Abstract
Primary lead is produced in the United States by the pyrometallurgical smelting of lead sulfide (galena, pbs) concentrates, which poses sulfur dioxide and lead air pollution control problems. The federal Bureau of Mines has investigated an alternative hydrometallurgy procedure that does not generate gaseous sulfur oxides and diminishes the potential for the escape of lead into the atmosphere. The procedure involves leaching galena flotation concentrates with ferric chloride (fecl3) solution to obtain lead chloride (pbcl2) and elemental sulfur as expressed by the following chemical reaction: pbs + 2fecl3 -> pbcl2 + 2fecl2 + s deg. At 100 deg c, over 99 pct of the pbs in the concentrate is converted to pbcl2 in less than 15 min. The leach solution, composed of brine (nacl) containing slightly more than the theoretical required amount of fecl3, dissolves the pbcl2 as it is formed, leaving a residue of elemental sulfur plus gangue. High- purity pbcl2 (>99.9 pct) crystallizes from the leach filtrate on cooling and is electrolyzed in a low-temperature, fused-salt cell to obtain corroding-grade metal (>99.94 pct pb). Spent leach solution (fecl2) is regenerated for further use be reaction with the chlorine obtained in the electrolysis of lead chloride. Other values, such as ag, cu, zn, and s deg, are recovered by additional treatment of either the leach solution or leach residue.
