Insight into the interaction mechanism of iron ions with soil humic acids. The effect of the pH and chemical properties of humic acids

Evaluation of Commercial Humic Substances and Other Organic Amendments for the Immobilization of Copper Through 13C CPMAS NMR, FT-IR, and DSC Analyses

“…In this band there were not important differences between Cu concentrations at either pH. However, Huang et al [20] observed changes at 1614 cm −1 with the addition of Cr(VI), although the reaction involved was the reduction of this metal ion, instead of its complexation; other authors [46,47] have also reported increasing intensities at this band with higher Fe and Zn concentrations, especially at higher pH conditions due to the increase of negative charge on humic surfaces and the lower competition with protons [44].…”

“…This band was less intense at pH 5.0 and disappeared with 100 mg L −1 of Cu (HS100), whereas at pH 2.5 it did not show great variation due to the higher amount of non-dissociated carboxyl groups [46]. Other studies [8,9,20,46,47] also observed a decreasing intensity of this band with higher concentrations of metals (Cu, Cr, Fe, and Zn), corroborating the important role of COOH groups as active centers for metal complexation. In contrast to our results, Boguta and Sokolowska [46] showed that part of the signal of this band did not disappear at pH 5.0, suggesting that not all carboxylic groups are involved in metal binding, probably due to steric effects.…”

“…This drop of absorption with increasing Cu suggests the binding of this metal by these OH groups, such as phenol and carboxyl. Boguta and Sokolowska [46] also observed decreasing intensities at these bands with the addition of Zn to different humic acids, due to metal binding by OH groups, whereas Boguta et al [47] reported higher intensities with Fe because of the involvement of OH groups in metal complexation by the production of aqua-complexes. Álvarez-Puebla et al [8] also observed changes in the signals of these bands due to the formation of complexes of Cu with carboxylic acid groups.…”

“…On the other hand, the signals of the peaks between 1575 and 1590 cm −1 , corresponding to aromatic C=C and C=O of ketones and carboxyl [2,11,20,32,33], exhibited a greater intensity at pH 5.0 than at pH 2.5. Boguta et al [47] reported that this band at low pH was broadened and shifted due to a possible rearrangement of the coordination between humic acids and the metal ion. Inversely, Zhang et al [24] reported a decreasing intensity with higher pH at 1540 cm −1 .…”

Insight into the cadmium and zinc binding potential of humic acids derived from composts by EEM spectra combined with PARAFAC analysis

“…Until now, the structural information of many HAs such as aromatic derivatives, phenolic fragments, substituted benzoic acids, quinones, carbohydrates, fatty acids, and peptides has been described by researchers [15]. As many of the functional groups carried on HAs interact with heavy metals [16], it might be feasible to use HAs to affect the mobilization behaviour of heavy metals. However, the compositions of HAs differ because they are formed from different raw materials [17], so it is necessary to compare the binding capacity of different HAs to heavy metals.…”