Formation of hydrogen peroxide by sphalerite

Abstract

Formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by sphalerite ((Zn, Fe) S) was examined during its grinding process. It was observed that sphalerite generated H2O2 in pulp liquid during wet grinding and also when the freshly ground solids placed in water immediately after dry grinding. The generation of H2O2 in either wet or dry grinding was thought to be due to a reaction between sphalerite and water where the mineral surface is catalytically active to produce OH free radicals by breaking down the water molecule. Effect of pH on the formation of H2O2 by sphalerite showed that acidic pH values generated more H2O2. Mixtures of pyrite, chalcopyrite and galena with sphalerite on the formation of H2O2 were also probed. It was shown that the concentration of H2O2 increases with increasing pyrite or chalcopyrite fraction in pyrite–sphalerite or chalcopyrite–sphalerite or galena–sphalerite mixtures but with an increase in galena proportion, the concentration of H2O2 decreased. The oxidation or dissolution of one mineral than the other in a mixture can also be accounted with the extent of H2O2 formation in the pulp liquid in addition to galvanic interactions. H2O2 plays a greater role in the oxidation of sulfides or aiding the extensively reported galvanic interactions since the amount of H2O2 generated with a specific mineral followed the rest potential series of sulfide minerals. This study highlights the necessity of relooking into the role of H2O2 in electrochemical and/or galvanic interaction mechanisms between pyrite, chalcopyrite and galena with sphalerite.