Radiological investigation of phosphate fertilizers: Leaching studies. (July 2017)

• Record Type: Journal Article
• Authors: Hegedűs, Miklós; Tóth-Bodrogi, Edit; Németh, Szabolcs; Somlai, János; Kovács, Tibor
• Is Part Of: Journal of environmental radioactivity. Volume 173(2017)
• Page Start: 34
• Page End: 43
• Publication Date: 2017-07
• Subjects: Fertilizer -- Leaching -- Gamma-spectrometry -- Alpha-spectrometry -- NORM; Radioactivity -- Periodicals; Radiation, Background -- Periodicals; Radioecology -- Periodicals; Radioactive pollution -- Periodicals; Environmental Pollutants -- Periodicals; Radioactive Pollutants -- Periodicals; Radioactivity -- Periodicals; Radioécologie -- Périodiques; Pollution radioactive -- Périodiques; Fond de rayonnement -- Périodiques; 539.752
• DOI: 10.1016/j.jenvrad.2016.10.006
• Languages: English
• ISSNs: 0265-931X

Abstract

Abstract: The raw materials of the phosphate fertilizer industry are the various apatite minerals. Some of these have high levels of natural radionuclides, and thus phosphate fertilizers contain significant amounts of U-238, K-40 and Ra-226. These can leach out of the fertilizers used in large quantities for resupplying essential nutrients in the soil and can then enter the food chain through plants, thereby increasing the internal dose of the affected population. In the current study, the radiological risk of eight commercially available phosphate fertilizers (superphosphate, NPK, PK) and their leaching behaviours were investigated using different techniques (gamma and alpha spectrometry), and the dose contributions of using these fertilizers were estimated. To characterize the leaching behaviour, two leaching procedures were applied and compared –the MSZ 21470-50 (Hungarian standard) and the Tessier five-step sequential extraction method. Based on the evaluation of the gamma-spectra, it is found that the level of Th-232 in the samples was low (max.7 ± 6 Bq kg −1 ), the average Ra-226 activity concentration was 309 ± 39 Bq kg −1 (min. 10 ± 8 Bq kg −1, max. 570 ± 46 Bq kg −1 ), while the K-40 concentrations (average 3139 ± 188 Bq kg −1, min. 51 ± 36 Bq kg −1 ) could be as high as 7057 ± 427 Bq kg −1 . The high K-40 can be explained by reference to the composition of the investigated fertilizers (NPK, PK). U concentrations were between 15 and 361 Bq kg −1, with the average of 254 Bq kg −1, measured using alpha spectrometry. The good correlation between P2 O5 content and radioactivity reported previously is not found in our data. The leaching studies reveal that the mobility of the fertilizer's uranium content is greatly influenced by the parameters of the leaching methods. The availability of U to water ranged between 3 and 28 m/m%, while the Lakanen-Erviö solution mobilized between 10 and 100% of the U content. Highlights: The radiological risk of phosphate fertilizers was studied by α and γ spectrometry. The leaching of uranium from phosphate fertilizers was investigated by two methods. Activity concentrations and leaching characteristics show great variation. Excess dose contributions of using these fertilizers were estimated. Speciation of U indicates availability to the environment between 43 and 98%.