750 atw 57. Jg. (2012) Heft 12 | Dezember

Uranium in the Environment

Environmental prospects of uranium from mineral phosphatesEwald Schnug, Brunswick/Germany, and Nils Haneklaus, Stuttgart/Germany

Uran(U)istalsnatürlicheRessourceu.a.inRohphosphat(P)vorhanden.JedesJahrbringensoz.B.Landwirteca.167tUranaufihreBödendurchDüngungauf.Dies ent-sprichtinderEnergieerzeugungimmerhinderMengeanUran,mitderrund2,4Mio.deutscheDurchschnittshaushaltebeimEin-satzalsKernbrennstoffineinemKernkraft-werkversorgtwerdenkönnten.DerTransfervonUranausPhosphatdün-

gernkönnteeinunkonventionellerBeitragderLandwirtschaftzumKlimaschutzsein.UnterderAnnahmederavisiertenCO2-Pö-nalenfürKraftfahrzeugewürdederWertdesUransinPhosphatdüngernderenRohstoff-preisdeutlichübertreffen.ZudemwäredieExtraktionvonUranaus

PhosphateneinBeitragzurMinimierungdesmöglichenEintrags indieNahrungskette.InsbesonderekönntendamitUmlagerungs-prozessevonUranausBödenindasOberflä-chenwasser und letztendlich Trinkwasservermiedenwerden.

Anschriften der Verfasser: Ewald Schnug

Technical University BraunschweigFaculty 2 Life Sciences

Pockelsstraße 1438106 Braunschweig, Germany

Nils HaneklausInstitute of Nuclear Technology and

Energy Systems (IKE)University of Stuttgart

Pfaffenwaldring 3170569 Stuttgart, Germany

* formerly affiliatedNUKEM Technologies GmbH

Industriestraße 1363755 Alzenau, Germany

Uranium in rock phosphates and its potential for electricity generation

U is an accompanying element of phos-phate rocks. Depending on the geographi-cal and biogenic origin of the rock phos-phate U concentrations can be as high as 150 mg kg-1 in sedimentary and 220 mg kg-1 in igneous rock phosphates [Kratz and Schnug 2006]. Approximately 6 % of the world’s known P deposits exhibit U in recoverable concentrations [Orris and Chernoff2002]. Countries possessing such P/U deposits are Afghanistan, Angola, Aus-tralia, Belgium, Brazil, Canada, Central-Af-rica, Ecuador, Finland, Greenland, Hunga-ry, India, Israel, Jordan, Mauritania, Mo-rocco, Mozambique, New Zealand, Saudi Arabia, Senegal, South Africa, Spain, Swe-den, Syria, Togo, Turkey, and the United States of America [Orris and Chernoff2002; Ragheb2008].

The basic idea of using U from rock phosphates for energetic purposes while minimising adverse environmental effects due to fertiliser-derived U loads to agricul-tural soils has been proposed by Hu et al. [Hu et al., 2008]. Technically the extrac-tion of U during fertiliser processing is no problem [Imphos 2009]. Before it became uneconomic in the mid-1990s about 20 % of US U came from central Florida’s P de-posit [WorldNuclear 2012]. Several meth-ods exist for the extraction of U from rock phosphates such as precipitation of U from phosphoric acid, ion exchange separation with a chelating resin, membrane separa-tion of U, froth flotation and solvent ex-traction of U [Kratz and Schnug2006]. De-tailed descriptions of these methods are provided by Gupta and Singh [Gupta and Singh, 2003]. The technology experiences a worldwide revival as for instance the con-tract between France and Morocco signed

in 2009 on the extraction of U from rock phosphates [Ellersick 2007] and the at-tempt of NukemInc. and CFIndustries to build a Uranium Recovery Facility in Flori-da [Frame 2011] show.

It can be expected that on a long-time basis the prices for P fertilisers will remain unaffected when U is going to be extracted on a global scale as the demand for U is rapidly increasing. The price for U at the world market remains on a constantly high level as the U supply from conversion of nuclear weapons is decreasing and the de-mand is increasing. Other U secondary re-covery sources are bottom and fly ashes from coal combustion and sea water. Here-by, the energetic use of coal is in a similar dilemma as is the agricultural utilisation of phosphates: Coal and fly ashes show U con-centrations which are in a similar range as those in rock phosphates. The extraction of U from fly ashes is explored with respect to limited U reserves.

Rock phosphates and processed phos-phorus (P) fertilisers are a main source of U contamination and accumulation in ag-ricultural soils [Rogasik et al. 2008; Kratzand Schnug 2006]. U is a radioactive and toxic metal. Its translocation into water bodies with yet unknown effects on human health can be regarded as critical [Knolleet al. 2011; Smidtet al. 2011]. IAEA [IAEA, 2011] speculated that extraction of U from phosphates in the future depends on the development of the world market price for U, or environmental regulations which re-quest re-installation of the process. In ad-dition, the argument that a lower U con-tent of the ore in U mines increase the price costs for fuel production and the life-cycle contribution to the CO2 balance would be no longer valid if the U source is a side-product of fertiliser production. The esti-mated amount of U available from uncon-ventional P deposits ranges from 9 to 22

751atw 57. Jg. (2012) Heft 12 | Dezember

Uranium in the Environment

Tab. 1. Energetic and ecological characteristics of various energy sources.

million tonnes and could deliver U for an-other 440 years for the same price as con-ventional U resources which is about 5 times longer than the time span calculated for conventional U reserves [Comby 2008; OECD 2005; Ragheb 2008; WorldNuclear2012].

