Formation of hydrogen peroxide by galena and its influence on flotation

• Galena can generate H2O2 in pulp liquid.
• H2O2 generated in the presence or devoid of dissolved oxygen in water.
• H2O2 are produced at acidic pH less than 4.5.
• In pyrite–galena mixture the formation of H2O2 increased with increasing pyrite proportion.
• In chalcopyrite–galena mixture the formation of H2O2 increased with increasing chalcopyrite proportion.

The formation of hydrogen peroxide (H2O2), an oxidising agent stronger than oxygen, during the grinding of galena (PbS) was examined. It was observed that galena generated H2O2 in the pulp liquid during wet grinding and also when the freshly ground solids were placed in water immediately after dry grinding. The generation of H2O2 during either wet or dry grinding was thought to be due to a reaction between galena and water, when the mineral surface is catalytically active, to produce OH free radicals by breaking down the water molecule. It was also shown that galena could generate H2O2 in the presence or absence of dissolved oxygen in water.The concentration of H2O2 formed increased with decreasing pH. The effects of using mixtures of pyrite or chalcopyrite with galena were also investigated. In pyrite–galena mixture, the formation of H2O2 increased with an increase in the proportion of pyrite. This was also the case with an increase in the fraction of chalcopyrite in chalcopyrite–galena mixtures. The oxidation or dissolution of one specific mineral rather than the other in a mixture can be explained better by considering the extent of H2O2 formation rather than galvanic interactions. It appears that H2O2 plays a greater role in the oxidation of sulphides or in aiding the extensively reported galvanic interactions. This study highlights the necessity of further study of electrochemical and/or galvanic interaction mechanisms between pyrite and galena or chalcopyrite and galena in terms of their flotation behaviour.

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