University of Tehran

Sorption and desorption studies of metallic zinc on an alluvial soil

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Background concentrations of heavy metals in soils, which depend on the local geology, may be supplemented to different degrees by anthropogenic inputs. Many industrial processes and operations generate stack emissions, solid wastes and sludges that contain heavy metals, which enter atmosphere and also find their way into aquatic and terrestrial ecosystems. Being non-biodegradable,  heavy metals are environmentally persistent and may have long-term effects on the crop, animals, human health, soil properties, and quality of the whole environment. Sorption of metals from aqueous solution onto solid particles is an important process that influences their accumulation and transport in the environment. In the past, interaction of heavy metals with soil inorganic particles has been extensively studied employing macroscopic, kinetic or equilibrium approaches, and many attempts have been made to model adsorption of metals on mineral surfaces. These studies have revealed that various factors such as presence or absence of other ions, pH, temperature, and residence time can affect the sorption/desorption of heavy metals from soils, soil clay fractions, and other soil  components (Eick et al., 1999; Martinez et al., 1999; Atanassova and Okazaki, 1997; Atanassova, 1995; Backes et al., 1995; Harter, 1992).The effective remediation of contaminated soils needs a basic and thorough understanding of the mechanism(s) of heavy metal interaction with soil media particles, and factors that affect their retention and/or release from these particles. Zinc is one of the most abundantly occurring elements in the earth’s crust and an essential micronutrient for all living things. Zn usually occurs in +2 oxidation state and forms complexes with inorganic and organic ligands, which affect its adsorption reactions with soil surface. Zn is readily adsorbed by clay minerals, carbonates, or hydrous oxides. A large fraction of the total Zn in polluted soils and sediments becomes associated with Fe and Mn oxides (Hickey and Kittrick, 1984; Kuo et al., 1983).

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