Extraction of various valuable elements from oceanic manganese nodules using coal gasification slag via reduction roasting-acid leaching process

Abstract

In line with the concept of coal gasification slag treatment and marine mineral exploitation, this research proposed a residual carbon roasting-acid leaching process to extract various valuable metals from oceanic manganese nodules. The residual carbon obtained from coal gasification coarse slag was enriched via gravity separation without chemical treatment, and this carbon-high product served as an inexpensive reducing agent. The feasibility of carbon-high reduction of oceanic manganese nodules was explored using a thermogravimetric-mass spectrometric coupling system and thermodynamic analysis. The influence of mass ratio, roasting time, and roasting temperature on the reduction effect of oceanic manganese nodules was examined, and optimal conditions were determined through orthogonal tests. The results demonstrated that under the optimized conditions, the leaching rate of Mn exceeded 98%, and that of Cu, Co, and Ni exceeded 96%. The reduction and leaching processes were elucidated at the crystal scale through various ways. Finally, a comprehensive process flow diagram was summarized for the extraction of various valuable metals from oceanic manganese nodules using the residual carbon roasting-acid leaching process. This research will pave the way for the design of cost-effective and sustainable roasting reductants and reduction roasting processes for manganese oxide ores, contributing to economic and environmental benefits.