Kinetics of polarographic reduction of uranium(VI) in phosphoric acid solutions

Modelling of uranium(VI) extraction by D2EHPA/TOPO from phosphoric acid within a wide range of concentrations

“…The present model is an extension of the equations reported in our previous studies [21][22][23] taking into account the non-ideality behavior of the aqueous phase as reported in the mass balance equations (9), (10) and (11). However, for the sake of simplicity, and due to the fact that D2EHPA and TOPO exhibit very low aqueous solubilies, and thus have only a weak contribution to the mass balance of these two compounds in the global liquid-liquid system as far as the phase ratio volume remains close to 1, the variations of the activity coefficients of HL, L -and TOPO in aqueous phase with the concentration of H 3 PO 4 have been ignored in these equations.…”

“…where the definition of each parameter is given in Table 1 and  is the complexation factor of uranium(VI) by phosphate, hydrogenophosphate and phosphoric acid in aqueous phase: (11) with referring to the concentrations of the various aqueous species of uranium(VI) complexed by phosphate, hydrogenophosphate, phosphoric acid, etc.…”

Recovery of Uranium from Wet Phosphoric Acid by Solvent Extraction Processes

“…Several studies report that uranium­(VI) in phosphoric acid exists as neutral, charged, and uncharged complexes such as UO 2 ­H 3 ­PO 4 2+ , UO 2 ­H 2 ­PO 4 + , UO 2 ­(H 2 ­PO 4 ) 2 , UO 2 ­(H 2 PO 4 )­H 3 ­PO 4 + , UO 2 ­(H 2 PO 4 ) 2 ­H 3 ­PO 4 , UO 2 ­(H 2 PO 4 )­(H 3 PO 4 ) 2 + , UO 2 ­(H 2 PO 4 ) 3 – , UO 2 ­(HPO 4 ) 2 ­(H 2 O) 2 , and UO 2 ­(HPO 4 ) 3 ­(H 2 O) 4 2– depending on pH and phosphoric acid concentration. − However, only three papers describe the speciation of uranium in concentrated phosphoric acid. , Thamer suggested that uranium complexation by phosphate ligands leads to the formation of UO 2 ­(H 2 PO 4 ) 2 ­H 3 PO 4 and UO 2 ­(H 2 ­PO 4 ) 2 when phosphoric acid concentration is greater than 2 mol L –1 . At high phosphoric acid concentration (above 2 mol L –1 H 3 PO 4 ), the predominant species was postulated to be UO 2 (H 2 PO 4 ) 2 H 3 PO 4 .…”