aaron noble - Academia.edu (original) (raw)

Papers by aaron noble

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022

Minerals, 2022

The development of processing techniques for the extraction of rare earth elements and critical m... more The development of processing techniques for the extraction of rare earth elements and critical minerals (REE/CM) from acid mine drainage precipitates (AMDp) has attracted increased interest in recent years. Processes under development often utilize a standard hydrometallurgical approach that includes leaching and solvent extraction followed by oxalic acid precipitation and calcination to produce a final rare earth oxide product. Impurities such as Ca, Al, Mn, Fe and Mg can be detrimental in the oxalate precipitation step and a survey of the literature showed limited data pertaining to the REE precipitation efficiency in solutions with high impurity concentrations. As such, a systematic laboratory-scale precipitation study was performed on a strip solution generated by the acid leaching and solvent extraction of an AMDp feedstock to identify the optimal processing conditions that maximize REE precipitation efficiency and product purity while minimizing the oxalic acid dosage. Given ...

Minerals Engineering, 2021

Abstract Recent efforts have shown that acid mine drainage precipitates (AMDp) may be a promising... more Abstract Recent efforts have shown that acid mine drainage precipitates (AMDp) may be a promising source of rare earth elements and critical materials (REE/CM). To better understand this resource, several particle characterization studies were conducted on AMDp samples from three AMD treatment sites in Northern and Central Appalachia. This work included the determination of particle size, size distribution, morphology, mineralogy, chemical speciation, and rare earth content. While the particle characteristics and mineralogy varied considerably from site to site, sequential extraction tests showed that the largest portion of REEs (45% to 75%) were found in soluble phases bound to Fe-Mn oxides. Carbonates (5% to 16%) and insoluble residues (4% to 24%) were also found to be significant in some samples, suggesting that different AMD chemistry and AMD treatment approaches can lead to substantial variation in the deportment of REEs to the various chemical phases. Altogether, the results suggest that chemical extraction of REEs from AMDp can be achieved under mild conditions with high recovery values; however, the significant site-by-site variation will necessitate detailed testing of individual samples to determine the overall economic viability.

Minerals, 2021

In recent years, acid mine drainage (AMD) has emerged as a promising unconventional source of rar... more In recent years, acid mine drainage (AMD) has emerged as a promising unconventional source of rare earth elements (REEs) and other critical minerals (CMs) such as cobalt and manganese. In this regard, AMD provides a natural heap leaching effect that extracts and concentrates REE/CM from the host strata creating a partially enriched feedstock suitable for downstream extraction, separation, and recovery. While several prior studies have described processes and approaches for the valorization of AMD, very few have described the supply chain and infrastructure requirements as well as the associated economic assessment. To that end, this paper provides a fundamental economic assessment of REE/CM recovery from AMD using a network sourcing strategy in addition to a robust, flexible feedstock separations and refining facility. The methodology of this paper follows that of a typical techno-economic analysis with capital and operating costs estimated using AACE Class IV (FEL-2) guidelines. To...

Mining, Metallurgy & Exploration, 2021

International Journal of Coal Preparation and Utilization, 2019

A novel approach to robust optimization of coal blending operations is proposed. While many rigor... more A novel approach to robust optimization of coal blending operations is proposed. While many rigorous mathematical approaches have been developed for this problem in the past, most neglect the uncertainty associated with both the inherent coal quality attributes as well as the sampling and measurement protocols used to measure those attributes. This uncertainty may lead to the imprecise estimation of quality values and force operators to adopt a conservative blend strategy based on safety factors and simple heuristics. One promising approach to rigorously address this shortcoming is through robust optimization (RO), a unique approach to handle data with uncertain and unspecified statistical distributions. In the current work, we first derive a deterministic optimization problem using the premium/penalty structure in typical coal sales contracts. This formulation is then translated to a robust formulation and solved as a Mixed Integer Nonlinear Program (MINLP). A numerical example is presented to demonstrate the utility of the method and to compare the deterministic solution, as the most optimistic and risky blending plan, with the RO solution, as the more pessimistic, yet robust, plan. The proposed strategy can help decision-makers achieve the economic and strategic goals of the operation at acceptable risk levels.

Minerals, 2020

Many studies have been published in recent years focusing on the recovery of rare earth elements ... more Many studies have been published in recent years focusing on the recovery of rare earth elements (REEs) from coal-related materials, including coal, coal refuse, coal mine drainage, and coal combustion byproducts particularly fly ash. The scientific basis and technology development have been supported by coal geologists and extractive metallurgists, and through these efforts, the concept has progressed from feasibility assessment to pilot-scale production over the last five years. Physical beneficiation, acid leaching, ion-exchange leaching, bio-leaching, thermal treatment, alkali treatment, solvent extraction, and other recovery technologies have been evaluated with varying degrees of success depending on the feedstock properties. In general, physical beneficiation can be a suitable low-cost option for preliminary upgrading; however, most studies showed exceedingly low recovery values unless ultrafine grinding was first performed. This finding is largely attributed to the combinati...

