Behavior Of Natural Radionuclides Research Articles

INVESTIGATION OF EUDIALYTE CONCENTRATE DECOMPOSITION BY SORPTION CONVERSION IN NITRIC AND HYDROCHLORIC ACID MEDIA

The influence of the sorption conversion conditions for the eudialyte concentrate in low-concentration nitric and hydrochloric acid solutions (concentration and consumption of acid, temperature and duration of the process, sorbent consumption) on the valuable metals extraction efficiency (zirconium, hafnium, niobium, rare earth elements, titanium, manganese) into sulphocationite was studied. Optimal conditions for the process have been determined. It has been shown that sorption conversion in nitric acid solutions is more effective for separating valuable components from the silica component of eudialyte concentrate compared to both the traditional method decomposition by nitric acid and the method of sorption conversion in sulfuric and hydrochloric acid environments. The reasons for the loss of valuable metals and the behavior of natural radionuclides are discussed.

Mineralogy and physico-chemical parameters on the behavior of natural radionuclides in the riverine environs of Hemavathi, South India

Systematic studies were carried out to understand the influence of mineralogy and physico-chemical parameters on the behavior of natural radionuclides in the riverine environs of Hemavathi, one of the important rivers of South India. The physico-chemical parameters, granulometric content, magnetic susceptibility and mineral compositions were measured in the soil and sediment samples to understand the factors affecting the activity concentration of radionuclides in the river ecosystem. The mean activity of 226Ra, 232Th, and 40K in the soil was found to be 37.65 Bq kg−1, 36.79 Bq kg−1, and 301.47 Bq kg−1, respectively. The mean activity of 226Ra, 232Th, and 40K in the sediment was 64.26 Bq kg−1, 100.43 Bq kg−1, and 379.02 Bq kg−1, respectively. Elevated level of radionuclide concentration was observed in the sediment samples. In order to trace the source of the radionuclides, the mineral composition of the soil and the sediment was studied using FTIR and extinction coefficient of major minerals were calculated. Multivariate statistical analyses were carried out to determine the possible correlation between radionuclides, Physico-chemical parameters and the minerals. In particular, Magnetic susceptibility shows significant correlation with 226Ra in both soil and sediment. The statistical analyses suggested that quartz and clay mineral kolanite play a major role in enhancing the radionuclide content in soil and sediment.

Behavior of Natural Radionuclides, Radiological Hazard Parameters, and Magnetic Minerals in Rock Samples of Kolli Hills, Eastern Ghats, India

The natural radionuclide (238U, 232Th, and 40K) content of the 15 rock samples collected from Kolli hills along the Eastern Ghats, India, has been analyzed using a 4″ × 4″ NaI (Tl) scintillation detector-based gamma-ray spectrometer. The activity concentrations of 238U, 232Th, and 40K were between 12.97–49.89, 6.4–27.05, and 51.85–95.84 Bq kg−1, respectively. To understand the entire radiological characteristics of the collected samples, the various radiological hazard parameters have been calculated and were compared with the global recommended mean values. From the magnetic studies, values of χ ranged from 33.1 to 510.7 × 10−8 m3 kg−1. Moreover, in rock samples of Kolli hills, ferrimagnetic minerals are found to be the main magnetic carrier. Statistical analyses were performed to study the relation between the natural radionuclides, radiological hazard parameters, and magnetic minerals. The results of Pearson’s correlation analysis shows that 238U and 232Th strongly correlate with the radiological hazard parameters, and a poor correlation was noted between magnetic and radiological parameters. However, a positive and a near-positive correlation was also observed between SIRM/χ (0.501–0.578) and κFD% (0.471–0.481) with U and Th activity concentrations, respectively. This indicates that the carrier and grain size dependence parameters also play a significant role in increasing the activity concentrations of U and Th and its associated radiological parameters. From the cluster analysis, it is found that the content of ferrimagnetic minerals is higher in sample nos. 4, 5, 11, and 12, which greatly improves the properties of concrete when used for building construction purposes.

Partitioning behavior of natural radionuclides during combustion of coal in thermal power plants

ABSTRACTCoal-fired power generation produces huge amounts of fly ash and bottom ash of different properties. Coal contains many naturally occurring radionuclides, which on burning are enriched in the ashes; their discharge to the environment may cause significant exposure of the public to this technologically enhanced naturally occurring radioactive material. Most of these nuclides tend to become particle bound and hence are adsorbed on the ash particles. It is thus important to assess the behavior of radionuclides under combustion in the particle phase. To study the behavior of radionuclides in the particle phase, i.e., in combusted coal ashes, radioactivity measurement of coal and ash samples from different power plants was carried out using alpha and γ-ray spectrometry. The activity of 210Po in fly ash ranged from 12.6 to 91.3 Bq kg−1, while the range of activity concentrations of 238U, 226Ra, 232Th, 40K in fly ash were 56.1–133, 44.3–119, 9.3–144, and 34.5–221 Bq kg−1, respectively. Partitioning behavior of the radionuclides, their relative enrichment factors, and effect of particle size on enrichment of the nuclides in fly ash were also studied. Radionuclides were also grouped using their relative enrichment factors, a consequence of their volatile nature. A good correlation between the partitioning behavior, volatility, and relative enrichment factors of the radionuclides was observed in this study. This outcome of the study could be very useful for determining the fate of the radionuclides, from the bulk low-concentration mineral state in coal mines to the high-concentration particle phase of ashes after burning in power plants. This is important since it is the higher concentration of radionuclides in the particle phase that is a potential source of exposure to the public.

