Trivalent europium in phosphoric media

To find which complexes of Europium (III) form in concentrated phosphoric acid we studied by gamma radiometric analysis the partition of 152-Eu. The two-phase system was HDEHP-C6H6/H3PO4-(LiClO4,2H2O) with μ=0.22. The range of variation in pH and total H3PO4 concentration were 0.7<pH<4 and CH3PO4<4.2M respectively, these variations cover those of pH and free H3PO4 concentration found in pure H3PO4 up to 4.2 M. In aqueous phases we have found numerous complexes of europium (III) and measured their stability constant relative to europium (III) and H3PO4. In pure H3PO4, which is the concentration of the solution resulting from the treatment of phosphate ores to obtain phosphoric acid, europium (III) is engaged in two cationic complexes which can be written as (EuH2PO4)2+ 45% and (EuH5P2O8)2+ or (H2PO4)(H3PO4)2+ 53%. 29 refs.; 16 figs.; 6 tabs. (author)