Fuel, 2020

Lithium recovery from the density fractions of Baker (namely West Kentucky No. 13) seam coal was ... more Lithium recovery from the density fractions of Baker (namely West Kentucky No. 13) seam coal was investigated in this study. Proximate and elemental analyses showed that lithium contents in the 1.8-2.2 SG and 2.2 SG sink fractions were 185 ppm and 150 ppm, respectively, which are significantly higher than the average content of coal sources (12 ppm) and coal ashes (66 ppm) worldwide. Moreover, due to the high lithium contents and mass distribution, nearly 90% of the lithium present in the Baker coal sample was distributed in the two density fractions. Direct leaching using a HCl solution resulted in less than 10% lithium recovery, which was due to nearly 90% of the lithium being associated with insoluble solids as determined by the results from sequential extraction tests. Calcination of both density fractions under 600°C for two hours followed by leaching resulted in recovery increases in the range of 70% to 80%. The pyro-metallurgical pretreatment step converted most of the associated lithium minerals to more easy-to-leach forms such as carbonate and metal oxide. Based on mineralogy characterization and leaching test results, it was concluded that the positive effects of calcination on lithium leachability resulted from the dehydration and disintegration of kaolinite as well as dehydroxylation and expansion of muscovite/illite. An analysis of the leaching kinetics revealed that the leaching rate of lithium was controlled by interface transfer and diffusion across the product layer and was negatively impacted when the calcination temperature exceeded 600°C due to sintering of the kaolinite. China also controlling significant holdings [6]. Given the criticality of this resource and the importance to consumer and energy products, several researchers have recently assessed a number of alternative and unconventional sources of lithium [7,8]. Coal and coal byproducts are known to contain numerous trace elements, sometimes at elevated concentrations [9-11]. Since 2014, the U.S. Department of Energy has investigated the technical and economic feasibility of extracting rare earth elements (REEs, i.e. Sc, Y, and the lanthanides) from coal-related materials such as coal, coal refuse, coal combustion ash, and acid mine drainage [12-15]. Support from this program has led to the development of several novel processes, which were first evaluated at the bench scale and later validated at the pilot scale [13,15-23]. For example, Honaker et al. [16] has designed, constructed, and tested a unique REE recovery process that incorporates physical preparation, roasting, acid leaching, and selective precipitation. This process has been integrated into a pilot plant (https://www. youtube.com/watch?v=jR70j-MzWNE&t=3s) that has proven capability of continuously producing rare earth oxides concentrates exceeding 95% purity. Recent efforts in this program have expanded the

Fuel, 2020

Abstract Three segments of a core sample collected from the Guxu coalfield (Sichuan Province, Chi... more Abstract Three segments of a core sample collected from the Guxu coalfield (Sichuan Province, China) were evaluated to determine the rare earth element (REE) leachability and mineralogy. Elemental analysis of the three samples showed that the roof and floor strata contained as high as 2087 ppm of total REEs, a value much higher than other coal-based materials reported in the literature. For the floor samples, 47% to 65% of the light REEs (LREEs) were leached within 5 min of contact time using 1 M mineral acid, and prolonged contact, up to 120 min, increased the LREE recovery to as high as 75%. For the roof sample, only 25% of the LREEs were leached at extended contact times. Unlike the LREEs, heavy REE (HREE) recovery from both the roof and floor materials was less than 25%. The relatively high REE content of the feed materials facilitated detailed SEM-EDX and TEM-EDX analyses of the samples. These studies confirmed the presence of several rare earth carbonate minerals, including bastnaesite and parasite, as well as rare earth phosphate minerals such as florencite and apatite. Given the prevalence and rare earth content of the particles analyzed via SEM-EDX, the data suggests that the LREEs present in the floor and roof samples were primarily associated with carbonates and phosphates, respectively. Further SEM-EDX analysis of the leaching residues showed that florencite was the only LREE-bearing species remaining after prolonged acid leaching, indicating that florencite is less soluble relative to the other rare earth minerals. The leaching results corroborate the SEM-EDX and TEM-EDX findings, while providing critical fundamental information on the relationship between REE content, REE mineralogy, and REE leachability in coal refuse materials.

