Gow - Hydroprocess template.pdf
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Transcript of Gow - Hydroprocess template.pdf
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Electrochemistry of Enargite:Reactivity in Alkaline Solutions
R. Nick GowMontana Tech / University of Montana
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Introduction to Enargite
Project Objectives
Thermodynamic Database
Raman Spectroscopy
Cyclic Voltammetry
Updated EH - pH Diagram
Conclusions
Further Work
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Cu-As Sulfosalts CuAsS Lautite Cu3AsS4 Luzonite (tetragonal) Cu3AsS4 Enargite (orthorhombic) Cu6As4S9 Sinnerite Cu12As4S13 Tennantite
Usually some Sb substitution(will see in the sample MLA scans)
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Environmental/Processing Issues
Smelter limitations 0.5% As with futureconsideration to be lowered to 0.3%
One of the more refractory copper sulfides
Higher reagent consumption for gold processes Copper competes for cyanide Arsenic competes for oxygen
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Potential Processing Methods Reductive Pre Roast Selective Flotation Sulfuric Acid Bake
Bioreduction of Sulfur Bioleach of Copper
Albion -Ultrafine Grind
Galvanox Pyrite Catalyzed Leach Acidic Pressure Leach Nitrogen Species Catalyzed
Hypochlorite Sunshine -Alkaline Sulfide
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PROJECT OBJECTIVES
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Task 1 Compile a thermodynamic database for Cu-As-S system Comparison of Cu-As-S Mass Balanced and Line Plot Diagrams
(Oxidation to Sulfate vs Oxidation to Sulfide)
Task 2 Modification and Validation of Thermodynamic Models using acombination of Raman Spectroscopy and Cyclic Voltammetry
Reactivity in Alkaline Solutions (Selective As Leach) Reactivity in Acidic Solutions (Co-dissolution of As and Cu) Addition of HS- as a lixiviant
Task 3 Determine Viability of Arsenic Adsorption using aNanographene Material
Novel nano-graphene material as an arsenic adsorbent
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Task 1 Compile a thermodynamic database for Cu-As-S system Comparison of Cu-As-S Mass Balanced and Line Plot Diagrams
(Oxidation to Sulfate vs Oxidation to Sulfide)
Task 2 Modification and Validation of Thermodynamic Models using acombination of Raman Spectroscopy and Cyclic Voltammetry
Reactivity in Alkaline Solutions
Reactivity in Acidic Solutions (Co-dissolution of As and Cu) Addition of HS- as a lixiviant
Task 3 Determine Viability of Arsenic Adsorption using a Nanographene Material Novel nano-graphene material as an arsenic adsorbent
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THERMODYNAMIC DATABASE
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Over 100 Cu-As-S Species compiled from severalsources Minteq (primary database) USGS Several other species taken from individual authors
Species G (kcal) Species G (kcal)
Cu3AsS4 Enargite -49.808 Cu(AsO2)2 -169.2
Cu12As4S13 Tennantite -180.908 Cu3As - Domeykite -3.184
Cu6As4S9 Sinnerite -110.256 H3AsSO2 -103.412
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StabCal Thermodynamic Stability Program (Huang, 2013)
Mass balanced EH pH diagrams (@ 25C) at the followingmolecular ratios (Cu:As:S)
0.66 - 0.44 - 1 (Sinnerite) 0.75 - 0.25 - 1 (Enargite) 0.92 - 0.77 - 1 (Tennanite) 1 - 1 - 1 (Lautite)
Sulfur vs Sulfate Oxidation States
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Previous Cu-As-S Stability Diagram
Activity of soluble species 0.1, 25C
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Cu + AsH3 vs
Padilla et al, 2008.
Cu3As
CuO + HAsO42- vsCu2AsO4OH
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Cu-As-S Stability Diagrams:Oxidation to Sulfate
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Cu-As-S Stability Diagrams:Oxidation to Sulfur only
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RAMAN SPECTROSCOPYMineral phase determination in conjunction with RRUFF database
(Downs, 2006)
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Raman Spectroscopyn Renishaw Raman 100 InVian 100 mW He-Ne laser (632.8 nm)
n Pt counter electroden Ag/AgCl Sat. KCl ref. electroden Mineral working electrode
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MLA - Butte MLA - Peru
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Characteristic Raman of Enargite
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Covellite (CuS) pH 9, 300 mV, 60 minChalcocite (Cu2 S) pH 12, -600 mV, 10 min
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Enargite Surface Progression - pH 9, -1000 mV vs SHE, 60 min
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Enargite Surface Progression - pH 9, 0 mV vs SHE, 60 min
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Possible Olivenite
Enargite Surface Progression - pH 9, 500 mV vs SHE
Arsenate Hydroxyl (Frost et al, 2002)
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CYCLIC VOLTAMMETRYMultifile Raman program to frequently scan the surface as the potentialcycled
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Voltammetry ProfileScan direction Negative or PositiveScan speed 5 mV/sUpper Potential 800 mV vs Ag/AgCl saturated KClLower Potential -1200 mVStart Potential -200 mVNumber of cycles 3Not stirred
Raman Spectra 5 sec per scan100% Laser power
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pH 8 CV Scan
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pH 8 CV Scan
C1C2
C3C4
Cycle12
3
Cu3AsS4 Cu12As4S13 Cu2S + As Cu0
C1 C2 C3
CuS CuxS Cu2S
C4
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pH 8 CV ScanCycle
12
3A1
A3A2
(A5)
(A4)
Cu0 Cu2S CuS
Cu(OH)2
Cu2AsO4OH
A1 A2
A3 As HAsO43-(A4)
Cu3AsS4 Cu2AsO4OH
(A5)
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MODIFICATIONS TO THE EH PHDIAGRAMS
Oxidation to sulfur only database.
Based on Raman results - removed CuO, Cu2O, and Cu3As.
Region of elemental sulfur formation included
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The dotted line indicates the regions of water stability, copper-only transitions are indicated bythe dashed line, and area above the bolded line indicates stability of elemental sulfur.
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Updated EH-pH Diagram for the Cu-As-S system overlaid with CV Inflection Points
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Nonstoichiometric transition between CuS and Cu2S
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Potential operating region: ~ -300 mV, pH >12
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CONCLUSIONS & FINDINGS Potential identification of olivenite
Arsenic depletion layer (CuxS/S) causes sulfurformation above -200 mV
Cu3AsS4 AsO43- + CuxS/Cu(OH)2 + 3 S0
Non-stoichiometric metastable copper sulfides may explainsome of the CV transitions
Operating region corresponds to the expected regionfor alkaline sulfide
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Acknowledgements
Co-authors H. Huang and C. Young Montana Tech G. Hope Griffith University
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QUESTIONS?