The extraction behavior of some dicarbollylcobaltate crown extraction systems

The extraction of cesium, strontium and barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of various crown ethers has been investigated and the influence of the substituent of crown to the extraction possibility has been observed. It has been found, that the addition of DB15C5, DB18C6 and DB21C7 (but not DB24C8 and DCH24C8) increases the distribution ratio of Cs by one order of magnitude. The five-membered crowns are usually more efficient extractants for strontium than DCH18C6, which is widely used for strontium separation. The distribution ratio of strontium DSr decreases in the order 15-crown-5 > benzo-15-crown-5 > 2-hydroxymethyl-15-crown-5 > cyclohexyl-15-crown-5 > dibenzo-15-crown-5 > nitrobenzo-15-crown-5. The selectivity α(Sr/Ca) decreases in the order 15C5 > B15C5 > DB15C5 > 2HM15C5 > CH15C5. A selectivity factor α(Sr/Ca) ≥ 1000 can be reached in the presence of 15C5 and B15C5. Six-membered and four-membered crowns extract strontium worse than most of the five-membered crowns. The selectivity factors α(Sr/Ca) ∼ 100 have been reached for six-membered crowns and α(Sr/Ca) < 1 has been found for 12C4. The extraction of barium by a nitrobenzene solution of dicarbollylcobaltate in the presence of 15C5 is even more efficient as the extraction of strontium. In that system DSr > 104 and DBa > 104 have been found for the extraction of Sr and Ba by a 0.01M nitrobenzene solution of dicarbollylcobaltate (cB=0.01 mol/l) from 0.1M HNO3. Maximal values of separation factor α(Ba/Sr) have been found in the system containing DB21C7. (author)