Mining, Metallurgy & Exploration, 2019

A field study was undertaken to experimentally measure the concentrations of rare earth elements ... more A field study was undertaken to experimentally measure the concentrations of rare earth elements (REEs) contained in the process streams generated by a group of 20 coal preparation plants located in the eastern USA. For each site, representative samples of clean coal product, coarse refuse, and fine refuse were collected. Each sample was then partitioned into preselected size and density classes by wet screening/sieving and float-sink testing. The resultant products were dried and subjected to laboratory analyses to determine ash contents and rare earth element concentrations including Yttrium and Scandium. A detailed analysis of the database generated by this exercise showed that coal-based products from these preparation plants contained significant quantities of rare earth elements. In particular, the coarse refuse streams currently discarded by the 20 plants examined were found to contain a sufficient tonnage of REEs to satisfy the current domestic demand for these important elements. The data also showed a strong positive correlation between ash content and REE concentration, which suggested that the primary association of REEs in eastern USA bituminous coal sources is likely within fractions containing inorganic impurities. This association was well described using a simple power equation relating ash content and REE concentration. The ratio of heavy-to-light rare earth elements was discovered to be significantly higher in organically rich fractions of clean coal, suggesting that mineral impurities intimately associated with carbonaceous matter have elevated concentrations of heavy rare earth elements. A similar trend was observed for a grouping of rare earth elements (Y, Nd, Eu, Tb, and Dy) that are likely subject to near-term supply shortages. Finally, the database showed that a linear correlation existed between La for many REEs of interest, although there were several notable exceptions for some high-value REEs (Lu, Pr, and Tb).

Mining, Metallurgy & Exploration, 2019

The conventional rare earth element (REE) industry has historically sought to develop ore deposit... more The conventional rare earth element (REE) industry has historically sought to develop ore deposits where geologic processes have produced mineralized zones with commercially attractive REE concentrations. These deposits are extremely uncommon, particularly in the USA. Given the criticality of these materials and the need for sustainable domestic supply, the current research seeks to leverage other autogenous processes that lead to concentrated REE resources. One such process is the generation of acid mine drainage (AMD). AMD is very common in many coal mining districts and results from the exposure and oxidation of pyrite during mining. During the generation and migration of AMD, liberated sulfuric acid mobilizes several metal ions including REEs. Treatment of AMD is required under U.S.C §1251, the Clean Water Act, and often consists of neutralization, oxidation, and metal hydroxide precipitation. To investigate the deportment of REEs during this process, a field sampling campaign was undertaken, whereby the concentration of REEs in AMD and AMD precipitates was measured directly. In the nine sites evaluated in this study, the REE concentrations of the precipitates varied from 29 to 1286 ppm with an average of 517 ppm among the sampled sites. The individual elements were enriched compared with the associated bulk Northern Appalachian (NAPP) coal material by factors ranging from 3 to 15. Furthermore, the distribution of REEs in all precipitate samples favored the heavy REEs (HREEs) when compared with traditional REE ores. This research represents the first part of multi-part research endeavor to characterize, classify, and determine the practicality of refining REEs from AMD and its by-products.

International Journal of Coal Geology, 2019

This study provides data on the occurrence and distribution of rare earth elements, yttrium, and ... more This study provides data on the occurrence and distribution of rare earth elements, yttrium, and scandium (REY + Sc) in coals and non-coal lithologies associated with coals from various Colombian coalfields. A number of authors have characterized the REY + Sc content of various international coal deposits; however, no study to date has specifically addressed the REY + Sc content of Colombian coals, despite Colombia's prominence as a global coal producer. In this study, 24 samples were collected from seven coalfields and subjected to REY + Sc analysis, density fractionation, and modified release tests. Overall, the Colombian coals analyzed in this study have an average REY + Sc abundance of 45 ppm on a dry whole coal basis (459 ppm on a dry ash basis) whereas the non-coal lithologies have an average REY + Sc content of 222 ppm. In particular, materials collected from the Antioquia-Viejo Caldas coalfield were found to contain a relatively higher amount of REY + Sc (> 100 ppm) relative to the rest of the samples, which may be attributed to the volcaniclastic character of the sediment associated with the seams. Moreover, test results from the density fractionation and modified release tests show that the inorganic constituents are the major hosts of REY + Sc in Colombian coals, which is reflected by a strong and positive linear relationship existing between REY + Sc and sample ash yields.

Powder Technology, 2018

A laboratory REE release test procedure was designed to better understand the association and lib... more A laboratory REE release test procedure was designed to better understand the association and liberation characteristics of rare earth elements (REEs) from coal-based material, such as coal middlings and refuse. For this particular study, three samples of mixed-phase, middling material was collected from three coal preparation plants operating in three different coal basins and coal seams, namely Fire Clay, Middle Kittanning, and West Kentucky #13. In these release tests, the mixed-phase material was first ground in a laboratory ball mill for a designated amount of time and subsequently decarbonized using staged flotation. The REE content of the high ash tailings and low ash concentrate was determined, and the process was repeated for various target grind sizes down to the micron range. The results indicate that smaller grind sizes produce increased REE concentrations in the high ash tailings, and this result is predominantly driven by the increased ash content in the decarbonized tailings. The grinding characteristics of the Fire Clay coal source showed that more energy is needed to achieve the desired particle size reduction; however further size reduction of this sample resulted in a significantly higher ash and REE content in the tailings material due to improved liberation. For the Middle Kittanning and West Kentucky #13 sources, the grinding and release data indicates that the mineral matter is liberated at a coarser particle size, and micronizing the coals only produces marginal improvements in rare earth mineral liberation and recovery.

