Solvent extraction of strontium(II) as ion-pairs with tetraphenylborate anion

Solvent extraction of strontium(II) and sodium(I) as ion-pairs with tetraphenylborate ion(TBP-) into nitrobenzene or hexane containing trioctylphosphine oxide (TOPO) has been determined under various conditions. The extraction of strontium(II) from water into nitrobenzene is rather independent of the extractant concentration but that into TOPO-hexane is second order dependent on the extractant, while the extraction of this metal ion from 0.1 mol dm-3 sodium perchlorate solution into nitrobenzene is second order dependent on the extractant concentration. The extraction of strontium(II) at a certain extractant concentration into nitrobenzene is greatly impaired by an addition of sodium perchlorate, while that into TOPO-hexane is not very much affected by the added salt. The extraction of sodium(I) with TPB- into TOPOP-hexane is complicated. On the basis of these results, separation of strontium(II) from cesium(I) or potassium(I) by extraction as ion-pairs with TPB- into nitrobenzene was considered. It was concluded that the separation is not possible in the absence of co-existing sodium salt in the aqueous phase; an effective masking agent for strontium(II) is necessary under such conditions. On the other hand, the separation is good in the presence of a sodium salt in the aqueous phase and the separation improves as the extractant concentration decreases. (author)