Minerals

Separation of heavy rare earth elements from calcium and light rare earth elements extracted from Estonian phosphorite ore by acid leaching and subsequent liquid extraction has been conducted and analyzed. For initial leaching, nitric acid, hydrochloric acid, and orthophosphoric acid with different concentrations have been utilized. For the final separation of heavy rare earth elements, a liquid extraction with bis(2-ethylhexyl) phosphate (D2EHPA) or 2-ethylhexyl hydrogen-2-ethylhexyl phosphonate (P507) at different acidic concentrations has been applied. After leaching and extraction, all samples were characterized using the inductively coupled plasma mass spectrometry method (ICP-MS/MS). Optimal conditions for both extracting agents have been established. All rare earth elements + Y have been recovered in acid leaching, and heavy rare earth elements (elements Gd-Lu) have been selectively recovered by D2EHPA with 5 M nitric acid leaching and by P507 with 1 M nitric acid leaching. The presence of Sc has not been detected in Estonian phosphorite ore.

Increasing constraints related to water consumption and operational complexity have intensified interest in dry coal beneficiation as an alternative to conventional wet cleaning, particularly for low-calorific coals used in thermal power plants. In this study, the performance of a gravity-based dry beneficiation process using an air table was experimentally investigated for run-of-mine coals from the Soma Coal Basin, utilized in the Soma A Thermal Power Plant. The coal was crushed to −10 mm and classified into three size fractions, 5–10 mm, 3–5 mm, and 1–3 mm, before beneficiation. A pilot-scale air table with a capacity of 10 t/h was employed, and operating parameters including table inclination, airflow rate, and vibration frequency were optimized for each size fraction. Clean coal yields of 86.8–88.7% were achieved, while the ash content was reduced from 32 to 35% in the feed to 27.8%–29.7% in the clean coal (dry basis), remaining within the acceptable ash limits of the boiler design. The reject fractions exhibited high ash contents of approximately 71%–72%, indicating effective de-stoning and removal of high-density gangue minerals. Low and consistent E_p values (0.05–0.06) together with nearly constant cut-point densities (D₅₀ ≈ 1.82%–1.83 g/cm³) demonstrated sharp and stable density-based separation. The dust fraction remained limited (1.4%–2.1%), confirming mechanically stable operation. The removal of approximately 10% of the feed as high-density reject was found to reduce coal milling energy demand and lower the energy consumption of ash handling and disposal systems. Overall, the results show that air table-based dry beneficiation enables water-free and energy-efficient pre-concentration of low-calorific coals, offering strong potential for application in water-scarce regions.

The Three-Product Dense Medium Cyclone (TPDMC) has been widely applied in the coal preparation industry, yet the adaptive optimization of its parameters based on feed characteristics remains under-researched. This study utilizes a semi-industrial experimental platform with a JX300/240 TPDMC to investigate the influence of pump frequency (PF) and four second-stage structural parameters—cylindrical section length (L_2cy), overflow pipe insertion depth (Dep_2o), overflow pipe diameter (D_2o), and conical section length (L_2co)—on the separation performance of three feed materials with distinct washability characteristics. Experiments conducted with density tracer particles revealed a distinct hydrodynamic coupling effect: PF and D_2o were the only factors modulating inlet pressure (varying from 0.12 to 0.45 bar), which directly altered the clean coal yield. In contrast, L_2cy, Dep_2o, and L_2co primarily influenced the second-stage internal flow field and concentration effect, thereby affecting the yield and ash content of middling coal (gangue). To quantify feed-specific sensitivities, a new index, Near-Gravity-Range Material (NGRM), was proposed. Results demonstrated that Sample-3 exhibited the highest sensitivity to parameter variations, with its middling coal yield variation reaching 41.25% due to its high NGRM of 71%. Furthermore, statistical analyses were conducted to quantify the influence of each parameter on the heavy product partition ratio across different density fractions. Based on these findings, the following targeted optimization strategies are proposed: (1) for feeds rich in the 1.40–1.50 RD range, increasing PF or decreasing D_2o is recommended to enhance clean coal yield; (2) for materials dominated by the 1.7 ± 0.10 RD fraction, increasing D_2o, PF, or L_2cy maximizes middling coal recovery; and (3) for feeds high in the 1.90 ± 0.10 RD fraction, reducing Dep_2o, PF, L_2cy, or L_2co effectively minimizes middling coal contamination by high-density particles.