Electrochemical Extraction of La and Zn-La Alloy Codeposition in Chloride System†

doi:10.7503/cjcu20170605

Abstract

Abstract:

The electrochemical behavior of La(Ⅲ) ions was studied in LiCl-KCl and LiCl-KCl-ZnCl₂ melts on the Mo electrode at 723 K by cyclic voltammetry, square-wave voltammetry and open-circuit chronopotentiometry. The results showed that the reduction of La(Ⅲ) to La(0) is a one-step irreversible reaction controlled by diffusion. In LiCl-KCl-ZnCl₂ solutions, the underpotential deposition of La formed four kinds of Zn-La intermetallic compounds on pre-deposited Zn. Zn-La alloy was obtained by galvanostatic electrolysis at 923 K. The microstructure and micro-zone chemical analysis of Zn-La alloy were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS). Based on the previous electrochemical results, square-wave voltammetry was used to determine the concentration changes of La during potentiostatic electrolysis, the concentration of La(Ⅲ) was close to zero, and the extraction efficiency was 99.55% after potentiostatic electrolysis for 50 h.

Key words: LiCl-KCl melt salt system, Electrolysis in molten salt, Electrochemical extraction of La, Zn-La alloy, Extraction efficiency

CLC Number:

O616

TrendMD:

XUE Yun, CAO Meng, YANG Xue, XU Yanlu, YAN Yongde, JI Debin, MA Fuqiu. Electrochemical Extraction of La and Zn-La Alloy Codeposition in Chloride System^†[J]. Chem. J. Chinese Universities, 2018, 39(6): 1145.

Figures/Tables 8

Fig.1 Cyclic voltammograms curves on a Mo electrode(S=0.322 cm2) in the LiCl-KCl melt salt sytem before(a) and after(b) the addition of 1.3×10-4 mol/mL LaCl3 at 723 K(scan rate: 0.2 V/s)

Fig.2 Cyclic voltammograms curves of LiCl-KCl-LaCl3(1.3×10-4 mol/mL) melt salt sytem on a Mo electrode(S=0.322 cm2) at different scan rates at 723 KInset: relationship of the cathodic peak current with the square root of the sweep rate.

Fig.3 Square wave voltammogram obtained on a Mo electrode(S=0.322 cm2) in the LiCl-KCl-LaCl3(1.3×10-4 mol/mL) melt salt system at 723 KPulse height: 25 mV; potential step: 1 mV; frequency: 10 Hz.

Fig.4 Open-circuit chronopotentiogram for a Mo electrode(S=0.322 cm2) in the LiCl-KCl-LaCl3(1.3×10-4 mol/mL) melt salt system at 723 K[deposition potential: -2.4 V(vs. Ag/AgCl); deposition time: 70 s]

Fig.5 Cyclic voltammograms curves on a Mo electrode(S=0.322 cm2) in LiCl-KCl-ZnCl2(1.2×10-4 mol/mL)-LaCl3(1.3×10-4 mol/mL) melt salt system at different cathodic limits at 723 K(scan rate: 0.1 V/s)

Fig.6 Square wave voltammogram(A) and open-circuit chronopotentiogram(B) on a Mo electrode in the LiCl-KCl-ZnCl2(1.2×10-4 mol/mL)-LaCl3(1.3×10-4 mol/mL) melt salt system at 723 K(A) Pulse height: 25 mV; potential step: 1 mV; frequency: 10 Hz; (B) deposition potential: -2.4 V(vs Ag/AgCl); deposition time: 30 s.

Fig.7 XRD patterns of the deposits obtained under galvanostatic electrolysis at a Mo electrode in LiCl-KCl-ZnCl2(8.8×10-4 mol/mL)-LaCl3(1.8×10-4 mol/mL) melt salt system at 923 K at 2 A for 2.5 h

Fig.8 Cross-sectional SEM images(A—C) and EDS analysis(D—F) of the deposit obtained by galvanostatic electrolysis at -6.25 A/cm2 for 2.5 h on a Mo electrode in LiCl-KCl-ZnCl2(8.8×10-4 mol/mL)-LaCl3(1.8×10-4 mol/mL) melt salt system at 923 K(A) SEM image; (B) mapping of La; (C) mapping of Zn; (D)—(F) represent points 001, 002, 003 in (A), respec-tively.

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