J Brent Hiskey

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Books

• Hiskey, J. B. (2013). Innovative Strategies for Copper Hydrometallurgy. Denver, Colorado: Society for Mining, Metallurgy and Exploration SME.
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  Invited Chapter in the SME book Innovation in Metallurgical Processing. This book resulted from the MPD Symposium held as part of the 2013 SME Annual meeting, Denver, Colorado, February 24 -27, 2013.

Journals/Publications

• Hiskey, J. B., & Novak, M. (2014). Silver and Silver Sulfide Leaching in Thiosulfate-Ferric-Thiourea Solutions. 2014 SME Annual Meeting Preprints.
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  This paper was published as an SME Preprint for the 2014 SME Annual Meeting and was presented in the Mineral & Metallurgical Processing Division session Leaching I.
• Hiskey, J. B., & Snowberger, J. (2014). Ion Exchange Recovery of Rhenium from Copper Leach Solutions using Weakly Basic Anion Exchange Resins. 2014 SME Annual Meeting Preprints.
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  Preprint and presentation at the 2014 SME Annual Meeting in the Mineral & Metallurgical Processing Division session SX-IX.
• Hiskey, J. B. (2012). Mechanism and thermodynamics of floating slimes formation. TMS Annual Meeting, 101-112.
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  Abstract: The global copper industry faces a technological challenge to develop processing schemes for more complex and impure ores and concentrates. Group 15 elements (As, Sb, and Bi) represent impurities that are troublesome both in terms of environmental impact and metallurgical processing. The so-call "dirty" copper concentrates are either unacceptable for smelting and refining or incur high penalties. The behavior of the Group 15 elements is of critical importance in maintaining product quality and process performance. During copper electrorefining, these impurities are released to the electrolyte by electrochemical dissolution of the anode. Depending mainly on temperature, concentration, and oxidation state these elements can spontaneously coprecipitate from the electrolyte. Some of these precipitates are referred to as floating slimes and their formation can have extremely detrimental effects on cathode purity. In this paper, the mechanism of floating slimes formation will be discussed and the fundamental thermochemistry will be reviewed and analyzed in relation to solubility properties.
• Nebeker, N., & Hiskey, J. B. (2012). Recovery of rhenium from copper leach solution by ion exchange. Hydrometallurgy, 125-126, 64-68.
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  Abstract: There is current interest in recovering rhenium from solutions produced as a result of copper heap and stockpile leaching. Copper-bearing leach solutions typically contain rhenium at concentrations near 1 mg/L. This work has demonstrated that rhenium can be efficiently extracted from these solutions using weakly basic anion exchange resins. Breakthrough of Re occurs after approximately 5000 BVs of solution flow. Rhenium is eluted from the resin using 1 M NaOH, producing a rhenium-rich solution containing about 1400 mg/L Re. The overall concentration ratio is about 2400:1. © 2012 Elsevier B.V. All rights reserved.
• Bhide, R., Jinshan, L. i., Free, M. L., Miller, J. D., & Hiskey, B. J. (2008). Evaluation of ferric ion reductants in sulfate based copper electrowinning electrolyte. Hydrometallurgy 2008: Proceedings of the 6th International Symposium, 618-624.
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  Abstract: In order to improve energy efficiency and avoid acid mist an alternative anodic source of oxidation of ferrous ions has been proposed as an alternative to water hydrolysis in the conventional copper electrowinning process. However, because ferrous ions are converted to ferric ions at anode, there is a need for reduction of ferric ions to ferrous ions to facilitate an acceptable overall process. In this study sulfur, mineral sulfides, sulfur dioxide and hydrogen were studied since these were found to carry out the reduction without introducing any impurities in the solution, which may affect the actual electrowinning process. The performance of these compounds was evaluated in relation to overall process requirements.
• Lee, J., & Hiskey, J. B. (2008). Electrochemical study of gold cementation in thiosulfate solutions with an electrochemical quartz crystal nanobalance. Hydrometallurgy 2008: Proceedings of the 6th International Symposium, 811-816.
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  Abstract: Gold-copper alloy formation has been observed during gold cementation on copper from ammoniacal thiosulfate solution. The electrochemistry of this system is very complex and has required the use of multiple techniques to investigate the reaction fully. In general, cyclic voltammetry and linear sweep voltammetry yield very little information regarding the cathodic reduction of gold(I)-thiosulfate species on copper. Fortunately, the electrochemical quartz crystal nanobalance (EQCN) provides a useful method to determine the reduction potential of the various species. Linear sweep voltammetry was used to determine the reduction potential of both gold(I)-thiosulfate and copper complexes with EQCN. It was observed that gold(I)-thiosulfate is reduced at -250mV vs. SHE. The normal reduction potential of copper calculated by Nernst equation is -404 mV vs. SHE and the experimental value is -430 mV vs. SHE. When the solution contains 50 ppm [Au] and 80 ppm [Cu] initially, it was observed that copper reduced at -310 mV vs. SHE which is more positive than the theoretical potential. It confirms that copper deposition on gold in thiosulfate solution exhibits underpotential deposition behavior. The UPD phenomena can explain the characteristic formation of a series of gold-copper alloys.
• Moats, M. S., & Hiskey, J. B. (2006). The effect of anode composition on passivation of commercial copper electrorefining anodes. 2006 TMS Fall Extraction and Processing Division: Sohn International Symposium, 6, 507-518.
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  Abstract: As commercial copper electrorefineries look to expand their capacities by increasing their operating current density, the likelihood of anode passivation intensifies. To improve the industry's understanding of the passivation phenomena, the role of anode composition was evaluated. While previous studies have focused on studying one impurity element at a time, this study was conducted using forty-four commercial electrorefining anode samples supplied by ten copper companies The passivation response of each sample was evaluated under accelerated galvanostatic conditions in synthetic copper electrowinning electrolyte at 65°C. This information allows for correlations between composition and passivation tendencies over a wide range of impurity elements and concentrations. It was found that selenium, tellurium, silver, lead and nickel accelerated passivation. It appeared that oxygen accelerated passivation when increased from 500 to 1500 ppm, but further increases did not have an effect. Arsenic was the only impurity found that inhibited passivation.
• Young, S. E., Hiskey, J. B., & Ruiz, J. (2006). Copper isotope variability in acid ferric sulfate dissolution of natural djurleite (Cu_1.94S). IMPC 2006 - Proceedings of 23rd International Mineral Processing Congress, 1346-1353.
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  Abstract: The resurgence of interest in transition metal isotope chemistry is the result of improved instrument precision and sensitivity. This has been achieved using multiple collector inductively-coupled mass spectrometry (MC-ICPMS) which allows simultaneous measurement of several isotope ratios in low concentrations. Copper isotope investigations have benefited from this improved technology. This study has demonstrated that appreciable Cu isotope ratio variability accompanies progressive acid ferric sulfate leaching of natural djurleite, Cu1.94S. Copper-bearing solutions from early stages of reaction (less than 10% cumulative copper dissolution) are enriched in 65Cu (δ65Cu = 1.2 ± 0.04%) compared to the initial djurleite experimental feed material (δ65Cu = -0.05 ± 0.04%). With continued reaction, 65Cu of the copper solutions steadily decreases, approaching the isotopic value of the original djurleite. As Cu:S ratio of the remaining solid material decreases, mineralogy of the residuum progresses through a series of non-stoichiometric copper sulfide phases until reaching a kinetic barrier at about 44% copper dissolution. XRD analyses has verified that the mineralogy at this boundary is dominated by the mineral yarrowite, Cu 1.12S. From djurleite to yarrowite, the average Cu-S bond length increases, resulting in an increased proportion of 4-coordinated Cu-S polyhedra over 3-coordinated geometries. This trend suggests that Cu isotope fractionation may be linked to the preference of the heavier 65Cu isotope for the lower coordinated configuration.
• Hiskey, J. B. (2005). Metal deposition and the electrocrystallization process. Proceedings of the Jan D. Miller Symposium - Innovations in Natural Resource Processing, 2005, 21-32.
