Jerome P. Downey

Drying, Roasting, and Calcining of Minerals

Electronic reproduction. Palo Alto, Calif. : ebrary, 2015. Available via World Wide Web. Access may be limited to ebrary affiliated libraries. ;

Synthesis of Carbide Ceramics via Reduction of Adsorbed Anions on an Activated Carbon Matrix

Current commercial processes for producing ceramic carbides require temperatures of 1400–2000 °C and often use extensive milling operations to produce a powder product. A process that could reduce the energy requirements of commercial carbide production could allow for these materials to be implemented in a greater number of applications. In this study, tungstate (WO4 2−) and silicate (SiO3 2−) anions were adsorbed onto activated carbon and converted into silicon carbide (SiC) whiskers and a mixture of tungsten and tungsten carbide (W/WC) crystals via carbothermal reduction using inert and reducing gas atmospheres at temperatures much lower than what is required by current commercial processes (950 °C for W/WC/W2C and 1200 °C for SiC). The adsorption process was statistically-optimized via a central composite response surface analysis using DesignExpert 9. Inductive coupled plasma optical emission spectroscopy (ICP-OES) was used to measure, and optimize, adsorption efficiency while the carburization products were characterized using X-ray diffraction and scanning electron microscopy.

Synthesis of Nanocrystalline Carbide Ceramics Via Reduction of Anion-Loaded Activated Carbon Precursors

Commercial ceramic carbide operations require large thermal and mechanical energy inputs in order to produce a powder product. A process that could reduce the energy requirements needed to make these materials would allow for these materials to be implemented in a greater number of industrial applications. In this study, silicon carbide (SiC), tungsten carbide (WC), and molybdenum carbide (Mo2C) were synthesized via the carbothermal reduction of activated carbon loaded with silicate, tungstate, and molybdate anions adsorbed from aqueous solutions. Carburization was carried out under reducing and inert gas atmospheres, at temperatures lower than those utilized by commercial operations. Silicon carbide “whiskers” were synthesized under H2 at 1400 °C, while molybdenum carbide and mixed crystals of WC, W2C, and W were synthesized at temperatures below 1000 °C. X-ray diffraction and scanning electron microscopy were used to characterize the carburization products, and inductively coupled plasma-optical emission spectroscopy (ICP-OES) was used to determine the degree of adsorption onto the activated carbon matrix.

Selective Separation of Rare Earth Chlorides Utilizing Vapor Phase Extraction

The Metallurgical and Materials Engineering Department at Montana Tech is investigating a new method of extracting and refining rare earth elements (REEs) from mineral ores and concentrates. The relative stabilities of various REE compounds at elevated temperatures were evaluated using thermogravimetric and differential thermal analyses (TGA/DTA). The results, in combination with thermodynamic analyses, revealed that vapor phase extraction and selective condensation is a potentially viable separation method for rare earth halides. Selective vaporization and condensation experiments were performed on selected rare earth chlorides. A series of close-coupled tube furnaces provided a temperature gradient ranging from 1150 to 400 °C. Within the condensation regions, a series of one-inch-diameter ceramic tube sections were packed with stainless steel (316L) wool to create high surface area for condensate collection. The ceramic tube sections and stainless steel wool were leached in 18 MΩ water. Analysis of the leachate samples revealed that selective separation had occurred but oxychlorides were detected in the non-volatile matter.

Effects of Oxide Precursor Preparation Parameters on the Electrochemical Reduction of Tantalum Pentoxide in Calcium Chloride Melt

Successful electrochemical reduction of a metal oxide to its constituent metal depends upon two broad unit operations: (i) preparation of the oxide precursor with ideal morphological features and (ii) electrochemical reduction under optimum process parameters. The critical parameters that affect mechanical strength and open porosity of the precursor are oxide particle size; green pellet preparation; and sintering time, temperature, and atmosphere. A judicious combination of these process parameters will produce an ideal precursor for achieving complete reduction. Uniaxial pressing was utilized to prepare 13 mm diameter cylindrical pellets, which were sintered in either oxidizing (air) or reducing atmospheres. Sintered pellets were characterized by XRD, SEM-EDS, and porosity measurement techniques. Electrochemical reduction experiments were performed with a molten calcium chloride electrolyte in a cell with a three electrode configuration. Transient electrochemical techniques were employed to assess the effects of the precursor parameters on the reducibility of the sintered oxide specimens.

Optimization of Rare Earth Leaching

The use of applied chemistry in the production and optimization of leach solutions from Rare Earth Element (REE) ores and concentrates is being investigated. Ore and concentrate samples were characterized using scanning electron microscopy/mineral liberation analysis (SEM/MLA), X-ray diffraction (XRD), and Atomic emission inductively-coupled plasma spectroscopy (ICP-AES). Multiple leach tests were performed to analyze the effects of temperature, residence time, and reagent concentration on the leaching of REEs. Analysis of leach solutions was carried out using ICP-AES. Modeling and statistical analysis of extraction behavior was carried out using DesignExpert 9. Modeling data for cerium extraction indicates that extraction is greatly influenced by temperature and reagent concentration, while leaching time plays a much less important role. Experimental design techniques are being utilized to optimize REE recovery. Results, conclusions, and directions for future studies will also be discussed.

Bromination Roasting of Rare Earth Oxides

The Metallurgical and Materials Engineering Department at Montana Tech is investigating various methods of extracting and refining rare earth elements from mineral ores and concentrates. As part of this research, an elevated temperature “roasting” process has been evaluated as a means of converting the rare earth elements contained in various matrices to bromides as a pretreatment step in preparation for downstream rare earth element extraction and recovery operations. Laboratory and bench-scale experiments have been performed to assess the effects of varying temperature (150 to 400° C), time (1 to 4 h), and the ammonium bromide to rare earth oxide molar ratio (6 to 24) in the roaster charge. The results show that nearly complete bromination of the rare earth oxide is achievable when the roast is performed under optimum conditions.

Sulfation Roasting of a Bornite Flotation Concentrate to Optimize Silver Extraction in a Ferric Chloride Leach

Research was performed to evaluate copper and silver extraction from samples of bornite flotation concentrate. Sulfation roasting experiments were performed in a rotary tube furnace, a fluidized bed reactor, and a static bed muffle furnace. Roasting was plagued with rapid, low-temperature calcine sintering, apparently related to the presence of organic matter in the concentrate. Calcine entered a weak acid leaching process to remove copper, and silver was extracted from the weak acid leach residue in a ferric chloride and hydrochloric acid solution. Copper extraction efficiencies in excess of 90% were attained in the weak acid leach while 90% silver extraction was achieved in the ferric chloride leach, along with copper and lead extractions as high as 93% and 99% respectively. The two-stage leaching process resulted in overall extraction efficiencies of 99% copper and 90% silver.

Experimental Determination of Density in Molten Lime Silicate Slags as a Function of Temperature and Composition

Abstract The Archimedean single bob technique was employed to secure density data in the range of 1350–1710°C for selected molten slag compositions in the CaO–SiO2, CaO–SiO2–MgO, CaO–SiO2–Al2O3, and CaO–SiO2–MgO–CaF2 systems. In each system, the measurements typically revealed minor to negligible density variations across the temperature range. In cases where density variations were apparent, density was observed to slightly decrease as temperature was lowered. The density variations between the different slag systems are significant, with lower densities generally associated with the more acidic (higher per cent silica) compositions.