Inhibition of Spent Ion Exchangers in Geopolymer Matrix Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech republic Dept. Of Chemistry of Geopolymers Laboratory of raw material treatment Hanzlicek T., Steinerova M., Perná I., Straka P. Report on Project No. FI –IM/128 reported 10/2005

Definition of problems Spent ion exchangers are gathered in area of nuclear power station in storage tanks with limited capacity. Spent ion exchangers are stored under the water level. Spent ion exchangers change their volume when dried and expand volume when watered. Storage of spent ion exchanger after their solidification and inhibition should be economically reasonable which means that one important condition is to fix maximum quantity of spent ion exchanger to any solidification matter.

Previous proves and tests The most important is to recognize the behavior of geopolymer matrix and its possibility to bind different type of metals in their soluble forms, which was studied and after it published in Journal of American Ceramic Society, titled „Immobilization of Toxic Metals in Solidified Systems of Siloxo-Sial Networks“ 2005, The main aim of the above mentioned paper was to identify that the metals are chemically bound to the geopolymer network and even when the samples were fine crushed the metals were not detected in leaching water.

Following control tests The geopolymer matrix acquired by alkali aqueous reaction with activated clay was tested when usual sodium or potassium in soluble form was substituted by cesium carbonate. Was found that solidificated matter could be reached and as well as in case of sodium or potassium, the cesium is able to form insoluble geopolymer matrix. That means that cesium is chemically bind to the siloxo-sial network and equilibrate the electro-negativity of such a formed network by oxygen bridges. Next study employed radioactive tracers 152 Eu, 134 Cs, 60 Co and 59 Fe in soluble form applied directly to the formatted geopolymer precursor., Leaching tests prove that 99,9 % of radioactive tracers are incorporated into the geopolymer network in case of water leaching and in case of sulphuric acid leaching the inhibition of radioactive tracers is about 40 %.

Complementary proves Solidification of geopolymer matrix was proved also by use of D 2 O instead of water, when alkali aqueous solution was alternated by alkali solution of D 2 O. Sample of a solidificated matter is insoluble in water with very hard surface and as in cases with water any separated liquid or partially decomposition of a solid was observed. Means that eventual problem with presence of deuterium will not bother the solidification of geopolymer matrix.

The assays with spent ion exchangers Spent ion exchangers with 50 % of water were applied directly to the geopolymer mixture in quantities starting at 10 wt.% and ended by 50 wt.%. In all cases the solidification is successful but immediately when submerged in water the samples are disintegrated into the small particles of matrix with visible ball shaped ion exchangers. Only in case of 10 wt % of applied ion exchanger the sample resists to submerge. Problem is a homogenous distribution of relatively light watered spherical shaped ion exchangers in geopolymer mixture and when dried the shrinkage of the ion exchanger balls. In all experiments we have to mentioned the open porosity of geopolymer matrix and than possibility of liquid to penetrate the solidificated body.

Picture of the sample cross cut

Observation The sample with 20 wt. % of spent ion exchangers present the above mentioned problems with no homogenous distribution of originally spherical shaped ion exchangers and visible pores around the shrinked balls. Also the compression resistance is lower ( 3,75 MPa) than allows acquired norm. The open porosity of matrix and possibility of ion exchanger volume extension are the reasons of the sample disintegration.

Propounded solution The main problem of shrinkage and extensions of a spherical shaped exchangers could be resolved by their friction. The volume change is unalterable even of the non-formatted particles of the ion exchangers, the small no defined shape could be less dangerous than originally spherical shape. Also the homogenization of no defined particles in geopolymer matrix could be reached more effectively. The prepared series containing 14,8 wt.% than 17,2 wt.% and 22,7 wt. % of dry spent ion exchanger in dry geopolymer matrix resist the water submersion – no crack or fissures were observed. Next series of samples were prepared with foamed geopolymer matrix with idea to allow the extension of spent ion exchangers into the free space in foamed matrix. In that case there is no disintegration of submerged samples but its necessary mentioned the growth of volume of the final material in order of percent.

Conclusion Next study should be orientated to the inhibition and encapsulation of radioactive tracers added to the smashed ion exchangers and according to the previous tests and assays we suppose the binding of radioactive metals into the geopolymer network. If there is a proof of inhibition than regardless to the compressive strength the geopolymer matrix could be used. Because the geopolymer matrix is prepared from waste industrially extracted clays and its activation and mixing is lowering considerably the price comparing it with cement we could recommend this method of solidification even up now the amount of radioactive waste in total will be 5 times bigger than amount of dry ion exchangers itself.