• Hiskey, J. B., & Lee, J. (2003). Kinetics of gold cementation on copper in ammoniacal thiosulfate solutions. Hydrometallurgy, 69(1-3), 45-56.
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  Abstract: The rate of cementation of gold on rotating copper discs was investigated in ammoniacal thiosulfate solutions as a function of rotational speed of the copper disc, initial gold concentration, initial copper concentration, and temperature. The cementation reaction exhibited two distinct kinetic regions, an initially slow rate followed by an enhanced rate. With a disc rotating at 1500 rpm in a solution containing 0.25 M [S2O32-], 30 ppm [Au]0, and 30 ppm [Cu]0, the apparent rate constant was 4.7 × 10-3 and 1.1 × 10-2 cm s-1 for the initial and enhanced regions, respectively. At low initial copper concentrations, the temperature dependence was well behaved, yielding an activation energy of 5.9 kJ mol-1. In a solution containing 30 ppm [Cu]0, there was a noticeable decrease in the reaction rate between 25 and 50 °C. This may be attributed to the decomposition of Cu(S2O3)35- and the formation of Cu2S, which creates a passivating film. The deposit morphology is relatively nodular under the conditions of this investigation. Importantly, EDS and XRD analysis confirmed that the deposits are Au-Cu alloys instead of pure gold. The composition ranged from Au3Cu to AuCu3 intermetallic alloys depending on the initial Cu/Au ratio in solution. © 2003 Elsevier Science B.V. All rights reserved.
• Hiskey, J. B., & Maeda, Y. (2003). A study of copper deposition in the presence of Group-15 elements by cyclic voltammetry and Auger-electron spectroscopy. Journal of Applied Electrochemistry, 33(5), 393-401.
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  Abstract: The behaviour of arsenic, antimony, and bismuth during electrolytic refining of copper has been investigated using cyclic voltammetry, scanning electron microscopy, X-ray diffraction analysis and Auger electron spectroscopy. Electrodeposition was conducted using Group 15 element additions to two different cupric sulfate electrolytes: commercial tank house electrolytes containing 45 g 1-1 Cu2+ and 200 g 1-1 H2SO4 and liberator cell conditions containing 10 g 1-1 Cu2+ and 400 g 1-1 H2SO4. Analysis of electrochemical kinetic parameters indicates that the copper cathodes were more active at the higher sulfuric acid concentrations. SEM analysis revealed that Sb and Bi additions promoted truncated copper crystals while As-containing electrolytes produced random crystals. XRD patterns indicated Group 15 elements favour the production of (2 2 0) crystallographic orientation. Surface analyses of the copper deposits using AES techniques show that arsenic and antimony are deposited electrochemically forming primarily solid solution phases with copper in commercial tank house electrolytes. Under liberator cell conditions, a Cu3As intermetallic phase forms when arsenic is present in the electrolyte. Antimony is present in solid solution under these conditions. Reduction of bismuth was not detected during these experiments.
• Lee, J., & Hiskey, J. B. (2003). Alloy formation during the cementation of gold on copper from ammoniacal thiosulfate solutions. Proceedings of the TMS Fall Extraction and Processing Conference, 2, 1167-1177.
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  Abstract: Gold-copper alloys are shown to form during the cementation of gold on copper in a solution containing 0.25M [S2O32-] at 25°C. The alloy composition is strongly dependent on the initial Cu:Au ratio in solution and ranges from Au3Cu to AuCu3. XPS results for Au, Cu, S, and O are reported as a function of depth through an entire deposited film with an initial solution containing 20 ppm [Au] and 30 ppm [Cu]. The deposit contained about 20 atomic % gold and was predominantly Cu3Au. Underpotential deposition (UPD) theory is discussed as a mechanism for explaining the formation of these alloys. Several other systems that produce alloys during contact reduction/cementation are also discussed.
• Morfín, O., Conklin, M. H., Corley, T. L., Hiskey, J. B., & Ruíz, J. (2003). The use of Pb isotopes, total metals analysis and total metals ratios to characterize Pb transport and fate in an interrupted stream, Aravaipa Creek, SE Arizona. Proceedings of the TMS Fall Extraction and Processing Conference, 2, 2013-2025.
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  Abstract: The most probable source of Pb contamination in the perennial reach of Aravaipa Creek, Arizona, has been determined using Pb isotope ratios and total metals analyses of samples collected from the ephemeral and perennial reaches and mine wastes located in the Aravaipa Mining District. Previously, elevated levels of Pb, Cd and As in fish in the perennial reach of Aravaipa Creek, a protected wilderness area, were assumed to be due to off-site transport from abandoned flotation tailings piles located at Klondyke, Arizona upstream of the wilderness area. Our work replaces this inference with isotopic data that allows us to confirm this hypothesis. The Pb/Zn deposits of the district were mined between the late 1890s and the late 1960s, with the most significant ore production coming from one deposit in a rhyolite dike swarm on the Western front of the Santa Teresa Mountains, a granitic pluton of Cretaceous-Tertiary age (∼65 ma). Mineralogy has been well constrained across the length of the lode system: Pb and Zn sulfides predominate in the NW sector, and a mixed suite of hypogene/supergene Pb sulfide and Pb oxide minerals comprises the majority of its SE corner. Total metals analyses and comparison of metals ratios serve to constrain the source and transport of certain metals within different parts of the system. Pb isotope ratios in samples, obtained by ICP-MS analysis, define two distinct contributors. The first end-member (208Pb/ 204Pb = 38.513 to 38.721 and 207Pb/204Pb = 15.550 to 15.598) is characteristic of the mixed, oxide/sulfide ores at the SE end of the deposit. A second end-member (208Pb/204Pb = 38.855 to 38.946 and 207Pb/204Pb = 15.610 to 15.625) characterizes samples taken from the NW, purely Pb sulfide end of the lode. Pb isotope ratios from perennial reach sediments are closely correlated with ratios given by samples from the Klondyke tailings site and by Pb sulfide samples from the NW sector, the primary source of ores processed at Klondyke.
• Moats, M. S., & Hiskey, J. B. (2000). Role of electrolyte additives on passivation behavior during copper electrorefining. Canadian Metallurgical Quarterly, 39(3), 297-306.
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  Abstract: Additives, such as chloride, thiourea and glue, are commonly added to electrorefining electrolyte to control deposition structure and morphology. Very few studies have been performed to observe their effects on anode passivation. Chronopotentiometry was utilized to observe the passivation behaviour of commercial copper anodes in synthetic electrolyte. The effect of chloride, thiourea and glue were investigated individually. A simulated electrolyte containing all three additives was used in conjunction with twenty commercial copper anode samples to determine possible interactions between additives and anode composition.
• Moats, M. S., Hiskey, J. B., & Collins, D. W. (2000). Effect of copper, acid, and temperature on the diffusion coefficient of cupric ions in simulated electrorefining electrolytes. Hydrometallurgy, 56(3), 255-268.
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  Abstract: Deposition and dissolution processes involved in copper electrorefining are significantly affected by the diffusion coefficient of copper within an electrolyte. It is believed that the diffusion coefficient of cupric ions under conditions similar to those encountered in commercial electrolytes is not precisely known. The effects of copper, acid, and temperature on copper diffusivity were measured for simulated industrial electrolytes. Copper and acid concentrations tested were 35-70 and 160-250 g L-1, respectively. Temperature was varied from 40 °C to 65 °C. Increasing the copper and acid concentrations slightly decreased the diffusivity of copper. The diffusion coefficient of cupric ions increased with increasing temperature according to the Arrhenius relationship. An activation energy of 19.2 kJ mol-1 was calculated from the data. The diffusivity data was utilized in a simple one-dimensional finite difference model. The model indicates that saturation of copper sulfate occurs very rapidly at the high current densities (3820 A m-2) used in accelerated passivation experiments.
