Options to recover high-purity MnO2 from leach liquors of manganese dust containing Mn3O4 and iron and zinc oxide as minor impurities

Abstract

Manganese dust, predominantly made up of manganese oxides is produced during the manufacturing of ferromanganese alloys at high temperatures. Pure Mn compounds can be recovered from manganese dust. In this study, a hydrometallurgical process was developed to recover pure MnO2 from manganese dust containing iron and zinc oxides. The oxide species Mn3O4 in manganese dust was first completely dissolved using a mixture of sulfuric and oxalic acids at room temperature. Small amounts of iron and zinc oxides were also dissolved during manganese leaching. Iron(III) in the clarified leach liquor was then completely separated by solvent extraction using D2EHPA. Zinc(II) in the Fe(III) free raffinate was separated by either solvent extraction with Cyanex 272 or by ZnS precipitation through the addition of Na2S. Addition of Mn powder to the leach liquor separated Zn(II) by cementation and increased the solution pH and hence Fe(III) was separated by precipitation. The MnO2 powder with a purity of 99.995% was recovered from real leach liquor of manganese dust after consecutive solvent extractions of Fe(III) and Zn(II) by D2EHPA and Cyanex 272, respectively and oxidative precipitation of MnO2 from the purified solution (raffinate) using NaClO at room temperature.