Chemical-mineralogical characterization of critical elements into ferromanganese crusts
Caroline Silva de Matos, Mariana Benites, Luigi Jovane, Carina Ulsen
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.