Аннотация:MINERAL SOLID SOLUTIONS AS MATERIALS FOR FIXATION OF RADIONUCLIDES
KOTELNIKOV A.R., AKHMEDZHANOVA G.M., SUK N.I., KOLPAKOVA T.G.
Institute of Experimental Mineralogy RAS, Chernogolovka, Moscow district, Russia
For immobilization of radwaste elements in the Earth crust for the first time we enunciate the principle of phase and chemical accordance in the system matrix – enclosing rock. This principle allows producing motivated synthesis of specific mineral matrixes. Mineral matrixes for immobilization of alkaline, alkaline-earth and rare earth elements – radionuclides were experimental synthesized. Besides that the methods of fixation and separation of noble metals (radwaste components) and halogenides (Br and I) were developed and tested. The problem of processing of glass matrixes (borosilicate and aluminophosphate glasses) to the stable crystalline mineral materials is considered. Existent methods of radwaste immobilization into glasses are not in accord with specification of defensive keeping of matrix materials because glasses are metastable phases.
In this paper two main problems of radwaste immobilization are considered: (1) synthesis of mineral matrix materials for radwaste fixation (based on the solid solutions of rock-forming and accessories minerals); (2) remaking of glass matrixes into stable mineral matrixes.
Determination of first problem provides for formation of matrix materials stable in conditions of long-time keeping in rocks of Earth crust. Total scheme of process can be presented by following way: water solution of radwaste elements → separation into element group → sorption from water solutions, precipitation and substitution reactions → phase transformation → mineral matrix for location in the rocks of Earth crust. Follow phase transformation transverses these materials into high stable mineral matrix materials geochemically compliant with rocks of assumed fields of location and dumping of matrixes with radionuclides.
Problems of glass matrixes (borosilicate and aluminophosphate glasses) remaking into stable crystalline mineral materials are considered.
In the run of experiments liquid immiscibility between borosilicate and phosphate (or aluminofluoride) melts and between silicate and aluminophosphate melts appeared. Herewith partition of elements between phases took place. Among elements – radwaste imitators Sr, La and Ce enrich phosphate (or aluminofluoride) phase and Cs concentrates in borosilicate glass. In water-bearing borosilicate-phosphate system and in the system aluminophosphate glass – SiO2 REE concentrate in monazite phase which is high stable in natural processes.
A different methods of fixation radwaste elements from glasses to solid solutions of minerals have been experimentally developed and presented (liquation method and salting out method).
