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The abiotic leaching behavior of a chalcopyrite ore, from Asarco’s Ray-Mine, was conducted in shake flasks and miniature columns at elevated temperatures. The shake flask tests, with an ore particle size of 1.18mm-2.38mm, found the highest Cu extraction was obtained using 1M NaCl in a 9.8g/L sulphuric acid solution at 60°C, with 69% Cu extracted in 16 days. The next highest extraction, 59% Cu extracted in 16 days, was achieved by adding fine pyrite at a 4:1wt ratio with the chalcopyrite content, in a 9.8g/L sulphuric acid solution at 60°C. Flask tests using other lixiviants and additions found copper extractions in the range of 30-40% Cu after 16 days. In the mini-column tests, the rates of copper extraction were similar for all test conditions. The rate of Cu extraction, even with a small particle size of 1.18mm-2.38mm and an elevated temperature of 50°C, was slow for all test conditions with an average rate of ~0.15% Cu per day. The conceptual engineering of a hot, abiotic heap-leach for low-grade chalcopyrite ore, including hypothetical heat and mass balances was conducted. The leaching time for a commercial operation was estimated from published data on laboratory column leaching of chalcopyrite ores and extrapolated to a commercial heap-leach by analogy with known leaching times for chalcocite ores. In commercial abiotic heap-leaches of chalcopyrite ore, the partial oxidation reactions generate insignificant heat to maintain an elevated heap temperature therefore the heat required to maintain the elevated temperature must be provided externally. In commercial biotic chalcopyrite heap-leaches, the in-situ total oxidation reaction generates more heat than the abiotic reactions but is still insufficient to rapidly raise and maintain an elevated heap temperature. For a low-grade Chalcopyrite heap-leach the most practical method of providing this heat is by injecting steam into the base of the heap using current air injection pipes. An external oxidant is required and for an abiotic heap-leach external ferric generation will be required. / Thesis (Master, Mining Engineering) -- Queen's University, 2011-02-15 15:59:38.15

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Heap leaching is a hydrometallurgical process used for the extraction of minerals within complex and typically low-grade ores. An important factor in the mineral dissolution process is the contact efficiency between the irrigation fluid (lixiviant) and the targeted mineral, which is influenced by both the solid and fluid properties of the system. One of the principal challenges related to the contact efficiency is preferential flow, cited to result in low extraction rates and in extreme cases, heap failure. Preferential flow reveals itself on two scales in drip irrigated heaps, referred to as the bed and solution scale. The bed scale takes a macro view of the heap and deals with uneven wetting profiles characterized by the presence of wet and dry sections. Linked to this is capillary suction effects which play an important role in the establishment of fluid flow profiles within the heap. The solution scale focuses on preferential flow behaviour in the wetted sections of the heap characterized by variations in the residence times of fluid elements. Such variations produce fast flowing, slow flowing and stagnant solution pools. Therefore, ideal solution flow behaviour in a heap result in uniform wetting at the bed scale and plug flow behaviour with similar fluid residence times at the solution scale. Though bed scale preferential flow can be visually observed, diagnosing symptoms at the solution scale typically requires the generation, analysis, and modelling of residence time distribution (RTD) curves. The main objectives of this study were to firstly explore the effects that important material and fluid properties have on the steady state fluid flow profiles in drip irrigated beds characteristic of those used in laboratory scale column leaching studies and quantified using step tracer tests. This is based on the underlying principle that the movement of inert tracer molecules within an irrigated bed at steady state is identical to the solution flow path within the bed. The second objective was to test the ability of nine empirical and semi-empirical solute transport models to adequately fit the generated flow profiles or RTD curves. The third was to compare the magnitudes of the quantified model parameters to ascertain the level of solution scale preferential flow in the different beds and determine the adequate level of model complexity