Adaptations of Uranium Hydrometallurgy: Case Studies in Copper in Situ Leaching and Supercritical Extraction of Rare Earth Elements
In this work, two uranium hydrometallurgical processes were adapted for other metals: in situ leaching was adapted to copper and supercritical extraction was adapted to rare earth elements. In situ leaching offers a way to extract copper from the subsurface without costly fragmentation. Applicability of in situ leaching is limited to deposits where sufficient permeability and leachable copper mineralogy exists. A computational copper in situ leaching model was developed to forecast recovered solution composition. This requires incorporating chemical reaction kinetics, mass transfer, and hydrology. These phenomena act over a range of length scales from centimeters up to hundreds of meters. Laboratory-scale leaching of ore provided data which was used to develop a list of geochemical reactions and associated rate laws. The risk of short-circuiting was treated probabilistically through geostatistical analysis of hydrophysical flow profiles, fracture spacing from Florence Copper's drill core database, and pumping tests. The geochemical reaction set and the geostatistical characteristics of hydraulic conductivity were brought together in a MATLAB model with a plugin to link to Geochemist's Workbench for computing chemical reaction pathways. Results highlighted the importance of large-scale flow patterns in copper recovery. The second part of this work pertains to rare earth element separation with supercritical carbon dioxide. Rare earth nitrates can be complexed with tributyl phosphate, thus forming a metal-ligand complex which is soluble in supercritical CO2. Rare earth elements were recovered from roasted and sodium hydroxide digested bastnäsite concentrate using supercritical carbon dioxide extraction with nitric acid/tributyl phosphate adducts. A range of tributyl phosphate/nitric acid adduct compositions were tested. A drop in recovery at higher acidities may indicate condensation of aqueous droplets which create an equilibrium limitation. To investigate the role of water, neodymium and holmium nitrate were extracted into supercritical CO2 with varying amounts of tributyl phosphate and water. Absorption spectroscopy was used to measure supercritical metal and water concentrations. It was found that holmium is preferentially extracted over neodymium. The results indicated that supercritical CO2 can be used to extract and separate rare earth elements from primary materials.
Chemical engineering; Copper; In Situ Leaching; Rare Earth Elements; Supercritical Carbon Dioxide; Uranium
Tester, Jefferson William
Cathles, Lawrence M.; Koch, Donald L.; Thompson, John Hugh
Ph. D., Chemical Engineering
Doctor of Philosophy
dissertation or thesis