THE SOLUBILITIES OF THE ALKALI-METAL SALTS AND THE PRECIPITATION OF CS-SOLUTION( FROM AQUEOUS)

Radioactive Cs-137 may be removed from nuclear waste aqueous solutions by precipitations. Alkali metal salt solubility trends show that the Cs+ salts have the largest range of solubilities for all of the alkali metal salts and that Cs+ should be the most likely ion of the group t o form a precipitate in solution. The tetraphenylborate anion (B(C5H5) 4-, TPB) precipitates Cs+ as the insoluble CsTPB. However, there are a number of problems associated with this compound and another precipit ating agent is needed. A potential substitute is the cobalt dicarbolli de anion (Co(B9C2H11)2-, CDC) which forms a slightly more soluble comp ound, CsCDC. The anion:cation volume ratios for several simple alkali metal salts, when compared with their solubility values, indicate that forces within the solid crystal control solubility. Similar compariso ns for the TPB and CDC anions indicate that the solubilities are contr olled by the hydrophobic nature of the anion. Some requirements are pr oposed for an anion to form a precipitate with Cs+.