Electrochemical Study Of The Pyrite Oxidation In Acidic Solutions

Pyrite （FeS2） is a common iron sulfide mineral, it is present in tailings and waste rockdumps. It is also present in many valuable raw mineral materials. Oxidative dissolution ofpyrite can produce acid mine drainage, a significant environmental problem in all miningregions. For the purpose of reducing of acid mine drainage at source, it’s essential toinvestigate the oxidation mechanism of pyrite, which will help to find an effective passivationmethod to suppression the oxidation process of pyrite.Electrochemical analysis methods, such as traditional electrochemical techniques （opencircuit potential, cyclic voltammetry, Tafel polarization curves） and scaning electrochemicalmicroscopy techniques are used to investigate electrochemical behavior of pyrite in acidicsolutions. The major conclusions are given below:The oxidation process of pyrite in acidic solutions is a two-step reaction: the first step isthe dissolution of iron moiety and that a passivation film composed of elemental sulphur，metal-deficient sulfide and polysulfide is formed; The second step is the further oxidation ofthese intermediate products to SO₄^2-. The final reaction products of pyrite oxidation are Fe³⁺and SO₄^2-in acidic solutions. In addition, the open-circuit potential and corrosion potential ispositively shifted, the peak current and the corrosion current increased with increase inconcentration of H2SO4solutions. This indicates that increasing acidity of the system isadvantageous to the oxidation of pyrite.Use the Pt microeletrode as probe, pyrite as substrate, scanning electrochemicalmicroscopy can detect Fe²⁺of pyrite dissolution sensitively, which can be used to study pyriteoxidation process. When the tip move toward the surface of pyrite substrate, the existence ofsubstrate blocks the diffusion of dissolved oxygen from the bulk solution to the tip, and thedissolved Fe²⁺from pyrite would consume oxygen, which makes a decreased OCP value. Inaddition, the tip current of reduction tends to zero, the tip current of oxidation graduallyincreases. The tip current of oxidation is lower when with nitrogen purging or the electrolyteconcentration decreasing. The surface electrochemical activity distribution information ofpyrite substrate at various states obtained by line scan and area scan experiments by scanningelectrochemical microscopy. When scratch or defect at surface of pyrite substrate exist, thesepositions show more strong activity, more vulnerable reaction dissolved.