Micelle Mediated Extraction of Neodymium and Electrochemical Characterization of AOT Reverse Micelles

Tuesday, 30 May 2017: 16:20
Marlborough A (Hilton New Orleans Riverside)
S. Anderson (FAMU-FSU College of Engineering), E. E. Kalu (Florida A&M University - Florida State University COE), C. Clark II (FAMU-FSU College of Engineering), and M. Nilsson (Chemical Engineering & Materials Science, UC Irvine)
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. Hence, interest exists in devising a technique to improve the separation factor. The anionic surfactant, AOT, is proposed to pre-concentrate the metal from an aqueous phase through third phase formation and increasing the conductivity of the organic phase of a LLX experiment so an electric field can be applied to drive the extraction. Surfactants within LLX experiments have been shown to from a third phase and it is theorized that this phase is predominantly the surfactant and target metal, thus pre-concentrating the metal. The use of an imposed external field (electrochemical) to improve the LLX has been explored in the literature with limited success due to conductivity issues. In this work, the use of reverse micelle solutions containing water/AOT/n-dodecane for pre-concentrating Nd and water/AOT-HDEHP/n-dodecane for improved electrical conductivity is explored. The results of a feasibility study of the pre-concentration and electrochemical modulated extraction of neodymium (Nd) using the reverse micelles/microemulsions will be presented.

A concentration of 0.2 M AOT in n-dodecane was used to form a third phase in the extraction/pre-concentration of Nd from an aqueous solution using LLX. At and above an initial Nd concentration of 12 mM, third phase formed. As the initial concentration of the Nd increased, more Nd was extracted from the aqueous phase. Post-extraction washing of the organic phase resulted in approx. 56% of the Nd being accounted for. ICP will be used to determine if there is Nd in the third phase. Below an initial Nd concentration of 10 mM, third phase did not form and Nd was extracted. Post-extraction washing of the organic phase resulted in approx. 90% of the Nd being account for.

Electrochemical impedance (EIS) technique was used to determine the effect of molar content of water, Wo, and temperature on the reverse micelle solution conductivity. Results showed that as Wo increases, conductivity increases until the reverse micelles burst and form a biphasic system. Addition of HDEHP caused a significant drop in solution conductivity. Temperature has a mild effect on increasing the conductivity. Limited to applying 7 V, electrochemical extraction showed small improvement in Nd extraction percent over traditional LLX. The extraction percent of Nd in a liquid-liquid extraction cell containing reverse micelles and the mechanism of electrochemical modulated liquid-liquid metal ion extraction will be discussed.