Synthesis and characterisation of mesoporous silica phases containing heteroatoms, and their cation exchange properties. Part 5: Cation exchange isotherms, and the measurement of radioisotope distribution coefficients, for an MCM-22 phase containing aluminium

Cation exchange isotherms were constructed for the replacement of Na cations by Li, K, Rb, Cs, NH4, Mg, Ca, Sr, Ba, and Al from a well characterised MCM-22 phase which contained aluminium as a heteroatom. Thermodynamic assessment of the isotherms enabled the construction of a selectivity series. Comparisons, including standard free energy values, have been drawn to similar results measured for other MCM-41 phases and some high-silica zeolites. This work additionally describes studies on the MCM-22 phase to examine its potential ability to scavenge radioisotopes from various solutions as simulants of those found in nuclear waste. The isotopes studied were 241-Am, relevant to spent nuclear fuel, and 137-Cs, 57-Co, 51-Cr, 59-Fe, 54-Mn, 89-Sr, 65-Zn present in nuclear wastes as fission products, from neutron activation in nuclear installations, and arising from medical uses. Measurement of distribution coefficients enabled the construction of selectivity series which demonstrated the versatility of the phases to scavenge specific isotopes. (C) 2010 Elsevier Inc. All rights reserved.