Comparative study of binding strengths of heavy metals with humic acid

Ivana Kostic,Dusica Pavlovic,Ruzica Nikolic,Tatjana Andjelkovic,Tatjana Cvetkovic,Aleksandar Bojic

doi:10.2298/hemind121107002k

Abstract

The complexation of humic acid with certain heavy metal ions (Co(II), Ni(II), Cu(II), Zn(II) and Pb(II)) was investigated. The stability constants of humate complexes were determined by method which is based on distribution of metal ions between solution and resin in the presence and the absence of ligand, known as Schubert?s ion exchange method. Experiments were performed at 25 ?C, at pH 4.0 and ionic strength of 0.01 mol dm-3. It was found that the 1:1 complexes were formed between metal ions and humic acid. Obtained results of the stability constants, log ?mn, of complexes formed between the metal ions and humic acid follow the order Co(II) < Ni(II) < Cu(II) > Zn(II) which is the same like in the Irving-Williams series for the binding strength of divalent metal ion complexes. Stability constant of complex between Pb(II) ions and humic acid is greater than stability constants of other investigated metal-humate complexes. The investigation of interaction between heavy metal ions and humics is important for the prediction of the distribution and control of the migration of heavy metals in natural environment.

Highlights

The complexation of humic acid with certain heavy metal ions (Co(II), Ni(II), Cu(II), Zn(II) and Pb(II)) was investigated
The stability constants of humate complexes were determined by a method based on the distribution of metal ions between solution and resin in the presence and the absence of ligand, known as Schubert’s ion exchange method
Obtained results of the stability constants, log βmn, of complexes formed between the metal ions and humic acid follow the order Co(II) < Ni(II) < Cu(II) > Zn(II), which is the same as in the Irving–Williams series for the binding strength of divalent metal ion complexes

Summary

Introduction

The complexation of humic acid with certain heavy metal ions (Co(II), Ni(II), Cu(II), Zn(II) and Pb(II)) was investigated. Heavy metals can be involved in a series of complex chemical and biological interactions Factors that affect their mobility through the soil/water system are pH, redox status of the environment, sorbent nature, presence and amount of organic and inorganic ligands, including humic and fulvic acids, root exudates and nutrients [4]. Humic acids have natural and powerful adsorbent properties and are deeply related to the transportation and accumulation of heavy metals [5,6] They are widely distributed in soils/waters and the type and structure of their functional groups depend on their genesis, and on the method of their isolation and purification [7,8]. Humic acid can serve as carrier of toxic metals, forming complexes that are stable and enhance transport of toxic metals in waters [10,11,12]

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