Studying digestion conditions of Vietnamese monazite with acid sulfuric for the recovery of rare earth elements, thorium and uranium

The monazite ore is a commercial source of Th, U and rare earth in Vietnam. There are two methods, which were often applied to decompose monazite ore are alkaline and sulfuric methods. But in Vietnam, sulfuric method is more suitable due to the simple technology. In sulfuric acid treatment its breakdown using sulfate process for recovering of REEs, thorium and uranium. In this study, the parameters such as ore/acid ratios, the digestion temperature and the time of degestion were investigated to determine optimal digestion conditions for high recovery of main ingredients (REEs, Th, U) in monazite ore. The results shown that the optimal parameters for the digestion are ore/acid ratio 1.2:1, digestion temperature - 300oC and time of digestion - 1 hour, the recoveries for REEs, Th and U are namely 90%, 85% and 65%, respectively.

Leaching the Unleachable Mineral: Rare Earth Dissolution from Monazite Ore in Condensed Phosphoric Acid

Monazite is a poorly soluble mineral of rare earth phosphate. It is an ore of the rare earths which is difficult to break down; in industry either concentrated sulphuric acid or caustic soda is used to attack finely ground monazite at between 140 °C and 400 °C. In these processes, the rare earths are converted into different solid compounds, undergoing an incomplete conversion. Here we show a new process for a direct and much faster breakdown of monazite by simple dissolution under milder conditions. Condensed phosphoric acid was used to dissolve rare earths (up to 96 g/L) from unground monazite sand from four sources. Greater than 99% of light rare earths dissolved within 30 min at 260 °C. The cooled solution can be diluted to an extent with water to reduce viscosity for analysis or further processing. This method of dissolution avoids the use of strong acids/bases and reduces the risk of dusk exposure from fine grinding of particles.

Study on Preparation and Characterization of La2O3 Derived from Thai Monazite Ore Processing Supported Coal Fly Ash Catalyst

This research aims to study the preparation and characterization of La2O3 supported coal fly ash catalyst. Studied La2O3 and coal fly ash (CFA) were obtained from Thai monazite ore processing and local supplier, respectively. The catalyst was prepared by wet impregnation method. The influences of La2O3 loading and impregnation temperature on the chemical composition, crystalline phase and surface morphology of the catalyst were examined by varying the amount of La2O3 (5, 10 and 20 wt%) and the impregnation temperature (room temperature, 100, 150 and 200 °C). Characterizations such as WDXRF, XRD and SEM were carried out. The XRD results demonstrated that the La2O3 was highly dispersed on the CFA support. A high La2O3 loading resulted in an increase free CaO dissolvation during the impregnation which inhibited the interaction between SiO2 and La2O3. The impregnation temperature had no significant effect on the chemical and physical properties of the catalyst. The coexist of Fe3O4 in the CFA support might impact to hinder the incorporation of La2O3 into SiO2 matrix.

Effect of La2O3 Derived from Thai Monazite Ore Chemical Processing on the Properties of SO4-1/ZrO2

La2O3 derived from Thai monazite ore chemical processing was used as a precursor to prepare SO4-1-1%La2O3/ZrO2 solid acid catalyst. The SO4-1-1%La/ZrO2 catalyst was synthesized by co-precipitation with subsequent impregnation method. Various characterization techniques such as X-ray diffraction (XRD), nitrogen adsorption-desorption (BET) and Fourier transform infrared spectroscopy (FTIR) were used to study crystalline structural, textural and acid properties of the prepared catalysts. XRD results revealed that the presence of stable La2O3/ZrO2 tetragonal phase for SO4-1-1%La2O3/ZrO2 was observed at calcined temperature up to 600 °C. No diffraction peaks of La2O3 appeared in the profile of SO4-1-1%La2O3/ZrO2, indicated that the La2O3 was finely dispersed on the ZrO2 support. The doping of SO4-1-ZrO2 with La2O3 led to a significant decrease in its BET surface area, total pore volume and pore diameter. A relatively uniform pore size distribution of SO4-1-1%La2O3/ZrO2 catalyst with average pore diameter of 6 nm was found at the calcined temperature of 600 °C. Lewis acid sites existed in the synthesized SO4-1-1%La2O3/ZrO2 were lower than that counterpart. A loss of sulfate species was noted at high calcined temperature. The prepared SO4-1-1%La2O3/ZrO2 will be further used as a solid catalyst for transesterification of waste cooking oil to biodiesel, and the addition of La2O3 on the support could lead to enhance the catalytic activity and thermal stability.

Incorporation of Indigenous Microorganisms Increases Leaching Rates of Rare Earth Elements from Western Australian Monazite

A large number of microbial species commonly called phosphate solubilizing microorganisms (PSMs) are efficient at converting insoluble phosphate to soluble forms to prevent phosphorus limitation. This study examined the impact that PSMs had on a sterile and non-sterile monazite source and determined that they could be applied for bioleaching purposes to recover rare earth elements (REEs). On sterile monazite, Penicillum sp. released a total REE concentration of 12.32 mg L-1 after incubation for 8 days, however, this doubled when inoculated on to non-sterile ore (23.7 mg L-1). Similar results were recorded with Enterobacter aerogenes, Pantoea agglomerans and Pseudomonas putida. Abiotic controls leached a total REE level of 0.65 mg L-1. Examination of the leachate by HPLC identified several low molecular weight organic acids that corresponded with decreases in the media pH. The presence of a native consortia from the monazite ore combined with a known PSMs was more effective at leaching REEs from the monazite matrix than a single isolates or by the native population alone.