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)₂A·nH₂O, (M=Pb²⁺, Sr²⁺), in the presence of 15-crown-5 (L) and tungstosilicic acid (H₄A) in acid media as found by radiometric precipitation titration. “Sandwich” structure of crown-ether complexes of lead and strontium could be expected due to the small size of cavity of 15-crown-5. Coprecipitation of PbL_2/su2+ 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⁺ complexes by protonisation of 15-crown-5 competes to the formation of ML₂ ²⁺ complexes (approximately twenty percent of 15-crown-5 are used for creation of HL⁺ complexes). Formation of low solubility salts was utilised for separation of lead from strontium in 0.01 mol·dm⁻³ HNO₃. The ratio of constant stability of lead and strontium β‘ 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 β_PbL2/β_SrL2 The precipitation method can be used for separation of metals with high constant stability with crown ethers from solutions containing other metals in the case of gradual addition of crown.