Rare earth elements (REEs) are critically important for high-tech, renewable energy and defense industries. However, rare earth minerals (REMs) are stable compounds, requiring aggressive conditions to decompose them for their extraction and use. One exception is the ion-adsorption clays (IACs) that are mined in South China. They were formed in nature via the adsorption of the REE ions on clay minerals; therefore, they can be readily extracted into solution under mild conditions using the ion-exchange leaching process using (NH4)2SO4 as lixiviant. It also happens that IACs are the largest source of the heavy rare earth elements (HREEs) that are critical, especially for the defense industry. At present, more than 80% of the HREEs are produced commercially from the IACs mined in Southeast Asia. The objective of the present research was to study the fundamental mechanisms involved in the formation and processing of IACs using the ion-change leaching process. The first part of the project was the synthesis of IACs by contacting kaolinite samples with known concentrations of rare earth chloride (REECl3) solutions at different pHs and analyzing the synthetic IACs for XPS studies. It was found that the REE adsorption on kaolinite stays constant in acidic pHs. At pH 7 and above, adsorption density increases sharply, possibly due to the formation of REE(OH)3 and/or REE(OOH). The IACs formed under these conditions responded well to the ion-exchange leaching process by reducing the pH to below 7. In the second part of the study, the effect of iron (Fe3+) species co-adsorbing with REEs on the kaolinite surface was studied. Unlike the colloidal phases of IACs formed at pH > 7, the synthetic IACs formed in the presence of iron did not respond to the ion-exchange leaching process using (NH4)2SO4 as lixiviant. This problem has been solved by subjecting the synthetic IACs to a reducing condition to convert the Fe3+ to soluble Fe2+ species at pH < 7. The driving force for the standard exchange leaching process is the large differences between the hydration enthalpies of the Ln3+ ions that are in the range of -3,400 kJ/mole and that of the NH4+ ions (-320 kJ/mole). In the present work, alkylammonium ions (CnH2nNH4+) of varying chain lengths were used as novel lixiviants and obtained excellent results. Since these are surface active species, their concentrations in the vicinity of the clay minerals that are negatively charged would be substantially higher than in the bulk. As a result, it was possible to achieve the same level of leaching efficiencies as obtained using ammonium sulfate at approximately ten times lower reagent dosages. One of the problems associated with extracting REEs from coal-based clays is that the REE concentrations are typically in the range of 300 to 600 ppm, which makes it difficult to extract the critical materials economically using ion-exchange leaching and other processes. As a means to overcome this issue, the REE-bearing particles, including IACs and REMs, were liberated by blunging and subsequently upgraded using the hydrophobic-hydrophilic separation (HHS) process. The results showed that blunging outperformed grinding in liberating the REE-bearing particles from the clayey materials in coal. It was shown that one can improve blunging by increasing the disjoining in the thin liquid films present between clay and other minerals by controlling the double-layer (EDL) forces. These findings should enhance our understanding of the fundamental mechanisms involved in upgrading critical materials and thereby increase the economic viability of REE recovery from coal-based materials. / Doctor of Philosophy / Rare earth elements (REEs) play a vital role in numerous modern industries, advanced technological applications, and defense industries. The United States accounts for about 15 % of the global demand for REEs. However, the country heavily relies on imported Chinese raw materials, creating vulnerability in the U.S. supply chain. REEs are rarely found in concentrations suitable for mining, and in certain cases, extracting and processing conventional REE deposits come with significant environmental hazards. The limited availability of rare earth elements (REEs) raises concerns regarding their production despite their critical role in high-tech industries. Consequently, various federal agencies and private enterprises have recently attempted to identify promising alternative resources due to these complex challenges. REEs have been found in several major coal basins and are evidenced to be associated with coal byproducts such as kaolinite clays–one of the major host materials of IACs. This research investigates the recovery of rare earth elements (REEs) from clayey materials through various processes. Emphasis is placed on the synthesis of ion-adsorption clays from kaolinite, and the factors influencing the ion-exchange leaching process are being studied. Furthermore, the impact of iron co-adsorption on REE binding to kaolinite is being examined, and reductive leaching is being evaluated as a means to overcome the hindrance caused by iron passivating layers. Novel lixiviants are being tested as alternatives to conventional lixiviant ((NH4)2SO4) for REE extraction. The application of hydrophobic-hydrophilic separation techniques for extracting REE-bearing particles from coal clay samples is also being explored, with a comparison made between grinding and blunging processes. Overall, valuable insights into the efficient recovery of REEs from clay minerals are being obtained, contributing to the development of cost-effective and novel approaches for their extraction.

