Abstract
One of the authors has already reported that artificial magnetite made from Fe2O3by the reduction at a temperature range 600°-800°C with a gas mixture composed of CO (10%), CO2 (90%) and SO2 (ca. 1%) was dissolved readily by dilute sulfuric acid (0.1N H2SO4) and the reduction product always contained sulfur to some extent. On the other hand, solubility of artificial magnetite made from Fe2O3by the reduction at the temperature range with SO2-free gas mixtures composed of CO (10%) and CO2 (20, 40 and 90%) is nearly equal to that of natural magnetite.
Then we have supposed three causes for the easy dissolution of the sulfur-containing magnetite:
1. The selective dissolution of the magnetite may occur electrochemically when magnetite contacts with FeS which is partially produced in magnetite under the reducing ambient with SO2by the reaction: Fe3O4+10CO+3SO2=3FeS+10CO2
The first of the assumptions was not considered by the results of electrochemical potential measurements of Fe3O4and FeS in 0.1N H2SO4and 0.07M FeSO4-0.1N H2SO4solutions. The electrochemical potentials of Fe3O4in the both solutions are always more noble than those of FeS.
2. The dissolution may occur by the formation of the solid solution between Fe3O4and FeS.
The existunce of the solid solution was not verified from a partially sulfidized natural magnetite by the device of an electron-probe microanalyzer for KαX-ray and O KαX-ray.
3. The dissolution of magnetite may be proved by hydrogen sulfide.
It was confirmed experimentally that the dissolution of magnetite was proved by the evolution of H2S resulted in the reaction between FeS and H2SO4, and in general, the reducing agents showed the positive effect on the dissolution of magnetite.
