The Robert M. Buchan Department of Mining Graduate Theses

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    Selective Separation of Nd, Dy, Pr, and Tb from Synthetic Leaching Solution of Rare Earth Elements using Solvent Extraction and Ultrasonically Generated Emulsion Droplets
    Yildiz, Deniz; Mining Engineering; Sadri, Farzaneh; Ghahreman, Ahmad
    Rare Earth Elements (REE) have characteristic features making them irreplaceable in modern applications. As developing countries become more environmentally conscious, there is a growing need for green technologies that utilize critical metals like REE, resulting in a significant shift away from traditional energy sources. In hydrometallurgical processes for purifying REE from concentrated solutions, the Solvent Extraction (SX) technique plays a vital role in separating and ensuring the purity of the elements. It is widely utilized in the industry owing to its high extraction capacity and easy applicability. However, several challenges are faced when SX is operated to treat solutions with a low concentration of metal ions. These challenges include phase disengagement, solvent loss, high capital expenditures, and increased consumption of solvents. The drawbacks associated with using conventional separation techniques, i.e., SX, have directed special attention toward alternative methods. Emulsion droplets stand out by creating a larger surface area, increasing the mass transfer capacity. This study aims to present the outcomes of two distinct experiments; the first involves a synergistic SX process using Cyanex 572 and D2EHPA, this work is the first to use Cyanex 572 and D2EHPA together on the synergistic effect. The second involves an ultrasonic-based SX process utilizing Cyanex 572 droplets to minimize the drawbacks of conventional SX. The findings of this study suggest that a mixture of 50% Cyanex 572 and 50% D2EHPA, employed at pH 0.25, could be the ideal combination for achieving selective separation. Nevertheless, it is noteworthy that using sole Cyanex 572 resulted in even higher single-stage extraction percentages of dysprosium (Dy) and terbium (Tb), at 99.33% and 98.97%, respectively. The results obtained from the SX process employing sole Cyanex 572 indicate that Heavy Rare Earth Elements (Dy, Tb) exhibit a superior extraction rate at all aqueous/organic ratios. Specifically, extraction rates ranging from 98.65% to 99.39% for Dy and 98.92% to 99.41% for Tb were observed. Conversely, the extraction rate for Light Rare Earth Elements (LREE) remained relatively low (ranging from 15.18 %- 43.82 for Nd and 6.91 % - 37.77% for Pr). This finding is promising in achieving selective separation between HREE and LREE, which was a principal objective of this study. However, during the SX experiments with Cyanex 572 droplets, it was found that the LREE extraction rate remained high across different A/O ratios due to the augmented surface area generated by ultrasonic means.
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    Purification and Fractionation of Rare Earth Elements from Synthetic Pregnant Leach Solution using Solvent Extraction Approach
    Yildiz, Ilkay; Mining Engineering; Sadri, Farzaneh; Ghahreman, Ahmad
    The purpose of this study is to examine a two-step purification process for the separation of rare earth elements (REE) from impurities in a chloride pregnant leach solution. The first step aimed to eliminate iron impurities through the use of alkaline reagents, with the goal of recovering the lost REE through subsequent acid leaching. The second step utilized various extractants through solvent extraction to achieve selective REE extraction from cobalt. The iron removal process yielded conclusive results, showing that Fe precipitation from the leach solution was complete at pH 4.0 through the use of 1M sodium hydroxide as the alkaline reagent. This method demonstrated the lowest REE losses in comparison to using 5 wt.% calcium hydroxide as the reagent. The REE losses that did occur with the use of sodium hydroxide were attributed to REE ion hydrolysis and lower REE chloride solubility compared to that of Ca chlorides. As a result of these findings, it was suggested that sodium hydroxide be used for the iron removal process, with the subsequent recovery of REE lost to the precipitation step achieved through acid leaching. The results of the solvent extraction process revealed that Ionquest 801 was a more efficient extractant than Cyanex 272 for the selective separation of REE from cobalt. Specifically, at pH 3.0, Ionquest 801 displayed extraction percentages of 90% or more for all REE and achieved complete selective separation with cobalt. Cyanex 272, on the other hand, exhibited less effectiveness overall, but appropriate extraction percentages for terbium and dysprosium, 100% and 89.1% respectively. The findings from this study have significant implications for the industry's utilization of REE. Future research can center around enhancing these processes, with the intention of increasing the efficiency of REE extraction and separation.
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    Mining Engineering
    Boron ores have distinct issues related to their sparingly soluble nature, resulting in the accumulation of undesirable levels of solubilized species spreading to the surrounding area and water contamination. The presence of arsenic sulphides such as realgar and orpiment can potentially cause even greater problems to the environment due to their toxicity. Arsenic contamination in water sources is a significant environmental issue in some regions, leading to adverse health impacts and requiring remediation measures. A detailed experimental investigation was conducted to study the fundamental surface properties of arsenic-bearing minerals. Based on the previous research on the relationship between native floatability and crystal structure, realgar and orpiment were known to be inherently hydrophobic. In this work, realgar is shown to be more hydrophobic than orpiment due to the additional role of its capacity to form elemental sulphur. Such differences were studied through the determination of wettability profiles from film-flotation experiments for arsenic-bearing minerals, but also other sulphide minerals. Although, it is an oxidation product from arsenic sulphides, arsenolite (As2O3) was found to be strongly hydrophobic, which was characterized with respect to pH and reactions with metal ions. A UV method was developed based on quantitative analysis of elemental sulphur from solvent extraction of sulphide minerals, which was correlated with their film-flotation profiles. Monoclinic pyrrhotite indicates much greater amounts of elemental sulphur on its surface than hexagonal pyrrhotite. FTIR studies provided additional support for the presence of elemental sulphur on sulphide minerals, but the quantitative correlation with film-floatability and UV studies was lacking, which was attributed to the much finer particle size range required in the KBr methodology. Micro-flotation experiments were carried out with single minerals and mixed minerals involving realgar-orpiment-arsenolite and colemanite. Micro-flotation results were in general agreement with film-flotation results. Both direct flotation and reverse flotation approaches were tested for the separation of arsenic minerals. The kerosene flotation system involving sodium silicate as a depressant for colemanite was found to be the best option for the removal of arsenic minerals.
