Development of a novel sorption-membrane process for removal of radioactive anions from liquid radioactive waste

The aim of the current research was development of a novel method for removal of radioactive anions from liquid radioactive waste. The approach that has been applied in this research was based on the fact that polynuclear hydroxo complexes of tri- and tetravalent metals are able to interact with some anions forming non ionic species. As a result, the anions can be easily separated from solution together with polynuclear species. The interaction of some anions and cations with the polynuclear hydroxo complexes of chromium(III), iron(III) and thorium(IV) was investigated applying a complex of physicochemical methods: dialysis, centrifugation, pH-metric titration, method of radioactive indicators, spectrophotometry. The results obtained allow one to make a conclusion that the anions investigated can be placed in the row by degree of their influence on the formation of polynuclear hydroxo complexes of the above metal ions according to stability of their complexes with the above cations. Thus, the anions forming weak complexes, like iodide do not show any visible effect on hydrolytic polymerization in solution. The anions with medium complexing ability do not decrease the total content of polynuclear hydroxo forms in solution and, at the same time, they are 'sorbed' on the polynuclear hydroxo complexes (iodate and phosphate). The anions with high complexing ability are able to totally cease the reaction of cationic polymerization in solution. If a foreign cation occurs in solution together with polymerising cation it can either hinder the polymerisation process, when it is in a form of hydrated cation, or be attached to the polynuclear species when it is in a form of mononuclear hydroxo complex. The fact that some anions can interact with the polynuclear hydroxo complex forming non ionic species suggests a possible way for their removal from solution using a membrane separation method. (author)