Abstract

Zircon (ZrSiO 4) exhibits a strong structural affinity for uranium and thorium together with a very high chemical durability. This makes it a potential crystalline host matrix to immobilize actinides issued from separation of nuclear wastes. Irradiation induces amorphization of the crystalline structure (the metamictization process) and thus may decrease the chemical durability of the material. Leaching tests have been conducted on natural zircons from Brazil and Madagascar at 96°C for a period of 1 month, using deionized water. Leachates have been analysed by inductively coupled plasma mass spectrometry (ICP-MS) and UV-visible spectrophotometry. Zircon solid surfaces have been investigated by coupling scanning electron microscopy and X-ray microanalysis (SEM–EDX) with nuclear microprobe analysis ( μPIXE, μRBS and μERDA). From the mass balance between leachates and hydrated surfaces, the probable mechanisms of zircon aqueous alteration are presented and discussed.

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