 niobium mining.png)
Figure 1: Dark sample resulted obtained by the Ge(HP)
detector.
Research Article
Like other mining countries, Brazil is struggling with
tailing disposal, which requires appropriate technological
solutions in order to mitigate the environmental and social
problems [1]. Social responsibility and sustainability are
constant concerns of all productive sectors. Mineral
tailings have potential application in building industry,
especially in the production of concrete and mortar
[2]-[4]. This alternative results in cost reduction, as well
as offers an environmentally sustainable solution in the
use of industrial byproducts and reduction in the
exploitation of natural resources to produce conventional
aggregates and cements [5] [6]. However, when sterile
rock sediments or sediments are manipulated by industrial
processes, natural radiation can be exposed from
radionuclides in explored geological formations. They
must be analyzed in the light of normative limits
regarding radioprotection [7]. The isotopes that mostly
contribute to natural radiation are radio nuclide series of
235𝑈, 238𝑈, 232𝑇ℎ, and 40𝐾 [8]. Measuring radiation
exposure using appropriate equipment that can detect
each type of radiation is essential for precautionary
purposes and exposure control, thus reducing risk. The
objective of this study is to quantify the radioactivity of
niobium tailings collected from an exploration area in the
city of Araxa in the Brazilian state of Minas Gerais.
Niobium mining plays an expressive role in Brazil,
as the country holds around 95% of all deposits in
operation in the world [9]. The carbonatitic complexes
are the greatest production potential, followed by
pegmatites associated with granitic magma. Reserves of
carbonatitic complexes are mined in pyrochlore rocks
[(𝑁𝑎, 𝐶𝑎)2𝑁𝑏2 𝑂6 (𝑂𝐻, 𝐹)], and reserves of pegmatite
complexes are mined in columbite-tantalite rocks
[(𝐹𝑒,𝑀𝑛)(𝑁𝑏, 𝑇𝑎)2 𝑂6 ] and rapakivi granites. In
addition, niobium also occurs in alkaline carbonatitic
complexes, which are rocks formed by magmatic
crystallization [9]. Alves and Coutinho [10] verified that
the niobium production wastes contain radionuclides,
especially 238𝑈, 226N𝑎, 210𝑃𝑏, 232𝑇ℎ and 228N𝑎. The
analysis aims to evaluate the potential radioactivity risk
for occupationally exposed person or the general
public using niobium tailings as raw material for the construction industry compared to radiation protection
standards [11].
Two samples were provided by the niobium mining
industry located in the town of Araxa (MG, Brazil).
The geological formation from where the samples
were obtained has a diameter of 5 km [11]. The two
tailings analyzed were named “Light Sample” (obtained
from flotation stages), and “Dark Sample” (from
the magnetic separation stages) [12]. The main
mineral compositions of both samples are barite and
magnetite/hematite, respectively. They were collected by
a private company and transported in sealed containers to
Laboratory of Characterization of Construction and
Mechanical Materials at the Federal University of
Minas Gerais-DEMC/UFMG, in Belo Horizonte, MG,
Brazil.
| Dark sample | Light sample
| ||
Pulse (cps) | Dose (μ Sv/h) | Pulse (cps) | Dose (μ𝑆𝑣/ℎ) |
4.00 | 0.42 | 3.00 | 0.22 |
3.00 | 0.28 | 3.00 | 0.27 |
3.00 | 0.3 | 3.00 | 0.22 |
3.33±0.47 | 0.33±0.06 | 3.00±0.00 | 0.24±0.02 |
| Radio-226 (Bq/g) | Radio-228 (Bq/g)
| ||
Light sample | Dark sample | Light sample | Dark sample |
0,24 | 0,18 | 0,84 | 0,85 |
0,23 | 0,17 | 0,64 | 0,92 |
0,23 | 0,16 | 0,82 | 0,79 |
0,27 | 0,19 | 0,92 | 0,90 |
0,24 | 0,17 | 0,78 | 0,86 |
0.24±0.004 | 0.17±0.004 | 0.80±0.008 | 0.87±0.008 |