Incineration of municipal solid waste (MSW) is common for energy recovery, and management of municipal solid waste incineration (MSWI) ashes has received a growing attention around the world. In the U.S., generation of MSW has increased up to 65% since 1980, to the current level of 251 million tons per year with 53.8% landfilled, 34.5% recycled and composted, and 11.7% incinerated with energy recovery. In the process of incineration, MSWI ash is being produced as byproducts; about 80 to 90% of the MSWI ash is bottom ash (BA) and 10 to 20% is fly ash (FA) by weight. The current practice of the U.S. is to combine both BA and FA to meet the criteria to qualify as non-hazardous, and all combined ashes are disposed in landfills. European countries have utilized MSWI BA as beneficial construction materials by separating it from FA. The FA is mostly limited to landfill disposal as hazardous material due to its high content of toxic elements and salts. BA has been actively recycled in the areas of roadbed, asphalt paving, and concrete products in many of European and Asian countries. In those countries, recycling programs (including required physical properties and environmental criteria) of ash residue management have been developed so as to encourage and enforce the reuse of MSWI ashes instead of landfill disposal. Moreover, many studies have demonstrated the beneficial use of MSWI ashes as engineering materials with minimum environmental impacts. On the other hand, the U.S. has shown a lack of consistent and effective management plans, as well as environmental regulations for the use of MSWI ashes., Due to persistent uncertainty of engineering properties and inconsistency in the Federal and State regulations in the U.S., however, the recycling of the MSWI ashes has been hindered and they are mostly disposed in landfills. In this research work, current management practice, existing regulations, and environmental consequences of MSWI ashes utilization are comprehensively reviewed worldwide and nationwide with an emphasis of the potential area of its utilization in asphalt paving and concrete product. This research also entails a detailed chemical and microstructural characterization of MSWI BA and FA produced from a Refuse Derived Fuel (RDF) facility in Florida so that the MSWI ash is well characterized for its beneficial uses as construction materials. The material characterization includes Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD) techniques. In addition, leaching experiments have been conducted to investigate the environmental properties (e.g. leachate concentration) of BA and ash-mixed hot mix asphalt (HMA) and Portland cement concrete (PCC). Leaching results reveals the reduced leaching potential of toxic material from MSWI ashes while incorporated in HMA and PCC. Lastly, a preliminary experimental approach has been devised for the vitrification of FA which is a promising thermal process of transferring material into glassy state with higher physical and chemical integrity to reduce toxicity so that utilization of FA can be possible.

A laboratory scale study was carried out on a set of 6 borosilicate waste glasses made from simulated high-level nuclear waste. The test matrix was designed to explore the composition region suitable for the long-term geologic disposal of high-temperature-and high-waste-containing glasses. The glass compositions were selected to achieve maximum waste loading without a sacrifice in glass durability. The relationship between glass composition and chemical durability was examined. The qualitative effect of increasing B2O3 content on the overall waste glass leaching behavior has also been addressed. The glass composition matrix was designed by systematically varying the factors: %waste loading and (SiO2+Frit):B2O3 ratio, with (SiO2:Frit) ratio being held constant. In order to assess the chemical durability, the Product Consistency Test (ASTM C-1285) was performed. Under PCT protocol, crushed glass was allowed to react with ASTM type I water under static conditions. All leachate solutions were analyzed by the technique; Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES). A statistical regression technique was utilized to model the normalized release of the major soluble elements, Na, Si, and B, as a function of the individual as well as interactive chemical effects (B2O3, Al2O3, Fe2O3, MnO, SiO2, SrO, Na2O, B2O3*SiO2, B2O3*Al2O3, Fe2O3*Na2O, Al2O3*Na2O, and MnO*SiO2). Geochemical modeling was performed using the computer code EQ3/6 to: (1) determine the saturation states of the possible silicate minerals, a-cristobalite and chalcedony; and (2) predict the most stable mineral phase based on the mineral thermodynamic data. Mineral/water interactions were analyzed by representing the resultant glass data on a Na-Al-Si-O-H stability diagram.

