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Bull Environ Contam Toxicol (2014) 92:352357 DOI 10.1007/s00128-014-1205-x
Characteristics of Adsorption Interactions of Cadmium(II) onto Humin from Peat Soil in Freshwater and Seawater Media
Roy Andreas Jing Zhang
Received: 15 May 2013 / Accepted: 13 January 2014 / Published online: 25 January 2014 Springer Science+Business Media New York 2014
Abstract The present study examined Cd solubility in pH 212 fresh and seawater media with and without humin to determine Cd species composition. The study, based on the LangmuirHinshelwood kinetics model, was conducted to determine the kinetic parameters of Cd(II) adsorption onto humin. We employed the Langmuir and Freundlich models to derive thermodynamic parameters. Aquo (Cd(H2O)62?)
and chloro- (CdCl? and CdCl2) complexes were responsible for Cd(II) adsorption onto humin. Results showed Cd as Cd(II) and Cd(H2O)6?2 was water soluble at 2 \ pH \ 7;
with a portion of the soluble Cd precipitating as Cd(OH)2.
The Cd(II) rate constant (k) in freshwater was 0.5 9 10-3
(min-1), occurring in a single phase, while in seawater fast and slow phase values for k were 31.88 9 10-3 and
6.2 9 10-3 (min-1), respectively. The adsorption curves showed a better t with the Langmuir than the Freundlich model.
Keywords Humin Cadmium (II) Freshwater media
Seawater media
Many aquatic environments are exposed to heavy metal pollutants which may occur from natural sources in rivers, streams, lakes, and aquifers; or from anthropogenic such as mines, smelters and industrial discharges. Polluted water ultimately ows into the sea, interacting with various components (including organic substances) throughout the source ow. An understanding of these conditions can serve to elucidate the interactions between organic compounds and metals in fresh and seawater media. Heavy metals, such as silver (Ag), cadmium (Cd), chromium (Cr), copper (Cu), mercury (Hg), and lead (Pb) have potential toxic effects to organisms. In addition, organic compounds in aquatic environments dissolve in water, and are bound in sediments.
In general, organic compounds in water are divided into two types: non-humied and humied. Humied organic compounds known as humus or humic substances exhibit acid and alkali solubility. Gafney et al. (1996) divided humic substances into three fractions: (1) humin, a fraction of humic substance not soluble in acid or alkali; (2) fulvic acid, a fraction of humic substance soluble in acid or alkali;...