Effect of the synthesis method on the properties of a Pb-bearing (Y–Gd–Ce) rare-earth phosphate used for the confinement of high-level radioactive waste

详细信息    查看全文

• 作者：Nour-el-hayet Kamel ; Khadoudja Remil ; Malika Arabi ; Ziane Kamel ; Ahmed Zahri ; Samia Metahri
• 刊名：Journal of Nuclear Materials
• 出版年：2010
• 出版时间：June 2010
• 年：2010
• 卷：401
• 期：1-3
• 页码：104-112
• 全文大小：526 K

文摘

In this study, a Pb-containing (Y–Gd–Ce) rare-earth phosphate with the general chemical formula of (Y_0.1Pb_0.1Ce_0.4Gd_0.4)PO₄ was synthesized by two methods, namely the sol–gel and the metallurgical method. The sol–gel route consists of an external gel precipitation method, followed by two calcinations at 873 and 1473 K; and the dry route was a natural sintering at 1473 K of a mixture of micropowders activated at 873 K. The sol–gel route of synthesis gives a stronger and harder monazite mineral than the one obtained by the dry route of synthesis, both of them have a very low porosity. The sintering densities are 4.70 and 4.55 g/cm³ for both the sol–gel and dry-route made monazites. The X-ray diffraction (XRD) analysis shows a main monoclinic crystalline structure for the two ways of synthesis. However, a secondary anorthic phosphate phase appears for the dry-route made monazite. Three leaching tests simulating several radiological events were performed: an acidic static test at different pH, a static water leach test in an argilous media and a dynamic microwave leach test.

For the whole of leaching processes, the kinetic of dissolution is fast. The acidic tests at pH 1, 4 and 7 gave few amounts of dissolved Ce in the leachates, about 5.668, 0.189 and 0.346 × 10⁻² g/m² day at the steady-state, respectively. The Pb was totally dissolved at pH 1 and 3. The sol–gel made monazite has a weak chemical durability in acidic media. In neutral pH, both the sol–gel and the dry-route made monazites give comparable values of Ce normalized dissolution rates (0.346 × 10⁻² and 0.389 × 10⁻² g/m² day, respectively). The leaching in kaolin media decreases with a ten factor the amounts of leached Ce. However, for the whole of the leaching tests performed in neutral pH conditions, the monazite materials have a good chemical durability. The dissolution of the minerals under the microwave leaching is partially achieved, with only 3.5 % and 4.0 % of solubilised minerals, for both the sol–gel and dry-route made monazites, respectively, showing the good chemical durability of the studied monazite mineral.