B. G. Shabalin1, K. K. Yaroshenko1, I. L. Koliabina1,2
1SI «Institute of Environmental Geochemistry of NAS of Ukraine»,
34a, Palladin ave., Kyiv, 03142, Ukraine
2Institute of Geological Sciences of NAS of Ukraine,
55b, O. Honchara st., Kyiv, 01054, Ukraine
Selection and implementation of an efficient and environmentally friendly technology for decontamination of liquid radioactive waste (LRW) from Ukrainian nuclear power plants is of vital importance, since the current LRW treatment scheme has a number of significant disadvantages. One of such technologies is the sorption-sedimentary technology using natural or modified mineral sorbents, in particular zeolites, which have molecular sieve, sorption and selective properties towards radiocesium. The results of the study of natural, acid- and alkaline-modified zeolites of Sokyrnyts’ke deposit, their sorption / desorption of 90Sr and 137Cs radionuclides from model liquid radioactive waste solutions are presented in the article. The main mineral in zeolite is clinoptilolite ( ~70 ± 3 wt. %). It also contains traces of quartz and mica of ~12 and <3 %, respectively. The redistribution of exchange cations is shown to take place in the process of zeolite modification and the content of cations in the clinoptilolite lattice changes. Natural zeolite belongs to potassium-calcium-sodium clinoptilolites, sodium-modified zeolite – to sodium-potassium-calcium ones, and acid-modified zeolite – to potassium-sodium-calcium clinoptilolites. The Si/Al ratio increases in the series: natural zeolite -> sodium-modified zeolite -> acid-modified zeolite. It is found that modification of sodium clinoptilolite not only improves the thermal stability but also increases the adsorption of 90Sr and 137Cs radionuclides from model liquid radioactive waste solutions. The ion exchange isotherms show that the selectivity of sodium clinoptilolite towards these radionuclides is higher than the selectivity of natural clinoptilolite and acid modified clinoptilolite. The maximum sorption capacity of 90Sr by natural zeolite during the experiment (14 days) was 55 %, 137Cs – 90 %. The sorption capacity of 90Sr by alka-line-modified zeolite was 62.2 % and of 137Cs – 98.78 %. That by acid-modified zeolite was 18 % for 90Sr and 85 % for 137Cs. The analysis of the obtained results gives grounds to recommend zeolite from Sokyrnyts’ke deposit and its sodium forms as effective sorbents of radionuclides from liquid radioactive waste when introducing the sorption-sedimentary technology of decontamination.
Keywords: liquid radioactive waste, sorption, cesium, strontium, clinoptilolite, zeolite.
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