International Journal of Coal Preparation and Utilization, 2017

The energy sector in India is highly dependent on coal as a fuel. At present, most of the domesti... more The energy sector in India is highly dependent on coal as a fuel. At present, most of the domestically produced thermal coal is burned raw or after minimal beneficiation. This practice often results in higher operating and maintenance costs, poorer utilization efficiencies, and increased greenhouse gas (GHG) emissions. To improve the prevailing conditions, the Government of India is taking steps to increase clean coal production by promoting the installation of coal preparation plants across the country. The identification of optimal separation A c c e p t e d M a n u s c r i p t 2 densities and blending protocols for these pre-combustion cleaning facilities greatly influences the economics of the fuel supply chain and India's quest for additional low-cost energy. Traditionally, preparation plants have utilized float-sink (washability) data to determine suitable density separation set-points for their processing circuits. Very often, these set-points are based on the cumulative ash content required to meet contract specifications within India's bulk commodity coal markets. Unfortunately, the current study indicates that the optimal separation densities are largely independent of coal washability characteristics. This article demonstrates the use of micro-price optimization to identify optimal density set-points that maximize coal production for Indian coal feedstocks. This fundamental optimization technique assigns a unit price to each particle passing through the coal supply chain. This approach is in sharp contrast to the prevailing practice that assigns bulk prices to piles/lots of mixed coal and rock. Case studies for twelve different coal samples from India showed that (i) the historic constant cumulative ash method for determining set-points is suboptimal, (ii) the separation density of all plants/circuits should be held near-constant irrespective of feed washabilities, and (iii) misplacement of highash rock and low-ash coal must be prevented to avoid large reductions in the inherent worth of India's coal reserves.

Minerals Engineering, 2017

Powder Technology, 2016

The production of superior metallurgical-grade silicon requires the use of ultra-clean coal conta... more The production of superior metallurgical-grade silicon requires the use of ultra-clean coal containing less than 1.5% ash with no iron contamination. The magnetite suspension utilized for coal cleaning in a dense-medium cyclone (DMC) is a detrimental impurity in the final coal product that dramatically diminishes the purity of silicon. A prior study has demonstrated that several silica-based materials may be suitable alternatives that eliminate iron contamination. To further improve the separation performance and evaluate the silica-based media, DMC separation tests were conducted based on a statistically designed program to identify the role of various operational parameters (i.e. medium relative density, silica media blend ratio, and cyclone apex diameter) in maximizing organic efficiency and minimizing low-density bypass. An ideal medium composition with a bimodal particle size distribution considerably improves medium stability properties while also eliminating the undesirable effects of apex diameter on the DMC separation efficiency. Low-density cutpoints (<1.35) are hindered by medium instability, but these issues can be rectified by increasing the amount of fine media particles or decreasing the apex diameter.

Mining Technology, 2015

Publications, citations and h-index are three quantitative measures of scholarly productivity com... more Publications, citations and h-index are three quantitative measures of scholarly productivity commonly used to evaluate university academic staff members. The quantity and quality of an individual's publication record is often an integral part of promotion and tenure decisions as well as post-tenure notoriety and awards. In this study, the Scopus database was queried to provide information on the scholarly productivity of 83 mining engineering academic staff members at accredited mining engineering schools in the United States. The data retrieved in this study include the number of publications, number of citations and h-index, for each individual academic staff member. Data for individual academic staff members was then classified by academic level/rank, institution and primary research sub-discipline to produce meaningful comparative results. The data show that the average number of publications per academic increases from 4 to 22 to 49 for assistant professors, associate professors and professors, respectively. Citations (9–83–290) and h-index (1–3–6) follow similar trends. Further analysis indicates that mineral processing and mine electrical systems are the most highly cited sub-disciplines. When aggregated by academic institution, the data show that the productivity of academic staff is linked to Carnegie Research classification. Finally, the data show a clear Pareto tendency with the highest 20% of academic staff members contributing 80% of the overall citations.

Chemosphere, 2015

4-Methyl cyclohexane methanol (MCHM) is a flotation reagent often used in fine coal beneficiation... more 4-Methyl cyclohexane methanol (MCHM) is a flotation reagent often used in fine coal beneficiation and notably involved in the January 9, 2014 Elk River chemical spill in Charleston, WV. This study investigates the mechanisms controlling the transport and fate of MCHM in coal beneficiation plants and surrounding environments. Processes such as volatilization, sorption, and leaching were evaluated through laboratory batch and column experiments. The results indicate volatilization and sorption are important mechanisms which influence the removal of MCHM from water, with sorption being the most significant removal mechanism over short time scales (<1h). Additionally, leaching experiments show both coal and tailings have high affinity for MCHM, and this reagent does not desorb readily. Overall, the results from these experiments indicate that MCHM is either volatilized or sorbed during coal beneficiation, and it is not likely to transport out of coal beneficiation plant. Thus, use of...

