Papers by Keyword: Monazite

Abstract: Malaysia has many potential mineral resources including some rare earth elements (REE) minerals such as monazite. REE play critical roles in the applications of advanced materials. Alkaline fusion was introduce to monazite to break the bonding between Light Rare Earth Elements (LREE) and phosphate. In this study, critical parameter such as fusion temperature (100 °C to 250 °C) and duration (1 to 4 hours) were studied. The results shows that it is possible to recover nearly 100% of Neodymium after 2 hours fusion at 150 °C. In the other hand, more than 99% of Cerium and Lanthanum were recovered after 3 hours fusion at similar temperature. By recover most of the element, expectantly high yield of single LREE can be achieved in the forthcoming.

Abstract: The objective of this study to investigate microwave-assisted digestion as a rapid sample preparation method for the determination of REEs in Malaysian monazite using Inductively Coupled plasma-mass spectrometry (ICP-MS). Finely powdered monazite (D90 < 75μm) was the raw material for the digestion and fusion procedures. In the Li-borate fusion method, the digestion was achieved by lithium tetraborate: metaborate flux (Li₂B4O₇: LiBO₂) flux fusion followed by acid attack, using nitric acid (HNO₃). The second method, the microwave-assisted digestion method, involved digestion of the monazite in a mixture of H₂SO₄, HNO₃, and HF, followed by neutralization of the insoluble fluorides and complexation of residual HF. The concentrations of REEs, measured by both the methods, were in agreement with each other, except for the values of P and Si, which were slightly apart. Both the sample dissolution methods offer feasible means of quantifying REEs in the monazite sample, but only a combined microwave digestion-fusion technique yields complete quantitative data for monazite-type samples.

Abstract: The Brazilian reserves of rare earths were updated. Brazil is among the countries with the largest reserves of rare earths in the world. Rare earths present a series of applications in the high technology industry. Magnet production is one of the applications requesting largest volumes of rare earths. Another relevant application is catalysis and Petrobras needs 1000 tons/year of La₂O₃ for petroleum refining. CBMM mine has a pilot plant able to produce tons of separated rare earth oxides, notably didymium (a mixing of Nd and Pr oxides) used in magnet manufacture. Serra Verde mine in Goiás also produced separated rare earth oxides. The magnet production in Brazil can be important for the high efficiency electrical motors industry and also for the automotive industry.

Abstract: Monazite (LaPO₄) coatings were deposited on woven cloths of alumina fibers by heterogeneous nucleation and growth using solution precursors. Coatings were characterized by scanning electron microscopy, and X-Ray diffraction; thermogravimetric analysis was performed on LaPO₄ precursors. The results show that the optimum ration of La:citrate:P is 1:2:5 in the LaPO₄ precursor solution. Coating thickness distributions were measured and analyzed. Uniform monazite coatings (210-250nm) were obtained after depositing in the precursor solution, drying and heating at 900°C for 5 min for 6 recycles. Al₂O_3f/ Al₂O₃ composite with the LaPO₄coating as the CMC interface revealed goodmechanical strength and the fracture mode is ductile fracture. The tensile toughness is 142.2 MPa, the bending toughness is 288.6MPa and the fracture toughness12.2 MPa•m^1/2.

Abstract: Aspergillus niger PSSG8 is assisted bioleaching of monazite to recover the constituent metals were investigated. Bioleaching was carried out using Bromfield (BM1/10P & BM-P) and sucrose media (SM1/10P & SM-P) with different levels of Phosphate under rotary and stationary conditions. The growth of the A. niger PSSG8 significantly reduced the media pH to acidic. However, the media pH changed later in rotary shake flasks and were stable in roux bottles. A similar trend was observed for ORP. ORP increased as leaching progressed, but in rotary shake flasks ORP started decreasing after 15 days in Bromfield and 30 days in sucrose media. Fungal growth was maximum in SM when comparing to BM. The reduction and the omission of phosphate in both media did not significantly influence the culture parameters including the yield of biomass. ICP-AES analysis of leach liquor showed highest recovery of cerium (Ce) (1419 µg/L in BM-P) and thorium (Th) (182 µg/L in SM1/10P) in rotary conditions when comparing to the stationary conditions (229 µg/L Ce in BM 1/10P & 159 µg/L in SM-P). Reduction in the metal concentration was observed in the rotary shake flasks after 15 days of incubation. It was due to the biosorption of released metals by the fungal mycelium. Uranium was not detected in any of the media tested. SEM studies of the partially bioleached and control mineral particles show no changes in the surface features.

Abstract: Nanometer LaPO4 powders were synthesized by liquid-liquid direct precipitation method. La(NO3)3•6H2O and (NH4)3PO4•3H2O were used as raw materials. The calcining temperature was 900°C, 1000°C, 1100°C, respectively. DTA result shows that the LaPO4 precursor is LaPO4•4H2O. The calicined powders were characterized by X-ray powder diffraction (XRD) and Scanning Electron Microscope (SEM), and exhibited a pure LaPO4 phase with a monazite structure about 50-100 nm in diameter size. With the calcining temperature increasing, the crystallization of the LaPO4 became better and the grain shape changed from elongated grain shape to spherical grain shape.

Abstract: Monazite(LaPO4)-coated alumina-fiber/alumina-YAG (Y3Al5O12) matrix composites were fabricated by in-situ coating of monazite followed by hot-pressing, and the effects of coating and sintering condition on mechanical properties of the composite were examined. Alumina powder and YAG powder (weight ratio, 95:5) were used as raw materials for green sheets, which was fabricated by tape casting technique. Monazite was synthesized by the in-situ reaction of La(NO3) solution with H3PO4 on the surface of fibers. After slurry infiltration into the coated fiber bundles, the fiber cloths were laminated with the green sheets alternately, then they were heat-treated, finally sintered by hot-pressing at various temperatures. The mechanical properties of the composites were changed by the fabrication conditions. Non-brittleness of the composites reduced with the increase of sintering temperature. The composites sintered at 1200oC showed the highest Weibull modulus and pseudo-ductility.

Abstract: Thermal conductivity and microstructure of 3YSZ/monazite-type LaPO4 composites were investigated. Powders were prepared by two kinds of preparation methods such as conventional ball-milled and chemical precipitation of LaPO4 on the zirconia powder surface. Thermal conductivity of 3YSZ/monazite-type LaPO4 composites was lower than that of 3YSZ. That of 3YSZ/monazite-type LaPO4 composites was influenced on the powder preparation methods and as a function of measured temperature. Microstructure of 3YSZ/monazite-type LaPO4 composites was not much affected by the amount of dispersed LaPO4 particles. 3YSZ/monazite-type LaPO4 composites were observed to pores after thermal etched. The pore of synthesized specimens was observed remarkably in compared with conventional ball-milled specimens.

Abstract: Sintering behaviour of monazite powder was investigated as a function of the powder milling conditions. To this aim, two techniques were used: attrition-milling and mixer-milling. We show that it is of prime importance to control all the milling parameters in order to obtain controlled microstructure and to avoid abnormal grain growth or residual large porosity.