• Collins, D. W., & Hiskey, J. B. (1999). Additive monitoring and interactions during copper electroprocessing. 4th International Conference COPPER 99-COBRE 99, 461-477.
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  Abstract: Several organic and inorganic substances are widely used to control deposit structure and morphology during the electroprocessing of copper. Methods for monitoring the levels of thiourea, glue and guar gum during electrorefining and electrowinning have been successfully developed under the trade names of Reatrol and CollaMat. Other instrumental methods have been developed for additives and decomposition products associated with the electroplating of copper and other metals. Generally, these methods have been found to be either insufficiently sensitive or lacking in the desired selectivity for some or all of the additives. These procedures have mostly employed DC techniques; i.e., cyclic voltammetry, Tafel analysis, etc. In this work, chronopotentiometry (CP) and AC voltammetry were used to examine the interaction of glue, guar gum, thiourea and chloride during the electroplating of copper onto a platinum electrode. In addition, the interactions between the additives have been explored. It was found that glue in pure electrolyte (H2SO4 and CuSO4 only) had no effect on the chronopotentiogram. Glue was only active if chloride ions were present. The addition of thiourea resulted in several different chronopotentiograms depending on the presence of either chloride or chloride and glue. Thiourea used in conjunction with glue and chloride showed a significant increase in the polarization during copper deposition when compared to the electrolyte containing only glue and chloride. The use of a modified channel electrode further increased the sensitivity of CP. The use of AC voltammetry was explored as a technique to monitor some of the additives. AC voltammograms have more spectral detail then their DC counterparts and it is possible to monitor some of the additives at very low concentrations with AC techniques.
• Moats, M. S., & Hiskey, J. B. (1999). Post-passivation reactions occurring at the anode during copper electrorefining. 4th International Conference COPPER 99-COBRE 99, 405-424.
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  Abstract: A considerable amount of research has been conducted to determine the causes of anode passivation. Chemical and electrochemical reactions that occur after passivation have received little attention. Chronopotentiometry, linear sweep voltammetry, cyclic voltammetry, and impedance spectroscopy have been used to elucidate three reactions that occur after passivation of commercial copper anodes. These involve the dissolution of silver and subsequent cementation and transformation of selenides, the oxidation of lead sulfate to lead oxide, and oxygen evolution. The amount of silver dissolution depends on the silver content of the anode, the time to passivation, and the molar ratio of Ag/(Se+Te). The oxidation of lead from PbSO4 to PbOx explains a potential plateau of oxygen evolution. Silver affects the duration of oxygen evolution on the PbOx. Anodes containing kupferglimmer display a characteristic oxygen evolution potential. It is believed that kupferglimmer provides a lower overpotential for oxygen evolution than the other slime phases or passivated surface.
• Collins, D. W., & Hiskey, J. B. (1998). Observations of gold iodide adsorption on highly oriented pyrolytic graphite. TMS Annual Meeting, 985-998.
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  Abstract: The uptake of gold from halide solutions by activated carbon has been investigated using various techniques. Halide systems typically exhibit combined adsorption-reduction type behavior. In an attempt to gain more information about the nature of these processes, samples of synthetic highly-oriented pyrolytic graphite (HOPG) were contacted with aqueous solutions of gold-iodide. HOPG represents a model structure for activated carbon comprising of basal-plane sites, edge sites, and various defect sites. Two basic instrumental methods were used to examine the uptake of gold by HOPG. The first was standard X-ray photoelectron spectroscopy (XPs). The other involved several scanning probe techniques. XPS clearly indicated a preferred uptake of gold at edge sites. However, iodine appeared to be distributed on both basal-plane and edge sites. At low iodine additions, tapping mode AFM showed that clusters were concentrated along steps and surface defects. At high iodine concentrations, the HOPG surface was uniformly covered by iodine.
• Hiskey, J., & Cheng, X. (1998). Fundamental studies of copper anode passivation during electrorefining: Part III. The effect of thiourea. Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, 29(1), 53-58.
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  Abstract: Thiourea has been extensively used as a grain refiner in industrial copper electrorefining processes. The influence of thiourea on deposit structure and morphology has received considerable study; however, the effect of thiourea and its degradation chemistry on the passivation behavior of commercial copper anodes is still not fully understood. This study was conducted to provide useful information regarding the electrochemical response of a commercial copper anode in the absence and presence of thiourea. Chronopotentiometry measurements were performed in synthetic electrolytes containing different thiourea concentrations and in industrial electrolytes obtained directly from a commercial tank house. Passivation time (tp) and periodic passivation phenomena were found to be closely associated with thiourea concentration and degradation.
• Hiskey, J. B., & Qi, P. H. (1997). Thermal analysis of activated carbon loaded with different gold halides. Minerals and Metallurgical Processing, 14(3), 13-17.
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  Abstract: Activated carbon loaded with gold from different halide solutions was characterized by thermalanalysis (TA) techniques. The mechanism of gold uptake by carbon varies from predominately adsorption for gold iodide to predominately reduction for gold chloride. Thermogravimetry analysis (TGA) and differential thermal analysis (DTA) measurements confirm the existence of adsorbed gold-halide species within the micropore structure of carbon. These results suggest that the ratio of reduced to adsorbed gold increases for gold halides in the following order: Au-I < Au-Br < Au-Cl. In the case of Au-I, TA results for the loaded carbon were compared with pure compounds of I2, AuI and AuI3.
• Moats, M. S., Hiskey, J., & Campin, S. C. (1997). Characterization of passivating films on commercial copper anodes using impedance spectroscopy. TMS Annual Meeting, 37-49.
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  Abstract: Electrochemical techniques are a valuable means of analyzing the passivation of commercial copper anodes. Electrochemical impedance spectroscopy (EIS) provides information concerning transport and reaction phenomena occurring at an electrode surface. Commercial copper anodes of varying compositions have been examined using EIS. Experiments were conducted in a flat cell with an electrolyte of 40 g/l Cu2+ and 160 g/l H2SO4 maintained at 65 °C. Impedance spectra were obtained at the potentials characteristic of the open circuit voltage and passive region for each anode. The spectra of the passivating films exhibited a flattened resistive/capacitive loop at middle to high frequencies and an inductive loop at low frequencies. An equivalent circuit utilizing an inductor-resistor series in parallel with the double layer capacitance and charge transfer resistance was adequate in modeling the impedance data. The influence of anodes impurities on the components of the equivalent circuit is discussed and correlated with a bi-layer passivation model.
• Cheng, X., & Hiskey, J. B. (1996). Fundamental studies of copper anode passivation during electrorefining: Part I. Development of techniques. Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, 27(3), 393-398.
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  Abstract: Anode passivation is an extremely important phenomenon in commercial copper electrorefining operations. Due to the electrochemical nature of the refining process, various electrochemical techniques have been applied to examine anode passivation behavior. In this investigation, cyclic voltammetry, linear potential sweep, and chronopotentiometry measurements were carried out on several commercial copper anodes, as well as on pure electrowon (EW) copper cathode, in synthetic electrolytes simulating the primary constituents for industrial operations. The important parameters associated with anode passivation were identified and compared for the three electrochemical techniques. Chronopotentiometry is an extremely sensitive technique and proved to be the most suitable for analyzing and characterizing copper anode passivation.
• Cheng, X., & Hiskey, J. B. (1996). Fundamental studies of copper anode passivation during electrorefining: Part II Surface morphology. Metallurgical and Materials Transactions B: Process Metallurgy and Materials Processing Science, 27(4), 610-616.
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  Abstract: Passivation of commercial copper anodes and pure copper has been previously analyzed by performing electrochemical measurements. Chronopotentiometry results revealed four characteristic regions involving I - active dissolution, II - prepassivation, III - passivation onset, and IV - passivation, for commercial copper anodes, while only active dissolution was observed for pure copper under the conditions employed. In order to establish the relationship between surface morphology and passivation response, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray spectroscopy (EDS) were applied to characterize morphology of the product layers formed on a commercial copper anode surface for the distinctive electrochemical regions. The morphology studies suggested that the formation and stability of copper oxide surface films are critical to the onset and development of passivation. The structure and porosity of the slimes layer present in the outer layer of the anode influence the stability of copper oxide surface films which dominantly control the passivation response.
