This thesis describes an ion irradiation study of ordered Cu<sub>3M/sub>Au. Argon, Copper and Krypton ions of 50 and 100keV were implanted to nominal doses of 10¹¹ ions cm^-2 both at room temperature and at liquid helium temperature. The damage induced at low temperature was observed in-situ and after subsequent warming to room temperature. The collapse of collision cascades to vacancy dislocation loops was observed to occur with moderately high probability under all irradiation conditions at low temperature, with no subsequent increase in the number of loops on warming. Comparison of the collapsed fraction of cascades at low temperature with that produced by room temperature irradiation revealed that the collapse process is more efficient in the latter case. An increase in collapse probability with ion mass was also observed, although no dependence on ion energy was found over the range investigated. Quantitative analysis of the disordered zones which result in ordered Cu₃Au at individual cascade sites revealed that cascades which had collapsed to loops generally produced larger disordered zones. Additionally, increases in disordered zone size with ion mass, ion energy and irradiation temperature were identified. The observation that disordered zone sizes exceed the theoretically predicted cascade dimensions for the case of the highest energy density in this study (50keV Kr) is interpreted as evidence for leakage of energy from the cascade region to the surrounding lattice. A model is proposed which attributes the observed cascade collapse behaviour to vacancy migration during the cooling of the cascade region being systematically directed toward its centre, and accounts for the observed disordered zones in terms of extensive atomic rearrangement during the cooling. The major factors identified as controlling this vacancy and atomic motion are the initial spatial distribution of energy and vacancies within the region, and the rate at which the region cools.

No description available.

Compliant nanoporous gold is investigated with regards to its elastic modulus and deformation mechanisms. Samples are fabricated by dealloying AgAu alloys at elevated temperature and reduced dealloying potential compared with conventional methods in the literature. This procedure minimizes cracking and shrinkage that is typical from other dealloying methods. Furthermore, samples are found to be more compliant while immersed in water. Samples were tested in cyclic compression using a piezoelectric compression rig. Testing showed that the wet samples become stiffer upon drying and the effect is reversible with short drying times. This is attributed to microstructural effects as the ligament network becomes more connected as a result of drying, effectively shifting the dominant deformation mode from three-point bending to cantilever bending. At longer dry times, the effect is irreversible due to contact weld formation. Preliminary results on sputter deposited AgAuPt alloys show altered dealloying kinetics and crack formation.

Compliant nanoporous gold is investigated with regards to its elastic modulus and deformation mechanisms. Samples are fabricated by dealloying AgAu alloys at elevated temperature and reduced dealloying potential compared with conventional methods in the literature. This procedure minimizes cracking and shrinkage that is typical from other dealloying methods. Furthermore, samples are found to be more compliant while immersed in water. Samples were tested in cyclic compression using a piezoelectric compression rig. Testing showed that the wet samples become stiffer upon drying and the effect is reversible with short drying times. This is attributed to microstructural effects as the ligament network becomes more connected as a result of drying, effectively shifting the dominant deformation mode from three-point bending to cantilever bending. At longer dry times, the effect is irreversible due to contact weld formation. Preliminary results on sputter deposited AgAuPt alloys show altered dealloying kinetics and crack formation.

This thesis presents the development and application of a dynamic model of gold adsorption onto activated carbon in gold processing. The primary aim of the model is to investigate different carbon management strategies of the Carbon in Pulp (CIP) process. This model is based on simple film-diffusion mass transfer and the Freundlich isotherm to describe the equilibrium between the gold in solution and gold adsorbed onto carbon. A major limitation in the development of a dynamic model is the availability of accurate plant data that tracks the dynamic behaviour of the plant. This limitation is overcome by using a pilot scale CIP gold processing plant to obtain such data. All operating parameters of this pilot plant can be manipulated and controlled to a greater degree than that of a full scale plant. This enables a greater amount of operating data to be obtained and utilised. Two independent experiments were performed to build the model. A series of equilibrium tests were performed to obtain parameter values for the Freundlich isotherm, and results from an experimental run of the CIP pilot plant were used to obtain other model parameter values. The model was then verified via another independent experiment. The results show that for a given set of operating conditions, the simulated predictions were in good agreement with the CIP pilot plant experimental data. The model was then used to optimise the operations of the pilot plant. The evaluation of the plant optimisation simulations was based on an objective function developed to quantitatively compare different simulated conditions. This objective function was derived from the revenue and costs of the CIP plant. The objective function costings developed for this work were compared with published data and were found to be within the published range. This objective function can be used to evaluate the performance of any CIP plant from a small scale laboratory plant to a full scale gold plant. The model, along with its objective function, was used to investigate different carbon management strategies and to determine the most cost effective approach. A total of 17 different carbon management strategies were investigated. An additional two experimental runs were performed on the CIP pilot plant to verify the simulation model and objective function developed. Finally an application of the simulation model is discussed. The model was used to generate plant data to develop an operational classification model of the CIP process using machine learning algorithms. This application can then be used as part of an online diagnosis tool.

