Hyperfine structure of Fe57 in iron-bearing minerals from a

Hyperfine structure of Fe57 in iron-bearing minerals from a mangnese ore deposit
Nascimento, C. K.,1 COUCEIRO, P.R.C.,2 and FABRIS, J. D.3
1 UNIVERSIDADE
FEDERAL DE MINAS GERAIS - Belo Horizonte MG Brazil
Federal do Amazonas - Manaus AM Brazil
3 Universidade Federal de Minas Gerais - Belo Horizonte MG Brazil
2 Universidade
INTRODUCTION
Several primary geochemical processes on the earth allow
the fundamental mechanisms of mineral genesis to be traced
to the present day. Intrinsic chemical elemental factors such
as low geomobility and original abundance in the earth s
crust make iron an interesting indicator of mineral genesis [1].
Some of its chemical, crystallographic and hyperfine properties are indicative of how the minerals were formed and transformed in the geodomain [2]. This work focuses on the characterization of structural iron in manganese minerals, particularly in rhodochrosite (MnCO3 ) from a manganese ore, mainly
with Fe57 Mössbauer spectroscopy. The studied sample corresponds to a source material of significant commercial, industrial and geochemical interest from the Precambrian Morro da
Mina mineral deposit in Paraopeba, city of Conselheiro Lafaiete, Minas Gerais, Brazil. The sample was collected from the
central portion of a sampling pit; the lithology is dominated
by queluzite, a siliceous-carbonate rock.
FIG. 1: Powder XRD pattern of the carbonate-rich sample. Gr
= Graphite (C), Rc = Rhodochrosite (MnCO3 ) , Sp = Spessartine
(Mn3 Al2 (SiO4 )3) Hu = huntite (CaMg3 (CO3 )4 ), Qz = Quartz (SiO2 ).
EXPERIMENT
The ore sample was ground to 53 /um, dried in air and subsequently characterized using different analytical techniques.
Powder X-ray diffraction (XRD)from a synchrotron source,
with the sample at 298 K (l = 1.76051 A, Fe57 Mössbauer
spectroscopy and XRF.
FIG. 2: Mössbauer parameters of the spectrum obtained at 110 K.
ACKNOWLEDGEMENTS
RESULTS AND DISCUSSION
This work has been supported by the Brazilian Synchrotron
Light Laboratory (LNLS) / Brazilian Biosciences National
Laboratory (LNBio) under proposal D10B - XPD 9920 ,CNPq
and FAPEMIG. CAPES grants the Visiting Professor PVNS
fellowship to JDF at UFVJM.
CONCLUSION
The hyperfine parameters and results Powder XRD pattern
suggests: (i) the occurrence of siderite, FeCO3 . It has a rhomboedral structure and contains divalent iron in the high spin
state. (ii) The occurrence of distorted siderite due to isomorphous substitution of Fe2+ by others cations such as Ca2+ and
Mg2+ , which causes an asymmetry in line shape, pointing to
a second doublet with larger quadrupole splitting. (iii) Fe2+
in the structure of silicates, probably in the spessartine structure. (iv) Fe3+ in the structure of silicates , probably in the
spessartine structure.
LNLS 2010 Activity Report
[1] Fabris, J.D., Coey, J.M.D.: Tópicos em Ciências do Solo, 47-102
(2002).
[2] Souza, J., Fabris, J.D., Mussel, W.N., Garg, V.K.: Hyp. Interact.
2, 47 (1997).
1
Brazilian Synchrotron Light Laboratory