Chemical-mineralogical characterization of critical elements into ferromanganese crusts

Abstract

The demand for critical chemical elements applied in clean energy technologies is increasing and, although deep-sea mining feasibility still is an open question, it might be a pathway to overcome the problem. Among areas of interest for seabed mining, the Rio Grande Rise is an ocean ridge in the southwest Atlantic Ocean known for hosting a large polymetallic mineral deposit containing various critical elements at high concentrations. Therefore, this mineralogical and chemical study characterizes the Rio Grande Rise FeMn crusts and establishes features from a structural-chemical perspective that can guide further studies from various locations. Combining X-ray diffractometry, Raman spectroscopy, chemical analysis, and Scanning Electron Microscopy, it was found that samples are composed by manganese oxides, MnOx; ferryxite or goethite, FeOOH; magnesian calcite, Ca,Mg(CO3)2; and carbonate fluorapatite, Ca5(PO4,CO3)3F. The external portion of analyzed rocks consists of younger crust layers enriched in critical metals, such as cobalt (Co) and nickel (Ni), associated with MnOx – mainly vernadite and asbolane; titanium (Ti), associated with iron oxyhydroxides; and rare earth elements (REE), at distinct bearing minerals. Therefore, the data herein reported show that regions where the FeMn crusts have a thicker young layer host a higher content of critical elements. In addition, the information about the elemental distribution and mineral associations can guide further mineral and metallurgical processing steps.

Keywords

• Ferromanganese crusts
• Technological characterization
• Deep sea mining
• Critical metals
• Manganese oxides