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2022

Minerals, 2022

The development of processing techniques for the extraction of rare earth elements and critical m... more The development of processing techniques for the extraction of rare earth elements and critical minerals (REE/CM) from acid mine drainage precipitates (AMDp) has attracted increased interest in recent years. Processes under development often utilize a standard hydrometallurgical approach that includes leaching and solvent extraction followed by oxalic acid precipitation and calcination to produce a final rare earth oxide product. Impurities such as Ca, Al, Mn, Fe and Mg can be detrimental in the oxalate precipitation step and a survey of the literature showed limited data pertaining to the REE precipitation efficiency in solutions with high impurity concentrations. As such, a systematic laboratory-scale precipitation study was performed on a strip solution generated by the acid leaching and solvent extraction of an AMDp feedstock to identify the optimal processing conditions that maximize REE precipitation efficiency and product purity while minimizing the oxalic acid dosage. Given ...

Minerals Engineering, 2021

Abstract Recent efforts have shown that acid mine drainage precipitates (AMDp) may be a promising... more Abstract Recent efforts have shown that acid mine drainage precipitates (AMDp) may be a promising source of rare earth elements and critical materials (REE/CM). To better understand this resource, several particle characterization studies were conducted on AMDp samples from three AMD treatment sites in Northern and Central Appalachia. This work included the determination of particle size, size distribution, morphology, mineralogy, chemical speciation, and rare earth content. While the particle characteristics and mineralogy varied considerably from site to site, sequential extraction tests showed that the largest portion of REEs (45% to 75%) were found in soluble phases bound to Fe-Mn oxides. Carbonates (5% to 16%) and insoluble residues (4% to 24%) were also found to be significant in some samples, suggesting that different AMD chemistry and AMD treatment approaches can lead to substantial variation in the deportment of REEs to the various chemical phases. Altogether, the results suggest that chemical extraction of REEs from AMDp can be achieved under mild conditions with high recovery values; however, the significant site-by-site variation will necessitate detailed testing of individual samples to determine the overall economic viability.

Minerals, 2021

In recent years, acid mine drainage (AMD) has emerged as a promising unconventional source of rar... more In recent years, acid mine drainage (AMD) has emerged as a promising unconventional source of rare earth elements (REEs) and other critical minerals (CMs) such as cobalt and manganese. In this regard, AMD provides a natural heap leaching effect that extracts and concentrates REE/CM from the host strata creating a partially enriched feedstock suitable for downstream extraction, separation, and recovery. While several prior studies have described processes and approaches for the valorization of AMD, very few have described the supply chain and infrastructure requirements as well as the associated economic assessment. To that end, this paper provides a fundamental economic assessment of REE/CM recovery from AMD using a network sourcing strategy in addition to a robust, flexible feedstock separations and refining facility. The methodology of this paper follows that of a typical techno-economic analysis with capital and operating costs estimated using AACE Class IV (FEL-2) guidelines. To...

Mining, Metallurgy & Exploration, 2021

International Journal of Coal Preparation and Utilization, 2019

A novel approach to robust optimization of coal blending operations is proposed. While many rigor... more A novel approach to robust optimization of coal blending operations is proposed. While many rigorous mathematical approaches have been developed for this problem in the past, most neglect the uncertainty associated with both the inherent coal quality attributes as well as the sampling and measurement protocols used to measure those attributes. This uncertainty may lead to the imprecise estimation of quality values and force operators to adopt a conservative blend strategy based on safety factors and simple heuristics. One promising approach to rigorously address this shortcoming is through robust optimization (RO), a unique approach to handle data with uncertain and unspecified statistical distributions. In the current work, we first derive a deterministic optimization problem using the premium/penalty structure in typical coal sales contracts. This formulation is then translated to a robust formulation and solved as a Mixed Integer Nonlinear Program (MINLP). A numerical example is presented to demonstrate the utility of the method and to compare the deterministic solution, as the most optimistic and risky blending plan, with the RO solution, as the more pessimistic, yet robust, plan. The proposed strategy can help decision-makers achieve the economic and strategic goals of the operation at acceptable risk levels.

Minerals, 2020

Many studies have been published in recent years focusing on the recovery of rare earth elements ... more Many studies have been published in recent years focusing on the recovery of rare earth elements (REEs) from coal-related materials, including coal, coal refuse, coal mine drainage, and coal combustion byproducts particularly fly ash. The scientific basis and technology development have been supported by coal geologists and extractive metallurgists, and through these efforts, the concept has progressed from feasibility assessment to pilot-scale production over the last five years. Physical beneficiation, acid leaching, ion-exchange leaching, bio-leaching, thermal treatment, alkali treatment, solvent extraction, and other recovery technologies have been evaluated with varying degrees of success depending on the feedstock properties. In general, physical beneficiation can be a suitable low-cost option for preliminary upgrading; however, most studies showed exceedingly low recovery values unless ultrafine grinding was first performed. This finding is largely attributed to the combinati...

