Grain Size Distribution and Clay Mineral Distinction of Rare Earth Ore through Different Methods

Abstract

Although clay mineral content in ion-absorbed rare earth ores is crucial for migrating and releasing rare earth elements, the formation, distribution, and migration of clay minerals in supergene rare earth ores have not been fully understood. Therefore, this study analyzes the characteristics of clay mineral type and content, soil particle size, pH value, leaching solution concentration, and leaching rate. This analysis was performed using different methods, such as regional rare earth mine soil surveys, in situ leaching profile monitoring, and indoor simulated leaching. The results showed that the grain size and volume curve of rare earth ore have unimodal and bimodal shapes, respectively. X-ray diffraction showed the differences in clay mineral types formed by different weathered bedrocks. The principal clay minerals were kaolinite, illite, chlorite, and vermiculite, with their relative abundance varying with parent rock lithology (granite and low-grade metamorphic rocks). In the Ganxian granite weathering profile, the kaolinite content increased from top to bottom. The decomposition of feldspar minerals to kaolinite was enhanced with an increase in the SiO2 content during weathering. The in situ leaching profile analysis showed that the kaolinite content increased initially and then decreased, whereas the illite/mica content exhibited the opposite trend. Under stable leaching solution concentration and leaching rate, clay mineral formation is favored by lower pH. Low pH, low leaching rate, and highly-concentrated leaching solution (12 wt%) resulted in a slow increase in kaolinite content in the upper part of the profile (30 cm). A lower concentration of the leaching solution (4 wt%) resulted in rapid enrichment of kaolinite after 15 days. Low pH, leaching solution concentration, and leaching rate promoted the formation of distinct kaolinite horizons. We suggest that by disregarding other control factors, rare earth recovery of over 90% can be achieved through leach mining with solutions of 8 wt% and a pH of 5 at a leaching rate of 5 mL/min.

Effects of Clay Minerals on Enzyme Activity as a Potential Biosensor of Soil Pollution in Alice Township

“…As leaching progressed, they observed an increase in kaolinite and illite-mica content and a corresponding decrease in quartz content. They also observed a weak correlation between kaolinite, feldspar, and quartz minerals [19].…”

Spatial Heterogeneity of Rare Earth Elements: Implications for the Topsoil of Regional Ion-Adsorption Type Rare Earth Deposit Areas in Southern China

“…et Champ, together with herbs such as Dicranopteris dichotoma under the forest. The main exposed lithology is Yanshanian granite due to continuing weathering under special climatic, topographic, and geomorphic conditions [30]. A very thick crust of granite weathering is formed and the ionic REE ores are deposited by clay mineral adsorption over time.…”

“…The area at the top of the completely weathered layer is just the beginning of the weathering leaching zone. The peak range of mineral particles appears from 2.1-17.2 µm and the particle size in this area is approximately 70%, which is distributed as fine particles [12,30]. This particle size of clay minerals favors Ce enrichment.…”

“…The enrichment of ionic type rare earth deposits in Southern China is controlled by many factors, including original parent rock, pH values, weathering degree, landform, grain size, clay mineral content, soil organic matter, and so on [12,16,17,22,30,59]. The above ore forming factors of ionic type rare earth deposits can be used for reference in the spatial distribution and distribution pattern of REEs in topsoil.…”

Editorial for Special Issue “Leaching of Rare Earth Elements from Various Sources”

“…Four papers are dedicated to low-grade ores, such as coal and its derivates, clay minerals, soils, and red mud. The grade of the REEs of some of these ores ranges from 200 to 1000 ppm, with some remarkable advantages, including the easy leaching ability due to the simple ion-exchange mechanism [8,9]. Zhang et al [8] described a comprehensive literature survey with relevant scientific and technological discussions.…”