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    Flotation Investigations on Ni-Cu Sulphide Ores With Pyrrhotite, Talc and Pre-Oxidation Issues
    Arslangil, Sinan; Mining Engineering; Kelebek, Sadan
    Canadian Ni-Cu sulphide ores vary in complexities from location to location posing serious processing issues. This thesis represents an experimental investigation of the fundamental characteristics and flotation of two Ni-Cu sulphide samples, namely, an oxidized ore blend and a fresh ore blend. Bench-scale flotation tests were conducted to better understand the effects of complexity associated with gangue mineralogy involving talc, chlorite and pyrrhotite (Po) in the behaviour of low-grade blends assaying 0.4-0.5% Ni & 0.5-0.7% Cu. Po content at 5.8-7.5% was much higher than the pentlandite (Pn) and chalcopyrite (Cp) combined. The reagents included a collector (PIBX) and depressants (CMC, DETA, SMBS, YTD & FTD). The colour of the oxidized ore blend was yellowish brown due to the formation of iron oxide species compared to the dark greyish colour of the fresh ore blend. The ionic conductivities of the oxidized ore blend slurry were much higher than those with the fresh-ore blend, which were, in turn, higher than the case with the tap water used. The pH value of the oxidized ore blend slurry was lower than the fresh-ore blend case due to acid-producing reactions, requiring about 2.2 more lime in batch tests. As part of characterization, extraction tests were conducted using toluene and EDTA/DETA to quantify elemental sulphur and metal ions suspected of causing inadvertent activation of Po. Through flotation investigations, CMC, YTD & FTD for depression of talc/chlorite and DETA & SMBS for Po depression were demonstrated to be effective when used in selected combinations. Flotation selectivity was assessed using plots of concentrate grade/recovery and relative recoveries of Po vs Pn and Cp. The relation between extracted sulphur and the mineralogical composition of the concentrates investigated using multivariable regression indicated strong correlations for collectorless flotation of the oxidized ore blend, indicating elemental sulphur is associated primarily with Pn and secondarily with Cp. Flotation kinetics involving the reagent systems and particle size effects were analyzed using the first-order models. Overall, the most effective reagent formulation for Po depression was SMBS/DETA combination, but YTD was also highly effective. Particle size distribution was found to be a significant factor, with finer particle sizes resulting in increased recovery of Pn and Cp but decreased recovery of Po.
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    Studies on Bastnaesite Flotation: Mineral-Mineral Interactions and Selectivity Issues
    Ust, Selami; Mining Engineering; Kelebek, Sadan
    This thesis describes an experimental study on the flotation of a Canadian REE ore. The mineralogical analysis carried out indicated bastnaesite as the REE mineral containing Ce, La, Nd, and others in decreasing order of their concentrations. The focus was the examination of the separation trends of the major gangue mineralogy associated with bastnaesite. Collectors used were carboxylic types (e.g., NaOL, and veg. oil) and phosphate types (cetyl, PCP and dodecyl, DDP) and various depressants (e.g., sodium silicate, citric acid, and others). Micro-flotation techniques served to screen these reagents for their effectiveness in various combinations using both single-mineral and mixed mineral as well as batch-flotation experiments. NaOL was generally too strong for selective flotation despite using some depressants. PCP indicated promising results in micro-flotation but was not effective in batch flotation. DDP was better than PCP in batch flotation tests. Sodium silicate was effective for the depression of quartz if it was not heavily activated. TB is a soft depressant in comparison with sodium silicate. In many cases, the results that appeared to be promising according to single mineral micro-flotation tests were not effective when mixed minerals were used. Calcite exhibited a strong antagonistic effect on bastnaesite flotation with various collectors. The best results on selective separation of bastnaesite were obtained using NaOL and Sodium hexametaphosphate (SHMP) combination. SHMP consistently depressed bastnaesite in both single and mixed mineral cases, allowing for reverse flotation of calcite, which was studied in detail using the Box-Behnken method of DoE statistical analysis. Batch flotation tests further revealed the importance of mineral-mineral interactions, especially as induced by calcite. However, in batch tests, calcite’s interaction was not antagonistic. It induced inadvertent activation on quartz while actively participating in flotation by itself as its concentration increased in the feed. TB was found effective in the depression of quartz. DDP produced the best grade-recovery for bastnaesite in batch flotation using DI water indicating its high sensitivity to water chemistry. The findings of this study have implications for the development of selective flotation strategies for bastnaesite ores, which are important sources of rare earth elements in various industrial applications.