Hyperfine Interact DOI 10.1007/s10751-009-0102-x
Mössbauer spectroscopy study of a mineral sample from Oshno Hill, District of Chavín de Pariarca, Huanuco Region, Peru A. Bustamante · D. Lovera · R. Quille · A. V. Arias · J. Quiñones
© Springer Science + Business Media B.V. 2009
Abstract The analysis by X-ray diffraction of a mining sample collected from Oshno hill, which is located in the District of Chavín de Pariarca, Huamalies Province, Huanuco, Peru, indicates the presence of lepidocrocite (γ-FeOOH) and goethite (α-FeOOH). The room temperature Mössbauer spectrum (MS) doublet with broad lines displays hyperfine parameters corresponding to the presence of particles of iron hydroxides smaller than 100 Å in a superparamagnetic regime. The measurement of a MS at 4.2 K allowed confirming the presence of goethite and lepidocrocite (with average magnetic fields of 49.21 T and 44.59 T, respectively). Keywords Goethite · Lepidocrocite · Mössbauer spectroscopy
1 Introduction In the Marañón Basin, Peru, there is a Regional Geology named Complejo Marañón, consisting of metal minerals such as copper, silver and gold in schists (which are rocks that can easily be split in thin layers) that is a good candidate for mining exploitation. The minerals form part of a group of medium-grade metamorphic rocks mainly prominent by the preponderance of laminate minerals such as mica, chlorite, talc, hornblende, graphite, and others in contact with intrusions, as well as with nickel, cobalt, titanium, and platinum minerals, among others. The metallurgy tests carried out in our laboratory indicate a good metallurgy recovery of the concentrate obtained of Chalcopyrite mineral, which means a good
A. Bustamante (B) · R. Quille Laboratorio de Cerámicos y Nanomateriales, Facultad de Ciencias Físicas, Universidad Nacional Mayor de San Marcos, Lima, Perú e-mail: abustamanted@unmsm.edu.pe D. Lovera · A. V. Arias · J. Quiñones Facultad de Ingeniería Geológica, Minera, Metalúrgica y Geográfica, Universidad Nacional Mayor de San Marcos, Lima, Perú
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Fig. 1 Oshno part of the hill where the sample is collected
economic possibility for the Marañón Basin [1]. The samples of Oshno as metallic powder grain are of interest to small and medium steel industry. Although the usual mineralogical techniques allow identifying the sample minerals as well as the presence of iron oxides with a magnetization degree that indicates the presence of metals in areas where the samples are taken from, it is not possible to study with more detail the system because of the very small particles that make up the iron oxides. In this work, we apply Mössbauer spectroscopy to understand the size and nature of the particles of the iron oxides found in one mineral sample.
2 Experimental The sample was collected at the Oshno hill, which is located in the Chavín de Pariarca District, Province of Huamalies, Huanuco Region, Peru. Figure 1 shows the place where the sample was collected. The characterization of minerals of this area is made by optical microscopy, Mössbauer spectroscopy at RT, and multi-elemental chemical analysis. In the Laboratory of Extractive Metallurgy-UNMSM we proceeded to develop metallurgical processes and operations commissioned: crushing, grinding and sifting to take a size suitable for the chemical and physical characterization. The X-ray powder diffraction patterns were recorded with a BRUKER D8 Focus using a graphite monochromator to select the CuKα-doublet, in the range 8◦ to 80◦ with steps of 0.02◦ . The chemical composition was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) using the method ICP-40B that consist in multi-acid (four acid) digestions that is a combination of HCl (hydrochloric acid), HNO3 (nitric acid), HF (hydrofluoric acid) and HClO4 (perchloric acid). Because hydrofluoric acid breaks down silicates, these digestions are often referred to as “near-total digestions”. There can be a loss of volatiles during digestion (e.g. B, As, Pb, Ge, and Sb). Multi-acid digestion is a very effective dissolution
Mössbauer spectroscopy study of a mineral sample from Oshno Hill Fig. 2 X-ray diffraction of sample Oshno. G Goethite, L Lepidocrocite
80
G: Goethite α-FeOOH 02 0273 L: Lepidocrocite γ-FeOOH 74 1877
Normalized Intensity
70 60
G L
50 L
L
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G L G GG
G G
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G L
GL G
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Table 1 Chemical analysis of the sample Oshno
Major elements (ppm) Cu Zn As Mn Ba Minor elements (ppm) Cr V W Sr Cd Co Ag La Sc Sn Ni Fe
968 3,996 367 1,118 282 92 66 34 197.8 23 23 6.8 38.7 12.3 24 18 7.39
procedure for a large number of mineral species and is suitable for a wide range of elements. For the sample presented in this paper, Mössbauer spectra were recorded in transmission geometry using a constant acceleration spectrometer and a 512 multichannel analyser. The source is of 57 Co in Rh matrix. Spectra were recorded at 300 K and, in this particular case, also in a liquid helium cryostat at 4.2 K with a sinusoidal velocity variation. Isomer shifts are given relative to the centroid of the spectrum of an absorber of α-Fe at room temperature. Spectra were analyzed by least-squares fits using lorentzian line shapes. For the spectrum at 4.2 K the fittings were performed with the NORMOS program [2] that allows analyzing the data with hyperfine field distributions.
