Semester

Spring

Date of Graduation

2024

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mining Engineering

Committee Chair

Qingqing Huang

Committee Member

Deniz Talan

Committee Member

Ihsan Berk Tulu

Committee Member

Hassan Amini

Abstract

Non-fuel minerals and commodities vital to the modern economy and national security are known as critical minerals. They are essential to modern high-tech industries, defense applications, clean technology, fuel cells, mobile phones, high-capacity batteries, permanent magnets, phosphors, and metal catalysts, among other things. Over fifty elements are deemed essential to varying degrees (European Commission, 2017; Department of Energy, 2020; Burton, 2022). Given their current position, a single supplier or small group of producers can easily dominate the mineral pricing as they supply the majority of these essential minerals. Due to the extended area of usage, ongoing population expansion, and increased technology use, industrial demand is still predicted to rise even though the market prices of several essential minerals decreased somewhat as a result of source diversification (Guyonnet et al., 2015). For instance, the market for rare earths, valued at about $9 billion in 2019, and is expected to reach over $20 billion by 2024 (Song et al., 2017). While some of the essential minerals can be extracted from traditional sources, most of them cannot, necessitating the discovery of new and alternative sources. Based on these projections and concerns, increasing the reserves of currently available resources and creating new ones have become extremely important. According to recent research, a variety of critical minerals can potentially be recovered in significant quantities from coal-based resources, such as coal refuse, coal ash, and acid mine drainage (Huang et al., 2018; Zhang et al., 2018; Valentim et al., 2019; Zhao et al., 2019; Zhou et al., 2021; Bagdonas et al., 2022). A review of previous and present state-of-the-art processing technologies for a few key minerals was carried out because of their significance in the development of high-tech products, the manufacturing of batteries, and the applications of these minerals in military and defense systems. These minerals include rare earth elements (REEs), cobalt, and manganese from various sources. The objective of the review study is to provide insight into the potential advancement of cutting-edge separation methods in the future for recovering various critical minerals from coal and coal-based sources. In this manner, several acid mine drainage treatment sludges were characterized for critical minerals. iii Following the characterization studies, the Tobby mine sample was identified as the primary feedstock. Subsequently, a novel separation method was developed to recover aluminum, rare earth elements, manganese, and magnesium. The presence of high impurities in the sample, such as silicon and iron, posed a significant challenge in the recovery of critical metals. Initially, critical metals were extracted using the sulfuric acid leaching method. Subsequently, iron, one of the major impurities, was systematically removed through stage-wise precipitation. The oxidation precipitation method was employed during this stage, and optimization studies were conducted on H2O2 dosage and time parameters. Following the successful removal of iron, aluminum was the second most abundant metal recoverable at low pH. Given its classification as a critical metal according to the USGS list, studies were conducted to recover aluminum. Reaction time and pH optimization studies were undertaken to produce a pre-concentrate. As a result of the optimization studies, an aluminum pre-concentrate was generated with a purity of 25.95% by weight. After this point, two options were considered. The first involved implementing a multi-stage precipitation process to generate pre-concentrates. The second option entailed conducting comprehensive experiments using solvent extraction to subsequently generate pure concentrates. The outcome of the multi-stage precipitation method resulted in the production of both pre-concentrate and concentrate. Various pH conditions were explored for pre-concentrate production. Test results revealed that at pH 8.6, the initial product was manganese pre-concentrate with a purity of 37.64% Mn, 2.05% Total Rare Earth Elements (TREEs), 1.12% Ni, 0.27% Co, 3.73% Zn, and 2.80% Mg. Subsequent studies were undertaken to obtain magnesium concentrate. In order to generate a purer product, pH values and different precipitants were tested. In this context, precipitation studies were conducted using sodium hydroxide and ammonium hydroxide. The results of the studies carried out with sodium hydroxide at pH 10 yielded a magnesium concentrate containing 39% Mg by mass. The second option involved the loading of rare earth elements into the organic phase using the solvent extraction method. Bis(2-ethylhexyl) phosphate was used as the organic solvent and dissolved in kerosene. The impurities in the REEs-loaded organic phase were initially scrubbed, resulting in the removal of approximately 60% of zinc, as well as manganese, magnesium, and other impurities. Subsequently, the organic phase underwent a stripping process with hydrochloric acid, achieving a stripping efficiency of close to 100% for the REEs. Simultaneously, the aqueous phase from the REE extraction step transitioned into the manganese extraction process. This led to the loading of approximately 90% of manganese into the organic phase, leaving the remaining solution enriched in magnesium. This provided an opportunity for the recovery of magnesium, a critical metal in the solution. The loaded organic was further stripped using sulfuric acid, with optimization studies leading to the selection of 0.5M sulfuric acid for manganese stripping, considering minimal differences in co-stripped metals. The resulting solid product, containing 49.5% manganese by mass, was obtained from the stripped solution. iv On the other hand, studies on magnesium recovery from magnesium-rich solution following manganese extraction were conducted. Despite minimal impurities in the solution, a manganese, nickel, and cobalt-rich pre-concentrate was initially obtained, which can be further purified. The critical metal concentrations in this obtained pre-concentrate are 5.54% Mn, 5.40% Mg, 3.75% Ni, 0.76% Co, and 0.12% Cu. Subsequently, when magnesium recovery studies were carried out with the remaining filtrate solution at a higher pH, a concentrate containing 38.07% magnesium by weight was produced. Consequently, five products were obtained from AMD treatment sludge. Two of these products are pre-concentrates, while the other three are concentrates. One pre-concentrate contains 26.95% aluminum, while the other contains 5.54% Mn, 5.40% Mg, 3.75% Ni, 0.76% Co, and 0.12% Cu. In addition, a rare earth oxalate product with 1 18.16% total rare earth elements was produced. In comparison, the other two manganese and magnesium products with a purity of 49.5% Mn and 38.07% Mg, respectively, were also obtained from the developed process.

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