Beneficiation of Low-Grade Rare Earth Ore from Khalzan Buregtei Deposit (Mongolia) by Magnetic Separation

The global demand for rare earth elements (REEs) is expected to increase significantly because of their importance in renewable energy and clean storage technologies, which are critical for drastic carbon dioxide emission reduction to achieve a carbon-neutral society. REE ore deposits around the world are scarce and those that have been identified but remain unexploited need to be developed to supply future demands. In this study, the Khalzan Buregtei deposit located in western Mongolia was studied with the aim of upgrading low-grade REE ore via magnetic separation techniques. The total REE content in this ore was ~6720 ppm (~3540 ppm light REE (LREE) + ~3180 ppm heavy REE (HREE)) with bastnaesite, pyrochlore, synchysite, and columbite-(Fe) identified as the main REE-bearing minerals. As the particle size fraction decreased from −4.0 + 2.0 mm to −0.5 + 0.1 mm, the recovery by dry high-intensity magnetic separation (DHIMS) increased from 20% to 70% of total rare earth oxide (TREO) while the enrichment ratio reached 2.8 from 1.3. Although effective, gangue minerals such as quartz and aluminosilicates were recovered (~22%) due most likely to insufficient liberation. Meanwhile, the wet high-intensity magnetic separation (WHIMS) could produce a magnetic concentrate with TREO recovery of ~80% and enrichment ratio of 5.5 under the following conditions: particle size fraction, −106 + 75 μm; feed flow rate, 3.2 L/min; magnetic induction, 0.8 T. These results indicate that combining DHIMS and WHIMS to upgrade the low-grade REE ore from the Khalzan Buregtei deposit is an effective approach.

Application of environmental magnetism to trace sediment sources contributing to Kruger National Park reservoirs

Sediment source fingerprinting using environmental magnetism has successfully differentiated between sediment sources in different regions of South Africa. The method was applied in the natural landscape of the Kruger National Park to trace sediment sources delivered to four reservoirs (Hartbeesfontein, Marheya, Nhlanganzwani, Silolweni) whose contributing catchments were underlain by a range of igneous, metamorphic, and sedimentary rocks. This research attempted to evaluate the impact of vegetation, lithology, and particle size controls on the ability of magnetic signatures to discriminate between lithology-defined potential sources. Potential source samples were collected from each lithology present in all catchments, except for the Lugmag catchment where the lithology was uniform, but the vegetation type varied significantly between woodland and grassland. One sediment core was taken in each of the four catchment reservoirs where there was more than one lithology present in order to unmix and apportion contributing sediment sources. Sampling time in the field was often restricted to short periods, dependent on anti-poaching activities and movement of free-roaming wildlife across the Park. This occasionally led to the sub-optimal collection of enough source samples to capture source signature variability. Mineral magnetic parameters were unable to discriminate between vegetation-defined sediment sources in the Lugmag catchment (homogenous underlying lithology) but were able to discriminate between lithology-defined sediment sources (to varying degrees) in the other four catchments. The contributions of each lithology-defined sediment source were estimated using a straightforward statistical protocol frequently used in published literature that included a Mann-Whitney U or Kruskal-Wallis H test, mass conservation test, discriminant function analysis, and an (un)mixing model. A contribution from each lithology source to reservoir sediment was estimated. Connectivity was a significant factor in understanding erosion in each of the catchments. Both longitudinal (e.g., drainage density) and lateral connectivity (e.g., floodplain - river) were important. Travel distance of eroded sediment to reservoirs was also an essential element in two of the four catchments. There are no defined floodplains, so channel bank soils are very similar to the catchment soils. Therefore, channel bank storage potential would be similar to the storage potential within the catchment. Vegetation played a crucial role in protecting soils, by reducing ii erosion potential as well as trapping and storing sediment, thereby interrupting lateral connectivity. Underlying geology and soils are determining factors of vegetation type and density. A published study estimated catchment area-specific sediment yields for different KNP catchments, including the Hartbeesfontein, Marheya, Nhlanganzwani and Silolweni catchments. The published data was used in combination with the (un)mixing model source contribution estimates of this thesis to determine specific sediment yields by lithology, i.e., for each catchment source. The polymodal particle size characteristics of the sample material led to an investigation into particle size controls on the ability of magnetic signatures to discriminate between potential sources. Due to time constraints, only the Hartbeesfontein and Marheya catchments were tested for grain size differences. For each catchment, one bulk sample was created for each lithology source. This bulk sample was divided into 10 subsamples. The samples were then fractionated into four particle size fraction groups: coarse (250 – 500 μm), medium (125 – 250 μm), fine (63 – 125 μm), and very fine (<63 μm). Reservoir samples were also bulked to create 10 down-core samples for each reservoir, and the samples were also fractionated into the four fraction groups. The same statistical protocol was applied to the fractionated samples and contribution estimates were obtained by lithology for each particle size fraction group. The goodness of fit and uncertainty of the (un)mixing model varied in each catchment, with the two measures of accuracy often showing an inverse relationship. The fractionated modelling estimated the same primary source in the two catchments as in the unfractionated modelling. However, additional information on the secondary and tertiary sources was obtained. Connectivity remained a significant factor in interpreting the results of the fractionated analysis. Specific sediment yields were estimated for each catchment source per particle size fraction group. These sediment yields provided a deeper understanding of sediment transport through a catchment and which particle size groups are most important in catchment erosion. An original contribution to research was made by estimating source contribution estimates for the four reservoirs, quantifying sediment yields for each catchment lithology and then for each catchment lithology by particle size. Mineral magnetic tracing of the catchments was applied for the first time in this region of South Africa.