• Hiskey, J. B., & Sanchez, V. M. (1995). Alkaline pressure oxidation of a gold-bearing arsenopyrite concentrate. Mineral Processing and Extractive Metallurgy Review, 15(1-4), 61-74.
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  Abstract: The aqueous pressure oxidation of gold bearing arsenopyrite concentrates in alkaline solution was investigated as a function of O2 pressure and NaOH concentration. Dissolution of gold from the leach residue was accomplished by standard cyanidation. Gold extraction was found to be proportional to the degree of arsenopyrite oxidation. Alkaline pressure oxidation at 160°C, 2413 kPa O2 and 2 M NaOH resulted in about 98% sulfur oxidation and 86% arsenic dissolution. Cyanidation of the leach residue resulted in 82% Au extraction. This value for gold extraction is lower than what is typically achieved by acid pressure oxidation followed by cyanidation. A preliminary mineralogical study of the pressure oxidation leach residues was undertaken. The degree of gold recovery from the leach residues is believed to be linked to its association with oxidized products such as iron arsenate hydrate and iron oxide.
• Sole, K. C., & Hiskey, J. (1995). Solvent extraction of copper by Cyanex 272, Cyanex 302 and Cyanex 301. Hydrometallurgy, 37(2), 129-147.
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  Abstract: The mechanisms of copper(II) solvent extraction by Cyanex 272, Cyanex 302 and Cyanex 301 are discussed. Extraction from sulfate media is strongly dependant upon sulfur substitution in the phosphinic acid and complete extraction of copper by Cyanex 302 and Cyanex 301 occurs below pH 0. Since conventional slope analysis is not possible under these conditions, the complex stoichiometries and geometries are inferred from analysis of the electronic, 31P-NMR and FAB-MS spectra of the complexed species. Cu(II) is reduced to Cu(I) on extraction by the sulfur-containing ligands, accompanied by the corresponding oxidation of the extractant. It is shown that copper combines in a 1:1 stoichiometric ratio with these ligands to form multinuclear oligomeric complexes, in which the ligands bridge between metal centers. The enhanced stabilities of the complexes formed with the sulfur-containing ligands are explained in terms of the Hard-Soft Acid-Base concept and pi bonding between the d orbitals of the metal center and the donor atoms. © 1995.
• Parks, H. G., Hiskey, J. B., & Yoneshige, K. (1994). Mechanistic study of the deposition of metals from HF solutions onto silicon wafers. Materials Research Society Symposium Proceedings, 318, 245-256.
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  Abstract: Process chemicals in use today are quite pure, depending on the grade used but can easily be contaminated with metal ions through improper handling or storage techniques. Such metal impurities, if deposited on wafer surfaces during processing can increase reverse-bias junction leakage, degrade oxide breakdown strength and increase metal oxide semiconductor capacitor leakage which in turn can adversely affect the function of ultra large scale integrated (ULSI) circuits. Because of these device effects and since metal contamination can come form several sources it is important to know the deposition level and mechanism on Si wafers from a given process solution. HF based process solution have been investigated due to their historical use in patterning, etching, and their increased use in advanced wafer cleaning processes.
• Sole, K. C., Ferguson, T. L., & Hiskey, J. (1994). Solvent extraction of silver by Cyanex 272, Cyanex 302 and Cyanex 301. Solvent Extraction and Ion Exchange, 12(5), 1033-1050.
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  Abstract: The solvent extraction of silver from nitrate media by the extractants Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid), Cyanex 302 (bis(2,4,4-trimethylpentyl)thiophosphinic acid) and Cyanex 301 (bis(2,4,4-trimethylpentyl)dithiophosphinic acid) acid characterized. Extraction shifts to lower pH with increasing sulfur substitution in the phosphinic acid, in accordance with the increased extractant acidity imparted by the soft nature of the sulfur donor atoms. The effects of extractant concentration, aqueous-phase ionic strength and organic-phase diluent on the extraction behavior are examined. The stoichiometry of the extraction reactions and the geometry of the extracted complexes are postulated based on slope analysis and spectroscopic measurements. All three extractants behave as bidentate ligands and combine in a 1:1 stoichiometric ratio with silver. The sulfur-containing ligands form multinuclear oligomeric complexes in which the ligands bridge between metal centers.
• Qi, P. H., & Hiskey, J. B. (1993). Electrochemical behavior of gold in iodide solutions. Hydrometallurgy, 32(2), 161-179.
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  Abstract: The electrochemistry of gold in different halide solutions, with special emphasis on iodide is presented. The electrochemical techniques used during this investigation included cyclic and linear sweep voltammetry. A glassy carbon rotating disk electrode was used to investigate the electrochemistry of the iodide and a gold rotating disk electrode to explore the oxidation behavior of gold in iodide solutions. The effects of iodide concentration, electrode rotation and sweep rate on the electrochemical behavior of gold were examined. In addition, reduction of iodine species at the gold electrode was also investigated. Iodide is shown to be a powerful complexing agent for gold. Cyclic voltammograms of gold in the presence of 10-2 M chloride, bromide and iodide, respectively, show that the anodic currents for the oxidation of gold in iodide solution are much greater than that in either bromide or chloride. Two oxidation peaks, which represent the oxidations of Au to Au(I) and to Au(III), were observed. It is confirmed that iodide is oxidized sequentially to tri-iodide and then to iodine and both of these reactions are reversible. At high concentrations of iodide and/or a slow scan rate, passivation, which is caused by the formation of solid iodine at the gold electrode surface, was found. The cathodic reduction curves show that reduction of iodide species on gold is a function of iodine concentrations but it is insensitive to iodide concentration. © 1993.
• Sole, K. C., Peihao, Q. i., & Hiskey, J. (1993). An evaluation of the physicochemical degradation of gold ion-exchange resins in hypochlorite solutions. Metallurgical Transactions B, 24(1), 17-25.
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  Abstract: The long-term operating characteristics of ion-exchange resins suitable for the hydrometallurgical recovery of precious metals remain largely unknown. This study examines some physicochemical properties of two promising ion-exchange resins for gold, SR-3 and PAZ-8, when subjected to experimental conditions similar to those of a typical alkaline-chlorination gold recovery process. It is shown that the degradation behavior may be related to both the micro- and macrostructural properties of the resins. Severe resin degradation occurs on pro-longed, agitated contact of the SR-3 resin beads with hypochlorite solutions at ambient tem-perature; the low cross linkage of the resin facilitates mechanical damage, while chemical degradation occurs by dehydration, oxidative scission of the functional groups, and breakdown of the polymer matrix. The PAZ-8 resin is highly cross linked and is more resistant to both mechanical and chemical attack under similar conditions. © 1993 The Minerals, Metals & Material Society.
• Sole, K. C., & Hiskey, J. (1992). Solvent extraction characteristics of thiosubstituted organophosphinic acid extractants. Hydrometallurgy, 30(1-3), 345-365.
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  Abstract: Organophosphorus reagents are well known in solvent extraction. Commercial operations for the separation of cobalt from nickel have been successfully carried out using organophosphoric, -phosphonic, and -phosphinic acid extractants. Two new reagents in this class are the mono and dithio analogs of the commercial dialkylphosphinic acid, Cyanex 272. The replacement of oxygen by sulfur in these reagents enables extraction to be carried out at much lower pH. Characterization of Cyanex 272, Cyanex 302 (bis-(2,4,4-trimethylpentyl)-thiophosphinic acid), and Cyanex 301 (bis-(2,4,4-trimethylpentyl)-dithiophosphinic acid) has been undertaken. A comparison of the solvent extraction behavior of metallurgically important first-row transition metal ions from acidic sulfate solution by these reagents is reported. Distribution coefficients shift to lower pH with increasing sulfur substitution and decreasing pKa of the extractant, the greatest effect being observed for nickel. Stoichiometry of the extraction reactions, and the nature of the metal complexes formed have been determined using slope analysis techniques and spectroscopic measurements. © 1992.
