Management of SO₂ from Diluted Streams in the Met-Mex Peñoles Lead Smelter

Met-Mex Peñoles processes lead sulfide concentrates in its lead smelter using the sinter-blast furnace process. The rich sulfur dioxide gas (6% SO₂) generated in the sintering process is used to produce sulfuric acid, meanwhile the more dilute SO₂ streams (<1.5% SO₂) are sent to an ammonium sulfate plant to absorb the SO₂ with a water-based ammonium solution creating a rich ammonium bisulfite/sulfite by means of a counterflow packed scrubber with five sections. This first step produces ammonium bisulfite at 35% concentration in water. The plant was designed to then produce an ammonium sulfate solution at 42% concentration through acidification and the regenerated SO₂ gas was used to produce liquid sulfur dioxide or gas which could be sent to the acid plants, and the liquid ammonium sulfate was sent to Peñoles’ fertilizer plant, Fertirey for crystallization. Fertilizer production has not been economically attractive for several years, so the company has looked for alternatives, and is now focused on selling the 35% ammonium bisulfite solution, which is a widely used reagent in the mining industry. It is used in cyanide detoxification and floatation circuits for Pb-Cu separation. The present paper describes the ammonium bisulfite process and the results of its use at industrial level for cyanide detoxification.