Simultaneous incorporation of Mn and Al in the goethite structure
Two series of (Al,Mn)-substituted goethites were synthesized from ferrihydrite made in alkaline media, with different Al/Mn mole ratios ([Al + Mn]/Fe molar ratio up to 0.12). Powder X-ray diffraction and extended X-ray absorption fine structure (EXAFS) techniques were used to assess the structural c...
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todo:paper_00167037_v71_n4_p1009_Alvarez2023-10-03T14:14:38Z Simultaneous incorporation of Mn and Al in the goethite structure Alvarez, M. Rueda, E.H. Sileo, E.E. aluminum crystal structure goethite manganese Rietveld analysis X-ray diffraction Two series of (Al,Mn)-substituted goethites were synthesized from ferrihydrite made in alkaline media, with different Al/Mn mole ratios ([Al + Mn]/Fe molar ratio up to 0.12). Powder X-ray diffraction and extended X-ray absorption fine structure (EXAFS) techniques were used to assess the structural characteristics of the simultaneous substitution in goethite. XRD patterns revealed that all the obtained solids remain in a goethite-like structure. Rietveld refinement of X-ray diffraction data indicates that the increasing Mn substitution and consequent decrease of Al substitution causes an increase in the unit cell volume. This change is accompanied by the increment of the various Me-Me distances. XANES spectra at the Al and Mn K-edge confirm the octahedral coordination of Al and the trivalent oxidation state of the Mn ion in all the synthesized samples. EXAFS spectra at the Fe K-edge indicate that the local order around the Fe atom remains practically constant upon (Mn,Al) substitution. Measurements in the Mn K-edge show that distances Mn-Me suffer different changes with the increase in Mn substitution: a marked decrease in E and a slight decrease in E′, while DC remains constant. E and E′ values correspond to the distance between one Mn and one neighboring Me (Fe, Mn, Al) atom, both situated in two polyhedra linked by an edge. These polyhedra belong to the same double row of the goethite structure. DC value corresponds to the distance between one Mn and one Me (Fe, Mn, Al) atom, situated in two octahedral linked by one corner and belonging to two adjacent double chains. All the intermetallic distances are minor than the corresponding singly substituted goethites, this fact is attributed to the structure contraction due to the presence of Al(III) which restrains the axial distortion of Mn. Dissolution-time curves, resulting from exposure to 6 M HCl at 318 K, show that the dissolution rate slows with increasing Al substitution and consequent decrease of Mn substitution, and the shape of the curve becomes increasingly sigmoidal for mixed goethite with large Al content and Al-goethite. Dissolution kinetics of most samples are well described by the Kabai equation. Al dissolves almost congruently with respect to Fe, implying that it is homogeneously distributed in the structure. However, the convex χMn:χFe curve indicates that Mn tends to be concentrated in the outer layers of the goethite particles. © 2006 Elsevier Inc. All rights reserved. Fil:Sileo, E.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. JOUR info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar http://hdl.handle.net/20.500.12110/paper_00167037_v71_n4_p1009_Alvarez |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-134 |
| collection |
Biblioteca Digital - Facultad de Ciencias Exactas y Naturales (UBA) |
| topic |
aluminum crystal structure goethite manganese Rietveld analysis X-ray diffraction |
| spellingShingle |
aluminum crystal structure goethite manganese Rietveld analysis X-ray diffraction Alvarez, M. Rueda, E.H. Sileo, E.E. Simultaneous incorporation of Mn and Al in the goethite structure |
| topic_facet |
aluminum crystal structure goethite manganese Rietveld analysis X-ray diffraction |
| description |
Two series of (Al,Mn)-substituted goethites were synthesized from ferrihydrite made in alkaline media, with different Al/Mn mole ratios ([Al + Mn]/Fe molar ratio up to 0.12). Powder X-ray diffraction and extended X-ray absorption fine structure (EXAFS) techniques were used to assess the structural characteristics of the simultaneous substitution in goethite. XRD patterns revealed that all the obtained solids remain in a goethite-like structure. Rietveld refinement of X-ray diffraction data indicates that the increasing Mn substitution and consequent decrease of Al substitution causes an increase in the unit cell volume. This change is accompanied by the increment of the various Me-Me distances. XANES spectra at the Al and Mn K-edge confirm the octahedral coordination of Al and the trivalent oxidation state of the Mn ion in all the synthesized samples. EXAFS spectra at the Fe K-edge indicate that the local order around the Fe atom remains practically constant upon (Mn,Al) substitution. Measurements in the Mn K-edge show that distances Mn-Me suffer different changes with the increase in Mn substitution: a marked decrease in E and a slight decrease in E′, while DC remains constant. E and E′ values correspond to the distance between one Mn and one neighboring Me (Fe, Mn, Al) atom, both situated in two polyhedra linked by an edge. These polyhedra belong to the same double row of the goethite structure. DC value corresponds to the distance between one Mn and one Me (Fe, Mn, Al) atom, situated in two octahedral linked by one corner and belonging to two adjacent double chains. All the intermetallic distances are minor than the corresponding singly substituted goethites, this fact is attributed to the structure contraction due to the presence of Al(III) which restrains the axial distortion of Mn. Dissolution-time curves, resulting from exposure to 6 M HCl at 318 K, show that the dissolution rate slows with increasing Al substitution and consequent decrease of Mn substitution, and the shape of the curve becomes increasingly sigmoidal for mixed goethite with large Al content and Al-goethite. Dissolution kinetics of most samples are well described by the Kabai equation. Al dissolves almost congruently with respect to Fe, implying that it is homogeneously distributed in the structure. However, the convex χMn:χFe curve indicates that Mn tends to be concentrated in the outer layers of the goethite particles. © 2006 Elsevier Inc. All rights reserved. |
| format |
JOUR |
| author |
Alvarez, M. Rueda, E.H. Sileo, E.E. |
| author_facet |
Alvarez, M. Rueda, E.H. Sileo, E.E. |
| author_sort |
Alvarez, M. |
| title |
Simultaneous incorporation of Mn and Al in the goethite structure |
| title_short |
Simultaneous incorporation of Mn and Al in the goethite structure |
| title_full |
Simultaneous incorporation of Mn and Al in the goethite structure |
| title_fullStr |
Simultaneous incorporation of Mn and Al in the goethite structure |
| title_full_unstemmed |
Simultaneous incorporation of Mn and Al in the goethite structure |
| title_sort |
simultaneous incorporation of mn and al in the goethite structure |
| url |
http://hdl.handle.net/20.500.12110/paper_00167037_v71_n4_p1009_Alvarez |
| work_keys_str_mv |
AT alvarezm simultaneousincorporationofmnandalinthegoethitestructure AT ruedaeh simultaneousincorporationofmnandalinthegoethitestructure AT sileoee simultaneousincorporationofmnandalinthegoethitestructure |
| _version_ |
1807321337045188608 |