• Sole, K. C., & Hiskey, J. B. (1992). Solvent extraction characteristics of thiosubstituted organophosphinic acid extractants. Array.
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  Abstract: Commercial operations for the separation of cobalt from nickel have been successfully carried out using organophosphoric, -phosphonic, and -phosphinic acid extractants. Two new reagents in this class are the mono and dithio analogs of the commercial dialkylphosphinic acid, Cyanex 272. Characterization of Cyanex 272, Cyanex 302 (bis-(2,4,4-trimethylpentyl)-thiophosphinic acid), and Cyanex 301 (bis-(2,4,4,-trimethylpentyl)-dithiophosphinic acid) has been undertaken. A comparison of the solvent extraction behavior of metallurgically important first-row transition metal ions from acidic sulfate solution by these reagents is reported. (from Authors)
• Qi, P. H., & Hiskey, J. B. (1991). Dissolution kinetics of gold in iodide solutions. Hydrometallurgy, 27(1), 47-62.
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  Abstract: Of the halogens, the gold iodide complexes are the most stable in aqueous solutions. A series of experiments were performed to investigate the kinetics and mechanism of the leaching reaction between gold and iodide. Using a rotating disk technique, the effects of rotation speed, iodide and iodine concentration, temperature, pH and the presence of different electrolytes were measured. Oxygen and hydrogen peroxide were also examined as oxidants in the iodide system. A first order reaction rate was found with respect to I3- and half order reaction rate with respect to I-. A comparison of gold leaching between iodide and cyanide is also presented, in which a rate of about 2.6 × 10-9 mol/cm2 sec for 10-2 M Nal and 5 × 10-3 M I2 was obtained. This value is close to that for typical cyanidation. © 1991.
• Sanchez, V. M., & Hiskey, J. B. (1991). Electrochemical behavior of arsenopyrite in alkaline media. Minerals and Metallurgical Processing, 8(1), 1-6.
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  Abstract: Electrochemical oxidation of arsenopyrite (FeAsS) has been investigated as an attempt to gain a better understanding of its dissolution chemistry. Rest potential measurements, cyclic voltammetry and constant potential experiments were conducted in the pH range from 8 to 12 in the absence and the in the presence of cyanide. A two-step reaction sequence is suggested by the electrochemical measurements. sequence is suggested by the electrochemical measurements. The initial step is described by: FeAsS + 6H2O = Fe(OH)3+ H2AsO3- + S° + 7H+ + 6 e. The second step involves the oxidation of the arsenite and sulfur according to the following reactions: H2AsO3- + H2O = HAsO42-$/ + 3 H+ 2 e and S° + 4 H2O = SO42- + 3 H+ + 6 e. Stoichiometric determinations confirm that 14 electrons are involved in the overall reaction.
• Hiskey, J. B., & Jiang, X. H. (1990). Recovery of gold from chloride solution with ion exchange resins. Advances in Gold and Silver Processing, 277-284.
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  Abstract: The extraction of gold from chloride solutions by ion exchange is examined. It is shown that at initial gold concentrations between 1-5 ppm, 20 g/l Cl- and pH 5, the kinetics of loading on weak base resins are slightly slower than those observed with activated charcoal. Equilibrium loading of auric chloride varies considerably as a function of pH from one resin to another. For all of the resins studied, nearly complete gold extraction was achieved between pH 2 and pH 6.5. Sodium hypochlorite was found to exhibit a slight effect on the equilibrium loading of gold chloride.
• Hiskey, J. B., & Qi, P. H. (1990). Leaching and electrochemical behavior of gold in iodine solutions part I. Dissolution kinetics. Preprint - Society of Mining Engineers of AIME, 8p 112.
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  Abstract: Of the halogens, the gold iodide complexes are the most stable in aqueous solutions. A series of experiments were performed to investigate the kinetics and mechanism of the leaching reaction between gold and iodide. Using a rotation disk technique, the effects of rotation speed, iodide and iodine concentration, temperature, pH and in the presence of different electrolytes were measured. Oxygen and hydrogen peroxide were also examined as oxidants in the iodide system. The first order reaction rate was found with respect to I3- and half order reaction rate with respect to I-. The comparision of gold leaching between iodide and cyanide is also presented, in which a rate constant of about 2.6×10-9 mol/cm2·sec for 10-2 M I- and 5×10-3 M I2 was obtained. This value is close to that for typical cyanidation. Cyclic voltammetry experiments were also performed to examine the electrochemical nature of the reaction.
• Hiskey, J. B., & Sanchez, V. M. (1990). Mechanistic and kinetic aspects of silver dissolution in cyanide solutions. Journal of Applied Electrochemistry, 20(3), 479-487.
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  Abstract: The factors influencing the dissolution kinetics of pure silver in cyanide solution have been analysed in terms of an electrochemical mechanism. A kinetic model is presented which incorporates coupled diffusion and charge transfer for the anodic branch, and combined diffusion, adsorption and charge transfer for the cathodic branch. The anodic oxidation of silver has been investigated using a silver rotating-disc electrode for concentrations between 10-3 and 10-1m NaCN. Oxygen reduction on silver has been studied at oxygen partial pressures between 0.104 and 1.00 atm. Mechanistic aspects of the oxygen discharge reaction are considered in explaining the kinetic differences between gold and silver dissolution in cyanide solution. It is shown that under conditions typical of conventional cyanidation gold dissolves measurably faster than silver. © 1990 Chapman and Hall Ltd.
• Hiskey, J. B., Jiang, X. H., & Ramadorai, G. (1990). Fundamental studies on the loading of gold on carbon in chloride solutions. Array, 369-376.
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  Abstract: The extraction of gold from chloride solutions with activated carbon is examined. It is shown that the uptake of gold by activated carbon from chloride solution follows a mechanism whereby gold is reduced to the metallic state. Metallic gold appears as deposits both on the carbon surface and in pore space within the carbon particle. The deposition rate is dependant on the carbon particle size and pH. At low initial gold concentrations, the initial rate is insensitive to gold concentration. Sodium hypochlorite exhibits an adverse effect on the reduction reaction. The overall loading and initial rate of reduction are both decreased in the presence of NaC10. The effect of iodide on the loading of gold was also examined in an attempt to overcome the superficial deposition of gold on carbon.
• Law, K. J., & Hiskey, J. B. (1990). Dissolution of lead smelter dust compounds by humic acid. Array, 61-67.
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  Abstract: The ability of humic acids to complex metal ions is well established; however, the chemistry of lead dissolution and structure of the organo-metallic compound is not well understood. To better understand these problems, experiments were undertaken reacting the common smelter by-products PbSO4, PbCO3, and PbO with humic acid as a function of time, pH, and humic acid concentration. Examinations were made of the structure and mechanisms of complexing through the use of model humic acid functional group compounds and infra-red spectroscopy. Low pH conditions and increased humic acid concentrations favor PbO and PbCO3 complexing. Lead sulfate complexation was favored by increased pH and humic acid concentrations. At low pH values the particulate lead compounds adsorbed humic acid inhibiting lead dissolution. Active sites of complexation found through infra-red analysis were at carboxyl, phenol, phenyl, and aliphatic groups, along with formation of metalocyclohexanes and pentanes. Model functional group analysis proved inconclusive for characterization of active complexing sites.
• Hiskey, J. B., & Atluri, V. P. (1989). Resin-in-leach cyanidation of a carbonaceous gold ore. Minerals and Metallurgical Processing, 6(3), 113-116.
