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Molybdate adsorption by birnessite
Abstract Molybdate (MoO4 2−) adsorption by manganese (Mn) oxide was investigated using a synthetic birnessite. Experiments were carried out in a batch experiment as a function of time (1min to 28 d), pH (2–10) and the competitive anions sulphate (SO4 2−), phosphate (PO4 3−), selenate (SeO4 2−) and selenite (SeO3 2−). Furthermore, MoO4 2− adsorption was described as a function of equilibrium concentration at pH4–7 and the data were evaluated with the Freundlich and Langmuir equations. The amount of adsorbed MoO4 2− was strongly dependent on time and reached roughly an equilibrium after three days. An increase in the pH by 1.15 units within 28days indicates ligand exchange of surface hydroxyls with MoO4 2−. Molybdate adsorption showed high sensitivity to pH and reached a maximum at pH3, near the pK a1 and pK a2 for molybdic acid. The Freundlich equation adequately reconstructed the adsorption data. Molybdate adsorption also conformed to the Langmuir equation for the investigated pH values. The competition sequence of anions for MoO4 2− adsorption by Mn oxide was SeO3 2− >SeO4 2− >PO4 3− >SO4 2−, assuming a strong adsorption mechanism of MoO4 2− onto the surface of birnessite. These results indicate that Mn oxides have a strong effect on the adsorption of MoO4 2− especially due to their higher specific surface area compared to aluminium or iron oxides. This is important regarding the availability of MoO4 2− in soils under agricultural conditions (pH4–7) as well as for the treatment of soils and groundwater affected by elevated intake from industries.
Graphical abstract Display Omitted
Highlights Molybdate was adsorbed by birnessite. The amount of adsorbed molybdate was strongly dependent on time. Increasing pH during adsorption indicated ligand exchange of surface hydroxyls. Molybdate adsorption was highly influenced by competing anions.
Molybdate adsorption by birnessite
Abstract Molybdate (MoO4 2−) adsorption by manganese (Mn) oxide was investigated using a synthetic birnessite. Experiments were carried out in a batch experiment as a function of time (1min to 28 d), pH (2–10) and the competitive anions sulphate (SO4 2−), phosphate (PO4 3−), selenate (SeO4 2−) and selenite (SeO3 2−). Furthermore, MoO4 2− adsorption was described as a function of equilibrium concentration at pH4–7 and the data were evaluated with the Freundlich and Langmuir equations. The amount of adsorbed MoO4 2− was strongly dependent on time and reached roughly an equilibrium after three days. An increase in the pH by 1.15 units within 28days indicates ligand exchange of surface hydroxyls with MoO4 2−. Molybdate adsorption showed high sensitivity to pH and reached a maximum at pH3, near the pK a1 and pK a2 for molybdic acid. The Freundlich equation adequately reconstructed the adsorption data. Molybdate adsorption also conformed to the Langmuir equation for the investigated pH values. The competition sequence of anions for MoO4 2− adsorption by Mn oxide was SeO3 2− >SeO4 2− >PO4 3− >SO4 2−, assuming a strong adsorption mechanism of MoO4 2− onto the surface of birnessite. These results indicate that Mn oxides have a strong effect on the adsorption of MoO4 2− especially due to their higher specific surface area compared to aluminium or iron oxides. This is important regarding the availability of MoO4 2− in soils under agricultural conditions (pH4–7) as well as for the treatment of soils and groundwater affected by elevated intake from industries.
Graphical abstract Display Omitted
Highlights Molybdate was adsorbed by birnessite. The amount of adsorbed molybdate was strongly dependent on time. Increasing pH during adsorption indicated ligand exchange of surface hydroxyls. Molybdate adsorption was highly influenced by competing anions.
Molybdate adsorption by birnessite
Matern, Katrin (author) / Mansfeldt, Tim (author)
Applied Clay Science ; 108 ; 78-83
2015-01-25
6 pages
Article (Journal)
Electronic Resource
English
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