Characterization and beneficiation of Malatya / Kuluncak rare earth elements ore

Abstract

As a consequence of technological development, the beneficiation of the minerals of REEs has been gaining more importance. Nowadays REEs are an indispensable parts of magnetic, phosphor, metal alloys, catalysts, ceramics, glass, polishing, and defense systems industries due to their unique chemical and magnetic properties and also diverse colors. Currently, China is the largest supplier in the world with a production of more than 95% of the world's Rare Earth Oxides and dominates 43% of global known ∑REO+Y resources, which Australia, Canada, Russia, Brazil, Greenland, and the USA follow China by 10%, 8%, 10%, 8%, 6%, and 3% respectively. On the other hand, China has had a raising dominance in the global REEs market since the 1990s. Therefore, the export restriction imposed by China in 2010 on some valuable minerals (including REEs) against Japan was a breaking point. This decision caused supply security concerns to come into fore in the global REEs market. To break this dominance of China, exploration projects speeded up to diversify REEs sources and provide supply security. Turkey is one of the countries making contributions to exploration and beneficiation studies for REEs production. With the research and studies of the National REEs Institute (NATEN) and the General Directorate of Mineral Research and Exploration (MTA), Turkey is contributing to these studies to unearth these valuable and strategically important elements. On the other hand, Eskişehir/Beylikova REEs deposit has been studied in terms of beneficiation possibilities, and a pilot scale plant was established to process this important REEs deposit. Malatya/Kuluncak deposit is another important REEs and rare metal-bearing deposit in Turkey. Relevant beneficiation studies have been carried out under the coordination and organization of the National REEs Institute (NATEN). As part of these studies, Istanbul Technical University Department of Mineral Processing Engineering is currently performing physical and physico-chemcial beneficiation tests on the samples obtained from Malatya/Kuluncak REEs deposit. Within the scope of the thesis, chemical analysis of the raw sample, MLA, and XRD were conducted by ESAN, MTA, and Istanbul Technical University Department of Geology respectively. The chemical analysis gave the result of 0.33% (3,268 ppm) total REO grade and XRD provided significant data about silicate dominance in sample composition. MLA results confirmed these outcomes and proved that more than 70% of the ore sample was consisting of silicate gangue minerals. According to MLA results, major REEs-bearing minerals in ore composition gave low liberation ratios even in -38+32 µm. Therefore, it was concluded that the ore minerals have a tendency of being liberated at -20 µm, which is an ultrafine size fraction. Shaking table is a gravity separator that feeding material subjects with bumping action during the flow on the riffled desk and heavy particles accumulate behind the riffles while light particles pass over riffles, which a particle size fraction of -1.65+0.074 mm is suitable for such a process. Gravity methods were tested on REEs samples in many studies in literature, e.g., Jordens et al. (2016), Jordens et al. (2014), and Norgren et al. (2021), which these methods were mostly combined with magnetic separation. Therefore, shaking table tests were performed on Malatya / Kuluncak REEs samples within the scope of this thesis. Magnetic separators work based on differences in minerals' magnetic properties in the orbit of the nucleus of the atom spin around and cause a magnetic field. In most cases, electrons exist as electron pairs and each electron spins in the opposite direction of the other in pair. Hence, the magnetic fields of two electrons in a pair neutralize each other and prevent magnetic properties. That's the reason why elements containing unpaired electrons have magnetic properties utilized for separation. Sc, Y, La, and Lu are diamagnetic due to not having uncoupled electrons on the 3d orbital of Sc, the 4d orbital of Y, and the 4f orbital of La and Lu. Other REEs are all paramagnetic and Gd, Tb, Dy and Tm show ferromagnetism. These magnetic properties and the most important properties of REEs, being technologically utilized magnets, led magnetic separation tests to be performed within the scope of this study. As examples of magnetic separation of REEs minerals, Jordens et al. (2016)., Nguyen et al. (2021), Faris et al. (2019) and other researchers also performed experiments with combinations of gravity separation methods Electrostatic separation is a method based on