A Critical Review on Evaluation of the Marine Resources Mining versus the Land-Based Ones for REE

It is now scientifically proven that specific categories of submarine raw materials, especially deep seas such as Mn and Fe oxides, polymetallic nodules, polymetallic sulfides (SMS) and some deep-sea sediment categories, can have significant potential for some critical metals for future use. One characteristic of these deposits is that although they often have lower Rare Earth Elements (REE) contents than the well-known land deposits, their sizes are very extensive, much higher than the land-based deposits. Therefore, the future use of these submarine formations as a source of REEs can be an important alternative to the exponentially growing demand for these strategic metals. These formations have significant potential to be a source of REEs in the markets when they are extracted as byproducts of the most critical metals such as copper, nickel, cobalt and manganese, from Mn nodules. To prove how realistic, the extraction of REE from those deposits is in market terms, we studied the economotechnical dimension and the potential or REEs compared to those of the well-known on-land REE deposits. Two studies are presented concerning the existing exploration pre-feasibility cases for REEs originated from two existing licences granted by the International Seabed Authority (ISA) in the Clarion Clipperton Zone (CCZ). The examination of these two cases has clearly shown that compared to the corresponding deposits of REE inland, the total basket prices of these submarine deposits are higher due to the higher contents of heavy REE such as Nd, Pr and Dy and Sm, Eu, Gd, Tb and Y in these marine deposits. Considering that the prices in the international markets for most of the REE oxides between 2019 and 2021 were very high, they gave these deposits even greater economic value. The significant advantage of the mining and metallurgical treatment of these manganese nodules and cobalt-rich manganese crusts is also related to the fact that REEs are not part of the crystal lattice of the minerals that host them, in contrast to what happens with land-based deposits. This makes their metallurgical processing more manageable and cheaper. This fact makes mining and metallurgical treatment economically favourable. On the other hand, the very low Th and U concentrations in these deep-sea deposits do not pose environmental risks in many well-known land-based REE deposits.