A fundamental thermodynamic study was undertaken in order to establish the speciation of copper(I) and copper(II) during the leaching and recovery of gold from thiosulfate-copper-ammonia solutions. Despite considerable research into this complex leaching system, the lack of important fundamental chemistry has delayed the implementation of the thiosulfate process as an alternative to cyanidation. Over the last two decades, research in this field has focused on the kinetics and electrochemistry of leaching, which involves the use of copper(II) as an oxidant. However, the fundamental thermodynamic data for copper(I) and copper(II) in this system is limited. Ion association was found to significantly affect the dissociation constant of the ammonium ion in solutions containing sodium sulfate and/or sodium thiosulfate, thus influencing the free ammonia concentration in solution. These findings highlight the importance of using the correct dissociation constant value in thermodynamic studies that involve ammonia in order to obtain precise stability constants. It has been established that the mixed-ligand complexes Cu(NH3)(S2O3)23- and Cu(NH3)(S2O3)- exist in solution and they are more stable than the other species Cu(S2O3)35-, Cu(NH3)2+ and Cu(NH3)3+ at high concentrations of ammonia and/or thiosulfate. The relative proportions of each two species is dependant on the [NH3]:[S2O32-] ratio in solution. This is reflected in two- and three- dimensional speciation diagrams that have been constructed for typical leaching and recovery processes using the stability constants obtained in this study. The 3-dimensional diagrams reveal subtle speciation trends that are not easily discernable from the 2-dimensional diagrams. An investigation into the effect of high sulfate and chloride concentrations showed that these anions are not involved in the complexation with copper(I)-ammonia or copper(I)-ammonia-thiosulfate species under the experimental conditions studied. However, these anions and perchlorate formed relatively stable species with the copper(II)-ammine complexes in the absence of thiosulfate. Stability constants were obtained for the species Cu(NH3)4SO40, Cu(NH3)4Cl+ and Cu(NH3)4ClO4+ and it is suggested that these anionic ligands form outer-sphere complexes with the Cu(NH3)42+ ion. Various methods of predicting stability constants for mixed-ligand complexes from those for the corresponding single ligand systems have been evaluated for this copper(I) system. Although the results have not been quantitatively accurate, the trends suggest that an appropriate method may serve as a useful qualitative tool to predict the possible existence of mixed-ligand complexes. The combined application of 2- and 3-dimensional speciation and potential diagrams could be used as a hydrometallurgical tool in the design, optimization and control of possible future processes for the extraction of gold using thiosulfate in the presence of copper ions and ammonia. The work presented in this thesis adds to our understanding of the chemistry of copper(I) and copper(II) in this leaching system.

The form and location of gold in the structure of arsenopyrite and pyrite minerals, and the mechanisms for the mobility agglomeration of gold in arsenopyrite during thermal treatment, have been studied using a combination of Rietveld X-ray diffraction refinement, Convergent Beam Electron Diffraction (CBED) and Atomic Location by Channelling Enhanced Microanalysis. The basic structure of all the arsenopyrite compositions studies, has been shown to be monoclinic P2(subscript)1/c, regardless of the variation in stoichiometry. An increase in the arsenic to sulfur ratio in the natural arsenopyrites was found to be associated with an increase in unit cell dimensions accompanied by expansions within the iron-centred octahedra along the [101] direction of the monoclinic cell and concommitant contractions of the octahedra in the (101) plane. There was no obvious relationship between variation in stoichiometry and structure of arsenopyrite which could provide information as to possible substitution of gold in its structure. However, atomic displacements caused by twinning or disorder, may help to incorporate gold.The synthesis of auriferous arsenopyrites showed that gold has to be in an ionic form to be taken up in the structure. The form of the gold species affects the distribution of gold in the structure, being chemically zoned when derived from a dichloro complex and more evenly distributed when derived from a hydrosulfido complex. It is suggested that rapid crystallisation, with resultant displacement faults along the b-axis, may contribute to higher concentrations of gold in the natural arsenopyrite structure. Electron probe microanalysis showed a possible slight iron-deficiency in some of the auriferous arsenopyrite grains analysed. However, the errors in the analyses were too high to provide conclusive evidence of gold substitution in the iron sites, as has been ++ / proposed in the literature.Analyses of natural and synthetic pyrites showed no deviations in structural parameters which could indicate possible substitution of gold or other impurities within the structure.Electron channelling experiments showed that gold was located on the sulfur sites in pyrite. In arsenopyrite, there was some evidence for gold located on the iron sites, however, most gold was interstitial, probably situated between the octahedra. This location is probably facilitated by the presence of the displacement faults as observed by CBED in the synthetic auriferous arsenopyrite.Breakdown of arsenopyrite under thermal treatment was topotactic along its b-axis, which converts to the a-axis in the pyrrhotite structure, following a reconstruction mechanism based on the preferential removal of arsenic over sulfur. Gold was visually recorded exsolving from the arsenopyrite structure and agglomerating as liquid metal globules as the arsenopyrite was chemically altered during thermal treatment under the Transmission Electron Microscopy electron beam. Gold became mobile on the decomposition of arsenopyrite, but this was not observed until a temperature of approximately 470 degrees celsius was reached. Above the temperature both solid solution and particulate gold became mobile. The interaction of arsenic vapour and gold reduced the melting point of gold.The observations on the effects of arsenic residence time, and the relative mobility of solid solution and particulate gold during the thermal decomposition of auriferous arsenopyrite and pyrite, have significant implications for improved industrial extraction of gold from these minerals.

University, Diss., 2004--Kassel. / Download lizenzpflichtig.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1910. / The entire thesis text is included in file. Typescript. Illustrated by author. B. H. Dosenbach determined to be Benjamin Harrison Dosenbach from "Forty-First Annual Catalogue. School of Mines and Metallurgy, University of Missouri". Degree of Bachelor of Science in Mining Engineering determined from "1874-1999 MSM-UMR Alumni Directory". Title from title screen of thesis/dissertation PDF file (viewed March 17, 2009)