Determination of enrichment processes and the concentrations of radon in underground mines of fluorite and coal in Santa Catarina state
DOI:
https://doi.org/10.22456/1807-9806.135755Keywords:
Radon, Fluorite, Coal, radioactivity, gamma spectrometryAbstract
This work presents the determination of Rn concentrations in the environment of underground mines, aiming to establish correlations between the Rn concentrations and the geological characteristics of fluorite and coal underground mines in the State of Santa Catarina, Brazil. To determine the concentration of Rn, nuclear trace detectors (CR-39 Diglycol Allylic Carbonate) were used. Passive Rn detectors were installed in places with the greatest circulation of people such as galleries, access corridors, meeting rooms, storerooms, workshops, and shafts. The quali-quantitative analyses of radioactivity in the rocks were carried out using a gamma spectrometry system. The results show that coal mines have low values of Rn concentration in the air (< 500 Bq/m3) and do not require protective actions. This can be explained by the fact that U has no direct geochemical association with coal. The low concentrations of Ra in the rocks (hanging wall and footwall sandstones and siltstones) and in the coal confirm this hypothesis. In addition, the efficiency of ventilation normally required due to the presence of methane, a combustible gas, contributes to the reduction of eventual concentrations of Rn in the mining environment. The concentrations of Ra-226 in the hanging wall and footwall rocks, as well as in the coal, do not show any correlation with the Rn concentration in the air. This lack of correlation is expected since it is not possible to achieve secular equilibrium inside the mine, since the efficient ventilation system removes the exhaled Rn and its progeny from the mining environment. The RB and NF fluorite mines have high concentrations of Rn in the air, which are above the recommended action levels as per the International Atomic Energy Agency. The MF fluorite mine presents a concentration of Rn-222 in the air between 500 and 1500 Bq/m3. The Ra-226 concentrations of the normal granite, green fluorite, and purple fluorite, do not show any correlation with the Rn-222 concentrations in the air. However, the Ra-226 concentration in the altered granite shows a tendency towards a positive correlation with the concentration of Rn in the air. Inside the mine, the altered granite significantly contributes to the increase in the concentration of Rn-222 in the air, when compared with the normal granite and the fluorite. This higher contribution can be explained by the modification of the granite by weathering processes, such as open pores and fractures, and the alteration of primary minerals, thus facilitating the exhalation of Rn from the altered granite.
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