Copper(II) and lead(II) complexation by humic acid and humic-like ligands

Abstract

The stability of metal-humate complexes is an important factor determining and predicting speciation, mobility and bioavailability of heavy metals in the environment. A comparative investigation of the complexation of Cu(II) and Pb(II) with humic acid and humic-like ligands, such as benzoic and salicylic acid, was performed. The analysis was realized at pH 4.0, a temperature of 25 °C and at an ionic strength of 0.01 mol dm -3 (NaCl) using the Schubert ion-exchange method and its modified form. The stability constants were calculated from the experimental data by the Schubert method for complexes with benzoic and humic acid. A modified Schubert method was used for the determination of the stability constants of the complexes with salicylic acid. It was found that Cu(II) and Pb(II) form mononuclear complexes with benzoic and humic acid while with salicylic acid both metals form polynuclear complexes. The results indicate that Pb(II) has a higher binding ability than Cu(II) to all the investigated ligands. The Cu(II)-salicylate and Pb(II)-salicylate complexes showed noticeable higher stability constants compared with their complexes with humic acid, while the stabilities of the complexes with benzoic acid differed less. Salicylic and benzoic acids as humic-like ligands can be used for setting the range of stability constants of humic complexes with Cu(II) and Pb(II).

Comparative study of binding strengths of heavy metals with humic acid

“…The isotherms for each metal ion were investigated at 25 °C temperature and pH 4.0 in order to avoid hydrolysis of metal ions and carbonate formation. Humic acid was characterized in detail previously [24].…”

“…The isotherm linear range was obtained for each metal, in order to estimate D 0 and choose the appropriate concentrations for preventing the effect of metal loading [21][22][23][24]. Table 1 gives a summary of the percentage of total metal bound to exchange resin, α 0 , distribution coefficient between the resin and solution phase for metal ion in the absence (D 0 ) and presence (D) of ligand for each of five metals, and values of stability constants, log β mn .…”

“…The position of Cu(II) in the Irving-Williams order is considered out-of-line (Mn(II) < Fe(II) < Co(II) < Ni(II) < < Cu(II) > Zn(II)), probably as a consequence of the fact that Cu(II) often forms distorted octahedral complexes. The different affinity of Pb(II), Cu(II), Zn(II), Ni(II) and Co(II) can be explained by their chemical properties such as the size of ion radius (r M 2+ ), charge (z) of the metal ion, that is ionic potential, Ip = z/r, the electronegativity of the element, ligand field stabilization energy effects and classification, which is based on the electron configuration of the cations and the concept of hard/soft acids and bases (HSAB theory) [23,24].…”

Removal of heavy metals by homolytically functionalized poly(acrylic acid) with hydroquinone

“…Under the actual experimental conditions, the exchange capacity is in this order: Pb(II) [ Cu(II) [ Cd(II). The adsorption capacity of the adsorbent is more for lead when compared to other metals, because the stability constants of complexes of lead with carboxylates and phenols are greater than those for other metals [33,34]. The cross-linked poly(acrylic acid-co-Kryptofix-22-DM) [36], the tetrahydroxybenzenefunctionalized PAA [5], and the tetrahydroxybenzenefunctionalized PAAm [14] showed the same order of sorption capacity.…”

Antimicrobial activity of copper‐humate‐cellulose sheets

“…The most commonly used bases for extraction are potassium hydroxide and sodium hydroxide, [28][29][30][31] where the resulting alkaline humates are potassium humate and sodium humate. These alkali humates bind well to metals mainly by their carboxyl and hydroxyl groups, [32][33][34][35][36] and can also bind well to cellulose fibres. 16,37 The functional groups in humate form metastable complexes with metal and other cations.…”