Cenosphere-Based Zeolite Precursors of Lutetium Encapsulated Aluminosilicate Microspheres for Application in Brachytherapy.

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.