H.A. Friedman

Spectrophotometric studies of dioxouranium(V) in aqueous media. I. The perchlorate medium

The spectrum of UO2+ in aqueous perchlorate medium is described as two absorption bands at 9400 and 7380 A, with higher energy absorption beginning at ∼ 6500 A and increasing at shorter wavelengths to at least 5000 A. Thermodynamic values of K, ΔF°, ΔH° and ΔS° for the disproportionation of UO2+ were determined to be 7 × 104, −6·6 kcal, −18·6 kcal and −40 e.u., respectively. The value of S° for UO2+ was determined to be −11 e.u.

Polymerization of Pu(IV) in aqueous nitric acid solutions

Abstract The polymerization of Pu(IV) in aqueous nitric acid solutions has been studied spectrophotometrically both to determine the effects of large UO2(NO3)2 concentrations on the polymerization rates and, more generally, to review the influence of other major parameters on the polymer reaction. Typically, experiments have been performed at 50°C and at 0.05M Pu in aqueous solutions of HNO3 at concentrations ranging from 0.07 to 0.4M. An induction period usually precedes the polymer growth stage, during which time it is believed that primary hydrolysis products form and begin to aggregate. Uranyl nitrate retards the polymerization reaction by approximately 35% despite the counteracting influence of the nitrate ions associated with this solute. The rate of polymer formation at 50°C has been shown to be third order in Pu(IV) concentration.

The photochemistry of neptunium in aqueous perchloric acid solutions

The photochemistry of neptunium ions in aqueous perchloric acid (0.1–4.0 N) has been investigated using 254 and 300 nm UV radiation. In the absence of other reagents, Np(IV) and (V) oxidized to Np(VI), in a stepwise fashion, with individual quantum efficiencies for each step that vary from 0.02 to 0.004. Decreasing acid concentration favors the Np(IV) → Np(V) reaction whereas it hinders the Np(V) → Np(VI) photo-oxidation. When ethanol, acetaldehyde and other mild reducing agents are added to neptunium-perchloric acid solutions which are then photolyzed, the Np species are reduced to Np(III) in a stepwise fashion with individual quantum efficiencies that vary from 0.07 to 0.006. The overall photoredox reactions of neptunium are subject to competing secondary product reactions that become significant as the photolysis products accumulate. Absorption spectrophotometry was used to monitor the changes in Np oxidation states and reference spectra of the various Np oxidation states are given for 1.0 N HClO4. The Np species have absorption bands in the 300–1320 nm region that obey Beers law only when they were properly resolved.

The IR spectrum of Pu(IV) polymer

Abstract The IR spectrum of Pu(IV) polymer has been measured from 200–4000 cm −1 . Major bands which could be associated directly with the oxygen-bridged polymer occured at 360 and 3400 cm −1 . These were assigned, respectively, to a PuO vibration similar to the lattice vibration of high-fired PuO 2 and to an OH stretching vibration of a water group which is either hydrated or occluded in the polymer structure. In addition, weaker bands were observed in the 1000 cm −1 region which were correlated with the age of the polymer. The dried polymer precipitate was found to have a very great affinity for CO 2 , absorbing it to form CO 3 2− groups which gave characteristic bands at 890 cm −1 ( v 2 ) and 1359, 1500 cm −1 (split v 3 ). From chemical analyses, the carbon content of the polymer was found to be as high as 1.5 wt% when equilibrated in the room air.

Photochemical reactions of aqueous plutonium systems—II☆

Abstract The photochemical shift of the Pu 4+ disproportionation equilibrium in aqueous perchloric acid solutions has been measured and shown to be reversible. Ratios of equilibrium quotients between light and dark conditions have been measured for 0.01 M Pu ion concentrations in 0.53 to 1.24 N acid solutions exposed to 0.5 Watt of UV light. The photodecomposition of time- and temperature-aged Pu(IV) polymers in perchloric and nitric acid solutions have been examined as a function of aging conditions. Effects similar to those seen previously for fresh polymers have been observed in the aged perchloric acid solutions.

Photochemically induced reduction of trace Np(VI) in U(VI)HNO3 solutions

Abstract Dilute Np(VI) can be reduced to Np(V) in the presence of large amounts of UO 2 (NO 3 ) 2 by a photochemical reaction which first involves the photo-reduction of NO 3 − to NO 2 − . Although UO 2 2+ competes strongly for photons, the accompanying stabilization of Np(V) by UO 2 2+ tends to compensate for the UO 2 2+ screening effect. Experiments have been performed using 254 and 300 nm radiation on 0.1 and 1.0 M HNO 3 solutions containing 1M UO 2 (NO 3 ) 2 and either 0.01 or 0.001 M NpO 2 2+ . Because the primary photochemical reaction involves photo-reduction of NO 3 − to No 2 − , still lower concentrations of Np(VI) are expected to be reducible by this process.