Abstract
The extraction and separation of metal ions in the lanthanide series using the liquid-liquid extraction (LLX) technique poses a major challenge due to the chemical similarities of the metals and hence interest exists in devising a technique to improve the separation factor. In this work, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) is explored for improved organic phase conductivity to aid the use of an imposed external field to improve the LLX. The electrochemical impedance spectroscopy (EIS) technique was used to determine the effect of molar water content, AOT and HDEHP (bis(2-ethylhexyl) phosphoric acid) concentration, and the temperature on the reverse micelle solution conductivity. Results showed that as AOT concentration and water content increases, conductivity increases until the reverse micelles collapse. The addition of HDEHP caused a significant drop in solution conductivity. For a mixed AOT and HDEHP system and at a small applied external field range of 0–1.4 kV m−1 and 60 rpm stir rate, a significant improvement in Nd extraction was observed relative to the traditional LLX using HDEHP only. With AOT only, a 40% improvement in extraction was observed with applied field relative to the absence of field. Cost consideration favors the use of mixed AOT and HDEHP at a slow stir rate for improved Nd extraction.
Highlights
The extraction and separation of lanthanides and actinides from nuclear waste provides multiple benefits
We examine the effect of water content (Wo), AOT concentration, HDEHP concentration and temperature on the reverse micelle-containing liquid-liquid extraction (LLX) system
The goal of our work was to use AOT to increase the conductivity of the organic phase of a liquid-liquid extraction system in order to apply an electric field to aid in extraction
Summary
The extraction and separation of lanthanides and actinides from nuclear waste provides multiple benefits. In traditional LLX, mechanical mixing increases the surface area between two phases where metal ion transfer can occur and is a large driving force for extraction and separation. Adding another driving force, such as an externally applied electric field, could enhance the extraction by increasing the amount of metal that is removed [15,16,17,18]. In addition to increasing the conductivity of the organic phase, these reverse micelles may provide an added enhancement to the LLX system by reducing the surface tension between the aqueous and organic phases, allowing for increased Nd extraction [26]. Results of this work could be useful in the modification of industrial LLX operations to be less costly and increase the amount of metal extracted while using fewer separation stages
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