A contribution to sodium polyuranate chemistry

Thermodynamic Modeling of the SRS Evaporators: Part I. The 2H and 2F System

“…Likewise, finely dispersed sodium diuranate phases were found to form readily at 25°C in about 10-60 minutes, 32 reaching equilibrium in about 5 days. 53 Since the reactions that form the sodalite and sodium diuranate deposits in the SRS 2H-Evaporator are relatively fast kinetically, the equilibrium activity diagrams (normally applicable on geologic time scales) are useful models for understanding and modeling the mineral scale deposits forming under evaporator conditions.…”

“…The ratio of the Na:U in the polyuranate phase that forms is a function of pH of the solution and the length of time that the Na has to diffuse into the crystal structure. 32 Specifically, when NaOH was added to dilute solutions of uranyl nitrate, the first species to form was a polymerized ion of the form [UO 2 33 It should be noted that in both of these studies 32, 33 the Na 2 U 2 O 7 precipitates were very small and suspended in the NaOH solutions, i.e., the precipitates had to be centrifuged in order to be examined. Finely dispersed sodium diuranate phases were found to form readily at 25°C in about 10-60 minutes, 32 reaching equilibrium in about 5 days.…”

“…32 Specifically, when NaOH was added to dilute solutions of uranyl nitrate, the first species to form was a polymerized ion of the form [UO 2 33 It should be noted that in both of these studies 32, 33 the Na 2 U 2 O 7 precipitates were very small and suspended in the NaOH solutions, i.e., the precipitates had to be centrifuged in order to be examined. Finely dispersed sodium diuranate phases were found to form readily at 25°C in about 10-60 minutes, 32 reaching equilibrium in about 5 days. 34 Hobbs and Karraker 35 studied the precipitation of Na 2 U 2 O 7 in simulated evaporator solutions under simulated evaporator conditions.…”

Thermodynamic Modeling of the SRS Evaporators: Part II. The 3H System

“…The ratio of the Na:U in the polyuranate phase that forms is a function of pH of the solution and the length of time that the Na has to diffuse into the crystal structure. 32 Specifically, when NaOH was added to dilute solutions of uranyl nitrate, the first species to form was a polymerized ion of the form [UO 2 Longer contact with the NaOH rich solution at high pH causes n to become ≤3 causing a change in the crystal structure. At n=2 the final stable Na 2 U 2 O 7 •2H 2 O composition is formed.…”

“…33 It should be noted that in both of these studies 32, 33 the Na 2 U 2 O 7 precipitates were very small and suspended in the NaOH solutions, i.e., the precipitates had to be centrifuged in order to be examined. Finely dispersed sodium diuranate phases were found to form readily at 25°C in about 10-60 minutes, 32 reaching equilibrium in about 5 days. 34 Hobbs and Karraker 35 studied the precipitation of Na 2 U 2 O 7 in simulated evaporator solutions under simulated evaporator conditions.…”