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ARS Home » Research » Publications at this Location » Publication #88205
Title: METAL-INDUCED SULFATE ADSORPTION BY SOILS: III. APPLICATION OF LANGMUIR EQUATIONS

Author
item AJWA, HUSEIN
item TABATABAI, M. - IOWA STATE UNIVERSITY

Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Reactions involved in sulfate adsorption by soils can be vital for plant nutrition. Sulfate is present in soils as salts of various metals, that significantly affect sulfate adsorption reactions on colloidal surfaces and, consequently, its mobility in soils and availability to plants. We evaluated mechanisms controlling sulfate and metal adsorption by soils to better predict the influence of the soil-solution composition on sulfate and metals mobility in soils. We used emperical equations that are used in predictive models to describe the effect of metals on sulfate adsorption by soils. This study provided constants that can be used to describe sulfate adsorption behavior in diverse soils and to predict sulfate concentration associated with various metals in soil solution.

Technical Abstract: The one- and two-surface Langmuir equations were evaluated in studies of the effect of metal type, valence, and concentrations on sulfate adsorption by four diverse soils, two from Iowa (dominated by permanent charge) and one each from Chile and Costa Rica (two highly weathered soils with variable charge). The adsorption parameters, calculated using the "one-surface" Langmuir equation, showed that sulfate adsorption by the soils in the presence of trivalent metals was relatively higher than in the presence of mono- or divalent metals. The calculated parameters of the "two-surface" Langmuir equation for the sulfate adsorption data of the two Iowa soils with predominant permanent charge showed that this equation gave one line instead of two. For all the sulfate adsorption data, two bonding constants were found, suggesting the presence of two different adsorption sites or different mechanisms, each with a different bonding energy. The results provide evidence that sulfate adsorption by soils is caused by more than one mechanism and that the associated metal ion significantly affects sulfate adsorption, regardless of the mechanism involved.