The behavior of tellurium during copper ore processing at the American Smelting and Refining Company (Tucson, AZ)

Thesis (M.S.) University of Alaska Fairbanks, 2016Essentially all tellurium (Te), an element used in solar panels and other high technology devices, is recovered as a byproduct of copper mining. Recent increases in demand have sparked questions of long-term supplies of Te (crustal abundance ~3 μg∙kg-1). As part of a larger study investigating Te resources, this project examines the behavior of Te during Cu ore mining, smelting, and refining at the American Smelting and Refining Company (Tucson, AZ) as a first step toward optimizing Te recovery. Mass balance calculations estimate that only 4 ± 1% of the Te in the ore reports to the Cu anodes, while 60 ± 30%, 0.8 ± 0.2% and 5.8 ± 0.4% is lost in the tailings, slag, and dust, respectively. The uncertainties reported are the standard deviation of analytical measurements, but due to heterogeneity of Te distribution in the ore, the actual uncertainty is likely higher. Microprobe data shows that Te in the concentrate is mainly present as telluride minerals, but substitution into sulfides most likely also occurs. X-ray fluorescence (XRF) mapping showed that Te is collocated with S in the raw anode slimes, pressed anode slimes, and doré furnace soda slag. X-ray absorption spectroscopy (XAS) was used to examine Te speciation in anode slimes. It was found that Te oxidizes during the Cu ore smelting process, with 44% Te4+ in the flash furnace SO₂ filter. Te also showed 32% Te4+ in the raw and pressed anode slimes. The doré furnace soda slag and dust filter showed the most oxidation of Te at 57% Te4+ and 60% Te6+ respectively. These results indicate several points in the extraction process that could be examined further to determine if additional Te might be recovered from the overall process.Chapter 1 Introduction -- 1.1. What is Tellurium? -- 1.2. Tellurium End Uses and Market -- 1.3. Global Supply of Tellurium -- 1.4. Tellurium Scarcity and Criticality -- 1.5. Current Copper Extraction Process -- 1.5.1. Copper Mining -- 1.5.2. Copper Smelting -- 1.5.3. Copper Refining -- 1.6. Tellurium Byproduct Recovery -- 1.6.1. Mineralogy of Tellurium in Ore Deposits -- 1.6.2. Behavior of Tellurium during Copper Concentration -- 1.6.3. Behavior and Mineralogy of Tellurium in Copper Anodes and Anode Slimes -- 1.6.4. Extraction of Tellurium as a Copper Byproduct -- 1.7. Research Objectives -- Chapter 2. Site Description -- 2.1. The Mines -- 2.2. The Smelter -- 2.3. The Refinery -- Chapter 3. Methods -- 3.1. Sample and Standard Collection, Preparation, and Preservation -- 3.2. Elemental Analysis -- 3.2.1. Inductively Coupled Plasma Mass Spectrometry -- 3.2.1.1. Method Development of Sodium Peroxide Sinter -- 3.2.1.2. Sample Preparation for ICP-MS -- 3.2.1.3. ICP-MS Elemental Analysis -- 3.2.2. Wavelength Dispersive X-Ray Fluorescence -- 3.2.2.1. Sample Preparation and Analysis of WD-XRF -- 3.3. Mass Balance Calculations -- 3.4. X-Ray Absorption Spectroscopy -- 3.4.1. Bulk S XAS -- 3.4.1.1. Bulk S XAS Collection -- 3.4.1.2. S XAS Data Analysis -- 3.4.1.3. S Linear Combination Fitting -- 3.4.2. Bulk Te XAS -- 3.4.2.1. Bulk Te XAS Collection -- 3.4.2.2. Te XAS Data Analysis -- 3.4.2.3. Te Linear Combination Fitting -- 3.5. Microfocused X-Ray Fluorescence Map Collection and Analysis -- 3.5.1. Experimental Conditions -- 3.5.2. Map Analysis -- 3.6. Electron Microprobe Analysis -- 3.6.1. Experimental Conditions -- Chapter 4. Results -- 4.1. Method Development and Verification -- 4.2. Elemental Analysis of Samples -- 4.3. Mass Balance -- 4.4. X-Ray Absorption Spectroscopy -- 4.4.1. Sulfur -- 4.4.2. Tellurium -- 4.5. Micro-focused X-Ray Maps -- 4.6. Electron Microprobe Analysis -- Chapter 5. Discussion -- 5.1. Mass Balance -- 5.2. Mine -- 5.3. Smelter -- 5.4. Refinery -- Chapter 6. Conclusions -- 6.1. Future Directions -- References