Effect of humic substances on Cu(II) solubility in kaolin-sand soil

Abstract

The type and amount of organic matter present in industrially contaminated soils will influence the risk they pose. Previous studies have shown the importance of humic and fulvic acids (important components of soil organic matter) in increasing the solubility of toxic metals but were not carried out using toxic metal levels and the pH range typical of industrially contaminated soils. This study investigated of the influence of three humic substances (humates, fulvates and humins) on the solubility of copper(II) ions in kaolinitic soil spiked with Cu at levels representative of industrially contaminated soil.Humates, fulvates and humin were extracted from Irish moss peat, and controlled pH batch leaching tests were conducted on an artificial kaolin-sand soil that was spiked with each. Further leaching tests were conducted on soil spiked with each humic substance and copper nitrate. Dissolved organic contents were determined by titration and total and free aqueous copper concentrations in the leachate were measured using AAS and ion selective electrode potentiometry respectively (dissolved complexed copper levels were determined by difference).It was found that humates and fulvates are partially sorbed by the soil, probably by chemisorption on positively charged gibbsite (Al-hydroxide) sites in the kaolinite.The addition of 340 mg/kg Cu(II) ions did not significantly affect the amount of humate or fulvate sorbed. Dissolved humates and fulvates form soluble complexes with copper over the pH range 3 to 11. However, in the presence of kaolinite, soluble copper humates and fulvates are unable to compete with the kaolinite for Cu ions at pH 6 to 7. Above pH 8, humate and fulvate complexes are the only forms of dissolved Cu. Humin is largely insoluble and has little effect on Cu mobility between 2 pH 2 and 12. The implication of this study is that measurement of total soil organic content and water leaching tests should be a standard part of contaminated site investigation.

Assessment of heavy metals in soils of a vineyard region with the use of principal component analysis

“…Geoavailability of Cu is strongly influenced by the amount of organic matter and the nature of the humic substances in the soil (Wu et al, 2002). Soluble humic and fulvic acids may increase the solubility and mobility of the elements; once in a neutral to alkaline reaction environment they form stable complexes with the carboxyl, hydroxyl and amino groups of these compounds (Wu et al, 2002;Schnitzer & Kahn, 1972).…”

Physico-chemical characteristics of gleyic luvisols and gleyic listosols production areas of garden produce in Nieki Valley, South-east of Cote d'ivoire

“…There is a provision in the middle of the proton of which the binding is highly competitive on the exchange sites and those sorption (Baize, 1997). Dissolution of metal salts or the destruction of the retention phase may also take place under acidic conditions (Wu et al, 2002).…”

“…This affinity is of great importance in the behavior of toxic metals. For example, the dissolved organic matter is capable of complexing the metal and to increase their solubility (Wu et al, 2002). Due to their small size, their high surface site and their filling properties, organic soil colloids may potentially have a greater affinity for the metal than the other soil components.…”

Self-doped Anthranilic Acid-Pyrrole Copolymer/Gold Electrodes for Selective Preconcentration and Determination of Cu(I) by Differential Pulse Anodic Stripping Voltammetry

“…It is probably due to this fact that the humic substances do not have a potential high enough to form complexes with copper ions at low concentrations in acidic medium. 32 In spite of this, the total copper concentration was measured voltammetrically after irradiation of the analysis sample with ultraviolet light to decompose the organic ligands like humic and fulvic acids. The result was comparable with the result obtained by AAS.…”