Fuel, 2020

Lithium recovery from the density fractions of Baker (namely West Kentucky No. 13) seam coal was ... more Lithium recovery from the density fractions of Baker (namely West Kentucky No. 13) seam coal was investigated in this study. Proximate and elemental analyses showed that lithium contents in the 1.8-2.2 SG and 2.2 SG sink fractions were 185 ppm and 150 ppm, respectively, which are significantly higher than the average content of coal sources (12 ppm) and coal ashes (66 ppm) worldwide. Moreover, due to the high lithium contents and mass distribution, nearly 90% of the lithium present in the Baker coal sample was distributed in the two density fractions. Direct leaching using a HCl solution resulted in less than 10% lithium recovery, which was due to nearly 90% of the lithium being associated with insoluble solids as determined by the results from sequential extraction tests. Calcination of both density fractions under 600°C for two hours followed by leaching resulted in recovery increases in the range of 70% to 80%. The pyro-metallurgical pretreatment step converted most of the associated lithium minerals to more easy-to-leach forms such as carbonate and metal oxide. Based on mineralogy characterization and leaching test results, it was concluded that the positive effects of calcination on lithium leachability resulted from the dehydration and disintegration of kaolinite as well as dehydroxylation and expansion of muscovite/illite. An analysis of the leaching kinetics revealed that the leaching rate of lithium was controlled by interface transfer and diffusion across the product layer and was negatively impacted when the calcination temperature exceeded 600°C due to sintering of the kaolinite. China also controlling significant holdings [6]. Given the criticality of this resource and the importance to consumer and energy products, several researchers have recently assessed a number of alternative and unconventional sources of lithium [7,8]. Coal and coal byproducts are known to contain numerous trace elements, sometimes at elevated concentrations [9-11]. Since 2014, the U.S. Department of Energy has investigated the technical and economic feasibility of extracting rare earth elements (REEs, i.e. Sc, Y, and the lanthanides) from coal-related materials such as coal, coal refuse, coal combustion ash, and acid mine drainage [12-15]. Support from this program has led to the development of several novel processes, which were first evaluated at the bench scale and later validated at the pilot scale [13,15-23]. For example, Honaker et al. [16] has designed, constructed, and tested a unique REE recovery process that incorporates physical preparation, roasting, acid leaching, and selective precipitation. This process has been integrated into a pilot plant (https://www. youtube.com/watch?v=jR70j-MzWNE&t=3s) that has proven capability of continuously producing rare earth oxides concentrates exceeding 95% purity. Recent efforts in this program have expanded the

Fuel, 2020

Abstract Three segments of a core sample collected from the Guxu coalfield (Sichuan Province, Chi... more Abstract Three segments of a core sample collected from the Guxu coalfield (Sichuan Province, China) were evaluated to determine the rare earth element (REE) leachability and mineralogy. Elemental analysis of the three samples showed that the roof and floor strata contained as high as 2087 ppm of total REEs, a value much higher than other coal-based materials reported in the literature. For the floor samples, 47% to 65% of the light REEs (LREEs) were leached within 5 min of contact time using 1 M mineral acid, and prolonged contact, up to 120 min, increased the LREE recovery to as high as 75%. For the roof sample, only 25% of the LREEs were leached at extended contact times. Unlike the LREEs, heavy REE (HREE) recovery from both the roof and floor materials was less than 25%. The relatively high REE content of the feed materials facilitated detailed SEM-EDX and TEM-EDX analyses of the samples. These studies confirmed the presence of several rare earth carbonate minerals, including bastnaesite and parasite, as well as rare earth phosphate minerals such as florencite and apatite. Given the prevalence and rare earth content of the particles analyzed via SEM-EDX, the data suggests that the LREEs present in the floor and roof samples were primarily associated with carbonates and phosphates, respectively. Further SEM-EDX analysis of the leaching residues showed that florencite was the only LREE-bearing species remaining after prolonged acid leaching, indicating that florencite is less soluble relative to the other rare earth minerals. The leaching results corroborate the SEM-EDX and TEM-EDX findings, while providing critical fundamental information on the relationship between REE content, REE mineralogy, and REE leachability in coal refuse materials.

