Comparative study of electrochemical and thermal oxidation of pyrite

The oxidation of pyrite was studied as a function of grain size, employing voltammetric and thermal analysis. The data obtained with the electrochemical experiments are consistent with the results shown in the the thermogravimetry-differential thermogravimetry (TG-DTG) records. The use of both techniques revealed that oxidation of the mineral is affected by the grain size employed. The maximum yield of SO42- was obtained from electrodes constructed with < 210 mum-sized particles. The same behavior was observed during thermal decomposition. When the temperature surpasses 490 degreesC, the small particles ( < 210 mum) oxidize in a single step which is not affected by changes in the rate of air flow, indicative of their higher reactivity among the ground mineral electrodes. The comparison between the results obtained by the two methods suggests that, below 490 degreesC or 0.6 V, pyrite oxidation, either in air or in aqueous media, is similar and depends on the semiconducting properties of the mineral.