The role of Acidithiobacillus ferrooxidans in the ocean polymetallic nodules reductive bioleaching: Electrochemical insights into interface processes

The influence of A. ferrooxidans on polymetallic nodules reductive dissolution in the imitated bioleaching medium was investigated. Firstly, the features related to metal extraction and manganese leaching kinetics of the nodule were determined using Fe²⁺ ions as reductants in the presence of A. ferrooxidans. The obtained apparent activation energy is 13.9 kJ mol^-1 for the Mn-reduction. Secondly, the courses of the dissolution of polymetallic nodules were measured by multi-transient and steady electrochemical methods. The obtained results indicated that in A. ferrooxidans simulated bio-leaching system, the reductive leaching of polymetallic nodules is characterized by step-step processing, and the interface chemical reaction is the rate-controlling process. The interface exchange reactions are expressed in a two-electron transfer process corresponding to the cathodic conversion of MnO₂/Mn²⁺, while in one-electron transfer of Fe²⁺to Fe³⁺ for anodic response with the presence of Fe³⁺ ions and A. ferrooxidans. Based on this study's findings, the role of A. ferrooxidans in the polymetallic nodule reductive dissolution is concluded with three effects: A. ferrooxidans as electron-proton carrier or buffer facilitate interfacial species transfer; A. ferrooxidans as catalyzer for the transformation of Fe³⁺/Fe²⁺pair cause Mn-oxide reducing quickly; A. ferrooxidans as enhancer promote intermediate and products migration and transformation.