Characterization of PM-Bound Heavy Metal at Road Environment in Tianjin: Size Distribution and Source Identification

To determine the size distribution and source identification of PM-bound heavy metals in roadside environments, four different particle size (<0.2 μm, 0.2–0.5 μm, 0.5–1.0 μm and 1.0–2.5 μm) samples were collected and analyzed from four different types of roads during the summer of 2015 in Tianjin. The results showed that the concentrations of PM-bound heavy metal from the roadside environment sampling sites were 597 ± 251 ng/m3 (BD), 546 ± 316 ng/m3 (FK), 518 ± 310 ng/m3 (JY) and 640 ± 237 ng/m3 (WH). There were differences in the concentrations of the heavy metal elements in the four different particle size fractions. The concentrations of Cu, Zn, Cd, Sn and Pb were the highest in the larger particle size fraction (0.5–2.5 μm). Cd, Cu, Zn and Pb were the elements that indicated emissions from tire wear and brake pad wear. The concentrations of Cr, Co and Ni were the highest in the smallest particle size fraction (<0.5 μm), indicating that motor vehicle exhaust was their main source. The correlation analysis results showed that there are differences in the concentration, distribution and correlation of different PM-bound heavy metals in different particle size fractions. The PCA results show that the accumulative interpretation variances of PM0.2, PM0.2–0.5, PM0.5–1.0 and PM1.0–2.5 reached 80.29%, 79.56%, 79.57% and 71.42%, respectively. Vehicle exhaust was the primary source of PM-bound heavy metal collected from the roadside sampling sites, while brake pad wear and tire wear were the second most common sources of the heavy metal.

PROBABILITY-DETERMINED DESIGN PLANNING FOR DECOMPOSITION OF SILICON-CONTAINING SAMPLES

An alternative method of acid leaching of silicon-containing metallurgical samples using ultrasonic vibrations is proposed in order to extract Si quantitatively from the solid phase into the solution. The effect of ultrasonic vibration, leaching temperature, phase contact time, weight of the sample, particle size, fraction of hydrofluoric acid in the reaction mixture was investigated. The results of laboratory studies showed that acid leaching assisted by ultrasonic vibrations is an efficient, safe and economically profitable way of sample preparation of silicon-containing metallurgical samples.

Cathodoluminescence and Laser-Induced Fluorescence of Calcium Carbonate: A Review of Screening Methods for Radiocarbon Dating of Ancient Lime Mortars

ABSTRACTAccurate radiocarbon (14C) dating of lime mortars requires a thorough mineralogical characterization of binders in order to verify the presence of carbon-bearing contaminants. In the last 20 years, cathodoluminescence (CL) has been widely used for the identification of geologic calcium carbonate (CaCO3) aggregates and unreacted lime lumps within the particle size fraction selected for carbon recovery. These components are major sources of older and younger carbon, respectively, and should be removed to obtain accurate age determinations. More recently, laser-induced fluorescence (LIF) has provided another means of investigating the preservation state and composition of CaCO3 binders. Considered the growing interest of the mortar dating community in the latest advancements of these analytical methods, here we review the principles of CL and LIF of CaCO3, their instrument setup, and their application to the characterization of ancient lime mortars used for 14C dating. In addition, we provide examples of SEM-CL and LIF analyses using high-resolution instrumentation, we discuss current issues and propose future lines of research.

Laser Diffraction as An Innovative Alternative to Standard Pipette Method for Determination of Soil Texture Classes in Central Europe

The paper presents the comparison of soil particle size distribution determined by standard pipette method and laser diffraction. Based on the obtained results (542 soil samples from 271 sites located in the Nitra, Váh and Hron River basins), regression models were calculated to convert the results of the particle size distribution by laser diffraction to pipette method. Considering one of the most common soil texture classification systems used in Slovakia (according to Novák), the emphasis was placed on the determination accuracy of particle size fraction <0.01 mm. Analysette22 MicroTec plus and Mastersizer2000 devices were used for laser diffraction. Polynomial regression model resulted in the best approximation of measurements by laser diffraction to values obtained by pipette method. In the case of particle size fraction <0.01 mm, the differences between the measured values by pipette method and both laser analyzers ranged in average from 3% up to 9% and from 2% up to 11% in the case of Analysette22 and Mastersizer2000, respectively. After correction, the differences decreased to average 3.28% (Analysette22) and 2.24% (Mastersizer2000) in comparison with pipette method. After recalculation of the data, laser diffraction can be used alongside the sedimentation methods.

Effects of processing whole oats on the analysis and fate of mycotoxins and ergosterol

Grinding and dividing equipment were evaluated for their ability to comminute and divide ground oats in preparation for mycotoxin analysis. Four different grinders, using various settings, were evaluated for their ability to comminute oats and produce small particle sizes. Rotor beater type grinders produced the more desirable finer ground samples as compared to burr type mills. Four different division methods (manual scooping, rotary sample division, and two designs of gravity-fed dividers) were assessed for their ability to produce sub-samples with consistent particle size fraction distributions. No practical differences were observed on the particle size fraction distribution of test portions of finely ground oats produced using the four different division methods; therefore, no effects on mycotoxin analysis were anticipated. The effects of processing naturally contaminated whole oats on mycotoxin concentrations was also assessed. Laboratory scale dehulling, steaming, and kilning were examined. Dehulling showed the greatest impact and removed 60-100% of various Fusarium- and Alternaria-produced mycotoxins, as well as ergosterol, present on the naturally contaminated whole oats. Different from the other analytes studied, only 48% of the mycotoxin plant transformation product deoxynivalenol-3-glucoside was present in hulls and removed during dehulling. Steaming and kilning appeared to increase ergosterol in groats, as well as decrease deoxynivalenol and deoxynivalenol-3- glucoside. The observed inconsistent changes in concentrations of tentoxin after heat treatment of groats appeared to be due to sample heterogeneity.