Equilibrium Speciation of Cadmium, Copper, and Lead in Soil Solutions

Abstract

Determination of chemical speciation of trace metals may help us to better understand the bioavailability and toxicity to living organisms in terrestrial and aquatic environments. This paper reports the speciation data of cadmium (Cd), copper (Cu), and lead (Pb) in soil solutions sampled from areas around metal smelters. A column ion exchange technique (IET) using a cation exchange resin was applied to determine the concentrations of Cd 2þ , Cu 2þ , and Pb 2þ . It was shown that the pH and the amount of calcium (Ca) in solutions affected the distribution of metal ions to the resin. In the synthetic solutions involving Cl, SO 4 , and citrate, the metal-ligand complexes did not affect the measurement of free metal ions by the IET. In soil solutions, the concentrations of free ions were affected by solution pH, varying within 10 29 -10 27 M for Cd, 10 29 -10 26 M for Cu, and 10 29 -10 27 M for Pb. The IET results were comparable to those measured by Cu-ion selective electrode (ISE) and anodic stripping voltammetry (ASV). These findings suggest that the IET can be applied to soil solutions for metal speciation measurements.

Determination of Free Nickel Ion Concentrations Using the Ion Exchange Technique: Application to Aqueous Mining and Municipal Effluents

“…Ge et al (2005) have also found that the results of the IET were comparable with ion selective electrode (ISE) measurements for copper and satisfactory (within one order of magnitude) with anodic stripping voltammetry (ASV) measurements for Cd and Pb in lysimeter soil solutions from forest floors contaminated by trace metals. ASV measures the labile fraction, which is a representative sum of free metal ion and its inorganic and weakly dissociated metal-organic complexes.…”

“…In order to ensure that equilibrium was established, the last 15 ml of the effluent of each test sample was collected and tested. It is interesting to note that literature on IET, using similar conditions (especially resin mass) but testing metals other than nickel, report that only *20 ml of sample volume was required to reach steady-state (Fortin and Campbell 1998;Ge et al 2005). Nickel may be special as it was known to have slow equilibrium kinetics in natural waters (Xue et al 2001).…”

“…Previous reports indicate that the ion exchange technique (IET) provides an estimate of free metal concentrations of Cd, Cu, Pb, and Zn in controlled solutions and in the presence of dissolved organic matter (Fortin and Campbell 1998;Fortin and Caron 2000;Ge et al 2005). Ge et al (2005) have also found that the results of the IET were comparable with ion selective electrode (ISE) measurements for copper and satisfactory (within one order of magnitude) with anodic stripping voltammetry (ASV) measurements for Cd and Pb in lysimeter soil solutions from forest floors contaminated by trace metals.…”

Fractionation and Speciation of Trace Elements in Soil Solution

“…Regardless of these current limitations, computer models are often used in combination with data obtained by instrumental speciation techniques when assessing trace element speciation in the soil solution or in soil extracts (for example [147]), or to cross-validate the instrumental speciation techniques (for example [149]) or the models themselves (for example [150]) in various development stages.…”

Development of an In Situ Ion-Exchange Technique for the Determination of Free Cd, Co, Ni, and Zn Concentrations in Freshwaters

“…, and Zn 2? concentrations in synthetic and soil solutions containing various inorganic and organic ligands, including humic substances (Doig and Liber 2007;Fortin and Campbell 1998;Ge et al 2005;Holm et al 1995;Néron et al 2006;Vigneault and Campbell 2005). The IET was successfully used for Zn 2?…”