needed to describe their flow profiles which facilitates identifying the controlling variables within the system. Properties of the loading material that were identified as potentially most impactful with respect to heap operations were: porosity, wettability, particle shape and size distribution. Therefore, four different materials with unique inherent characteristics were selected for this study: glass beads (GB - spherical and non-porous), glass shards (GS - irregularly shaped and non-porous), greywacke (GW - irregularly shaped, porous, and highly wettable) and malachite ore (MO - irregularly shaped, highly porous, low wettability and non-uniform composition). In terms of fluid properties, current models have already established a correlation between the concentration of dissolved chemical species within a fluid and its viscosity. This was relevant due to the variety of lixiviant compositions used in previous heap hydrology studies and the fact that the composition also varies with time within a reactive heap. To study the effects of this parameter on the establishment of flow profiles, glycerol was used as a viscosity modifier to formulate solutions with viscosities ranging from 0.8 to 2.2 cP, representative of the range experienced in heap leaching systems due to varying SO4 2- concentrations. The packed beds were characterized using their bulk densities, void age, total liquid holdups, total bed saturations, 24-hour drain-down moisture percentages, solution and tracer breakthrough times. Beds containing both narrow and mixed particle size fractions were tested. The nine solute transport models used for RTD modelling included three compartmental model configurations (CM-1, CM-2, CM-3) and the tanks-in-series (TIS) model, all empirical in nature. The five semi-empirical models selected were the advection-dispersion (AD), piston exchange (PE), piston exchange-diffusion variant (PE-D) and piston dispersion and exchange (PDE) models. A novel model formulation called the piston dispersion and exchange-diffusion variant (PDE-D) model was also coded and tested, which incorporated both the longitudinal dispersion coefficient as well as a diffusional flux mass transfer mechanism. The CM-2, AD and TIS were mono porosity models assuming all solution volumes within the beds were actively flowing which limited their ability to account for solution scale preferential flow. The CM-1, CM-3, PE, PE-D, PDE, PDE-D models were dual porous, accounting for the presence of either dead or stagnant solution volumes. The model parameters used to account for preferential flow in the RTD profiles included: the fraction of dead to total solution volume, dynamic to total saturation fraction, number of TIS, ratio of parallel continuously stirred tank volumes, longitudinal dispersion coefficient, overall mass transfer coefficient and maximum diffusional pore length. The cumulative RTD responses for the bed systems composed of narrow size fractions were noticeably impacted by particle size. These systems displayed symptoms of increased solution channelling behaviour at steady state, based on their relatively short tracer breakthrough times, as the average particle size was increased from ∼1 to 15 mm. The incorporation of semi-empirical models which could account for stagnant volumes. The main comparative modelling results across all systems studied showed that the PDE and PDE-D models were the top performers, based on a model fit analysis. This was due to their dual porous nature and relatively higher levels of complexity. The mono porosity models (CM-2, TIS and AD) performed the worst due to their inability to account for isolated and immobile liquid volumes. However, when 10 mm during agglomeration will aid in increasing the fraction of mobile (actively flowing) liquid within the heap due to the increased presence of macro voids. High levels of particle porosities (>2.5 m2/g) will also aid in this aspect. This is proposed to be due to greater void network connectivity with an increase in porosity facilitating better mass transfer. These insights were obtained through the analysis of experimentally generated data and model simulations. They have provided a better understanding of the movement of fluid molecules within drip irrigated beds, which is essential for improved leaching performance. Building on this, the next step is to consider the effects of scale up and reactive systems on both empirical and simulated data.

Thesis (M.S.)--University of Nevada, Reno, 2007. / "December, 2007." Includes bibliographical references (leaves 166-176). Online version available on the World Wide Web.

