Solubility and Complexation of the Bismuthate Ion in Nitric Acid Systems

Abstract

The dissolution rate and solubility of NaBiO3 have been investigated in nitric acid systems ranging from 4 to 6 M HNO3 and were found to be 58–76 μg/cm2·d and 490–830 mM, respectively. The presence of 50 mM U­(VI) drastically increased the solubility to 540–1200 mM, while rates of dissolution were relatively unchanged. The solubility of NaBiO3 increased with an increase in U­(VI) concentrations at 4 M HNO3, with log–log analysis indicating a one-to-one complex between Bi and U and infrared spectroscopic evidence monitoring uranyl stretching, suggesting complex formation. Absorbance spectra were obtained experimentally and computationally with an absorbance band in the range of 450–600 nm that has been attributed to Bi­(V). The ingrowth and decay of Bi­(V) in solution was also studied as a function of mass of solid NaBiO3 present, acidity, and temperature. The activation energies of dissolution and decomposition were calculated to be 39 ± 4 and 61 ± 6 kJ/mol, respectively. These results indicate that dissolution of NaBiO3 into the respective Na+ and BiO3 –occurs prior to undergoing reduction, a process which conventionally has been believed to occur in the reverse order.

Interactions of the Bismuthate Anion with Alkali, Alkaline Earth, Lanthanide, and Actinide Metals in Nitric Acid Systems

“…At this point, the exact nature of the stronger dependence of the trivalent ions over the divalent ions is not clear, but a likely culprit is the overall reduction in the free energy of the system caused by a combination of a stronger interaction between the more highly charged M 3+ cations and the BiO 3 – , which, in turn, results in a decrease in entropy. This trend is not unexpected, as similar trends are seen for these metal cations in the complexation of the nitrate ligand, which is believed to have a similar geometric conformation . For example, at 25 °C and an ionic strength of 1, upon moving from Ca 2+ to Sr 2+ the log K values for the single nitrate complex, M­(NO 3 ) + , change from −0.06 to 0.05, while under the same conditions, moving from Nd 3+ to Bi 3+ the log K values change from 0.3 to 0.81, again for the single nitrate complex, M­(NO 3 ) 2+ .…”

“…The solution chemistry of the bismuthate anion, BiO 3 – , has only recently begun to be examined, with the first report of its UV–visible absorption spectra coming in our earlier work . The weak absorption band occurring in the range of ca.…”

“…To understand this behavior, the instability of BiO 3 – must also be considered. The degradation of the BiO 3 – , presumably to Bi 3+ , follows a first-order rate law (see Figure S3), which is in line with our previous findings . Unlike the ingrowth, there was a direct relationship between the Cs + concentration and the degradation rate of BiO 3 – , extending from 0–250 mM Cs + .…”

“…Nitric acid (69–70% Omni Trace, HNO 3 ) was purchased from EDM; bismuth­(III) nitrate pentahydrate (ACS > 98%, Bi­(NO 3 ) 3 ·5H 2 O), calcium nitrate tetrahydrate (ACS > 98%, Ca­(NO 3 ) 2 ·4H 2 O), cesium nitrate (99.8%, CsNO 3 ), magnesium nitrate hexahydrate (ACS 98–102%, Mg­(NO 3 ) 2 ·6H 2 O), neodymium­(III) nitrate hydrate (99.99%, Nd­(NO 3 ) 3 · x H 2 O), potassium nitrate (ACS 99%, KNO 3 ), samarium­(III) nitrate hexahydrate (99.9% REO, Sm­(NO 3 ) 3 ·6H 2 O), sodium bismuthate (ACS grade, NaBiO 3 ), sodium nitrate (ACS > 99.0%, NaNO 3 ), starch (ACS grade), and strontium nitrate (ACS > 99.0%, Sr­(NO 3 ) 2 ) were purchased from Alfa Aesar; potassium iodide (ACS grade, KI) and potassium iodate (Reagent grade, KIO 3 ) were purchased from Fisher Scientific; sodium hydroxide (ACS grade, NaOH), disodium ethylenediaminetetraacetic acid (Reagent grade, EDTA), and sodium thiosulfate (Reagent grade, Na 2 S 2 O 3 ) were purchased from VWR BDH Chemicals; KIO 3 was recrystallized before use, while all other chemicals were used as received. The NaBiO 3 has previously been found to be in the hydrated form, NaBiO 3 · n H 2 O by X-ray powder diffraction . Deionized (DI) H 2 O was obtained from an ELGA LabWater Purelab Flex ultrapure laboratory water purification system operated at 18.2 MΩ cm at 25 °C.…”

“…The behavior of the Bi­(V) as the bismuthate ion, BiO 3 – , was determined as previously reported, and a detailed experimental procedure can be found elsewhere …”