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Clays and Clay Minerals; October 2004; v. 52; no. 5; p. 650-656; DOI: 10.1346/CCMN.2004.0520511
© 2004 Clay Minerals Society
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EFFECTS OF {gamma} RADIATION ON CHROMATE IMMOBILIZATION BY CALCINED HYDROTALCITES

Sonia Martinez-Gallegos1,2 and Silvia Bulbulian1,*

1 Instituto Nacional de Investigaciones Nucleares, A.P.18-1027, Col. Escandón, Delegación Miguel Hidalgo, C.P. 11801, México D.F.
2 Facultad de Ciencias, Universidad Autónoma del Estado de México, Instituto Literario no. 100 Col. Centro, Toluca, Edo. de México, C.P. 50000

* E-mail address of corresponding author: sb{at}nuclear.inin.mx

The ability of hydrotalcites to retain anionic wastes was studied. In particular, Cr(VI)-adsorbed hydrotalcites were heated to immobilize Cr(VI) in the solid sample. When the heating temperature increased up to 500°C, the lamellar structure of hydrotalcite was lost. At high temperatures (1200°C), the solids were recrystallized in the form of a spinel. Lixiviation with 1 N and 5 N NaCl solutions were utilized to simulate the effect of sea water and of concentrated NaCl solutions in salt mines on the immobilization of Cr. Radiation damage on the solid containing the immobilized Cr was studied by {gamma}-irradiating with a 60Co source at 1000 and 6000 kGy. The Cr-containing samples heated at 1200°C, whether irradiated or not, safely immobilized Cr in the hydrotalcite mainly in the form of MgCr2O4 spinel. Irradiation of hydrotalcites revealed two different effects: (1) samples heated up to 1200°C evolved as a solid in which chromium was retained more firmly than in the non-irradiated material, irradiation enhancing the spinel formation; (2) the structure of samples heated at 1200°C developed a preferential crystallite orientation rather than a purely random one or new location of chromium ions, this effect did not affect Cr immobilization in the solid. Chromium lixiviation with 5 N NaCl solution was always less than the corresponding value with 1 N NaCl solution, probably due to the poor mobility of Cl–ions in the highly concentrated NaCl solution.

Key Words: Chromium Immobilization • Gamma Irradiation Effects • Hydrotalcite • Mg-Cr Spinel






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