The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution

There are four general pathways of dissolution of reducible metal oxides in acidic aqueous solution: proton-assisted (acid), ligand-promoted acid, reductive, and ligand-promoted reductive dissolution. The presence and reactivity toward the surface of protons, chelating ligands, and reductants dictat...

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Autores principales: Dos Santos Afonso, M., Morando, P.J., Blesa, M.A., Banwart, S., Stumm, W.
Formato: JOUR
Acceso en línea:http://hdl.handle.net/20.500.12110/paper_00219797_v138_n1_p74_DosSantosAfonso
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Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) de Universidad de Buenos Aires
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spelling todo:paper_00219797_v138_n1_p74_DosSantosAfonso2023-10-03T14:25:07Z The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution Dos Santos Afonso, M. Morando, P.J. Blesa, M.A. Banwart, S. Stumm, W. There are four general pathways of dissolution of reducible metal oxides in acidic aqueous solution: proton-assisted (acid), ligand-promoted acid, reductive, and ligand-promoted reductive dissolution. The presence and reactivity toward the surface of protons, chelating ligands, and reductants dictate the mechanism(s) controlling the dissolution. For the massive reductive dissolution of magnetic by ascorbic acid, the experimental rate law R = k[HA-]1 2[H+] suggests the involvement of surface ≡FeIII A- complexes. Adsorption isotherms of ascorbic acid onto hematite at pH 3 and 25°C yield a Langmuir-type surface complexation constant Ks = (9.57 × 108 M-1). Slow dissolution follows with an empirical rate law R = kobs(≡FeIIIA). It is concluded that the formation and kinetic reactivity of surface complexes determine the rate of dissolution. Dehydroascorbic acid also dissolves magnetite, but at slower rates. Oxalate accelerates the reductive dissolution of hematite by ascorbate even though it competes with ascorbate for surface sites; enhanced detachment of ≡FeII surface species by oxalate complexation may be involved. Autoacceleration of the reductive dissolution by dissolved FeII-carboxylate complexes is observed in EDTA/ascorbic acid mixtures; the rate reaches a maximum at intermediate [EDTA] values, where synergistic effects between EDTA and FeII-EDTA complexes are important. Autoacceleration may also operate in oxalate solutions. © 1990. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00219797_v138_n1_p74_DosSantosAfonso
institution Universidad de Buenos Aires
institution_str I-28
repository_str R-134
collection Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA)
description There are four general pathways of dissolution of reducible metal oxides in acidic aqueous solution: proton-assisted (acid), ligand-promoted acid, reductive, and ligand-promoted reductive dissolution. The presence and reactivity toward the surface of protons, chelating ligands, and reductants dictate the mechanism(s) controlling the dissolution. For the massive reductive dissolution of magnetic by ascorbic acid, the experimental rate law R = k[HA-]1 2[H+] suggests the involvement of surface ≡FeIII A- complexes. Adsorption isotherms of ascorbic acid onto hematite at pH 3 and 25°C yield a Langmuir-type surface complexation constant Ks = (9.57 × 108 M-1). Slow dissolution follows with an empirical rate law R = kobs(≡FeIIIA). It is concluded that the formation and kinetic reactivity of surface complexes determine the rate of dissolution. Dehydroascorbic acid also dissolves magnetite, but at slower rates. Oxalate accelerates the reductive dissolution of hematite by ascorbate even though it competes with ascorbate for surface sites; enhanced detachment of ≡FeII surface species by oxalate complexation may be involved. Autoacceleration of the reductive dissolution by dissolved FeII-carboxylate complexes is observed in EDTA/ascorbic acid mixtures; the rate reaches a maximum at intermediate [EDTA] values, where synergistic effects between EDTA and FeII-EDTA complexes are important. Autoacceleration may also operate in oxalate solutions. © 1990.
format JOUR
author Dos Santos Afonso, M.
Morando, P.J.
Blesa, M.A.
Banwart, S.
Stumm, W.
spellingShingle Dos Santos Afonso, M.
Morando, P.J.
Blesa, M.A.
Banwart, S.
Stumm, W.
The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution
author_facet Dos Santos Afonso, M.
Morando, P.J.
Blesa, M.A.
Banwart, S.
Stumm, W.
author_sort Dos Santos Afonso, M.
title The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution
title_short The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution
title_full The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution
title_fullStr The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution
title_full_unstemmed The reductive dissolution of iron oxides by ascorbate. The role of carboxylate anions in accelerating reductive dissolution
title_sort reductive dissolution of iron oxides by ascorbate. the role of carboxylate anions in accelerating reductive dissolution
url http://hdl.handle.net/20.500.12110/paper_00219797_v138_n1_p74_DosSantosAfonso
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