Radiological measurement of phosphate rock and phosphogypsum from fertilizer industries in India

Phosphate deposits are generally characterized by high levels of natural radionuclide concentrations. Natural radionuclides from the uranium and thorium series were measured, using high-resolution gamma-spectrometry in phosphate rock and phosphogypsum samples from the phosphate fertilizer industry in India. Equilibrium was found to be disrupted during the chemical processing of phosphate rock with 83 % of the ²²⁶Ra and only 5 % of ²³⁸U fractionating to phosphogypsum. Activity concentrations of ²³⁸U and ²²⁶Ra in phosphogypsum produced from various fertilizer industries of India showed levels < 1,000 Bq kg^?1 and pose no restriction for use in building/construction material.     

External gamma radiation levels and natural radioactivity in soil around a phosphate fertilizer plant at Mumbai

Fertilizers containing phosphate have been used worldwide in increasing quantities in order to replenish natural nutrients, which are being continuously depleted from the soil by virtue of farming activities. Phosphate rocks together with potassium ores and nitrogenous compounds are the main raw materials used for industrial fertilizer production. Rock phosphate ore processing and disposal of phosphogypsum contribute to enhanced levels of natural radionuclides in the environment. The levels of naturally occurring radionuclides such as ²³⁸U, ²³²Th, ²²⁶Ra and ⁴⁰K in soil samples collected around a phosphate fertilizer plant were estimated. Radium equivalent activity, external hazard index and external dose rate due to natural gamma background at various locations around the plant were also measured.     

Application of a Liquid Scintillation Technique to the Measurement of 226Ra and 224Ra in Samples Affected by Non-Nuclear Industry Wastes

Experiment procedures have been developed for the determination of ²²⁶Ra and ²²⁴Ra activity concentration in solid and liquid samples collected around a non-nuclear industrial area, by liquid scintillation counting. The different radiochemical procedures developed in this work, have been adaptations of a radiochemical procedure previously used, for ²²⁶Ra and ²²⁴Ra determinations by LSC in drinking water, which was improved, refined up and adapted to the type of sample to be applied. These improved radiochemical methods have been applied to waste samples (phosphogypsum) produced by two factories which are engaged in phosphoric acid production, and to waters collected from the Odiel river, where during the sampling period a fraction of these wastes were released. ²²⁶Ra activity concentrations in the phosphogypsum ranged from 673 to 1178 Bq/kg dry weight, indicating that the wastes are particularly enriched in this radionuclide. Consequently, high ²²⁶Ra levels were easily found in the river waters analysed, especially in the neighbouring zones of the waste discharges.     

Rapid sequential separation of actinides using Eichrom's extraction chromatographic material

The presence of ²²⁶ Ra in an estuary formerly affected by direct discharges of waste from a phosphate fertilizer complex has been investigated. Specific activities ranging from 3.6 to 45.2 mBq/l have been detected. In general, activity levels are lower than those detected when direct discharges were carried out. However, there is still a clear contamination due to the disposal of phosphogypsum in open air piles by the river. Moreover, it seems that ²²⁶ Ra is being redissolved from the contaminated bed sediments, which also contributes to an enhancement in the activity levels of the estuary waters.     

The226Ra/Ba-ratio as indicator for phosphogypsum contributions to226Ra levels in sediments

Phosphogypsum discharges by phosphate-ore processing industries pollute sediments of the Rotterdam harbour area with²²⁶Ra. Direct measurement of this radionuclide in sediments does not provide a reliable indication of the elevation of the levels, since²²⁶Ra levels in sediments depend on the particle size. To eliminate the size effect, the²²⁶Ra/Ba ratio in sediments was tested as a possible indicator for the²²⁶Ra in the discharges. The results indicate almost a doubling of the²²⁶Ra levels in sediment samples due to phosphogypsum discharges. The contribution of phosphogypsum to the sediment mass was calculated in the order of a few percent equivalent.     

Natural radionuclides and metals intake into soya,corn and lettuce grown on soil amended with phosphogypsum

Phosphogypsum is a by-product of the phosphate fertilizer industry. It is produced by precipitation during wet process of phosphate rocks, thus posing serious problems with its utilization and safe disposal. In Brazil, three main industries are responsible for the production and storage of about 5.5?×?10⁶ tons per year. Phosphogypsum may contain trace metals and radionuclides of U and Th series. Since, in Brazil, phosphogypsum has been used for many years as soil amendment, it is important to know its availability in the environment. The main objective of this study is to evaluate the radionuclides and metals transfer in the soil-to-plant system. To accomplish this task an experiment was carried out in a green house, where two major crop groups (soya bean and corn) and leafy vegetables (lettuce) were grown in two types of soil (clay and sandy) amended with phosphogypsum. The transfer-factors were evaluated for the metals (As, Cd, Cu, Ni and Pb, Ba, Co, Cr, Fe, Zn and REE) and for the radionuclides U, Th, ²²⁶Ra, ²²⁸Ra, ²¹⁰Pb and ²¹⁰Po. The addition of PG to the two soils studied, did not significantly alter the TFs values for all the elements studied.     

