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(last updated 1 Jan 2023)
The widely used sulphuric acid process concentrates most of the uranium and other toxic constituents in the product stream (fertilizers, detergents, etc.), while most of the radioactive decay products of the uranium series, such as Radium-226, end up in the waste gypsum.
Typical concentrations in phosphate fertilizer are 4 Bq (= 0.32 mg) Uranium-238 and 1 Bq Radium-226 per g P2O5.
The average radionuclide concentrations in phosphogypsum waste in the U.S. are 3 Bq/g for Radium-226, and 0.5 Bq/g for Uranium-238, among others. These radionuclide concentrations are lower than in most uranium mill tailings, but they have to be taken into account for the phosphogypsum waste management, see Management of Phosphate Tailings.
Various technologies exist to recover the uranium from the product stream, thus removing this unwanted constituent from the products and lowering the needs for uranium ore. Worldwide, there are approximately 400 wet-process phosphoric acid plants in operation.
Eight plants for the recovery of uranium from phosphoric acid have been built and operated in the United States since 1976 (Florida: 6, Louisiana: 2). Plants have also been built in Canada, Spain, Belgium, Israel, and Taiwan, see Facilities for Uranium Recovery from Phosphate.
Historical operating costs for the uranium recovery from phosphoric acid range from 22 to 54 US$/lb U3O8. These operating costs are by far higher than past uranium market prices, and most uranium recovery plants have been closed, therefore. In view of the recent increase of the uranium market price, the situation may change, again. (see also: Uranium Recovery from Phosphates)
East African phosphate fertilizers contain uranium concentrations found elsewhere in uranium ores:
"[...] This work assesses the uranium concentrations in four major phosphate rocks originating from East Africa and four mineral phosphate fertilizers commonly used in the region. The concentration measurements were performed using energy-dispersive X-ray fluorescence spectrometry. The results showed that the uranium concentration in phosphate rock ranged from as low as 10.7 mg kg-1 (Mrima Hill deposit, Kenya) to as high as 631.6 mg kg-1 (Matongo deposit, Burundi), while the concentrations in phosphate fertilizers ranged from 107.9 for an imported fertilizer to 281.0 mg kg-1 for a local fertilizer produced from Minjingu phosphate rock in Tanzania. In this context, it is noteworthy that the naturally occurring concentration of uranium in the earth crust is between 1.4 and 2.7 mg kg-1 and uranium mines in Namibia commercially process ores with uranium concentrations as low as 100-400 mg kg-1. This study thus confirms that East African phosphate rock, and as a result the phosphate fertilizer produced from it can contain relatively high uranium concentrations. [...]"
Uranium in phosphate rocks and mineral fertilizers applied to agricultural soils in East Africa , by Dennis A. Mwalongo, Nils H. Haneklaus, Jacob B. Lisuma, et al., in: Environmental Science and Pollution Research, Published online: 11 December 2022
Wide range of uranium and cadmium identified in fertilizer products sold for gardening: An analysis of five fertilizer brands sold in German garden centers revealed concentrations in the extraordinary wide range of 4 - 401 milligrams uranium and 3 - 40 milligrams cadmium per kilogram phosphate. These concentrations are not declared by the manufacturers, as there exists no such legal requirement nor any related concentration standard in Germany. (NDR Sep. 12, 2011)
By-product uranium production from phosphate in Louisiana to cease
Uranium waste solution from Port Hope fuel facility used as fertilizer (Ontario)
Use of Siemens' Richland, Washington, nuclear fuel plant waste solutions as fertilizer
Sequoyah Fuels Gore, Oklahoma, Uranium processing plant sprays radioactive waste as fertilizer
Radiological Considerations of Phosphogypsum Utilization in Agriculture by C.L.Lindeken, U.S. DOE, UCRL-84927, 1980, 22 p. (780k PDF - LLNL)
Handling of radium and uranium contaminated waste piles and
other wastes from phosphate ore processing
by G.Schmidt, C.Küppers; annex by P.Robinson
Nuclear Science and Technology, Report EUR 15448 EN. 121 p. ISBN 92-827-4076-5, published by the European Commission, Luxembourg 1995.
Rock phosphates and P fertilizers as sources of U contamination in agricultural soils , by S. Kratz, E. Schnug, in: Merkel B J, Hasche-Berger A (eds): Uranium in the environment. Springer, Berlin Heidelberg 2006, pp. 57-68. (446k PDF - FAL)
Presentations - 3rd Seminar on protecting water bodies from negative impacts of agriculture - Loads and fate of fertiliser derived from uranium, 4 - 5 June 2007, Braunschweig, Germany
Loads and Fate of Fertilizer-Derived Uranium, Edited by Luit J. De Kok and Ewald Schnug, Leiden 2008
To Extract, or not to Extract Uranium from Phosphate Rock, that is the Question , by Nils Haneklaus, Yajie Sun, Roland Bol, et al., in: Environmental Science & Technology 2017, 51, 753-754
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