Study of effects of different parameters on supercritical fluid extraction of uranium from acidic solutions employing TBP as co-solvent

Abstract

Uranium / Supercritical carbon dioxide / Pressure / Temperature / TBPSummary. In the supercritical fluid extraction of uranium from acidic medium employing TBP as co-solvent, effects of various parameters on extraction efficiency were studied. Variation in pressure (80-300 atm), temperature (308-353 K), CO 2 flow rate (0.5-3 mL/min), co-solvent percentage (1-10%), molarity of nitric acid (0.5-10 M) were found to influence uranium extraction efficiency. The uranium extraction efficiency depends on distribution ratio and kinetics of transport of U-TBP complex into supercritical CO 2 . In the 150-300 atm pressure range, variation in extraction efficiency was similar to that of uranium distribution ratio under equilibrium conditions. Whereas below 150 atm, it closely followed supercritical CO 2 density variation which could be attributed to non-equilibrium behavior that eventually attained equilibrium. In the non-equilibrium region, increased supercritical CO 2 density with pressure favored enhancement in solubility as well as extraction kinetics of the U-TBP complex. Increase in temperature generally resulted in enhanced volatility of U-TBP complex and a decrease in supercritical CO 2 density which in turn affected the extraction efficiency. Up to 333 K temperature, extraction efficiency gradually increased due to enhancement in volatility of U-TBP complex which more than compensates for decrease in the supercritical CO 2 density. Beyond this temperature, the steep fall in the extraction efficiency is attributed to combined effect of saturation in volatility of the U-TBP complex and significant decrease in the density of supercritical CO 2 approaching the critical value at which supercritical CO 2 tends to form large clusters thereby resulting in steep decrease in its solvating power. Extraction efficiency was found to increase with nitric acid molarity up to 7 M and afterwards showed small decrease possibly due to competitive co-extraction of HNO 3 . Up to CO 2 flow rate of 1 mL/min increase in extraction efficiency was observed which attained saturation afterwards. Linear increase in extraction efficiency was observed with the amount of TBP. Extraction efficiency was found to increase linearly with logarithm of extraction time. Under optimised conditions (150 atm, 333 K, 1 mL/min CO 2 flowrate, 10% co-solvent, 7 M nitric acid and 30 min dynamic extraction time) extraction efficiency was found to be (98 ± 2) %. Also, (100 ± 1) % mass balance was observed. 30 min dynamic extraction mode was found *Author for correspondence (E-mail: pradeep_barc@yahoo.com). equivalent to 40 min static mode. Online complexation mode was more efficient than in situ mode.

Supercritical Extraction of Lanthanide Tributyl Phosphate Complexes: Current Status and Future Directions

“…(For example, when aqueous acidity reaches ∼4 M HNO 3 , the organic phase experiences a simultaneous increase in water content and decrease in lanthanide content. , ) Therefore, it is logical to expect that the increased dissolution of water as pressure increases would lead to a simultaneous drop in metal extraction. Indeed, lanthanide (and actinide) extraction from a dilute aqueous solutions consistently shows decreased extraction with higher pressure in the same range, − , exactly the opposite of the aforementioned trend in dry systems. Therefore, when evaluating the effect of pressure on extraction, the evidence suggests that the amount of water is a critical factor.…”

“…This was motivated by the desire for a fission product separation process that does not generate contaminated organic wastes. Researchers demonstrated the extraction of uranium and other actinides from aqueous solutions − and from solid oxides or nitrates. − In 2009, a pilot plant demonstrated the supercritical extraction of uranium from incinerator fly ash …”

Studies on Complexation and Supercritical Fluid Extraction of Cd2+ with Calixarenes

“…The in situ mode of complexation was employed for SFE. The SFE setup that was used in the present study (obtained from JASCO, Tokyo, Japan), the detailed setup of SFE, and the procedure have been described elsewhere . The SFE study was performed with 1 mL (1250 μM) of ligand and 1 mL (250 μM) of metal ion solution loaded on the extraction vessel for the desired static time followed by dynamic extraction at a given temperature and pressure.…”

Supercritical Fluid Extraction of Uranium, Plutonium and Thorium

“…Solubility is combination of SC-CO 2 density and volatility of solute. The author has discussed in detail the effects of various parameters 65 .…”