Formation of Oceanic Cobalt-rich Crust: Progress and Perspectives

Cobalt-rich crust is an important seafloor mineral resource with unique economic value and scientific significance. Cobalt-rich crust is significantly enriched in Mn, Co, Ni, Cu, PGE (platinum group elements) and REY (rare earth elements + Y), and has special implications on the paleo-marine environmental records since the Cenozoic. Mn oxide (MnO2·xH2O) and Fe oxyhydroxide (FeOOH) are the dominant minerals that compose cobalt-rich crust, with most of them are nanoscale minerals. Vernadite and birnessite have a layer structure and a negative layer charge, which is compensated by cation sorption. The previous studies have extensively focused on the location of trace elements in minerals in the cobalt-rich crust, with the help of sequential leaching experiments, statistical analysis of element correlation, adsorption experiments and extended X-ray absorption fine structure (EXAFS) spectrum. Three main types of complexes in Mn oxide have been identified, i.e., edge-sharing (E), double-corner sharing (DC) and triple-corner sharing (TC). Studies have shown that the process of hydrogenetic cobalt-rich crust precipitation is basically inorganic colloidal-chemical and surface-chemical. Finally, we proposed some suggestions for the future research directions in this field. © 2023 Science Press. All rights reserved.