Rare earth element (REE)-bearing carbonatite deposits commonly contain a wide range of different REE- and REE-bearing minerals associated with various gangue matrices. In order to select the most-suitable mineral processing technique for these deposits, it is essential to identify and quantify the minerals of interest, including their liberation, associations and grain size distribution, along with whole rock compositions. These data are also vital for ore feed optimisation and metallurgical troubleshooting during and after designing a mineral processing flowsheet. This paper summarises the key mineralogical parameters needed before conducting metallurgical beneficiation tests, using the Songwe Hill carbonatite deposit as an example. This REE ore deposit consists of poorly-liberated synchysite-(Ce), which hosts the light rare earth elements including Nd plus some heavy rare earths and well-liberated apatite, which hosts 50% of Gd, 63% of Dy and 71% of Y (heavy rare earth elements) in the deposit. For all REE heavier than Gd, apatite is the most important REE host, however, for the two REE where data are available in both synchysite-(Ce) and apatite (Dy and Y), synchysite-(Ce) still accommodates >25% of the whole-rock HREE content. Both of these ore minerals are associated with ankerite, calcite, and to a lesser extent with iron oxides/carbonates, K-feldspar, strontianite and baryte. According to the quantitative mineralogical data, the possibility of using gravity separation, magnetic separation, froth flotation and leaching to process Songwe Hill carbonatite ore is discussed and a potential beneficiation flowsheet is presented.
Rare earth elements (REE) are considered as critical metals for electronics and green technology. The REE fluorcarbonates are one of the main REE ore minerals, common in many different types of REE deposit and yet some of their fundamental properties have still not been determined. This study measured the magnetic properties of pure REE fluorcarbonate single crystal minerals using a vibrating sample magnetometer (VSM) and determined their elemental compositions using electron probe microanalysis (EPMA). The results provide the first measurements of the magnetic behaviour and susceptibility of REE fluorcarbonates other than bastnäsite-(Ce). The magnetic susceptibility of REE fluorcarbonates varies systematically from one mineral to another and is highly dependent on the mineral chemistry. It is positive (paramagnetic) for bastnäsite-(Ce) and gradually decreases as the amount of Ca increases in parisite-(Ce), becoming negative (diamagnetic) for the Ca-rich member of the series, röntgenite. Synchysite-(Ce) is difficult to measure, generate good signal and acquire accurate readings because it practically always occurs as <5 mg crystals. Its magnetic susceptibility in samples from a REE ore deposit was experimentally determined by magnetic separation and checked by an associated study using a SQUID magnetometer, synchysite-(Ce) behaved as a diamagnetic mineral. This can be explained by the increase of Ca content and decrease of REE content, in addition to the variations in the layered structure common to the REE fluorcarbonate series minerals. Given the wide range of magnetic susceptibility of REE fluorcarbonates, it is important that the mineralogy is determined carefully before setting up a mineral processing flow sheet.
Nine sediment samples were collected from three sites at the banks (levees) of Sarraji, Hamdan and Abul khasib creeks branching from Shatt Al-Arab river, southeastern Basrah with depths of 0.5, 1.0 and 1.5m, respectively. Grain size distribution and statistical parameters revealed that the deposits are mainly composed of silt and clay with very small portion of sand, and have mud type texture. There is a tendency of increasing in silt percentage from Sarraji toward Abul Khasib area and decreasing in clay percentage with depth. Generally, the sediments are poorly sorted, coarse to strongly coarse skewed and platykurtic to very platykurtic deposited in quiet environment and low energy conditions. Chemical analysis showed that all samples have high concentration in SiO2 and CaO in comparison with Al2O3, Fe2O3, MgO, SO3, K2O and Na2O. These results are generally in agreement with the mineral composition. Mineralogically, the sediments understudy consists of quartz, feldspar, calcite, dolomite and gypsum. Clay minerals assemblages are: chlorite-montmorillonite mixed layers 37%, Illite 20%, Chlorite 18%, Kaolinite 14% and Palygorskite 11%. Increasing in Ch-Mont. percentage could be an evidence of high intensity of diagenetic alteration processes in depositional environment. The clay mineral assemblages proved that the recent sediments of the studied samples were derived from the basic igneous and metamorphic rocks, while acidic igneous and sedimentary rocks sources are less important. The deposition environment of these minerals may be characterized by an arid to semi-arid climate in the source area.
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