Behavior of natural radionuclides in wastewater treatment plants

56 samples, including influent, primary effluent, secondary effluent and final effluent wastewater from two Spanish municipal wastewater treatment plants (WWTPs), were analyzed to assess both the occurrence and behavior of natural radioactivity during 12 sampling campaigns carried out over the period 2007–2010. Influent and final effluent wastewaters were sampled by taking into account the hydraulic residence time within the WWTP. A wide range of gross alpha activities (15–129 mBq/L) and gross beta activities (477–983 mBq/L) in liquid samples were obtained. A correlation analysis between radioactivity in liquid samples and the performance characteristics of the WWTPs was performed. The results in liquid samples showed that gross beta activities were not influenced by treatment in the studied WWTPs. However, gross alpha activities behave differently and an increase was detected in the effluent values compared with influent wastewater. This behavior was due to the increase in the total dissolved uranium produced during secondary treatment. The results indicate that the radiological characteristics of the effluents do not present a significant radiological risk and make them suitable for future applications.

Behavior of natural radionuclides in surficial sediments from an estuary impacted by acid mine discharge and industrial effluents in Southwest Spain

The environmental degradation resulting from the acid mine drainage (AMD) and discharge from effluents of phosphogypsum (PG) piles in the watershed of Tinto and Odiel Rivers estuary over long periods of time has resulted in significant impact on the ecosystem of this estuary, resulting that the sediments are highly polluted by heavy metals and radionuclides from the discharge AMD and leachates from the PG. During resuspension of benthic sediments some of the radionuclides are desorbed making them bioavailable. In the present study, we investigate the spatial distribution of radionuclides U, Th and Ra and assess the factors and processes that caused the spatial distribution of these nuclides in this estuarine system. This study has global significance for other polluted environmental systems that are impacted by AMD and PG.

Evaluation of the radioactive impact of the phosphogypsum wastes used as amendment in agriculture soils

Some 3×109 kg of phosphogypsum (PG) wastes are annually generated by two fertiliser-production factories in Huelva (south-western Spain). PG has relatively high concentrations of 226 Ra and other radionuclides, with an special concern due to the 222 Rn emissions. These wastes could be used to improve the fertility of agriculture soils in a large former marsh area of the Guadalquivir river. Thus, it is interesting to study the levels and behaviour of natural radionuclides within this system to evaluate the radioactive impact of this amendment. An agronomical test is being conducted by one of the authors in an experimental farm in Lebrija (Seville). The soils are treated with 13 and 26 t ha-1 of PG, 30 t ha-1 of manure. Each treatment was repeated twice and continued for two years with beetroot and cotton plant production. We are measuring 226 Ra (by alpha counting and gamma spectrometry) and U isotopes (by alpha spectrometry and ICP-MS analysis) in drainage waters, soils and vegetal-tissues samples. The PG used in the treatment has 620 ± 70 Bq kg-1 of 226 Ra. The drainage waters have 226 Ra contents similar to those from non-contaminated natural waters, but the uranium concentrations are one order of magnitude higher. Our results are suggesting that the major uranium input comes from the application of phosphate-fertiliser. No significant levels of radionuclides were found in the vegetal tissues.

The partitioning of natural radionuclides in a large alpine river

In continuation of earlier radio-ecological studies, the results of specific investigations on the behavior of natural radionuclides ( 238U, 226Ra, 210Pb, 40K) in the freshwater environment of the Austrian part of the Danube River are presented. The investigations and interpretations of the results are carried out with regard to the partitioning of radionuclides in fresh water between the particulate and soluble phases. The underlying work is a mixture of radiometric analysis of in situ-samples of water, suspended matter and sediments of the fresh water environment of the Danube River, and grain size analysis. The affinities of the partitioning of the observed natural radionuclides to the artificial radionuclide 137Cs are shown. Specific attention is paid to the influence of non-radiometric parameters, such as, hydrological conditions (i.e., flow rate), solid particle concentration, and grain size distribution of suspended matter on the radionuclide partitioning and the dynamics of water/solid matter interactions. The results of this work can be used as a basis for investigations on special problems of fresh water radioecology (i.e., a more realistic parameter assessment for radio ecological fresh water models) in Alpine regions and for investigations of general environmental processes (i.e., distribution of atmospheric pollutants in a large river fresh water ecosystem; land erosion processes).

Behavior of natural radionuclides in lignites and fly ashes

The behavior of naturally-occurring radionuclides 238U, 226Ra, 210Pb, 228Ra ( 232Th) and 40K in lignites and fly ashes is described. The concentrations of 238U, 226Ra and 210Pb in lignites were increased with decreasing concentrations of 40K, resulting in an inverse relationship, whereas the concentration of 228Ra ( 232Th) increased with an increasing concentration of 40K. In fly ashes, 238U and 210Pb were enriched on smaller particles, while 40K decreased. The content of the two isotopes of radium, 226Ra and 228Ra, also decreased in finer particles of fly ash but the rate of decrease for 226Ra was found to be weaker than on the corresponding one of 228Ra as well as of 40K. The above observations are discussed.

Radionuclide behavior in coal-fired plants

The behavior of natural radionuclides in the coal-burning process was studied. Distribution of radionuclides near a coal-fired power plant and doses of power plant emissions of radionuclides to humans were analyzed. Coal-fired power plants are a major source of atmospheric radionuclides/ any attempts to increase coal use should be made after improvements in radionuclide control are indicated. 4 diagrams, 5 graphs, 16 references, 9 tables.

Behavior of natural radionuclides in western coal-fired power plants

Behavior of natural radionuclides in western coal-fired power plants