Galvanic interaction between wolframite and galena: ROS generation and its role in galena oxidation

The oxidation of galena is a critical environmental and geochemical process that controls the lead release and causes environmental contamination. However, galena exhibits a paragenetic association with wolframite in tungsten deposits, and the role of galvanic couples between oxides and sulfides remains little explored. This study investigated the effect of wolframite on the oxidation of galena, with a particular focus on the presence of galvanic interaction and the role of reactive oxygen species (ROS). By leaching experiment, electrochemical techniques, reactive oxygen species (ROS) analysis and density functional theory (DFT) calculations, we demonstrate that the galvanic interaction between wolframite and galena occurs and that ROS are generated in the presence of this galvanic effect. Wolframite acts as a cathode and facilitates the anodic oxidation of galena, where the electrons transfer from galena to wolframite. DFT calculations further reveal that the wolframite-galena heterojunction exhibits a type-II staggered band alignment, with a lower work function of galena higher than that of wolframite, which drives directional electron transfer from galena to wolframite. The electron transfer from galena promotes the reduction of O₂ on the surface of wolframite, thereby increasing the formation of ROS, which further facilitates the oxidation of galena. ROS analysis indicates that hydroxyl radicals (•OH) play a key role in the oxidation process of galena, which can be additionally generated through the Fenton reaction between hydrogen peroxide (H₂O₂) and Fe²⁺ released from wolframite. This work provides new insights into lead release in tungsten mining areas where galena and wolframite coexist, and has powerful implications for mitigating lead pollution.