U.S. Pat. 4,500,398, 1985 Feb; :1-4
Pb is recovered from sulfide materials such as ores by leaching the ore with H2SiF6 in the presence of an oxidizing agent (e.g., H2O2 and PbO2), forming S and PbSiF6 and then subjecting the PbSiF6 to electrolysis to produce Pb and H2SiF6. Thus, Pbs concentrate 200 g was leached in a 2-l beaker containing 1 l of H2SiF6 solution which contained 236 g of H2SiF6/l, 50 ml of 30% H2O2 and 98.5 G PbO2 at 90 deg C for 2 h. Prior to electrowinning, the concentrations of Pb and H2SiF6 in the leachate were adjusted by adding H2O and H2SiF6. Calcium lignosulfonate and bone gelatin were then added for grain refinement and leveling, respectively, and 1 g/l H3PO4 was added to control PbO2 formation at the anode during electrowinning. Electrolysis in a 2-l cell with a PbO2-coated Ti anode and a pure Pb cathode at current density 180 a/m2 gave 99.998% Pb at 96% current efficiency.