The two samples (Light and Dark) were analyzed with gas detectors type Geiger-Muller to check for the pres-ence of natural radioactivity in the Tailings. The analysis was carried out using surface radioactivity detectors, CE model RDS 80, with a sensitivity of 1 to 100000cps / 0.01 to 100𝑘𝐵𝑞/𝑐𝑚2 and the exposure rate meter, CE brand model RDS 30 with a sensitivity of 0.01μ𝑆𝑣/ℎ to 100𝑚𝑆𝑣/ℎ for photons from 48𝑘𝑒𝑉 to 1.3𝑀𝑒𝑉. The measurements were made at a fixed distance of 10 cm from the surface of the two samples (Table 1). The analyses with Geiger-Muller type detectors showed the presence of radioactivity in the two samples. To investigate the gamma energies emitted from the radionuclides found in the samples, the samples were placed in small plastic bags separately as Light and Dark samples and taken to the Internal Dosimetry Laboratory (LDI) in the CDTN/CNEN. The samples were analyzed using the gamma spectrometry system using the model 802. 3”x 3” sodium iodide crystal detector (NaI(Tl)) and an OSPREY multichannel analyzer connected to a computer. Each sample was placed close to the main entrance window of the NaI(Tl) detector and left there for 10 hours of monitoring. The Genie 2000 software of Canberra was used to obtain the two gamma spectra result from the Light and Dark samples. The results were published at BJRS [11]. Using the Neutron Activity Analyze (NAA) method, 1𝑔 of each sample passing in a #150 μm mesh was placed in the equipment. The samples were exposed to a neutron flux for 3 hours at the TRIGA Reactor at 𝑈𝑄𝑁N - 𝐿𝐴𝑁 Laboratory from 𝐶𝐷𝑇𝑁/𝐶𝑁𝐸𝑁. The activated samples were analyzed with a Canberra gamma spectrometry system using a coaxial Ge(HP) detector model 5019 (HP) with 50% nominal efficiency, 𝐷𝑆𝐴-2000 coupled to a microcomputer with a Multichannel Spectrum Acquisition Board and the 𝐺𝑒𝑛𝑖𝑒2000 program at the Nuclear Spectrometry 𝐿𝑎𝑏𝑜𝑟𝑎𝑡𝑜𝑟𝑦/𝐶𝐷𝑇𝑁/𝐶𝑁𝐸𝑁 (Table 3).
| Uranium (μg/g) | Thoron (μg/g) |
Light sample | 5±1 | 70±1 |
Dark sample | 12±2 | 137±1 |
The spectrum resulted obtained with the NaI(Tl) detec-tor showed photopeaks, above the background, of ener-gies characteristics of some radionuclides, although the low resolution of the NaI(Tl) detectors, the samples were taken and analyzed using the Ge(HP) from the Nuclear Spectrometry Laboratory (NSL) of CDTN/CNEN which has a higher resolution and allows to identify and quantify the isotopes of radium 226 and 228 [12]. The 14.65 g of Light sample and 16.64 g of Dark sample were analyzed for approximately 24 hours. The chemical and mineralogical analysis were carried out by the supplier, using X-Ray Fluorescence (FRX) [13].
| Oxide composition analysis (FRX)
| ||
Oxide/Elements | Tailing samples | Tailing samples |
| Light (%) | Dark (%) |
𝐵𝑎𝑂 | 77.24 | 1.08 |
𝐹𝑒 2𝑂3 | 2.13 | 91.83 |
𝑇𝑖𝑂 2 | 0.45 | 3.08 |
𝑁𝑑 2𝑂3 | 0.4 | - |
𝑆𝑖𝑂 2 | 0.39 | 0.2 |
𝑃𝑟6𝑂11 | <0.38 | - |
𝐿𝑎2𝑂3 | < | - |
𝐴𝑙2𝑂3 | 0.32 | 0.07 |
𝑁𝑏2 𝑂5 | 0.18 | 0.66 |
𝑇ℎ𝑂2 | 0.11 | - |
𝑀𝑛𝑂 | 0.05 | - |
𝑈3𝑂8 | 0.05 | - |
𝐶𝑒𝑂2 | 0.04 | - |
𝐶𝑎𝑂 | 0.03 | - |
𝑇𝑎2𝑂5 | - | <0.10 |
𝑃𝑏𝑂 | - | 0.04 |
The results of the gas detector are shown in Table 1. An
average exposure dose of 0.24 μ𝑆𝑣/ℎ±0.02 and
0.33μ𝑆𝑣/ℎ±0.06 were estimated for Light and Dark
sam-ples, respectively, as described in Table 1. The
spectra results showed the gamma-ray photopeak energies
identifying the energy characteristic of 214Bi(609 keV),
40K(1460 keV) and 208Tl (2614 keV) [11]. The results
indicated the difference of counts per channel of radiation
energy between the detection of background radiation and
radiation emitted by the samples. The measurements
obtained with HPGe detector allowed us to observe in the
spectra result, the presence of different radionuclides,
Figures 1 and 2. The amount of 226N𝑎 and 228N𝑎 obtained
with the Ge(HP) analysis is shown in Table 2 for both
samples. The estimated average concentration is shown in
Table 2. The results obtained using the NAA techniques
showed concentrations of uranium and thorium, in
both samples. The results are showed in Table 3. The
chemical composition of both samples provided by
the niobium mining industry are showing in Table
4.
