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2072 Goldschmidt Conference Abstracts

Monitoring nutrients cycles at Uranyl coordination chemistry on catchment scale and brucite surfaces: T.P. VAN TOL1 AND B. VAN DER GRIFT2* Polarisation dependent EXAFS 1Alterra, Wageningen University and Research Centre, P.O. A. VAN VEELEN1*, G.T.W. LAW1, A.J. SMITH1, Box 47, NL-6700 AA Wageningen, The Netherlands J.R. BARGAR2, J. ROGERS2 AND R.A. WOGELIUS1

([email protected]) 1 University of Manchester, School of Earth, Atmospheric and 2Deltares, P.O. Box 85467, NL-3508 TA Utrecht, The Environmental Sciences, Oxford Road, Manchester, M13 Netherlands 9PL, United Kingdom (*correspondence: (*correspondence: [email protected]) [email protected])

2Stanford Synchrotron Radiation Laboratory, PO Box 4349, In The Netherlands, the high concentration of nitrogen and Stanford, CA 94309, USA phosphorus has an adverse affect on the quality of our surface water. The abundant growth of algae, water plants and reed is Previous studies have examined uranium uptake by a recurring problem in Summer. Furthermore, the discharge of calcium carbonate ( and ) under nutrient-rich water into the sea is a real threat to the marine conditions pertinent to both natural and anthropogenically ecosystem. Unfortunately, the origin and fate of all these perturbed systems. However, research on uranyl uptake by nutrients often remains unclear. -rich minerals such as magnesite [MgCO ], brucite The total nutrient concentration in surface water is 3 [Mg(OH) ], nesquehonite [MgCO ·3H O] and determined by a range of sources, transport routes and 2 3 2 [Mg (CO ) (OH) ·4H O] has not, to the best of our chemical or biological processes. Nutrient cycles at a 5 3 4 2 2 knowledge, been previously conducted. Such experiments will watershed scale are therefore very complex. To come up with improve our understanding of the mobility of uranium and solutions to improve the water quality it is very important to other actinides in natural lithologies such as dolomitic gain insight into the origin of the sources, their transportation or mafic igneous emplacements, as well as provide time and what happens en route. In four typical watersheds in key information applicable to nuclear waste repository the Nederland’s we studied the biogeochemical cycling of strategies involving Mg-rich phases. Thus, experiments with nitrogen en phosphorus at regional scale. The main goal of the minerals powders were used to determine the partition project is to understand the relationship between long term 2+ coefficients and coordination of UO during adsorption and changes in nutrient surplus and the quality of the surface 2 coprecipitation with magnesite, brucite nesquehonite and water. The four watersheds are: a sandy with high loads of hydromagnesite. A second set of experiments used single nutrients due to intensive cattle breeding, a more natural sandy crystal magnesite (10.4) surfaces and MgO(111) area, a clay polder and a polder with peat soil. Each area has it surfaces engineered and hydroxylated to be equivalent to the own characteristics regarding the sources and transport route Mg(OH)2(00.1). Here EXAFS measurements were made at $ for nutrients. For this study we analysed soil, groundwater, o o = 0 and $ = 90 in order to use the polarisation of the incident sediment and surface water quality on several locations. The beam to unequivocally determine adsorbate and coprecipitate surface water quality and quantities were monitored structures. The selected minerals were reacted with uranyl continuously in the period 2004-2010. Combined with data chloride at three different concentrations (500, 50 and 5 ppm) collected on nutrient loads this resulted in an extensive dataset above and below solubility boundaries of schoepite to study biogeochemical cycling of nitrogen and phosphorus -3.5 (UO (OH) ·H O) at pH 8 and PCO2 = 10 atm. K values for in the soil-groundwater-surface water system at regional scale. 2 2 2 d Mg carbonate phases were comparable to or exceeded those A combined soil-groundwater-surface water model is used to published for calcium carbonates. EXAFS results showed predict the effectiveness of different source or transport route clear polarisation dependence of surface uranyl. The spectra oriented measures to improve the quality of the surface water. demonstrated consistently that the uranyl molecule is One of the major findings is the importance of sediments preferentially oriented with the axial oxygens perpendicular to in the binding and relase of phosphorus when transported form the surface. This implies the creation of local groudnwater to surface water and the rol of sulfate in this rutherfordine-like regions which may polymerise at high proces. uranyl activities into a thin film.

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