Complexation Study of Humic Acids Extracted from Forest and Sahara Soils with Zinc (II) and Cadmium (II) by Differential Pulse Anodic Stripping Voltammetry (DPASV) and Conductimetric Methods

Abstract

The complexation of heavy metals, present in their dissolved state at relevant trace levels, with new humic acids (HAs) isolated from Yakouren forest (YHA) and Sahara (Tamenrasset: THA) soils has been studied by differential pulse anodic stripping voltammetry (DPASV) at a hanging mercury drop electrode and conductimetry methods. After extraction and purification, humic acids were characterized by elemental analyses, atomic absorption spectroscopy, FT-IR, and solution state 13 C-NMR. Taking Zn(II) and Cd(II) as examples, the aim of this study was to gain direct information on the general level of importance of humic acids for the speciation of certain heavy metals in soil to determine the complexing capacities of AHs and stability constant of the complexes formed with these metal ions and to compare the complexation capacity of forest and Sahara soils with the commercial humic acid and other published AHs. The results determined by conductimetry method are interpreted using an excess function (Δk) which related the conductivity of the mixture and of the separated components. A positive value of this function is obtained. It indicates the complexation of humic acids with metallic ions. The DPASV method was used for determining metal ion complexing capacities and stability constants of metal ion complexes of HAs in solution at pH 7. In both types of soils, the commercial humic acid (CHA) is less efficient in complexing Zn(II) and Cd(II) than THA and YHA and the complexing capacity (CC M ) decreases in the order: THA > YHA > CHA. In general, the results of complexing capacity for all humic acids and stability constants of Zn(II) and Cd(II) complexes found by DPASV method showed good correlation with those of conductimetry method. CC M of THA and YHA calculated by DPASV were higher than those of CHA and the other natural HAs published in the literature at pH 7 basing on these results.

Lignitic Humic Acids as Environmentally-Friendly Adsorbent for Heavy Metals

“…The stability constant for the complex between lead and humic acids was greater than those for other metal-humic complexes. Terbouche et al [38] showed that the degree of association between metal ions and humic acids was greater for zinc than for cadmium, which corresponds with our results. Ren et al [39] divided Cd 2+ , Cu 2+ , Pb 2+ , and Zn 2+ ions occurring in contaminated soils into two groups: a fast exchangeable pool and a much slower exchangeable one.…”

Lanthanides and Actinides in Humic Acids of Soils and Paleosols of Forest-Steppe Conditions in the Southern Urals

“…This is due to HA's ability to accumulate, deposit, and store carbon, along with a wide range of trace elements for long geological periods, as well as the ability to inhibit chemical compounds that are toxic to living organisms. This ability of humic acids is well known [3][4][5][6][7].…”

Electrochemical sensors and devices for heavy metals assay in water: the French groups' contribution

“…In a close approach combining DPASV and conductometry, Terbouche et al examined the complexation of Zn(II) and Cd(II) by new humic acids from Algeria, these latter class of natural polymers being known to have an influence on heavy metals biogeochemical cycle and bioavailability (Terbouche et al, 2011 ). Based on the strong complexing capacities evidenced in this work, the authors suggested their humic acids to be used for metal uptake.…”