/pdf/four-dimensional-x-ray-micro-tomography-imaging-of-dynamic-sl2ztt1r.pdf

Four-dimensional X-ray micro-tomography imaging of dynamic processes in geosciences

Non-invasive multi-scale and multimodal 3D characterization of heterogeneous or hierarchically structured intact mesoscale samples is of paramount importance in tackling challenging scientific problems. Scanning hard X-ray tomography techniques providing simultaneous complementary 3D information are ideally suited to such studies. However, the implementation of a robust on-site workflow remains the bottleneck for the widespread application of these powerful multimodal tomography methods. In this paper, we describe the development and implementation of such a robust, holistic workflow, including semi-automatic data reconstruction. Due to its flexibility, our approach is especially well suited for on-the-fly tuning of the experiments to study features of interest progressively at different length scales. To demonstrate the performance of the method, we studied, across multiple length scales, the elemental abundances and morphology of two complex biological systems, Arabidopsis plant seeds and mouse renal papilla samples. The proposed approach opens the way towards routine multimodal 3D characterization of intact samples by providing relevant information from pertinent sample regions in a wide range of scientific fields such as biology, geology, and material sciences. 

/pdf/towards-routine-3d-characterization-of-intact-mesoscale-wcztus5k.pdf

Towards routine 3D characterization of intact mesoscale samples by multi-scale and multimodal scanning X-ray tomography

In this paper, the leaching of a sulfide concentrate, from “Sarcheshmeh Copper Complex”, by sulfuric acid is studied. The influences of sulfuric acid concentration and leaching temperature were scrutinized to optimize the processing parameters and to disclose the kinetics of the extraction process. The leaching rate of copper was not significantly improved with enhancing the temperature and concentration of sulfuric acid. The formation of elemental sulfur was found as a reducer of the leaching rate. Only ~70% of copper was extracted by adding 1M ferric sulfate as the oxidant agent, as well as increasing the leaching temperature up to 85 °C. By leaching the mechanically activated concentrate in Fe2(SO4)3-doped H2SO4 at 85 °C, the amount of extracted copper was ~90% after 180 min. The experimental results were excellently fitted with the diffusion-controlled kinetic model as the activation energy of ~27 kJ/mol was estimated.

/pdf/synergistic-effects-of-ferric-sulfate-addition-and-4nniera3dy.pdf

Synergistic effects of ferric sulfate addition and mechanical activation on leaching of Sarcheshmeh copper sulfide concentrate

Agglomeration and the associated curing process are critical as they both improve heap permeability and provide initial intimate contact between the leaching solution and the minerals. The evaporation of water from the agglomerate surface will drive liquid motion within agglomerates, redistributing dissolved species and increasing their concentration with the resultant potential for precipitation of previously dissolved species. Models have been proposed for the particle scale leach behaviour during the active irrigation phase of heap leaching, however no models currently exist for the leach behaviour during the curing process. The aim of this paper is therefore to propose and validate such a model by including important processes such as evaporation, unsaturated liquid transport, advective and diffusive transport of dissolved species, dissolution of mineral grains, and precipitation of species once saturation is reached. A set of small-scale column leaching tests were carried out, with the system being repeated scanned using X-ray Microtomography (micro-CT) over the course of the 65 day long curing experiments. Image analysis allowed the spatial distribution of both the initial mineral grains, as well as the precipitates to be tracked as a function of time. These were then used to demonstrate that the model captured the key features of the behaviour during the leaching process, as well as providing plausible ranges for the model parameters that could not be directly measured as input parameters. Both the model and the experiments showed that reprecipitation occurs preferentially towards the surface of the agglomerates. The model was also used to carry out a sensitivity analysis, with a key finding being that leach performance during curing improves with larger agglomerates and decreased evaporation rates. This is because of decreased loss of water. The particle size effect is the opposite of what would be expected during the subsequent leaching where mass transport into and out of the agglomerate is crucial, thus indicating the potential to optimise agglomerate size. 

Modelling the curing of agglomerated ores with comparison to micro-CT

Understanding the variability of leaching kinetics is extremely challenging due to the nature of leaching processes. Common experimental setups, such as column leaching experiments, only allow for quantification of apparent leach kinetics at the macroscale (e.g. at the particle or column level), failing to capture grain-scale variability. In this paper, we study variability in leaching kinetics at the micro- and macroscale using a combination of 4D imaging and standard chemical measurements. The impact of chloride ions on leaching performance was evaluated using column leaching experiments. Micro-computed tomography (micro-CT) was combined with SEM/EDX to isolate chalcopyrite from pyrite dissolution. Using in-house algorithms, the leaching behaviour of hundreds of thousands of grains was quantified and tracked over time. Morphological changes at the agglomerate level were assessed, coupling porosity network development and microcrack formation to leaching variability. It was concluded that a decrease in internal macro porosity does not significantly impact macro-scale leaching performance. Grain size had an impact, although grain location does not influence mass transport resistance. Another key finding was that leaching in chloride media is more selective for copper sulphides, evidencing virtually no pyrite dissolution. This study not only provides new understanding of the factors influencing the leach behaviour of chalcopyrite ore, but also generates data that represents the process more accurately and allows for better planning. 

The impact of chloride ions on chalcopyrite leaching: A multiscale and multimodal assessment

Microstructure evolution of chalcopyrite agglomerates during leaching – A synchrotron-based X-ray CT approach combined with a data-constrained modelling (DCM)

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Microstructure evolution of chalcopyrite agglomerates during leaching – A synchrotron-based X-ray CT approach combined with a data-constrained modelling (DCM)