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Relative transmissión (u.a.)
Fig. 3 Mössbauer spectrum at RT showing the Goethite (continuous line) and Lepidocrocite (dotted line) sub spectra
0,95 0,90 0,85 0,80 0,75 0,70 -3
-2
-1
0
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Velocity (mm/s)
Table 2 Hyperfine parameters for fitted Mössbauer spectra δ(mm/s) ± 0.03(mm/s) RT Lepidocrocite Goethite 4.2 K Lepidocrocite Goethite
or 2ε(mm/s) ± 0.03(mm/s)
0.37 0.37
0.51 0.98
0.36 0.36
−0.10
B (T) ± 0.5(T)
44.6 49.2
(mm/s) ± 0.02(mm/s)
A(%) ± 2%
0.37 0.48
53 47
0.35 0.35
δ is the isomer shift relative to α iron, Δ is the quadrupole splitting, 2ε is the quadrupole shift, Γ is the line width, A is the spectral fractional area as obtained from the fit, B is the hyperfine field
3 Results and discussion 3.1 X-ray difraction The X-ray diffraction (XRD) pattern is shown in Fig. 2. The analysis indicates the presence of two mineralogical phases, namely, lepidocrocite (γ-FeOOH ASTM 741877) and goethite (α-FeOOH ASTM 02-0273). 3.2 Chemical analysis The chemical analysis, shown in Table 1, indicates the presence of major elements Cu, Zn, As, Mn y Ba and Cr, V, W, Sr, Cd, Co, Ag, La, Sc, Sn, Fe y Ni as minor elements (Certificate No. 42876 of SGS company). 3.3 Mössbauer spectroscopy The Mössbauer spectrum (MS) at room temperature of the sample from Oshno hill shows a broadened doublet (Fig. 3). Two doublets are required to obtain a
Mössbauer spectroscopy study of a mineral sample from Oshno Hill P(B) Relative transmission (u.a.)
1,01 0,05 1,00 0,04
0,99 0,98
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Fig. 4 a Mössbauer spectrum at 4.2 K and, b the corresponding hyperfine field distributions P(B) that was fitted with two Gaussian lines. The dotted line corresponds to goethite and dashed one to lepidocrocite
good fitting. The first doublet has hyperfine parameters δ = 0.37±0.03 mm/s, = 0.51±0.03 mm/s and = 0.37±0.02 mm/s and corresponds to the presence of lepidocrocite [3]. The second doublet has δ = 0.37±0.03 mm/s, = 0.98±0.03 mm/s and = 0.48±0.02 mm/s and a wide line. It corresponds to particles of oxides or hydroxides with average diameters smaller than ≈100 Å in a superparamagnetic regime [4] (see Table 2). Figure 4a shows the MS at 4.2 K in zero external magnetic field. It displays a broadened sextet which was numerically analyzed using a hyperfine field distribution computer program that yielded an average isomer shift of 0.36 mm/s and a quadrupole shift close to −0.10 mm/s. The mean value of the magnetic field was determined from the hyperfine field distribution P(B) by fitting the histogram with two lines of Gaussian shape in the range of 30 to 53 T. The data show an average field of 49.21 T, confirming the presence of goethite, as showed in Fig. 4b (dotted line) (see reference [3] page 366 that reports δ = 0.34 mm/s, 2ε = −0.25 mm/s and B = 49.2 T) and lepidocrocite with an average magnetic field of 44.59 T (dashed line) (see reference [3] page 436 reports that δ = 0.342 mm/s, 2ε = 0.018 mm/s and B = 45.6 T).
4 Conclusions Using Mössbauer spectroscopy performed at liquid helium temperature it was possible to show that the iron material from Oshno hill is composed of superparamagnetic particles of Goethite and Lepidocrocite. Acknowledgements A.B.D thanks to the UNMSM for supporting this research, through the SEGUSM system and Dra. Rosa B Scorzelli from CBPF for the measurement at liquid helium temperature.
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