Obviously, the value of extraction constant is influenced by extraction mechanism, implicitly by the solvent polarity and extractant type. For extraction with TOA, the highest values of extraction constant were obtained when aminic adducts had formed, at lower polarity of organic phase. Contrarily, for extraction with D2EHPA, when the extraction mechanism is the same for all solvents, the increase in organic phase polarity influenced positively the value of extraction constant.