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  Abstract: Resin-in-leach (RIL) cyanidation experiments were performed on a refractory carbonaceous gold ore to determine if strong-base ion exchange resins could absorb the soluble aurocyanide complex in preference to natural preg robbing organic constituents. Direct cyanidation of the ore resulted in less than 2% gold extraction in 24 hr.RIL cyanidation resulted in about 70% gold recovery onto the resin. Kinetic experiments indicated that 50% of the gold is extracted after 1 hr of leaching. Resin breakage was investigated for as-received and preattrited resins. Similar results were obtained with three different strong base resins. Amberlite IRA-400, Amberlite IRA-900, and Amberlite XE-834.
• Hiskey, J. B., & Pritzker, M. D. (1988). Electrochemical behavior of pyrite in sulfuric acid solutions containing silver ions. Journal of Applied Electrochemistry, 18(3), 484-490.
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  Abstract: A systematic electrochemical study of pyrite in H2SO4 solutions containing dissolved silver was undertaken to gain more information about the transfer of silver ions to pyrite and their role in enhancing the direct oxidation of pyrite. The results of cyclic voltammetry experiments provide additional evidence of the formation of metallic silver on the FeS2 surface under open-circuit conditions. A pyrite electrode held at the open-circuit potential for 2 h in the presence of 10-3m Ag+ exhibits a large and sharp anodic peak at about 0.7V. The current associated with this peak is the result of the dissolution of metallic silver deposited during the initial conditioning period. There is no evidence of silver deposition without preconditioning until the potential drops below about 0.6V for Ag+ concentrations ranging from 10-4 to 10-2m. However, subsequent silver deposition appears to be very sensitive to the dissolved silver concentration in this range. There is also evidence that the state of the pyrite surface has a pronounced influence on its interaction with silver ions. Agitation has also been found to have a significant effect on the electrochemistry of the Ag-FeS2 system. © 1988 Chapman and Hall Ltd.
• Sanchez, V., & Hiskey, J. (1988). An electrochemical study of the surface oxidation of arsenopyrite in alkaline media. Metallurgical Transactions B, 19(6), 943-949.
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  Abstract: The electrochemical behavior of arsenopyrite (FeAsS) electrodes in alkaline cyanide solutions has been investigated in an attempt to gain a better understanding of its dissolution chemistry. Surface oxidation reactions of arsenopyrite have been studied using cyclic voltammetry for pH values between 8.1 and 12.0 and for cyanide concentration from 10-4 to 10-2 M. Anodic oxidation of FeAsS appears to be sensitive to both pH and cyanide, as indicated by a characteristic peak at 0.30 V vs SHE for pH 11.3 and 10-2 M CN-. The anodic process corresponding to the main peak is described by the reaction: FeAsS + 9H2O = FeOOH + H2AsO3 - + SO4 2- + 15H+ + 12 e - The oxidation of the H2AsO3 -to HAsO4 2- is detected by a second wave at higher potentials under quiescent conditions. At high pH, the main peak is insensitive to the presence of cyanide, whereas at low-alkalinity this peak is sensitive to cyanide. © 1988 The Metallurgical Society and ASM INTERNATIONAL.
• Hiskey, J. B., Phule, P. P., & Pritzker, M. D. (1987). Studies on the effect of addition of silver ions on the direct oxidation of pyrite. Metallurgical Transactions B, 18(4), 641-647.
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  Abstract: The nature of the reaction between Ag+ and pyrite in 0.25 M H2SO4 solutions has been investigated in order to determine whether Ag+ can enhance the ferric sulfate leaching of this mineral. Analysis of reacted pyrite particles using scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and low-angle X-ray diffraction (XRD) indicates that elemental silver and elemental sulfur are the primary surface species formed by this interaction. Rest potential measurements of a pyrite electrode immersed in a solution containing 10-2 M Ag+ are also consistent with what is expected for the deposition of metallic silver. Furthermore, the XRD data reveal that, at the most, only minor amounts of Ag2S are being produced. The presence of Ag2O has also been detected, but this is due to oxidation of silver after the experiment is complete and while the particles are being transferred for surface analysis. When 1 M ferric sulfate is contacted with pyrite which has been pretreated in a AgNO3 solution, most of the silver immediately redissolves and does not redeposit while ferric ions are present. This indicates that the kinetics of the transfer reaction between Ag+ and pyrite is slower than the reaction between Fe3+ and pyrite and suggests that Ag+ does not likely enhance the ferric sulfate leaching. © 1987 The Metallurgical Society and ASM International.
• Hiskey, J. (1986). TECHNICAL DEVELOPMENTS IN HYDROMETALLURGY.. Journal of Metals, 38(7), 41-46.
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  Abstract: The review covers leaching, chloride systems, reaction design and modeling, complex sulfides, biotechnology, solvent extraction, ion exchange and selective precipitation. It also covers the fundamentals research into electrochemistry, thermodynamics and solution chemistry; solution mining and work on precious metals.
• Hiskey, J. (1986). Technical Developments in Hydrometallurgy. JOM, 38(7), 41-46.
• Hiskey, J. B. (1986). TECHNICAL INNOVATIONS SPUR RESURGENCE OF COPPER SOLUTION MINING.. Mining Engineering, 38(11), 1036-1039.
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  Abstract: The author updates current US copper solution mining trends. Heap leaching is usually selected for moderate to high grade ores having a copper mineralization that is amenable to acid leaching (oxides, silicates and certain sulfides). Dump leaching practice usually involves leaching low grade waste rock placed on large dumps. In situ leaching is appropriate for either deep ore bodies or for recovering copper from low grade rock left behind in abandoned pit walls, stopes, and subsidence zones.
• Hiskey, J. B., & Ette, A. O. (1986). KINETICS OF AUROCYANIDE LOADING WITH AN ANION EXCHANGE RESIN.. Array, 295-310.
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  Abstract: Synthetic ion-exchange resins offer an attractive alternative to carbon for the recovery of gold from alkaline cyanide solutions. This paper describes an investigation of the kinetics of loading gold onto a new weak-base resin (PAZ-4) designed specifically for gold and silver cyano anions. The uptake of gold was determined at temperatures from 25 degree C to 450 degree C, pH's from 8. 5 to 11. 5, and free cyanide concentrations from 0. 20 g/l to 0. 80 g/l. The adsorption rate increases strongly with decreasing pH and to a lesser extent with increasing free CN** minus concentration. Temperature was observed to have very little effect on the loading kinetics. The initial loading kinetics obey a shell-progressive (shrinking core) diffusion mechanism and can be explained mathematically by the classical diffusion equation for spherical particles. An exchange mechanism involving reaction between aurocyanide and hydrogen cyanide is proposed to explain the results.
• Hiskey, J. B. (1984). CURRENT STATUS OF U. S. GOLD AND SILVER HEAP LEACHING OPERATIONS.. Array, 1-7.
• Hiskey, J. B. (1984). THIOUREA LEACHING OF GOLD AND SILVER - TECHNOLOGY UPDATE AND ADDITIONAL APPLICATIONS.. Annual Symposium on Uranium and Precious Metals, 95-99.
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  Abstract: The review of recent literature relating to the use of thiourea as a lixiviant for gold and silver indicates only a modest level of activity and interest. Alkali cyanide leaching system remains the popular choice for treating gold and silver ores. There is some interest in using thiourea as an alternative to cyanide in the processing of high grade concentrates. Thiourea does have potential for extracting gold and silver from refractory ores and concentrates that have sufficient value to justify the use of thiourea as a reagent. As illustrated by the leaching results for the bulk concentrate reported in this article, thiourea yields substantially higher levels of gold and silver extraction than does cyanide. Dissolution is generally much faster in thiourea than in cyanide solution.
• Hiskey, J. B. (1984). THIOUREA LEACHING OF GOLD AND SILVER - TECHNOLOGY UPDATE AND ADDITIONAL APPLICATIONS.. Minerals & Metallurgical Processing, 1(3), 173-179.
