Relative lability of trace metals Complexed in aquatic humic substances using Ion-Exchanger cellulose-hyphan

Julio C Rocha,Ilda A.S Toscano,Arnaldo A Cardoso

doi:10.1590/s0103-50531997000300010

Abstract

The purpose of this paper is to characterize the lability/inertness metal fractions complexed by aquatic humic substances (HS) in relation to pH, complexation time, and HS concentration. HS were preconcentrated by ultrafiltration and complexed with bivalent metal ions. These fractions were characterized by ion exchange with the chelating collector cellulose Hyphan by applying batch procedure. The metals were determined by atomic absorption spectrometry. The results show that the distribution coefficients, Kd, decreased with HS presence, and that the relative lability of metal fractions complexed by HS is dependent on variables such as pH, complexation time, and HS concentration. Until c.a. 15 min, the metal change between aquatic HS and ion exchanger occurs following a 2nd order reaction. Afterwards, the remaining metal fraction in the HS reacts following a 1st order reaction. For traces of metal ions bound to dissolved HS, the lability orderPb > Mn > Cd, Ni > Cu is revealed.

Highlights

humic substances (HS) are a complex mixture of related macromolecules formed by the biological decomposition of plants in soils, and transported to natural waters by leaching
In slightly alkaline solutions there is a large change of metals from aquatic HS to ion-exchanger
The present study demonstrates that the distribution coefficients, Kd, of metal ions are strongly influenced by pH and HS concentration

Summary

Introduction

HS are a complex mixture of related macromolecules formed by the biological decomposition of plants in soils, and transported to natural waters by leaching. These macromolecules exhibit a great number of functional groups, phenolic and carboxylic[1,2]. Metal-organic interactions, including complexation reactions of metal ions and HS, are becoming increasingly recognized as important factors in many natural systems[3]. The high stability of metal fractions when complexed with biological or artificial ligand sources interfere directly in the transportation, accumulation and bioavailability of metals in the environment[4].

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