COMPLEXATION OF EUROPIUM(III) BY AQUEOUS ORTHOSILICIC ACID

The interaction of europium(III) with orthosilicic acid, Si(OH)(4), wa s studied in aqueous solutions of 0.1 M ionic strength. Radiotracer-so lvent extraction of Eu-152, 154 and time-resolved laser-induced fluore scence spectroscopy of Eu(III) were used to measure the stability cons tants for the reactions Eu3+ + n OSi(OH)(3)(-) reversible arrow Eu(OSi (OH)(3))(n)((3-n)+) at pcH 4, 6, and 8.8, where n is 1 or 2. Measurabl e amounts of the 1:1 complex begin to form as low as pcH 3 in solution s containing millimolar orthosilicate concentrations and the europium bisorthosilicate complexes are present in such solutions when pcH grea ter than or equal to 8. The measured values of the stability constants under these conditions an log beta(1) = 7.26+/-0.20 and log beta(2) = 11.7 +/- 0.4.