Research on bismuth extraction from alkaline oxidative leaching residues of bismuth-rich lead anode slime by casting and electrolysis

Alkaline oxidative leaching residues of bismuth-rich lead anode slime were adopted to extract bismuth and enrich gold and silver by using carbothermal reduction casting and electrolysis process. Thermodynamics analysis indicates that the initial carbothermal reduction temperature of metal oxides from low to high are Cu, Bi, Pb, Sb, Sn. Bismuth oxides can obtain enough reduction thermodynamic driving force when the temperature excesses 800 ℃. The optimum technical conditions are as follows: temperature, 800 ℃; carbon addition, 5 % of the mass of leaching residue; Na₂B₄O₇ addition, 15 % of the mass of the leaching residue; time duration, 1.5 h. Under such conditions the average contents of bismuth, gold and silver were 84.29 %, 39.62 g/t and 6519 g/t, respectively. Compared with the raw lead anode slime, the content of gold and silver were enriched 1.8 times respectively. Kilogram-scale crude bismuth alloys were electrolyzed in HCl-NaCl-BiCl₃ system as anodic plates for 24 h, 48 h, 72 h, 112 h. The results indicated that the content of bismuth in the cathodal products exceeded 98 %, the current efficiency, 96 %, and the average content of gold and silver content were 222.94 g/t, 34287.6 g/t, respectively. Compared with the raw lead anode slime, the content of gold and silver were enriched 9.54 times and 10.13 times, respectively.