Abstract
An examination of the technical and economic feasibility of the combined mining of the rare-earth element-rich mud (REE-rich mud) and ferromanganese nodules (FN) around Minamitorishima (Marcus) Island in Northwest Pacific is introduced. A previous study showed that the mining of REE-rich mud around Minamitorishima Island was not economically feasible. Therefore, in this study, three changes from the previous mining model to improve its economy are proposed. The first one is combined mining with FN in the area. The second one is introducing a pulp-lifting system that can lift both REE-rich mud and FN at high concentrations through a riser pipe. The third one is the reuse of waste mud and processed slag for construction materials. The economic evaluation results show a change from a slightly negative to quite positive economy depending on the mixing ratio of REE-rich mud and FN in the pulp-lifting. In addition, some technical approaches necessary to realize the combined mining method are introduced.
Highlights
The presence of deep-sea rare-earth element-rich mud (REE-rich mud) in the Pacific seafloor which involves high contents of rare-earth elements was reported in a previous study [1]
In 2013, another higher content area was found by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) near Minamitorishima (Marcus) Island in the Japanese exclusive economic zone (EEZ) [5]
Among the specifications for the mining, the transportation, the metallurgical processing systems, and Capital expenditure (CAPEX) and Operating expenditure (OPEX) for 5000 t/d of ferromanganese nodule (FN) production in dry conditions in the International Seabed Authority (ISA) workshop report [60], the same tracked collector and lift subsystems for FN were assumed as the ones for REE-rich mud
Summary
The presence of deep-sea rare-earth element-rich mud (REE-rich mud) in the Pacific seafloor which involves high contents of rare-earth elements was reported in a previous study [1]. In 2013, another higher content area was found by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) near Minamitorishima (Marcus) Island in the Japanese exclusive economic zone (EEZ) [5] In this area, there are rare-earth element-rich layers with 5000–6500 ppm contents within 10 m below the seafloor, which is 5600–5800 m deep. An economic feasibility study on cobalt-rich FN inside the Cook Islands EEZ [22] stood out, because the high cobalt content in FN and a mechanical lift were assumed in the mining model. Though updated distribution models of the CCZ have been presented by the ISA in the last ten years [62,63], no effective economic feasibility study has been undertaken
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