Interphase Distribution of Elements during Two-Stage High Temperature Electrochemical Treatment of Lead-Bismuth Alloys

Abstract

Experimental simulation of the separation of the components of lead-bismuth alloy in a chloride melt is conducted. Using X-ray fluorescence, emission spectral and X-ray powder diffraction analyses, the interphase distribution of elements is estimated during high-temperature (550 С) electrochemical treatment of lead-bismuth alloys in molten NaCl–KCl–PbCl2 –ZnCl2 . Regimes of the two-stage process are substantiated when in the first stage (U = 7.4–15.6 V, ia = 0.5 A/cm2 ) the bismuth content in anode alloy is brought to 48.4 wt.% and then (U = 4.9-13.5 V, ia = 0.3-0.4 A/cm2 ) crude bismuth is separated containing, wt.%: 93.6 Bi, 4.1 Pb, 0.086 Ag, 0.0066 As, 0.006 Sb, 0.0013 Cu, 0.001 Sn, and 0.0014 Zn. The final anode product contains 93% bismuth and 0.4% lead from the original alloy. Crude lead obtained at the cathode contains, wt.%: 95.8–96.3 Pb, 0.007–0.06 Bi, 0.002–2.9 Na, 1.2–3.6 Zn, and ≤ 0.1 Cu. Sublimation of chlorides saturated with lead and action of oxygen from the air are the reasons for heterogenization of the electrolyte that gives rise to an increase in working voltage in the electrolytic cell. The relatively low anodic and cathodic current efficiency (50 and 38% respectively) are associated with electrical recharging of polyvalent ions on electrodes. Use of technology for treating intermediate products and waste refining will make it possible to organize production of crude bismuth from mineral and secondary lead-containing raw materials. Prospects for improving the efficiency of the process are associated with the sealing of electrolyzers and preliminary pyrometallurgical refining of lead-bismuth alloys from impurities (Cu, Zn, Sb, As, and Sn).