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  Abstract: The hydrometallurgical application of thiourea in processing precious metal ores and concentrates has reached the development stage. This paper reviews recent technical literature covering the process development of thiourea leaching. In addition, recent fundamental contributions are discussed. Most of the interest in thiourea leaching has involved treating high grade concentrates that have sufficient value to justify the use of thiourea as a reagent. An important development in thiourea technology is the addition of SO//2 to the leaching solution. This procedure effectively reduces the decomposition of thiourea and eliminates the problems of passive surface layers that limit the leaching efficiency. Results for the thiourea leaching of a bulk sulfide concentrate and a residue from the autoclave leaching of a smelter flue dust are also reported.
• Mooiman, M. B., Miller, J. D., Hiskey, J., & Hendriksz, A. R. (1984). COMPARISON OF PROCESS ALTERNATIVES FOR GOLD RECOVERY FROM CYANIDE LEACH SOLUTIONS.. Array, 93-107.
• Mooiman, M. B., Miller, J. D., Hiskey, J. B., & Hendriksz, A. R. (1983). PROCESS ALTERNATIVES FOR GOLD RECOVERY FROM CYANIDE HEAP LEACH SOLUTIONS.. Preprint - Society of Mining Engineers of AIME.
• Schlitt, W. J., Hiskey, J. B., & Pitt, W. G. (1983). OXIDATION OF AQUEOUS SULFUR DIOXIDE.. Transactions of the American Institute of Mining, Metallurgical, and Petroleum Engineers, Society, 274, 2051-2057.
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  Abstract: Aqueous SO//2 (sulfurous acid) functions as a reagent in various hydrometallurgical systems but also represents an undesirable constituent in pyro- and hydrometallurgical effluent solutions. When present in such streams, SO//2 can be oxidized to the more stable sulfate form to avoid exsolution of SO//2 as a source of fugitive emissions and to simplify standard water treatment plant operation. This study provides information on the stoichiometry, kinetics, and mechanism of SO//2 oxidation using oxygen and an iron salt catalyst with solutions containing 0. 05-20 g/L (0. 002-0. 7 oz per gal) SO//2. The effects of iron salt concentration, oxygen pressure, temperature, degree of agitation, and pH on SO//2 oxidation are also described.
• Hiskey, J. B., & Schlitt, W. J. (1982). AQUEOUS OXIDATION OF PYRITE.. Array, 55, 57-74.
• Schlitt, W., Pitt, W. G., & Hiskey, J. (1982). OXIDATION OF AQUEOUS SULFUR DIOXIDE.. Preprint - Society of Mining Engineers of AIME.
• Hiskey, J. B. (1981). THIOUREA AS A LIXIVIANT FOR GOLDAND SILVER.. Preprint - Society of Mining Engineers of AIME.
• Hiskey, J., & Wadsworth, M. E. (1981). ELECTROCHEMICAL PROCESSES IN THE LEACHING OF METAL SULFIDES AND OXIDES.. Journal of Macromolecular Science - Physics, 303-325.
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  Abstract: The kinetics of several metal sulfide and oxide systems are explained by electrochemical reactions related to mixed potentials which form as a result of coupled anodic and cathodic processes.
• Murr, L. E., & Hiskey, J. B. (1981). Kinetic effects of particle-size and crystal dislocation density on the dichromate leaching of chalcopyrite. Metallurgical Transactions B, 12(2), 255-267.
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  Abstract: Relatively pure, polycrystalline samples of Golden, New Mexico and Transvaal, South Africa chalcopyrite were ground and polished to fit into a density-compatible titanium alloy sandwich assembly and shock loaded (the Golden at 1.2 GPa, the Transvaal at 18 GPa peak pressure). The recovered samples were examined in the transmission electron microscope and observed to contain roughly 103 and 104 times more dislocations respectively than the natural, unshocked materials which contained roughly 107 cm-2. These materials were ground to three size fractions and leached in an acid-dichromate lixiviant at 50 and 70 °C (323 and 343 K). Corresponding size fractions were prepared from the unshocked material and leached for comparison; and these experiments were extended to a range of temperatures up to 90 °C (363 K) using a Bingham Canyon, Utah chalcopyrite. An unambiguous effect of dislocations was observed at the largest size fraction leached at 50 °C (323 K): the reaction rate constant increased from 1.44 × 10-3 to 1.62 × 10-3 to 2.73 × 10-3 min-1 for dislocation densities increasing from roughly 103 cm-2 to 1011 cm-2. A linear relationship in the leaching rate was observed between 25 and 60 °C (298 and 333 K) and the activation energy was calculated to be approximately 12 kcal/mol (50 kJ/mol). Above 60 °C (333 K) a conspicuous rate decrease was observed. This was related to a densification of the sulfur product layer, which at 50 °C (323 K) was a loose, porous precipitate while at 90 °C (363 K) it was a continuous, tenacious, glassy coating on the chalcopyrite particles. In addition, and more importantly, the high-temperature decline in leaching rate was inferred to be associated with adsorption of Cr(VI) ion which decreases with increasing temperature. The anomalous and unpredictable behavior of chalcopyrite leached in acid-dichromate lixiviant was therefore observed to be related to variations in a surface chemisorption mechanism as well as variations in the nature of the sulfur reaction product layer. These effects also mask the influence of crystal defects and other surface-related crystallographic effects in leaching. © 1981 American Society for Metals and the Metallurgical Society of AIME.
• Hiskey, J. B. (1980). HYDROGEN PEROXIDE LEACHING OF URANIUM IN CARBONATE SOLUTIONS.. Transactions of the Institution of Mining and Metallurgy, Section C: Mineral Processing and Extractive Metallurgy, 89, 145-152.
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  Abstract: Problems associated with the in-situ leaching of uranium are considered. Specifically, the kinetics of UO//2 dissolution in ammoniacal carbonate solutions were investigated with hydrogen peroxide as an oxidant. Also, the effects of hydrogen peroxide concentration, total carbonate concentration and pH were studied. For similar conditions, the rate of dissolution was considerably faster with hydrogen peroxide than with oxygen.
• Hiskey, J. B. (1979). KINETICS OF URANIUM DIOXIDE DISSOLUTION IN AMMONIUM CARBONATE.. Transactions of the Institution of Mining and Metallurgy, Section C: Mineral Processing and Extractive Metallurgy, 88, c145-c152.
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  Abstract: The kinetics of UO//2 dissolution in ammoniacal carbonate solutions were studied as a function of total carbonate concentration, oxygen pressure, temperature and pH value. The intrinsic leaching (no external potential) of UO//2 agreed well with an electrochemical surface-reaction model, in which anodic oxidation of UO//2 is coupled with cathodic reduction of oxygen. The experimenCtal data corroborate an anodic dissolution sequence that includes both charge-transfer and chemical-reaction steps. Experimental evidence indicates that the mechanism involves consecutive one-electron-transfer steps.
• Annamalai, V., & Hiskey, J. B. (1978). KINETIC STUDY OF COPPER CEMENTATION ON PURE ALUMINUM. Min Eng (New York), 30(6), 650-659.
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  Abstract: The kinetics of copper cementation on a rotating disc of pure aluminum were studied as a function of chloride ion concentration, copper ion concentyration, and temperature. The optimum experimental conditions for all the parameters were determined. Chloride ion was found to destroy the naturally existing aluminum oxide film, and enabled the cementation reaction to proceed. A two-step rate, observed in most of the experiments, was attributed to the attainment of a roughened surface. An Evans diagram for the copper-pure aluminum system was constructed and utilized in predicting the controlling mechanism of the system.
• Annamalai, V., Hiskey, J. B., & Murr, L. E. (1978). The effects of kinetic variables on the structure of copper deposits cemented on pure aluminum discs: A scanning electron microscopic study. Hydrometallurgy, 3(2), 163-180.
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  Abstract: The structural characteristics of copper deposits resulting from copper cementation on pure aluminum are presented. The effect of chloride ion concentration, rotational speed of the aluminum disc, hydrogen ion concentration, copper ion concentration, and temperature on the nature and morphology of the deposits was investigated. Different copper deposit structures, viz. bulbous, massive crystalline, thick dendrites with leaf-like secondary arms, and dendrites of different degrees of fineness and texture were observed in the present study utilizing the scanning electron microscope. Deposit morphology was greatly modified for variations of chloride ion up to 25 mg l-1 and for increases in temperature up to 40° C. The maximum rate of copper cementation on pure aluminum was usually associated with a fine, dendritic structure. © 1978.
