Met-Mex Peñoles processes lead sulfide concentratesSulfide concentrate in its lead smelterSmelter using the sinter-blast furnaceFurnace process. The rich sulfurSulfur dioxide gas (6% SO2) generated in the sintering process is used to produce sulfuric acidSulfuric acid, meanwhile the more dilute SO2 streams (<1.5% SO2) are sent to an ammonium sulfateSulfate plant to absorb the SO2 with a water-based ammonium solution creating a rich ammonium bisulfite/sulfite by means of a counterflow packed scrubberScrubber with five sections. This first step produces ammonium bisulfite at 35% concentration in water. The plant was designed to then produce an ammonium sulfateSulfate solution at 42% concentration through acidification and the regenerated SO2 gas was used to produce liquid sulfurSulfur dioxide or gas which could be sent to the acid plantsAcid plant, and the liquid ammonium sulfateSulfate was sent to Peñoles’ fertilizer plant, Fertirey for crystallizationCrystallization. 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 miningMining 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.