Mining, Metallurgy & Exploration, 2019

A field study was undertaken to experimentally measure the concentrations of rare earth elements ... more A field study was undertaken to experimentally measure the concentrations of rare earth elements (REEs) contained in the process streams generated by a group of 20 coal preparation plants located in the eastern USA. For each site, representative samples of clean coal product, coarse refuse, and fine refuse were collected. Each sample was then partitioned into preselected size and density classes by wet screening/sieving and float-sink testing. The resultant products were dried and subjected to laboratory analyses to determine ash contents and rare earth element concentrations including Yttrium and Scandium. A detailed analysis of the database generated by this exercise showed that coal-based products from these preparation plants contained significant quantities of rare earth elements. In particular, the coarse refuse streams currently discarded by the 20 plants examined were found to contain a sufficient tonnage of REEs to satisfy the current domestic demand for these important elements. The data also showed a strong positive correlation between ash content and REE concentration, which suggested that the primary association of REEs in eastern USA bituminous coal sources is likely within fractions containing inorganic impurities. This association was well described using a simple power equation relating ash content and REE concentration. The ratio of heavy-to-light rare earth elements was discovered to be significantly higher in organically rich fractions of clean coal, suggesting that mineral impurities intimately associated with carbonaceous matter have elevated concentrations of heavy rare earth elements. A similar trend was observed for a grouping of rare earth elements (Y, Nd, Eu, Tb, and Dy) that are likely subject to near-term supply shortages. Finally, the database showed that a linear correlation existed between La for many REEs of interest, although there were several notable exceptions for some high-value REEs (Lu, Pr, and Tb).

Mining, Metallurgy & Exploration, 2019

The conventional rare earth element (REE) industry has historically sought to develop ore deposit... more The conventional rare earth element (REE) industry has historically sought to develop ore deposits where geologic processes have produced mineralized zones with commercially attractive REE concentrations. These deposits are extremely uncommon, particularly in the USA. Given the criticality of these materials and the need for sustainable domestic supply, the current research seeks to leverage other autogenous processes that lead to concentrated REE resources. One such process is the generation of acid mine drainage (AMD). AMD is very common in many coal mining districts and results from the exposure and oxidation of pyrite during mining. During the generation and migration of AMD, liberated sulfuric acid mobilizes several metal ions including REEs. Treatment of AMD is required under U.S.C §1251, the Clean Water Act, and often consists of neutralization, oxidation, and metal hydroxide precipitation. To investigate the deportment of REEs during this process, a field sampling campaign was undertaken, whereby the concentration of REEs in AMD and AMD precipitates was measured directly. In the nine sites evaluated in this study, the REE concentrations of the precipitates varied from 29 to 1286 ppm with an average of 517 ppm among the sampled sites. The individual elements were enriched compared with the associated bulk Northern Appalachian (NAPP) coal material by factors ranging from 3 to 15. Furthermore, the distribution of REEs in all precipitate samples favored the heavy REEs (HREEs) when compared with traditional REE ores. This research represents the first part of multi-part research endeavor to characterize, classify, and determine the practicality of refining REEs from AMD and its by-products.

International Journal of Coal Geology, 2019

This study provides data on the occurrence and distribution of rare earth elements, yttrium, and ... more This study provides data on the occurrence and distribution of rare earth elements, yttrium, and scandium (REY + Sc) in coals and non-coal lithologies associated with coals from various Colombian coalfields. A number of authors have characterized the REY + Sc content of various international coal deposits; however, no study to date has specifically addressed the REY + Sc content of Colombian coals, despite Colombia's prominence as a global coal producer. In this study, 24 samples were collected from seven coalfields and subjected to REY + Sc analysis, density fractionation, and modified release tests. Overall, the Colombian coals analyzed in this study have an average REY + Sc abundance of 45 ppm on a dry whole coal basis (459 ppm on a dry ash basis) whereas the non-coal lithologies have an average REY + Sc content of 222 ppm. In particular, materials collected from the Antioquia-Viejo Caldas coalfield were found to contain a relatively higher amount of REY + Sc (> 100 ppm) relative to the rest of the samples, which may be attributed to the volcaniclastic character of the sediment associated with the seams. Moreover, test results from the density fractionation and modified release tests show that the inorganic constituents are the major hosts of REY + Sc in Colombian coals, which is reflected by a strong and positive linear relationship existing between REY + Sc and sample ash yields.

Powder Technology, 2018

A laboratory REE release test procedure was designed to better understand the association and lib... more A laboratory REE release test procedure was designed to better understand the association and liberation characteristics of rare earth elements (REEs) from coal-based material, such as coal middlings and refuse. For this particular study, three samples of mixed-phase, middling material was collected from three coal preparation plants operating in three different coal basins and coal seams, namely Fire Clay, Middle Kittanning, and West Kentucky #13. In these release tests, the mixed-phase material was first ground in a laboratory ball mill for a designated amount of time and subsequently decarbonized using staged flotation. The REE content of the high ash tailings and low ash concentrate was determined, and the process was repeated for various target grind sizes down to the micron range. The results indicate that smaller grind sizes produce increased REE concentrations in the high ash tailings, and this result is predominantly driven by the increased ash content in the decarbonized tailings. The grinding characteristics of the Fire Clay coal source showed that more energy is needed to achieve the desired particle size reduction; however further size reduction of this sample resulted in a significantly higher ash and REE content in the tailings material due to improved liberation. For the Middle Kittanning and West Kentucky #13 sources, the grinding and release data indicates that the mineral matter is liberated at a coarser particle size, and micronizing the coals only produces marginal improvements in rare earth mineral liberation and recovery.

