Abstract
Manganese dioxide was precipitated by ozone oxidation from acidified sulfate solutions of sulfuric acid concentration ranging from 0.25 to 5.0mol/l at temperature varying from 25 up to 80°C at an ozone partial pressure of the ozone-oxygen mixture gas of 2.8×10-2 atm. The precipitates were analyzed by X-ray diffraction using Cu-Ka line. The X-ray diffraction patterns consisted of the peaks indicating γ-MnO2, α-MnO2 or a mixture of the two, depending on the ozonation conditions. Based on the X-ray diffraction data for 52 MnO2 -samples, a diagram was constructed to represent the ozonation conditions, the temperature and the acid concentration, for the formation of the individual types of manganese dioxide. At each acid concentration above 1.0mol/l, γ-MnO2 was found to be an ozonation product below a border-temperature, where a mixture of γ-andα-MnO2was produced. The border-temperature was gradually descending as the acid concentration was increased. Manganese dioxide of a-type in stead of 7-type was produced in high temperature-acid concentration region.
In the X-ray diffraction diagrams for 7-Mn02 formed under varying conditions, a rise in ozonation temperature led to increased intensity and slight shift toward higher angles of the peaks. And an increase in acid concentration gave rise to broadening of the diffraction peakes.
It was also demonstrated in the X-ray diffraction diagrams that the formation of MnO2 by ozonation was not significantly affected by the presence of zinc sulfate in acidified sulfate solutions having similar composition as the electrolyte solution for zinc electrowinning.
