Effect of protonation and deprotonation reactions of clay on regulating pyrite flotation in the presence of clay

Abstract

The slurry pH shows significant effects on flotation, but the root cause of pH affecting flotation in the presence of clay is still not fully understood. In this work, the mechanisms of protonation and deprotonation reactions of clays at weakly acidic (pH = 4.5) and alkalescent (pH = 9.0) environment affecting pyrite flotation were investigated. The pyrite flotation in the presence of clays (montmorillonite (Mt), kaolinite (Kaol) and illite (I)) was improved with the deprotonation reactions at pH 9.0 compared with the protonation at pH 4.5. The protonation reactions made the edge surfaces of all the clays and the O basal surface of Kaol positively charged. Hence, the “house-of-cards” structure of Mt and the slime coating of Mt and Kaol occurred, which depressed the pyrite flotation. However, the deprotonation of clay took place at pH 9.0, and thus the face-to-face associations of clay were clearly observed by scanning electron microscopy (SEM). In addition, the negative potential of clay also increased with the deprotonation of clay, which affected the DLVO total interaction energy, making the attraction turning into the repulsive tendency between pyrite and clay. However, pyrite grade showed a little or no increase in the presence of I, which was ascribed to the 2:1 structure and non-swelling nature of I. Such findings can not only help understand the protonation and deprotonation of clay on regulating flotation in the presence of clay, but are expected to provide guidance for mitigating the negative effects of clay during the flotation in the future work.