The recovery of mineral from ore in the heap leaching process requires the mineral to come into contact with the leaching solution. However, heap hydrology is prone to non-uniform behaviour due to the inhomogeneity of the ore particles and the heap structure. The primary aim of this thesis was therefore to develop a magnetic resonance imaging (MRI) technique which would allow for the novel non-invasive imaging of the liquid hold-up in representative laboratory-scale heap leaching systems. The ferro- and paramagnetic species in the ore were found to cause significant distortions in frequency encoded MRI acquisitions. These distortions were mitigated through the application of single point imaging techniques. Comparison with equivalent X-ray CT acquisitions, which are immune to magnetic susceptibility distortions, confirmed the accuracy of the single point acquisitions. Spin echo single point imaging (SESPI) was demonstrated to be more robust than the simple single point imaging (SPI) technique because the effect of $\textit{T}$$_{2}$ weighting on the MRI signal was less significant than that of $\textit{T}$$_{2}$*. Mapping of the gas, liquid and solid distributions in unsaturated leaching columns using SESPI allowed for the quantification of the hold-up and voidage values. These compared favourably to gravimetric measurements and literature values, thereby confirming their validity. Novel measurement of the liquid film thickness and the interfacial areas between the three phases was achieved and insight into the liquid behaviour was obtained through different flow rate experiments as well as MRI tracer experiments. Drip irrigation of the ore was considered for beds of large, fine and agglomerated ore. Liquid distribution in the fine ore closely resembled that of irrigation of clay soils whereas flow through the large ore was gravity dominated. Slumping of the agglomerated ore caused permanent limitation of the liquid distribution and the effect of flow rate changes was observed to be limited to the region below the irrigation point. In both the column and drip irrigation experiments, increases in the liquid flow rate caused small increases in the liquid hold-up in the form of new, relatively thicker rivulets, thereby improving the liquid-solid interfacial area. However it did not affect capillary held liquid volume so the effect of flow rate changes decreased as the lateral distance from the irrigation point increased. Finally, X-ray CT images of a long term ferric leach were analysed to assess the factors affecting the mineral leaching. Proximity of the mineral to the ore surface was found to be the critical factor, as only mineral located within 2 mm of the surface was recovered, though liquid distribution effects were also observed.

La lixiviation en tas est une méthode industrielle utilisée pour traiter des minerais à basse teneur consistant en la percolation d’une solution de lixiviation à travers un tas de 6 à 9 mètres de haut afin d’en extraire l’élément d’intérêt. Cependant, la présence de nombreuses fines particules et d’argiles au sein du minerai peuvent causer l’apparition de phénomènes de colmatage dans les tas, diminuant l’efficacité de la lixiviation. Afin de résoudre ce problème, les industries du nickel, du cuivre ou encore de l’uranium agglomèrent le minerai, augmentant ainsi sa granulométrie par le rassemblement des fines particules. Néanmoins, l’agglomération de minerais uranifères ainsi que l’impact de la structure des agglomérats sur la lixiviation reste peu étudiée. Cette thèse a permis de caractériser l’évolution structurale et pétro physique des agglomérats de minerais d’uranium au cours de la lixiviation, d’étudier l’influence des conditions d’agglomération sur la structure des agglomérats résultants et enfin d’étudier la lixiviation des agglomérats à l’échelle du tas, par le biais d’essais en colonnes métriques. De plus, les causes de colmatage ont pu être identifiées comme provenant d’une dégradation mécanique des agglomérats entrainant une réduction de la perméabilité et de la porosité du tas / Heap leaching allows processing low grade ores. Basically, this industrial mining process consists in percolating a leaching solution slowly down through an ore heap of 6 to 9 meters high to extract the metals of interest. However, fine particles and clays are often the cause of clogging within heaps, leading to a decrease of leaching efficiency. To solve this problem, copper, nickel and uranium industry uses agglomeration of the ore particles. This process allows adjusting the particle size distribution by gathering fine particles. However uranium-ore agglomeration and the impact of the agglomerates structure on heap leaching remains poorly understood. The current thesis allowed characterizing structural and petrophysical properties of agglomerates and its evolution during leaching, studying the influence of agglomeration conditions on agglomerates structures and finally upscaling there results at the heap scale, using meter scale columns. Clogging phenomena were especially due to the mechanical degradation of agglomerates, causing a decrease of both heap porosity and permeability