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Gruvavfall från gruvbrytning kan utgöra stor problematik i och med läckage av metaller till omgivande miljö om gruvavfallet hanteras felaktigt. Från Falu Gruva har det brutits främst koppar och zink i över 1000 år innan det stängde. Gruvavfallet består av sulfidmineral som är vanligt brytningsmalm och besvärligt ur miljösynpunkt. Vid kontakt med syre oxiderar mineralen vilket kan öka metallernas löslighet. Gruvavfallet har använts som fyllnadsmaterial, som byggmaterial och en del ligger öppet i och omkring Falun. Då det i framtiden väntas kraftigare och mer intensiv nederbörd samt en högre temperatur behövs det fastställas hur dessa parametrar påverkar gruvavfallet. Tidigare forskning visar att det finns samband mellan metallhalter och nederbörd samt temperatur. Syftet med denna rapport är att ingående undersöka utsläppet av metaller vid Slussens mätstation som uppstått till följd av Falu Gruvas aktivitet i området. Rapporten avser också att undersöka hur metallhalterna kan komma att förändras i framtiden med ökad nederbörd och temperatur. Bly-, kadmium-, koppar- och zinkhalter i vatten har undersökts och analyserats vid Slussens mätstation med hjälp av regression under tidsperioden 1990–2020. Resultatet visar att samtliga metallhalter har sjunkit sedan gruvverksamheten stängde samt efter de saneringsåtgärderna som var pågående under cirka tio års tid. Trenden för metallhalter hölls övergripande stabil men på senare år fanns en ökande trend för bly, kadmium och zink medan koppar var den metall som uppvisade minskande trend hela tidsperioden. Samtliga metaller har säsongsvariationer med högst metallhalter under sommar och höst och alla metaller överskrider också årsmedelvärden i inlandsytvatten, vilket är anmärkningsvärt. Det fanns positiva signifikanta samband mellan temperatur och metallhalter där bly hade högsta sambandet och zink det lägsta. Det fanns även positiva signifikanta samband mellan nederbörd och metallhalter där bly hade det högsta sambandet och koppar det lägsta. / Mining waste from mining can be a major problem due to leakage of metals to the surrounding environment if the waste is handled incorrectly. From Falu Mine, copper and zinc have been mined mainly for over 1000 years before it closed and the mine waste consists of sulphide mineral. Sulphide mineral is a common mining ore and troublesome from an environmental point of view. Upon contact with oxygen, the mineral oxidizes, which can increase the solubility of the metals. The waste has been used as filling material, as building material and some is open in and around Falun. As heavier and more intense precipitation and a higher temperature are expected in the future, it is necessary to determine how these parameters affect the mining waste. Previous research shows that there is a connection between metal levels and precipitation as well as temperature. The purpose of this report is to thoroughly investigate the emissions of metals at Slussen's measuring station that arose as a result of Falu Gruva's activity in the area. The report also investigate how metal levels may change in the future with increased precipitation and temperature. Lead, cadmium, copper and zinc concentrations in water have been investigated and analysed at Slussen's measuring station using regression of the metal leaching from the period 1990–2020. The results show that all metal concentrations have fallen since the mining operations closed and after the decontamination measures that were ongoing for about ten years. The trend of metal levels is generally stable, but in recent years there has been an increasing trend for lead, cadmium and zinc, while copper was the metal that showed a declining trend throughout the period. All metals have seasonal variations with the highest metal contents during summer and autumn and all metals exceed annual average values ​​in inland surface water, which is remarkable. There were positive significant correlations between temperature and metal concentrations where lead had the highest correlation and zinc the lowest. There were also positive significant correlations between precipitation and metal levels where lead had the highest correlation and copper the lowest.