The Extraction And On-line Detection Of Lanthanum On Copper And Aluminum Electrodes In Molten Salts

The feasibility of electrochemical extraction of lanthanides was investigated on Cu and A1 electrodes in LiCl-KCl eutectic molten salts.The concentration of La(?)ion was detected during the extraction of La(?)on Cu and A1 electrodes.The detailed was as follows:(1)The electrochemical behavior of La(?)ions on W electrode was studied by cyclic voltammetry and square wave voltammetry.It was found that the reduction of La(?)ion on W electrode was a one-step involving three electrons and a quasi-reversible and diffusion-controlled process.(2)The electrochemical behavior of La(?)ions on Cu electrode was investigated by cyclic voltammetry,square wave voltammetry,chronoamperometry and open circuit chronopotentiometry.The results indicated that underpotential deposition of La(?)ion occurred on Cu electrode due to the formation of Cu-La intermetallic compounds.Meanwhile,the value of underpotential deposition of La(?)was calculated on Cu electrode.The thermodynamic data,such as the standard molar Gibbs free energies of formation for different Cu-La intermetallic compounds,activities and partial molar Gibbs free energies of La in Cu-La alloy were estimated by open circuit chronopotentiometry.The extraction of La on Cu electrode was carried out by potentiostatic and galvanostatic electrolysis in LiCl-KCl-LaCl3 melts.The products obtained were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM)equipped with energy dispersive spectrometry(EDS),which showed the formation of Cu5La,Cu2La,CuLa intermetallic compounds.(3)The electrochemical behavior of La(?)ions was studied on Al electrode by a variety of electrochemical techniques.The results of voltammetry and square wave voltammetry displayed the underpotential deposition of La on Al electrode due to the formation of a variety of Al-La intermetallics.Meanwhile,the value of underpotential deposition of La(?)was estimated on Al electrode.According to the electrochemical results,potentiostatic electrolysis was performed and Al-La alloy was prepared on Al electrode.The results of SEM-EDS indicated the Al-La alloys consisted of AlLa,Al2La,Al3La and AlLa3 intermetallic compounds.(4)The concentration change of La(III)ions was on-line monitoring during the process of electrochemical extraction of La.Firstly,the square wave voltammetry was performed in a specific concentration of La(?)ions in LiCl-KCl melts.And then,according to the relationship of peak current with the concentration of La(?),the calibration curves were obtained at different temperatures.Then,the concentration of La(?)ion was monitored in the process of electrolysis extraction of La in LiCl-KCl melts according to the peak current height of square wave voltammetry.Furthermore,the extraction efficiencies of La on different electrodes were calculated and compared each other.The results show the extraction efficiency of La(?)ion on A1 electrode was higher than the one on Cu electrode at same conditions.