ADVANCED MATERIALS & PROCESSES | NOVEMBER/DECEMBER 2023 25 TABLE 1 — EDS ANALYSIS OF POINTS OF INTEREST (POI) ATOM % Sample POI O P Mn Fe Y Al Ca Mg Si Na Possible Chemical Composition and Location Purpurite A1 58.36 19.19 5.69 16.77 x x x (Fe3+, Mn3+)PO4 Rainbow#4 Lode, Custer Co., South Dakota, USA A2 36.40 26.52 9.32 27.76 Churchite B1 79.34 12.54 x 8.12 Y(PO4)3·2H2O Maffei mine, Auerbach in der Oberpfalz, Bavaria, Germany B2 77.12 12.70 10.18 Wavellite C1 63.70 15.76 x 20.54 Al3(PO4)2(OH)3·5H2O Mauldin Mountain, Montgomery County, Mount Ida, Arkansas C2 73.87 10.27 15.86 Variscite with Crandallite D1 70.47 15.42 14.11 AlPO4·2H2O Little Green Monster mine, Fairfield, Utah Co., Utah D2 72.75 11.1 10.82 1.25 x 2.97 1.1 CaAl3(PO4)2(OH, H2O)6 with SiO2 Little Green Monster mine, Fairfield, Utah Co., Utah Eosphorite with Roscherite E1 67.54 11.01 6.54 x 11.4 x MnAl(PO4)(OH)2·H2O (Eosphorite) Minas Geriais, Brazil E2 76.69 12.32 x x x 4.7 6.29 x Ca2(Mn, Fe, Al)5Be4(PO4)6(OH)4 · 6H2O. (Roscherite) with MgO Minas Geriais, Brazil E3 54.53 12.23 12.7 8.65 7.74 4.16 x tained from Dakota Matrix Minerals Inc., Rapid City, South Dakota, except wavellite, which was obtained from Earth’s Treasures, Bozeman, Montana. For each specimen, a high-resolution digital picture was captured for the overview image. A small piece of sample was then carefully cut off from the specimen and the microstructures were examined using an FEI Quanta 650 FEG Scanning Electron Microscope (SEM) in second- ary electron (SE) and backscattered electron (BSE) mode. Chemical in- formation was obtained by energy- dispersive x-ray spectroscopy (EDS) which was conducted on the BSE images at different points of interests (POIs). 3D optical microscopy was performed with a VR-6000 optical profilometer. Manganese Phosphate Mineral: Purpurite. Purpurite is an anhydrous manganese phosphate mineral with the formula MnPO4. Purpurite commonly forms a series with the iron-bearing endmember heterosite with the formula (Fe3+, Mn3+)PO4 [19–21] and the amount of Fe can vary in the microstructure, which is also dependent on the source. industry and the uneven distribution of REE deposits (95% of the world’s REEs are produced from two ore deposit types in China) resulted in a global REE crisis and triggered the worldwide upsurge to discover the new sources. Recent studies indicate that sedimentary phosphate deposits (phosphorites) are significantly enriched in REEs, and the ease of extraction from the phosphorites make them the primary source of REEs[12–14]. Other potential applications are high-entropy phosphate catalysts and ceramics[15,16], anti-corrosion agents (phosphate pigment)[17,18] among others. A CASE STUDY OF PHOSPHATE MINERALS The phosphate minerals family is large and diverse. Only a few species are relatively common, which are from the apatite group. This article will examine some non-apatite minerals to better understand phosphate minerals for potential applications. Methodology. In this case study, selected phosphate minerals were ob- Fig. 1 – (a) Digital picture of purpurite: SEM micrographs of purpurite in (b) SE and (c) BSE images of the same region. (a) (ab) (c)
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