Abstract
Coal fly ash hollow aluminosilicate microspheres (cenospheres) of stabilized composition (glass phase-95.4; (SiO(2)/Al(2)O(3))(glass)-3.1; (Si/Al)(at.) = 2.6) were used to fabricate lutetium-176 encapsulated aluminosilicate microspheres as precursors of radiolabeled microspheres applied for selective irradiation of tumors. To incorporate Lu(3+) ions into cenosphere's aluminosilicate material, the following strategy was realized: (i) chemical modification of cenosphere globules by conversion of aluminosilicate glass into zeolites preserving a spherical form of cenospheres; (ii) loading of zeolitized microspheres with Lu(3+) by means of ion exchange 3Na(+) ↔ Lu(3+); (iii) Lu(3+) encapsulation in an aluminosilicate matrix by solid-phase transformation of the Lu(3+) loaded microspheres under thermal treatment at 1273-1473 K. Two types of zeolitized products, such as NaX (FAU) and NaP1 (GIS) bearing microspheres having the specific surface area of 204 and 33 m(2)/g, accordingly, were prepared and their Lu(3+) sorption abilities were studied. As revealed, the Lu(3+) sorption capacities of the zeolitized products are about 130 and 70 mg/g Lu(3+) for NaX and NaP1 microspheres, respectively. It was found that the long-time heating of the Lu(3+)-loaded zeolite precursors at 1273 K in a fixed bed resulted in the crystallization of monoclinic Lu(2)Si(2)O(7) in both zeolite systems, which is a major component of crystalline constituents of the calcined microspheres. The fast heating-cooling cycle at 1473 K in a moving bed resulted in the amorphization of zeolite components in both precursors and softening glass crystalline matter of the NaX-bearing precursor with preserving its spherical form and partial elimination of surface open pores. The NaX-bearing microspheres, compared to NaP1-based precursor, are characterized by uneven Lu distribution over the zeolite-derived layer. The precursor based on gismondin-type zeolite provides a near-uniform Lu distribution and acceptable Lu content (up to 15 mol.% Lu(2)O(3)) in the solid phase.