Mechanism Study Of Pyrite Atmospheric Oxidation Leaching

Pyrite is one of the most abundant metal sulfide minerals in the world.Although not economically valuable,it is found extensively in valuable minerals such as sphalerite,chalcopyrite and galena,as well as in various precious metal mines.Pyrite as an accompanying mineral,will affect the leaching behavior of other minerals and oxidant consumption.In this paper,the reaction temperature,the concentration of sulfuric acid and the oxidant of leaching behavior of pyrite in sulfuric acid system under atmospheric pressure were investigated.The leaching residue was determined by X-ray diffraction(XRD)and Scanning electron microscope-energy dispersive spectroscopy(SEM-EDS).Electrochemical testing technology was used to study the oxidation leaching mechanism of pyrite in sulfuric acid system and the electrochemical behavior of Fe(?)and Fe(?)couple on the pyrite surface was studied in acidic solutions at room temperature and atmospheric pressure.Under laboratory conditions,the leaching rate of pyrite increased significantly after it was leached by H2SO4 solution with Fe(?),H2O2 and HNO3 respectively.In H2SO4Fe(?)and H2SO4-HNO3 solutions,Fe(?)and HNO3 mainly play the role of oxidant.The reaction mechanism is similar to that of pyrite in H2SO4 solution,and the passivation film is formed under the open circuit potential and analysis of the leaching residue of the two solutions showed that the sulfur content of leaching residue increased.When pyrite was leached in H2SO4-H2O2 solution,H2O2 not only increased the redox potential of the solution,but also significantly changed the mechanism of oxidation and leaching.There was no passivation film formation at open circuit potential.The mechanism and kinetics of the Fe(?)/Fe(?)couple on the pyrite surface in sulfuric acid solution was systematically studied and the results showed that the oxidationreduction potential of Fe(?)/Fe(?)is independent of the concentration of Fe(?)and is consistent with the Nernst equation.In this study,the exchange current density of Fe(?)/Fe(?)redox reaction was 10-5 A·cm-2.The exchange current density of Fe(?)/Fe(?)redox reactions is so small that the oxidation capacity of Fe(?)is limited.The anode transfer coefficient clearly varies from 0.31 to 0.70 with increasing total iron concentration in solution,and from an electrochemical point of view,the rate-limiting step in the pyrite oxidation is the oxidation of Fe(?)to Fe(?).