Higher oxidation states of americium have long been known; however, options for their preparation in acidic solution are limited. The conventional choice, silver-catalyzed peroxydisulfate, is not useful at nitric acid concentrations above about 0.3 M. We investigated the use of sodium bismuthate as an oxidant for Am (3+) in acidic solution. Room-temperature oxidation produced AmO 2 (2+) quantitatively, whereas oxidation at 80 degrees C produced AmO 2 (+) quantitatively. The efficacy of the method for the production of oxidized americium was verified by fluoride precipitation and by spectroscopic absorbance measurements. We performed absorbance measurements using a conventional 1 cm cell for high americium concentrations and a 100 cm liquid waveguide capillary cell for low americium concentrations. Extinction coefficients for the absorbance of Am (3+) at 503 nm, AmO 2 (+) at 514 nm, and AmO 2 (2+) at 666 nm in 0.1 M nitric acid are reported. We also performed solvent extraction experiments with the hexavalent americium using the common actinide extraction ligand tributyl phosphate (TBP) for comparison to the other hexavalent actinides. Contact with 30% tributyl phosphate in dodecane reduced americium; it was nevertheless extracted using short contact times. The TBP extraction of AmO 2 (2+) over a range of nitric acid concentrations is shown for the first time and was found to be analogous to that of uranyl, neptunyl, and plutonyl ions.

We have studied the oxidation of sulfur dioxide by dissolved oxygen in highly dilute solutions with a new differential optical absorption technique. We measured the rate of oxidation catalyzed by iron(III) over a wide range of pH, ionic strength, and in the presence of various organic materials. The studies indicate that noncomplexing organic molecules are highly inhibiting at “high” pH values of 5 and above and are not inhibiting at “low” pH values of 3 and below. Furthermore, the order of the reaction with respect to iron is different in the two pH regimes. This suggests that the mechanism of this reaction differs in the two pH regimes and is probably a free radical chain at high pH and a nonradical mechanism at low pH. Some of the mechanisms proposed in the literature are discussed in the light of these new data. None of the proposed mechanisms give completely satisfactory agreement with the data. We propose a modified free radical chain mechanism for the high pH regime, which correctly predicts the organic inhibitions. For the low pH regime, mechanisms proposed by Conklin and Hoffmann (1988) and by Hoffmann and Jacob (1984) give fair agreement with the pH data and correctly predict the self‐inhibition, the sulfate inhibition, and the ionic strength inhibition. In view of the new data we believe that the iron(III) catalyzed reaction in tropospheric clouds can be a major contributor to the rate of sulfate formation, but there will be significant inhibition of this process by formic acid in some situations.

No abstract

No abstract

Complexation of neodymium(III) and europium(III) with lactate was studied at variable temperatures by potentiometry, absorption spectrophotometry, luminescence spectroscopy and microcalorimetry. ) with lactate is exothermic, and the complexation becomes weaker at higher temperatures. Results from optical absorption and luminescence spectroscopy suggest that the complexes are inner-sphere chelate complexes in which the protonated α-hydroxyl group of lactate participates in the complexation.