Using the results of the Geiger-Muller detectors, it is possible to estimate the risk of exposure dose from the samples. In a hypothetical calculation for 2000 working hours per year, radiation dose is about 0.48𝑚𝑆𝑣 (for Light Sample) and 0.66𝑚𝑆𝑣 (for Dark Sample) per year. According to the radiation protection standard, the radiation dose must be below 1𝑚𝑆𝑣.𝑦-1 (for general public) and 20𝑚𝑆𝑣.𝑦-1 (for workers) for an environment to be considered radiation-free [14]-[15]. The Ge (HP) gamma spectrometry analysis confirmed the peaks found in the previous analysis with NaI(Tl) detector, indicating the presence of 226Ra and 228Ra. In the process of geological changes and sedimentation, radium has an affinity for some elements, including barium [16]. Neutron Activity Analysis (NAA) was performed to determine the influence of uranium and thorium in the results of the Ge(HP) detector analyses. According to FRX analyses, has a much higher BaO content in the barite based sample (Light) than in the magnetite-based sample (Dark).
In his study the quantification the radioactivity of niobium tailings, collected from an exploration area in Araxa (MG, Brazil) was performed. The niobium mining plays an expressive role in Brazil, as the country holds around 95% of all deposits in operation in the world. The analysis aims to evaluate the potential radioactivity risk for occupationally exposed person or the public using niobium tailings as raw material for the construction industry compared to radiation protection standards. The Geiger-Muller detector was used to indicate the presence of radioactivity from gamma radiation in the waste, the results showed no risk of radioactivity to occupationally exposed persons or the public. The concentration of thorium and uranium detected after the NAA analysis was responsible for 226Ra and 228Ra quantified with the Ge(HP) detector. Although the occurrence of uranium and thorium is greater in the Dark sample (hematite/magnetite) than in the light sample, the activity of 226Ra is greater in the light sample (based on barite) than in the dark sample. This can be explained by the affinity of 226Ra for barium, which is confirmed by the XRF analysis. Assuming that the waste is used as a raw material to produce mortar and concrete, the 226Ra present in the waste may pose a health risk as 226Ra is a source of radon gas. Additional studies using alpha detectors should be conducted to understand the exhalation rate of radon from the waste and the materials produced from this waste.
Acknowledgements
The following Brazilian institutions support this research
project: Research Support Foundation of the State of
Minas Gerais (FAPEMIG); Brazilian Council for
Scientific and Technological Development (CNPq) and
Coordination for the Capacitation of Graduated Personnel
(CAPES).
Authorship contribution
E. J. D Soares (performed the experiments and
measurements, discussion results), F. C. R. Almeida
(supplier of tailings and chemical analysis), B. M.
Mendes (performed the spectrometric analysis), R.
G. Passos (discussion results and review the text)
T. C. F. Fonseca (discussion results and review the
text).
Funding
Research Support Foundation of the State of Minas
Ge-rais (FAPEMIG); Brazilian Council for Scientific and
Technological Development (CNPq) and Coordination for
the Capacitation of Graduated Personnel (CAPES)
Conflict of interest
This article has no conflict of interest and the authors have
non-financial interest to disclose.
Declaration
This research has been conducted ethically, reporting of
those involved in this article.
Similarity Index
I hereby confirm that there is no similarity index in
ab-stract and conclusion while overall is less than 5%
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it.
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[© 2023 Elydio J.D. Soares, et al.] This is an Open Access article published in "Graduate Journal of Interdisciplinary Research, Reports & Reviews" (Grad.J.InteR3) ISSN(E): 2584-2919 by Vyom Hans Publications. It is published with a Creative Commons Attribution - CC-BY4.0 International License. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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