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Novel Primary Processing of Scarce Element Ores


OBJECTIVE: The objective of this project is to develop and demonstrate at a relevant laboratory scale a novel, efficient, and environmentally friendly approach to the extraction, concentration, and separation of rare-earth elements from common ore stocks. This project supports the goals of the Materials Genome Initiative (MGI) in the area of Integrated Computational Materials Engineering (ICME). DESCRIPTION: The rare-earth elements find uses in hundreds of high tech applications, including cellular telephones, laptop computers, iPods, critical military applications, and green technologies. These reactive metals have a natural abundance that is similar to that of copper. Their high costs and relative scarcity are due to the high cost of their separation, concentration, and extraction from the ores. Current methods involve the leaching of the rare-earth elements from the ore, solvent ion-exchange reactions to concentrate the elements, followed by roasting. From this concentrated state, reduction using an adaptation of the Kroll process, that is the formation of halide gasses from the oxides followed by reduction using an alkali metal, is typical. The environmental issues behind the mining of rare-earth elements are also a concern. Using concentrated sulfuric acid leaching with high temperature calcination techniques, producing one ton of calcined rare earth ore generates: up to 12,000 m3 of waste gas containing ore dust concentrate, hydrofluoric acid, sulfur dioxide, and sulfuric acid; along with approximately 75 m3 of acidic wastewater; plus up to one ton of radioactive wet waste residue. Many ores contain Thorium, a radioactive element; so that the ore dust effluents, and residuals, are radioactive and contain many toxic heavy metals. Without special treatments, these waste products pose the threat of contaminating local water supplies and producing far-field environmental damage. The disposal of tailings, the components of the ore left behind after rare-earth extraction, also contributes to the problem. Most operations simply place tailings in large land impoundments for storage. These also present long-term environmental challenges without special treatment. A novel means of separation and fractionation of the multiple species in the ores, and concentrating these elements into separate streams using less-aggressive techniques environmentally, could enable the increased availability of these elements for engineering applications. Over the past decade, a number of liquid-liquid ion extraction processes for rare-earth elements have become available. These, however, involve the use of toxic organic compounds that require sophisticated handling technologies to work safely in an industrial scale extraction process. Novel chemistries for the extraction, concentration, and separation of these elements that a processing plant can implement in an environmentally benign manner would improve the availability, decrease the costs of extraction, and decrease the environmental impact of the extraction operations. The objective of this project is to develop and demonstrate a more environmentally benign technique for the extraction, concentration, and separation of rare-earth elements from ores. Phase I: The successful phase I project will develop and define concept chemistries, along with basic engineering evaluations of the relative suitabilities of the approaches and outlines of the likely relative environmental impacts. Phase II: The successful phase II project will down-select a concept extraction system from the phase I effort and perform detailed chemical engineering design on the proposed process. The investigators will show through combinations of modelling, simulation, and relevant experiments that the final design is suitable for insertion into a mining/extraction process. Phase III: Mining operations require the concentration, and separation of the relevant elements from the ores prior to subsequent purification and processing to final form. An efficient controllable process which is either environmentally benign, or can be easily controlled for minimal environmental impact, will decrease dramatically the overall costs associated with the extraction and enable mining and ore processing for deposits which are not currently profitable for exploitation. PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: The materials system developed in this project can play an important role in reducing the overall environmental impact and total cost of producing rare-earth compounds from ore systems. This we anticipate will increase the availability of these scarce materials, and reduce the overall costs for obtaining them. This will make significant changes in the ways that we can use these scarce materials in new designs.
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