COPRECIPITATION OF 15-CROWN-5 ETHER COMPLEXES OF LEAD AND STRONTIUM WITH TUNGSTOSILICIC ACID

Lead as well as strontium form low solubility compounds of composition (ML2)(2)A . nH(2)0, (M = Pb2+, Sr2+), in the presence of 15-crown-5 ( L) and tungstosilicic acid (H(4)A) in acid media as found by radiometr ic precipitation titration. ''Sandwich'' structure of crown-ether comp lexes of lead and strontium could be expected due to the small size of cavity of 15-crown-5. Coprecipitation of PbL22+ with crown complexes of strontium cation after adding tungstosilicic acid was studied in 0. 01 mol.dm(-3) HNO3. A significant influence of H+ cation in 1 mol.dm(- 3) HNO3 on coprecipitation of lead was observed. Formation of HL+ comp lexes by protonisation of 15-crown-5 competes to the formation of ML22 + complexes (approximately twenty percent of 15-crown-5 are used for c reation of HL+ complexes). Formation of low solubility salts was utili sed for separation of lead from strontium in 0.01 mol.dm(-3) HNO3. The ratio of constant stability of lead and strontium beta' with 15-crown -5 in 0.01 mol.dm(-3) HNO3 was calculated. The separation factor S(Pb/ Sr) depends on the ratio of stability constants beta(PbL2)/beta(SrL2) The precipitation method can be used for separation of metals with hig h constant stability with crown ethers from solutions containing other metals in the case of gradual addition of crown.