Speciation of Cadmium and Zinc with Application to Soil Solutions

Abstract

A two‐part method has been developed for determination of Cd and Zn species in 50‐mL soil solution samples containing low concentrations of Cd and Zn (1–10 μg Cd L−1 and 50–1000 μg Zn L−1). The method uses two cation exchange resins (Amberlite CG 120 and Chelex 100) in a batch‐column‐batch procedure and relies on analytical determinations of Cd and Zn by graphite furnace atomic absorption spectrophotometry. The first part (batch) of the method allows determination of free divalent Cd2+ and Zn2+. This part is experimentally sensitive to cation concentrations and ionic strength and these parameters should be controlled during the experimental procedures. However, it is shown that Cd and Zn concentrations and pH do not influence the method. Speciations performed on samples containing chloride and sulfate were in accordance with theoretical calculations. The second part (column‐batch) of the method operationally separates the complexed fraction into labile complexes, slowly labile complexes, and stable complexes. Chloro complexes were identified as labile complexes, while EDTA complexes were identified as stable complexes. The method works well with relatively small volumes of sample solutions and at low metal concentrations and may be useful in characterization of Cd and Zn in soil solutions.

Effects of rice straw on the speciation of cadmium (Cd) and copper (Cu) in soils

“…Cu and Pb have higher affinity for DOM and therefore a very small fraction of these metals exists as free hydrated metal ions in soil solution (Aualiitia and Pickering, 1986;Sauvé et al, 1998;Weng et al, 2001b). On the other hand, metals such as Cd, Ni and Zn are less prone to form such stable metal-organic complexes (Aualiitia and Pickering, 1986;Pinheiro et al, 1994;Holm et al, 1995). Thus, a larger fraction of these metals is recovered as free hydrated metal ions.…”

EDTA-enhanced phytoremediation of heavy metal contaminated soil with Indian mustard and associated potential leaching risk

“…Soil solution samples were collected from the extra control and EDTA pots 6, 12, 29 and 52 days after the EDTA was applied to the soil. Each soil solution sample was separated into several aliquots for analysis of pH, total organic carbon (TOC) content, and total and organic chelate combined Cu, Zn, Pb and Cd complexes concentrations by the methods of Holm et al (1995). The aboveground parts of Indian mustard were washed with tap water and rinsed with distilled water, oven dried at 80 • C, ground and digested with 3:2 (v/v) nitric/perchlolic acids.…”

Practical applications of ion exchange resins in agricultural and environmental soil research

“…Fotovat and Naidu (1997) reported favorable results when using cation exchange resin for speciation of zinc (Zn 2+ ) and copper (Cu 2+ ) compared to a geochemical model named MINTEQA2. Holm et al (1995) concluded, in a study on speciation of cadmium and zinc in soil solutions, that the ion exchange method determines the dissolved species experimentally with minimal changes in the sample composition, and thus is able to work in complex solutions with ill-defined organic ligands.…”