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264 Handbook on the Physics and Chemistry of Rare Earths leached REEs are retained in solution, not cocrystallizing into gypsum. Ogata et al. (2016) carried out adsorbent experiments for phosphoric acid which is produced from Phalaborwa apatite ores with 2 M H2SO4 treatment. The phos- phoric acid solution was passed through a column filled with EDASiDGA adsorbent and REEs selectively remained in the column. The REEs in column are easily recovered by low concentration acid treatment like 1 M H2SO4. As mentioned earlier, EDASiDGA has high collectivity of MREEs and HREEs, and Ogata et al. (2016) succeeded in increasing Dy concentrations by as much a factor of 24 compared with feed solution after the dissolution of the apatite ore. The described experiments are lab-scale, but their results demonstrate that EDASiDGA is effective for REE recovery from low-grade ores with impurities like Fe. In the future, REE adsorption experiments with EDASiDGA are des- perately needed on larger scale with due regard to economic REE production as by-product from apatite ores. 5 SUMMARY Carbonatites are high in REEs, and most of them are LREE-dominant type, because carbonatite magmas form by low degree of partial melting of garnet-bearing source mantle. In contrast, alkaline rocks are low in REEs, but some are rich in HREEs, due to higher degree of partial melting of the garnet-free magma sources. This indicates that HREE-dominant REE-rich deposits are uncommonly formed by magmatism. Ion-adsorption type deposits consist of LREE- and HREE-dominant types and are constrained by the degree of partial melting and magmatic differenti- ation. The formation of HREE-dominant ion-adsorption type deposits is related to the heavily differentiated and reduced granite. As established by geoscience, it is inevitable that LREEs are mainly pro- duced from carbonatites and HREEs are dominantly extracted from ion- adsorption type deposits underlain by HREE-rich granites. However, REE grades of ion-adsorption type deposits are low and almost all of the minable deposits have been found in southern China. In view of the future of REE sup- ply (considering both feasibility and sustainability), one of the most promising sources of REEs is apatite ores that are mined for fertilizer production, because apatite ores are sufficient in reserves and contain enough amounts of the whole REEs that can cover the world demand. ACKNOWLEDGMENTS We are grateful to Mr. Litshedzani Mutele and Dr. Stewart Foya (Council for Geoscience, Republic of South Africa) for supporting our fieldwork in South Africa. Thanks to Dr. Takeshi Ogata, Environmental Management Research Institute, AIST, for his comments and sugges- tions made during the writing of this paper. This study was supported in part by the Grant-in- Aid for Scientific Research (B) Nos. 19253005 and 10549885 and by Postdoctoral Fellowships for Research Abroad funded by the Japan Society for Promotion of Science (JSPS).PDF Image | HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS
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