With view to energetic and economic as-pects U in rock phosphates is a precious metal (Table1). Statistically up to 167 t/yr U have been applied on agricultural fields in Germany exclusively by P fertilisation. This amount would have been sufficiently high to satisfy the energy demand of 2.4 million households of average size. Thus this energy source equals the heating value of timber from 5.6 million ha of forest land. It can be concluded that the use of U ex-tracted from P fertilisers is an uncommon contribution of agriculture to climate pro-tection, which has been valued to 1.8 €/kg P when supposing an equivalent value to CO2 emission car tax bands in Germany. A detailed description of the calculation basis is provided below. Either a CO2 tax on min-eral P fertiliser products or a monetary re-ward for farmers in the form of a CO2 bo-nus are supposed to provide a strong moti-vation for the re-vitalisation of the existing technology for U extraction from rock phos-phates.

Uranium from phosphorus fertilisers to reduce CO2 emissions

“Perfection is attained, not when no more can be added, but when no more can be re-moved.” [AntoinedeSaintExupéry, 1900 to 1944]. The relevance of this quotation of AntoinedeSaintExupéry is most likely more important than ever if it comes to the com-parison of renewable energy sources and nuclear power. Renewable energy sources and nuclear power alike do emit carbon di-oxide not by burning fuel, but during their life cycle. Mining and milling of U has a

large share in the greenhouse gas (GHG) emissions of electricity generation with nu-clear power [IAEA 1997]. Extracting U as a side-product of P fertilisers reduces GHG emissions in the nuclear fuel cycle making electricity generation with nuclear power from an environmental point of view even more desirable than it already is.

Yet another, highly important environ-mental aspect is the fate of U after soil ap-plication. U from rock phosphates is un-doubtedly a desirable source as it other-wise enters the food chain. Fertiliser-de-rived U has been shown to be discharged into water bodies whereby rate and veloci-ty are closely linked to fertilizer practices and soil characteristics (Smidt et al. 2011). At an annual application rate of 9 g/ha U applied with 22 kg/ha P (which is a stand-ard fertiliser recommendation) a steady state concentration of 22 µg/L U is expect-ed in the percolating water (modelled by Jaqueset al. [Jaques 2008]). A preliminary, conservative estimate of the U concentra-tion in 369 water samples from areas in the plains of northern Germany where a high-er, geogenically originating U content can be excluded, revealed that 1/4 up to 2/3

(worst case scenario with concentrations above 0,1 µg/L) of all specimens may al-ready be contaminated by fertiliser-de-rived U (11 % > 2 µg/L; 0,5 % > 10µg/L; 0,3 % > 20 µg/L) [Smidt et al. 2011]. The studies of Smidtet al. [Smidt et al. 2011] revealed in addition that 2 million inhabit-ants in Germany (equalling 2.5 % of the to-tal population) have access to drinking wa-ter with >10 µg/L U and 15.1 million peo-ple use water which U concentration ex-ceeds the limit value of 2 µg/L for infants.

A possible measure to promote the ex-traction of U from P fertilisers could be a CO2 tax or a bonus for farmers. The follow-ing basic calculation provides an estimate on the saving potential in Germany using the key that is used to tax cars according to their CO2 emissions:

The codes of good agricultural practice (GAP) recommend to apply 22 kg P fertilis-er per ha farmland. This results in an an-nual freight of 10 g/ha U on German fields. However, 10 g/U could be used alterna-tively to generate 500 kW electricity, thus saving 500 kg CO2 if compared to generat-ing the same amount of electricity with coal. Emission car tax bands charges 2 € per g CO2 above a base rate of 100 g/km CO2. This means that a medium class car,

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752 atw 57. Jg. (2012) Heft 12 | Dezember

Uranium in the Environment

exhausting 250 g/km CO2 with an annual mileage of 15,000 km will be taxed with 300 € per year. Hence, 0.08 € per kg CO2 are charged. Accordingly the extraction of U from rock phosphates yields a CO2 tax/bonus of 40 €/ha. This means that the fic-tive CO2 bonus and commodity price are higher than the value of fertiliser P if a spot price of 1.07 € for 10 g U (as U3O8) is as-sumed as it was on an average in 2011 (NO 2012) and costs for 22 kg P of 32 € (includ-ing tax) as published on 28.01.2010 [Anon-ymous 2010].

Conclusion

The extraction of U from rock phosphates is a technically possible, yet currently eco-nomically unprofitable and therefore in Germany neglected procedure that com-bines the allocation of U for nuclear power with an efficient measure of environmen-tal protection in 2 ways. Firstly, it pre-serves the quality of drinking water that is in danger due to high U-loads in P fertiliz-ers which accumulate in soils and dis-charge into water bodies [Smidt et al. 2011]. Secondly, the recovered U can con-tribute to a significant reduction of CO2

emissions when used to generate electrici-ty. A CO2 tax/bonus according to German car tax bands seems to be an appropriate approach to promote U-free mineral ferti-liser products. Last but not least the use of U from worldwide P-resources opens huge stocks of U for future power generation while fostering cleaner fertilizers, cleaner soils, cleaner waters and cleaner atmos-phere.

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