Radium-226 in uranium mill tailings

A study of the physical state of²²⁶Ra in uranium mill tailings was undertaken by Chemex Laboratories Ltd. under contract to NUTP. A test portion of a leached uranium ore was collected just prior to neutralization with lime and subjected to repetitive batch water leaching. The leachates were analyzed for barium, lead,²²⁶Ra, iron and sulphate. The experimental results suggest that²²⁶Ra is co-precipitated with lead sulphate during uranium leaching of the ore with sulphuric acid. The attainment of equilibrium conditions in the pore water of the leached ore then allows a re-proportioning of²²⁶Ra between solid lead and barium sulphates resulting in a depletion of²²⁶Ra in the outer layers of the crystals of solid lead sulphate and an enrichment in²²⁶Ra in the outer layers of solid barium sulphate.     

Radium isotopes in suspended matter in an estuarine system in the southwest of Spain

The presence of²²⁶Ra and²²⁴Ra in suspended matter from an estuarine system which surrounds a phosphate fertilizer complex has been investigated. The results have confirmed an important radioactive impact from the industrial complex, since up to 2.5 Bq²²⁶Ra/g suspended matter (dry) has been measured. The influence of tides and seasonal conditions, through changes in salinity, has been found to be relevant. The distribution coefficients for²²⁶Ra between the suspended matter and the river water have been calculated. The values are in agreement by order of magnitude with those found in the literature, but they clearly depend on tidal state and seasonal conditions.     

Radionuclide levels and temporal variation in phosphogypsum

Summary Three samples of phosphogypsum of different ages were analyzed for natural radioelements using high-resolution gamma-ray spectrometry. The phosphogypsum samples were taken from the filter of a 10-year old pile, and a 50 year old pile. The distribution of ²²⁶Ra remains relatively constant as a function of storage time (up to 50 years) which confirms the immobility of ²²⁶Ra in the phosphogypsum matrix. However, the concentration of ²³⁸U and ²³² Th have shown a decreasing tendency going from the most recent sample to the oldest. For radionuclides belonging to the ²³² Th series, we noticed an enrichment factor of 1.5 for ²²⁸Ac in the most recent phosphogypsum, whereas the right proportions exist for the other two samples. This is due to the fact that most of the thorium fractionates to the phosphoric acid during the production process and the equilibrium between ²³² Th and its descendants is not yet reached for fresh phosphogypsum.     

Natural radionuclide-free phosphoric acid production

High-uranium phosphate rock from Itataia, Brazil, was milled for wet-process phosphoric acid production using the dihydrate method. Uranium contained in the phosphoric acid was recovered by solvent extraction. The distribution of long-lived natural radionuclides of the ²³⁸U and ²³²Th decay series involved in these operations was evaluated. ²²⁶Ra, ²²⁸Ra and ²¹⁰Pb were found to predominate in the phosphogypsum, while ²²⁸Th, ²³⁰Th and ²³²Th in the uranium-free phosphoric acid. Thorium is removed from the phosphoric acid by solvent extraction to produce a NORM-free phosphoric acid.     

Removal of radionuclides from acid mine waters by retention on adsorbing materials

Summary This study proposes a method for decontamination of acid drainage water from a uranium mine, as an alternative process to lime treatment. The research embodied the recovery of uranium with an ion-exchange resin, treatment of effluent resin with lime, or with inorganic adsorbents and biosorbents. The uranium decontamination level using the resin process was 94% and allowed the recovery of this element as a commercial product. Among the inorganic adsorbents studied, phosphogypsum was effective for ²²⁶Ra, ²²⁸Ra, and ²¹⁰Pb removal. Among the biosorbents, Sargassum sp.was superior in relation to its specific capacity to accumulate and remove ²²⁶Ra.     

Determination of the radon emanation fraction from phosphogypsum using LSC

A simple method for the determination of the radon emanation fraction was studied using a liquid scintillation counter. The radon activity of the gaseous phase in a closed container was measured 1 day and 35 days after sealing and used to calculate the radon emanation fraction. Radon leakage from the container was investigated using a ²²⁶Ra radioactive standard solution (SRM4967, NIST) to plot a radon growth curve. The method was applied to materials that typically contain a high level of radium, such as phosphogypsum, phosphate fertilizer and a rock sample. The effect of temperature on the radon emanation fraction from the materials was investigated at 0, 10, 20, 30 and 40 °C. It was found that there is a linear correlation (R ² = 0.746 − 0.946) between temperature and the emanation fraction. Within the temperature range, the radon emanation fractions were 0.241–0.466 for phosphogypsum, 0.225–0.351 for phosphate fertilizer and 0.154–0.351 for the rock sample.     

Use of radioactive thermal water after226Ra removal

The paper describes the possibility of efficient and safe use of geothermal water at a location in the town of Zagreb. Geothermal water is used exclusively for the purpose of sport and recreation. Due to elevated²²⁶Ra concentrations, the raw geothermal water must be used in limited proportions so as to exclude any potential health risk for the pool users. With application of adequate treatment methods, such as intense aeration (²²⁶Ra removal efficiency 13.7±3.5%) and filtration of aerated water with high pressure sand filters (removal efficiency 39.5±7.9%), the elevated²²⁶Ra content would be maximally reduced. The decrease of radioactivity enables that the proportion of geothermal water would be increased without any health risk, ensuring great cost reduction spent on the warming of pool waters.     

