| The purpose of the present work was to remove selectively manganese from a neutral leach zinc-rich solution at 80°C using the gas mixture of sulphur dioxide (SO2) and oxygen (O2) as oxidizing agent. In order to determine the optimum conditions for manganese removal using SO 2/O2, several semi-batch experiments were performed, where the effects of pH, ORP, SO2/O2 ratio, mixing intensity, etc. were investigated. Results of these tests showed that SO2/O 2 was a fast and effective oxidant for removing manganese down to ppm level provided that the appropriate reactor design, agitation and SO 2/O2 ratio were employed. In an attempt to improve the precipitate's characteristics, e.g. crystallinity and solid/liquid separation, a new technique called Step-Wise Oxidative Precipitation (S.W.O.P) was investigated using a two-reactor continuous circuit employing pH and ORP control and precipitate recycling. These tests revealed that a birnessite-like phase with general formula (Na0.7Ca0.3)Mn7O14•2.8H 2O was produced with co-precipitation of a significant amount of zinc apparently via substitution. The applied technique (S.W.O.P combined with recycling) proved effective in producing dense particles but not on lowering zinc losses. The biggest advantage of this novel oxidation technique was the total elimination of scaling. (Abstract shortened by UMI.)... |
