Cadmium(II) Speciation in Complex Aquatic Systems: A Study with Ferrihydrite, Bacteria, and an Organic Ligand

Understanding the chemical interactions that occur in complex natural systems is fundamental to their management. In this work, the distribution of cadmium in the presence of phthalic acid (H2Lp), ferrihydrite, and bacteria cells (Comamonas spp., heat killed) was measured and modeled for systems wit...

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Bibliographic Details
Published in:Environmental science & technology 2009-10, Vol.43 (19), p.7430-7436
Main Authors: Song, Yantao, Swedlund, Peter J, Singhal, Naresh, Swift, Simon
Format: Article
Language:English
Subjects:
Adsorption
Applied sciences
Aquatic ecosystems
Bacteria
Cadmium
Cadmium - chemistry
Cells
Comamonas
Comamonas - chemistry
Ecosystem
Environmental Processes
Exact sciences and technology
Ferric Compounds - chemistry
Minerals
Molecules
Phthalic Acids - chemistry
Pollution
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Summary:Understanding the chemical interactions that occur in complex natural systems is fundamental to their management. In this work, the distribution of cadmium in the presence of phthalic acid (H2Lp), ferrihydrite, and bacteria cells (Comamonas spp., heat killed) was measured and modeled for systems with incrementally increasing complexity. In binary systems, cadmium adsorption onto bacteria or ferrihydrite was accurately predicted using the nonelectrostatic four site model (NFSM) and the diffuse layer model (DLM), respectively. Phthalic acid (0.6 mM) enhanced Cd2+ adsorption onto ferrihydrite (due to surface ternary complex formation) but inhibited Cd2+ adsorption onto bacteria to the same extent as predicted by Cd−phthalate solution complex formation constants, implying no significant surface ternary interaction occurred in this system. In Cd−ferrihydrite−bacteria systems, Cd2+ adsorption was up to 10% lower than that predicted by additive adsorption onto the pure phases which suggests that an interaction between ferrihydrite and the bacteria is occupying or masking adsorption sites. By adding a generic reaction to the model for the interaction between ferrihydrite and the bacteria, the adsorption of Cd2+ onto Comamonas spp.−ferrihydrite was accurately predicted and Cd2+ distribution and speciation in systems containing ferrihydrite, Comamonas spp., and H2Lp could be predicted.
ISSN:0013-936X
1520-5851
DOI:10.1021/es901434v