J. Phys. IVFrance 104 (2003) 447 @ EDP Sciences, Les Ulis DOI : 10. 1051/jp4 : 20030120 Effect of leaching on the crystallographic sites of trace metals associated with natural céments (site of Maqarin, Jordan) : Case of Cr J. Rosé, N. Crouzet, L. Trotignon', S. Grimât, J. Susini2, H. Khoury3, E. Salameh3, A. Milodowski4 and F. Mercier5 CEREGE, Europole Méditerranéen de l'Arbois, BP. 80, 13545 Aix-en-Provence cedex 04, France DED/SMM, bah'menf 307, CE-Cadarache, 13108 Saint-Paul-lez-Durance, France 2 ESRF, BP. 220, 38043 Grenob/e cedex, France 3 Department of Geo/ogy and Mineralogy, University of Jordan, Amman, Jordan " Geochemistry, Mineralogy and Hydrogeo/ogy, British Geological Survey, K/ngs/ey Dunham Center, Keyworth, Moff/ngnam, U.K. 5 Université d'Er/, Evry, France Abstract. This paper reports an investigation of theoxidation state of Cr in samples of natural céments formed500 ky ago in Maqarin (Jordan). The analyses were conducted using the Scanning Microscopefrom the ID21 beamline at the ESRF (Grenoble-France) operated in fluorescence mode. Cr (IH) and Cr (VI) maps are collected on thèse samples at a resolution of t m. The results suggest the slow oxidation of Cr (tII) to Cr (V !) upon altération of the céments in conditions of high pH and low to intermediate oxygen fugacity. 1. ïntrodmctien Cementitious phases formed in industrial kilns, exhibit a high affinity for heavy metals (HM). This property has encouraged the industry to use hazardous waste as fuel for the cément kilns to trap HM [1. Also, the évaluation of long term retention properties of céments used in geological waste disposais, as near field barriers or as waste packages, focuses attention of the migration behaviour of HM in cementitious environments. To assess the environmental risks linked to the use of thèse céments, it is essential to study the effect of water on the physico-chemical stability of HM. Leaching tests are generally used to predict the long term behavior of HM. But thèse experiments are time limited. An other neat alternative is the study of natural analogue Systems. In that context the Maqarin site (Jordan) represents an interesting analogue for leached céments over geological timescales. The céments were formed after spontaneous metamorphic combustion of maris and limestones 105-106 years ago [2-4]. The minerais from thèse céments are similar to those present in industrial portland céments. Two types of natural cément samples were studied [2-3]. The first one is considered as an unaltered product having undergone a limited interaction with waters and the second cément is considered as' leached'material having been in contact with percolating waters. The case of Cr is of particular interest since this element reaches in Maqarin céments 400 ppm in concentration and is present in 2 oxidation states : Cr (III) and Cr (VI) which is known to be more toxic and mobile. The aim of this study is 1) to determine the initial Cr speciation in the bituminous limestone 2) to determine the leaching mechanisms of Cr after the interaction of the cément with water by determining the speciation of Cr in the fresh and leached céments from Maqarin site. We have used X-ray spectro- microscopy on the ID21 beam line at the ESRF, to assessthe spatial variability of Cr speciation as a function of the altération level.