the interaction between electrically charged particles and an electric field. A charge accumulates onto the particles on which an electric field is applied depending on their conductivities, surface areas and, maximum charge density, and then, these particles are attracted or repulsed. REEs are weak conductors in the exception of La. The main mechanism of MGS is that the pulp ore sample fed into the MGS through cleaner ring subjects centrifugal force and, as a result of it together with the shearing effect of shaking, heavy particles move through slurry film inside the drum towards concentrate output by a scraper, while light particles move towards the rear of the drum through wash water to be removed. The shaking effect prevents light particles to be entrapped by heavy particles in these systems by disrupting layers in the drum at a certain level (over-shaking causes heavy particles to be removed through light particle output) Because the minerals liberating in ultrafine size fractions can't be beneficiated efficiently by conventional gravity methods, the requirement of inventing concentrates working in ultrafine sizes occurred. Knelson is one of these concentrators. Knelson concentrator works based on centrifugal and fluidized bed separation principles, and the main part of it is a vertical conical bowl with a rotating shaft, in which the feed material moves towards the wall of the cone under centrifugal force, water is fed into the bowl in the opposite direction of bowl rotation at the same time, fluidized concentrate bed is generated and finally, heavy particles settle down the riffles on the bowl as concentrate, while light particles are removed from the unit. In terms of beneficiation of REEs, these methods are performed before flotation to obtain a proper pre-concentrate for flotation. During the time when MLA tests were ongoing, shaking table, magnetic separation, and electrostatic separation were performed to observe mineral beneficiation behaviors of ore minerals and their liberation tendencies in -1+0.3 mm and -0.3+0.074 mm size fractions. ∑REO grade was improved by shaking table experiments from an initial grade of 3,626 ppm to 6,437 ppm and 8,323 ppm in heavy products of both size fractions respectively. Magnetic separation increased ∑REO grade from 3,409 ppm to 4,963 ppm and 5,699 ppm in the magnetic products of both size fractions. Recovery values were higher compared with shaking table results. Although both methods above gave limited beneficiation results, it is thought that the main reason for this situation is due to the low liberation ratios of ore minerals in these size fractions. However, results indicate valuable clues about the beneficiation behavior of the ore. The electrostatic separation didn't give meaningful results at the desired level, which this situation is normal according to the literature. Following access to MLA data and report, a more comprehensive evaluation was made about liberation characteristics of ore minerals in sample composition. Since MLA results indicate finer liberation sizes, MGS and Knelson concentrator experiments were performed as the last stage of physical beneficiation in -74 µm size fraction (d80: 46 µm). MGS experiments with the raw sample delivered a limited increase in ∑REO grade and an initial grade of 3,480 ppm increased up to 3,987 ppm maximum in the middling product. The highest recovery was obtained from the heavy product by 61.5%, but the grade was lower than the middling product. MGS experiments with the slime product of Shaking Table experiments resulted in a wider range of ∑REO grade increase and ∑REO grade increased from 2,678 ppm up to 4,022 ppm. Knelson concentrator experiments could be performed with a limited amount of samples. According to the results, the ∑REO grade increased from 3,423 ppm to 5,983 ppm. Since the Knelson concentrator works with higher amounts of sample, concentrate weight remained limited and therefore, the recovery value was low. As a consequence, although the ore minerals were liberated at low levels, the results of the heavy products of the shaking table and magnetic products of REMS magnetic separator indicate that ore minerals have a tendency of being concentrated in these product groups. The results of MGS and Knelson concentrator experiments are more important since they were performed in finer size fractions. Trying different values of parameter variables and preparing higher amounts of feeding samples for Knelson concentrator experiments in further studies would be complementary to these preliminary beneficiation experiments. Also, it is recommended that magnetic separation experiments should be repeated in finer size fractions.