International Journal of Coal Preparation and Utilization, 2017

The energy sector in India is highly dependent on coal as a fuel. At present, most of the domesti... more The energy sector in India is highly dependent on coal as a fuel. At present, most of the domestically produced thermal coal is burned raw or after minimal beneficiation. This practice often results in higher operating and maintenance costs, poorer utilization efficiencies, and increased greenhouse gas (GHG) emissions. To improve the prevailing conditions, the Government of India is taking steps to increase clean coal production by promoting the installation of coal preparation plants across the country. The identification of optimal separation A c c e p t e d M a n u s c r i p t 2 densities and blending protocols for these pre-combustion cleaning facilities greatly influences the economics of the fuel supply chain and India's quest for additional low-cost energy. Traditionally, preparation plants have utilized float-sink (washability) data to determine suitable density separation set-points for their processing circuits. Very often, these set-points are based on the cumulative ash content required to meet contract specifications within India's bulk commodity coal markets. Unfortunately, the current study indicates that the optimal separation densities are largely independent of coal washability characteristics. This article demonstrates the use of micro-price optimization to identify optimal density set-points that maximize coal production for Indian coal feedstocks. This fundamental optimization technique assigns a unit price to each particle passing through the coal supply chain. This approach is in sharp contrast to the prevailing practice that assigns bulk prices to piles/lots of mixed coal and rock. Case studies for twelve different coal samples from India showed that (i) the historic constant cumulative ash method for determining set-points is suboptimal, (ii) the separation density of all plants/circuits should be held near-constant irrespective of feed washabilities, and (iii) misplacement of highash rock and low-ash coal must be prevented to avoid large reductions in the inherent worth of India's coal reserves.

Minerals Engineering, 2017

Powder Technology, 2016

The production of superior metallurgical-grade silicon requires the use of ultra-clean coal conta... more The production of superior metallurgical-grade silicon requires the use of ultra-clean coal containing less than 1.5% ash with no iron contamination. The magnetite suspension utilized for coal cleaning in a dense-medium cyclone (DMC) is a detrimental impurity in the final coal product that dramatically diminishes the purity of silicon. A prior study has demonstrated that several silica-based materials may be suitable alternatives that eliminate iron contamination. To further improve the separation performance and evaluate the silica-based media, DMC separation tests were conducted based on a statistically designed program to identify the role of various operational parameters (i.e. medium relative density, silica media blend ratio, and cyclone apex diameter) in maximizing organic efficiency and minimizing low-density bypass. An ideal medium composition with a bimodal particle size distribution considerably improves medium stability properties while also eliminating the undesirable effects of apex diameter on the DMC separation efficiency. Low-density cutpoints (<1.35) are hindered by medium instability, but these issues can be rectified by increasing the amount of fine media particles or decreasing the apex diameter.

Mining Technology, 2015

Publications, citations and h-index are three quantitative measures of scholarly productivity com... more Publications, citations and h-index are three quantitative measures of scholarly productivity commonly used to evaluate university academic staff members. The quantity and quality of an individual's publication record is often an integral part of promotion and tenure decisions as well as post-tenure notoriety and awards. In this study, the Scopus database was queried to provide information on the scholarly productivity of 83 mining engineering academic staff members at accredited mining engineering schools in the United States. The data retrieved in this study include the number of publications, number of citations and h-index, for each individual academic staff member. Data for individual academic staff members was then classified by academic level/rank, institution and primary research sub-discipline to produce meaningful comparative results. The data show that the average number of publications per academic increases from 4 to 22 to 49 for assistant professors, associate professors and professors, respectively. Citations (9–83–290) and h-index (1–3–6) follow similar trends. Further analysis indicates that mineral processing and mine electrical systems are the most highly cited sub-disciplines. When aggregated by academic institution, the data show that the productivity of academic staff is linked to Carnegie Research classification. Finally, the data show a clear Pareto tendency with the highest 20% of academic staff members contributing 80% of the overall citations.

Chemosphere, 2015

4-Methyl cyclohexane methanol (MCHM) is a flotation reagent often used in fine coal beneficiation... more 4-Methyl cyclohexane methanol (MCHM) is a flotation reagent often used in fine coal beneficiation and notably involved in the January 9, 2014 Elk River chemical spill in Charleston, WV. This study investigates the mechanisms controlling the transport and fate of MCHM in coal beneficiation plants and surrounding environments. Processes such as volatilization, sorption, and leaching were evaluated through laboratory batch and column experiments. The results indicate volatilization and sorption are important mechanisms which influence the removal of MCHM from water, with sorption being the most significant removal mechanism over short time scales (<1h). Additionally, leaching experiments show both coal and tailings have high affinity for MCHM, and this reagent does not desorb readily. Overall, the results from these experiments indicate that MCHM is either volatilized or sorbed during coal beneficiation, and it is not likely to transport out of coal beneficiation plant. Thus, use of...