and Metal Ions in Supramolecular Assembly Induced by Cu2+ and Tb3+ Measured by Gel Electrophoresis Techniques

“…Among various supramolecular formation processes, the formation of metal-induced HA supramolecules is one of the predominant factors controlling the dynamics of metal ions in the environment. − This is because HA strongly binds with metal ions to form supramolecules, which successively form large aggregates and precipitates. Because metal–HA complexes are often exposed to the nonequilibrium state in the environment (such as the flow of a water system), the development of characterization methods for kinetically stable (dissociative inactive) metal–HA complexes is important.…”

Nanoscale Insights into the Interaction Mechanism Underlying the Adsorption and Retention of Heavy Metal Ions by Humic Acid

“…This phenomenon mainly arises from the robust binding of cationic Cd(II) and Pb(II) with the deprotonated oxygen-containing functional groups (e.g., carboxyl and phenol groups) in HA molecules (Table S1), which leads to the bridging of HA molecules and the formation of HA aggregates. 32 In contrast, the size of HA aggregates in the presence of As(V) (Figure 2F) becomes much smaller (RMS roughness ∼0.45 nm), which is attributed to the relatively weak bonding of anionic As(V) (viz., arsenate) with HA. In Figure 2G, the morphology of the HA surface in the presence of anionic Cr(VI) (viz., chromate, RMS roughness ∼0.36 nm) is quite similar to that without HMs (Figure 2C), which indicates the negligible bonding of anionic Cr(VI) with HA molecules.…”

“…As illustrated in Figure D,E, the size of the HA aggregates formed considerably increases in the presence of Cd(II) and Pb(II), with the RMS roughness rising to ∼0.64 and ∼0.70 nm, respectively. This phenomenon mainly arises from the robust binding of cationic Cd(II) and Pb(II) with the deprotonated oxygen-containing functional groups (e.g., carboxyl and phenol groups) in HA molecules (Table S1), which leads to the bridging of HA molecules and the formation of HA aggregates . In contrast, the size of HA aggregates in the presence of As(V) (Figure F) becomes much smaller (RMS roughness ∼0.45 nm), which is attributed to the relatively weak bonding of anionic As(V) (viz., arsenate) with HA.…”