Use of radioactive thermal water after226Ra removal

The paper describes the possibility of efficient and safe use of geothermal water at a location in the town of Zagreb. Geothermal water is used exclusively for the purpose of sport and recreation. Due to elevated²²⁶Ra concentrations, the raw geothermal water must be used in limited proportions so as to exclude any potential health risk for the pool users. With application of adequate treatment methods, such as intense aeration (²²⁶Ra removal efficiency 13.7±3.5%) and filtration of aerated water with high pressure sand filters (removal efficiency 39.5±7.9%), the elevated²²⁶Ra content would be maximally reduced. The decrease of radioactivity enables that the proportion of geothermal water would be increased without any health risk, ensuring great cost reduction spent on the warming of pool waters.     

Nitrogen content determinations in different stages of thermal treatment involved in conversion of ammonium diuranate to uranium metal

Accurate, low-level measurement of ²²⁶Ra in high volume water samples requires rapid pre-concentration and robust separation techniques prior to measurement in order to comply with discharge limits and drinking water regulations. This study characterises the behaviour of ²²⁶Ra and interfering elements on recently developed TK100 (Triskem International) extraction chromatography resin. Distribution coefficients over a range of acid concentrations are given, along with an optimised procedure that shows rapid pre-concentration and separation of ²²⁶Ra on TK100 resin is achievable for high volume (1 L) water samples without the need for sample pre-treatment.     

Modeling of <Superscript>226</Superscript>Ra behavior in a Spanish estuary affected by the phosphate industry

The Odiel and Tinto rivers, southwest Spain, form a fully mixed estuary. An industrial area that includes a complex dedicated to the production of phosphate fertilizers is located by the Odiel River. This complex released phosphogypsum wastes directly to the Odiel River and also disposed them on open air piles located by the Tinto River. Due to new EU regulations, wastes are not directly released to the Odiel from 1998 on, although they are still disposed on the open air piles. The behavior of ²²⁶Ra in a system like this estuary is complex, since radionuclides are affected by tidal actions and interactions with sediments through adsorption/desorption reactions and erosion/deposition processes. A numerical 2D depth-averaged model of the estuary has been developed, including processes mentioned above. It has been applied to reproduce experimental data measured after a release from the industrial complex in the Odiel River and after an accidental release in the Tinto River from the gypsum piles. The model has also been applied to simulate the self-cleaning process observed in the estuary after the direct releases from the fertilizer complex were stopped.     

The natural radioactivity of Brazilian phosphogypsum

Phosphogypsum is a high volume by-product from the phosphoric acidindustries containing naturally occurring radionuclides. Envisaging the usesof phosphogypsum, a characterization of this material in terms of spatialdistribution of radionuclides was carried out by core samples taken from stacksof two important Brazilian phosphoric acid facilities. Samples were analyzedfor ²³⁸U, ²³⁴U, ²³²Th, ²²⁶Ra, ²²⁸Ra, ²¹⁰Pb and ²¹⁰Po using alpha- and gamma-spectrometryand UV-VIS spectrophotometry. Specific activities of ²³⁸U, ²³⁴U, ²²⁶ Ra and ²¹⁰Po obtained were comparablewith data reported in the phosphogypsum literature, while higher values werefound for ²³² Th and ²²⁸Ra.     

Determination and differentiation of <Superscript>226</Superscript>Ra and <Superscript>222</Superscript>Rn by gamma-ray spectrometry in drinking water

The analysis of ²²⁶Ra in natural waters can be tedious and time-consuming. For the determination and differentiation of activities of ²²⁶Ra and ²²²Rn in drinking water by γ-ray spectrometry a simple and fast method is presented. Activities of ²²⁶Ra > 0.5 Bq L⁻¹ can be determined according to stabilization of the sample without further procedures. For a more sensitive detection sample volumes of up to 5 litres are applicable by a rapid precipitation procedure without large expenditure. Further laborious enrichment methods are not necessary. Thus, detection limits of 0.1 Bq L⁻¹ can be obtained when using sample volumes of 5 litres. Therefore the method is suitable for the monitoring of radioactivity in drinking water samples in accordance with the legal guidance of the European Union.     

The dietary intake of238U,234U,230Th,232Th,228Th and226Ra from food and drinking water by inhabitants of the Walbrzych region

Intake with food and water of the natural radionuclides of the uranium and thorium series was determined for adult population of the south-western region in Poland, where in the 1950-ies an exploration of uranium ore was conducted. Concentration of the radionuclides was determined in food products and drinking water and their annual intake was estimated on the basis of the average annual consumption. The intake of²³⁸U,²³⁴U and²³⁰Th occurred mainly with water (33% to 68%), whereas the intake of²³²Th,²²⁸Th and²²⁶Ra was mainly with vegetables, potatoes, milk and flour. From the intake and dose coefficients the annual effective doses from the ingested radionuclides were calculated. The total dose was 5.6 Sv, of which 74% originated from²²⁶Ra.