The limiting effect of manganese phase of oceanic cobalt-rich crust reduction by sawdust in acid leaching

Abstract

Ocean cobalt-rich crust is rich in Co, Cu, Ni, Mn and other valuable metals. In this study, the valuable metals in cobalt-rich crust, which was reduced using waste sawdust, can be effectively recovered by acid leaching. The results show the formation of manganese oxide in the reduction process has a certain restriction on sulfuric acid leaching. The reduction process is gradually completed from the surface layer to the core (MnO2→Mn2O3→Mn3O4→MnO). The reduction products at any stage are always composed of one or two oxides of the adjacent valence state of manganese, which lead to different reaction processes and products with sulfuric acid. At the same time, manganese dioxide precipitates formed by Mn2O3 and Mn3O4 will remove a small amount of valuable metal ions from the solution, reducing the recovery of Mn, Cu, Co and Ni. The leaching efficiency of Mn, Cu, Co and Ni could reach 99.96%, 98.86%, 99.89% and 99.35% respectively using 0.5 mol/L sulfuric acid to leach 50 min at 25 °C.