Por Jorge Ganoza, metalurgista.AbstractFor many years, undesired pyrite activation in the zinc flotation circuit has been a problem especially when mineralogy is complex, or the ore is of low grade. The data is varied, and most of it has focused on the effect of the pH and level of regrind of the primary zinc concentrate (rougher concentrate). Understanding the chemistry of the activation process will help to understand flotability, as several factors will influence the undesired activation of pyrite.The mechanism of activation of sphalerite by copper sulfate prior to the addition of collector and frother has been practiced and studied extensively. It is important to mention that sphalerite is not the only sulfide whose flotability can be altered by the presence of copper ions. The possibility of inadvertent activation of pyrite and its undesirable flotation are factors to be considered for effective separation of sphalerite from pyrite. The presence of pyrite during the activation of sphalerite plays an important role in the activation process by affecting its kinetics .The activation of pyrite is related to the availability of active sites on its surface. The amount of copper adsorbed on the pyrite surface increases with increasing pyrite active sites with respect to sphalerite active sites .Sodium metabisulfite was evaluated to improve the separation of sphalerite from pyrite in the zinc cleaning circuit under alkaline conditions. This separation was the result of depressing the flotation of pyrite after evaluating the proper size of the sphalerite liberation. A further improvement in this separation was evident at the finer size. The results of spectroscopic studies have shown that metabisulfite tends to promote the oxidation of copper in pyrite as Cu hydroxide, thereby slowing its flotation, but has no effect on sphalerite. This increase in oxidation products on the pyrite surface reduces the adsorption of xanthate, which may explain the depression of pyrite in the presence of sodium metabisulfite .The primary zinc concentrate was regrinded and cleaned three times to produce a saleable concentrate. The effect of sodium metabisulfite was evaluated with different additions after regrinding. Results suggest an improvement in the quality of the zinc concentrate.