• Berry, V. K., Murr, L. E., & Hiskey, J. B. (1978). Galvanic interaction between chalcopyrite and pyrite during bacterial leaching of low-grade waste. Hydrometallurgy, 3(4), 309-326.
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  Abstract: The bacterial leaching of a low-grade chalcopyrite waste rock in a lixiviant containing thermophilic, Sulfolobus-like microorganisms at 60°C and a lixiviant containing Thiobacillus ferrooxidans at 28°C has been compared with the leaching in sterile lixiviant in terms of copper solubilized in elapsed time and the conversion of Fe3+ Fe2+. Bacterial action has been shown to drastically increase the ratio Fe3+ Fe2+ with elapsed time of leaching. Direct observations of the associated pyrite and chalcopyrite surface corrosion, utilizing scanning electron microscopy, showed that during the leaching of these sulfides as separate, non-contacting phases, the pyrite corroded more rapidly than the chalcopyrite in both sterile and inoculated media. This effect was more pronounced at elevated temperature and in the presence of bacteria. When the pyrite and chalcopyrite were in contact, the resulting galvanic interaction caused the chalcopyrite to corrode more rapidly than the pyrite, which was effectively passivated. The leaching of chalcopyrite is thereby enhanced in contact with pyrite. This effect is accelerated in the presence of bacteria. The corrosion of chalcopyrite was also markedly enhanced as a result of the oxidation of elemental sulfur (formed during the reaction) to sulfuric acid. This reaction was also accelerated by bacterial catalysis. The important implications of the enhanced chalcopyrite corrosion by galvanic interaction in the leaching of low-grade chalcopyrite waste and other galvanic-contact regimes involving metal sulfides are identified and discussed. © 1978.
• Murr, L. E., Cathles, L. M., Reese, D. A., Hiskey, J. B., Popp, C. J., Brierley, J. A., Bloss, D., Berry, V. K., Schlitt, W. J., & Hsu, P. C. (1977). CHEMICAL, BIOLOGICAL, AND METALLURGICAL ASPECTS OF LARGE-SCALE COLUMN LEACHING EXPERIMENTS FOR SOLUTION MINING AND IN-SITU LEACHING.. In Situ, 1(3), 209-233.
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  Abstract: It is well known that the variations in temperature, chemical reactivity, and reaction rates which are presumed to occur and which in some cases have been shown to occur in a leach dump or similar solution mining activity are difficult to duplicate or model on a small laboratory scale, and the degree to which such large-size metallurgical processes can be scaled is not well established. In the present investigations the design criteria and sampling methods for large-scale leach tests on low-grade copper waste are outlined and the results of studies of temperature profiles and associated chemical and biological activity in 185 ton waste samples (approx. 10. 75 m in height) are discussed. Various simple scaling features are presented, including drain-down characteristics and waste-body neutralization.
• Hiskey, J. B., & Ramadorai, G. (1976). KINETIC STUDY OF SULFIDE ION LEACHING OF WULFENITE.. Trans Soc Min Eng AIME, 260(3), 220-224.
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  Abstract: Wulfenite dissolves in the presence of sulfide ion according to the following reaction: PbMoO//4 plus S** equals reversible reaction PbS plus MoO** equals //4. Synthetic galena is formed and molybdenum is released to solution as molybdate ion. The reaction follows the shrinking core model and the leaching mechanism involves mixed kinetics where both diffusion and chemical reaction are rate controlling. Molybdenum extraction is explained in terms of temperature, particle size, and sodium sulfide concentration.
• Hiskey, J., & Wadsworth, M. E. (1975). Galvanic conversion of chalcopyrite. Metallurgical and Materials Transactions B, 6(1), 183-190.
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  Abstract: Galvanic interaction between particulate chalcopyrite (CuFeS2) and copper results in the rapid conversion of chalcopyrite to chalcocite. The effects of temperature, surface area, concentration of sulfuric acid and agitation were systematically evaluated. The kinetics were found to be controlled by a steady-state current flow controlled by the effective anodic and cathodic surface areas involved in the galvanic couple. The experimental activation energy was 11.5 and stoichiometric data and reaction products have been characterized. The overall kinetic system has been evaluated based upon an electrochemical model. © 1975 The Minerals, Metals & Materials Society - ASM International - The Materials Information Society.
• Hiskey, J., & Wadsworth, M. E. (1974). GALVANIC CONVERSION OF CHALCOPYRITE.. Array, 422-445.
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  Abstract: Galvanic interaction between particulate chalcopyrite (CuFeS//2) and copper results in the rapid conversion of chalcopyrite to chalcocite. The effects of temperature, surface area, concentration of sulfuric acid and agitation were systematically evaluated. The kinetics were found to be controlled by a steady-state current flow controlled by the effective anodic and cathodic surface areas involved in the galvanic couple. The experimental activation energy was 11. 5 and stoichiometric data and reaction products have been characterized. The overall kinetic system has been evaluated based upon an electrochemical model.
• Miller, J., & Hiskey, J. (1972). Electrokinetic behavior of fluorite as influenced by surface carbonation. Journal of Colloid And Interface Science, 41(3), 567-573.
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  Abstract: The electrokinetic response of fluorite, as a function of pH, is shown to be due to a surface carbonation reaction of the type:. CaF2(surf)+CO3→CaCO3(surf)+2F. The carbonation reaction can be predicted from thermodynamics of solution chemistry and has been verified by infrared measurements in the laboratory. In systems open to the atmosphere, 300 ppm CO2, the carbonation reaction begins above pH 8 at which point the electrokinetic response of fluorite becomes strongly dependent on pH. In addition, settling rate experiments revealed that the electrokinetic response of fluorite was sensitive to, and could be predicted by, the partial pressure of carbon dioxide. © 1972.

Proceedings Publications

• Hiskey, J. B., & Novak, M. (2014, 2014-06-22 to 2014-06-25). Kinetics of the Galvanic Reduction of Chalcopyrite Concentrates by Copper. In Hydrometallurgy 2014, Hydrometallurgy 2014 Proceeding of the 7th International Symposium, 363-374.
• Hiskey, J. B., & Snowberger, J. (2014, 2014-02-16 to 2014-02-20). Electrochemical Dissolution of Rhenium Bearing Supper Alloy. In 2-14 TMS Annual Meeting Rare Metal Extraction & Processing Symposium.

Presentations

• Hiskey, J. B. (2014, 2014-06-22 to 2014-06-25). Hydrometallurgy - Background and Historical Perspective. Hydrometallurgy 2014 - Short Course : Recent Key Developments and Current Industrial Trends. Victoria, British Columbia, Canada: Canadian Institute of Mining, Metallurgy and Petroleum.
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  Invited keynote address for the 3 day short course on recent key developments and current industrial trends in hydrometallurgy.
• Hiskey, J. B. (2014, Feb 26). Innovative Strategies for Copper Hydrometallurgy. 2014 SME Annual Meeting. Salt Lake City, Utah: Society for Mining, Metallurgy and Exploration SME.
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  Invited Mineral and Metallurgical Processing Division luncheon speaker.
• Hiskey, J. B. (2012, March). Mechanism and Thermodynamics of Floating Slimes Formation. T.T. Chen Honorar4y Symposium on Hydrometallurgy, TMS Annual Meeting. Orlando, FL.
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  Invited Lecture for Electrometallurgy and Materials Characterization Session.
• Hiskey, J. B. (2012, November). The Recovery of Energy-Critical Metals from Copper Leach Solution. 2012 MRS Fall Meeting and Exhibit. Boston, MA.
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  Keynote Address at the MRS Energy Critical Materials Symposium