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In many granular material simulation applications, DEM capability is focused on the dynamic solid particulate flow properties and on systems in which millions of particles are involved. The time of relevance is many seconds or even minutes of real time. Simplifying assumptions are made to achieve run completion in practical timescales. There are certain applications, typically involving manufactured particles, where a representative pack is of the order of a thousand particles. More accurate capturing of the influence of complex shape is then often possible. Higher accuracies are necessary to model the topology of the void space, for example, for further CFD simulation and optimisation of fluid flow properties. Alternatively, the accuracy may be critical for structural performance and the force or stress transmission through the contact points is to be controlled to avoid material damage and poor function. This paper briefly summarises methods for simulation of shape effects on packing structures in the granular community and narrows the scope to problems where shape effects are of overriding concern. Two applications of mono-sized, mono-shaped packing problems are highlighted: catalyst support pellets in gas reforming and concrete armour units in breakwater structures. The clear advantages of FDEM for complex-shaped particle interactions in packed systems with relatively few particles are discussed. A class of particulate problems, ‘FDEM-suited’ problems, ones that are ideal to be solved by FDEM rather than by DEM, is proposed for science and engineering use.

Scanning Electron Microscopy (SEM) based assessments are the most widely used and trusted imaging technique for mineral ore quantification. X-ray micro tomography (XMT) is a more recent to the mineralogy toolbox, but with the potential to extend the measurement capabilities into the three dimensional (3D) assessment of properties such as mineral liberation, grain size and textural characteristics. In addition, unlike SEM based assessments which require the samples to be sectioned, XMT is non-invasive and non-destructive manner. The disadvantage of XMT, though is that the mineralogy must be inferred from the X-Ray attenuation measurements, which can make it hard to distinguish from one another, whereas SEM when coupled with Energy-Dispersive X-raySpectroscopy (EDX) provides elemental compositions and thus a more direct method for distinguishing different minerals. A new methodology that combines both methods at the mineral grain level is presented. The rock particles used to test the method were initially imaged in 3D using XMT followed by sectioning and the 2D imaging of the slices using SEM-EDX. An algorithm was developed that allowed the mineral grains in the 2D slice to be matched with their 3D equivalents in the XMT based images. As the mineralogy of the grains from the SEM images can be matched to a range of X-Ray attenuations, this allows minerals which have similar attenuations to one another to be distinguished, with the level of uncertainty in the classification quantified. In addition,the methodology allowed for the estimation of the level of uncertainty in thequantification of grain size by XMT, the assessment of stereological effects in SEM 2D images and ultimately to obtain a simplified 3D mineral map from low energy XMT images. Copper sulphide ore fragments, with chalcopyrite and pyrite as the main sulphide minerals, were used to demonstrate the effectiveness of this procedure.

We studied leaching of Cu and Fe from naturally occurring chalcopyrite ore using aqueous solutions of ionic liquids (ILs) based on imidazolium and ethylammonium cations and hydrogensulfate, nitrate, acetate or dicyanamide anions. Liquid, solid and gas phases of the leaching systems were characterised. We have shown that nonoxidative leaching is greatly dependant not only on temperature and pH, but on the anion species of the IL. Solutions of 1-butylimidazolium hydrogen sulfate exhibited the best leaching performance among hydrogen sulphate ILs. We have suggested that the formation of an oxide layer in some ILs may be responsible for a reduced leaching ability. The analysis of the gas phase showed the production of CO2 and CS2 in all leached samples. Our results suggested that the CS2 produced upon leaching could be responsible for decreasing the sulfur, but not oxide, layer on the surface of chalcopyrite samples and therefore more efficient leaching. This is the first study, to our knowledge, to provide a systematic comparison of the leaching performance of ILs composed of different anions and cations and without added oxidants.

Heap leaching is one of the most important hydrometallurgical techniques for the extraction of valuable metals from low grade ores due to the relatively low capital costs and limited comminution requirements. However, it is typically affected by low recoveries, compared to conventional mineral extraction techniques such as froth flotation followed by smelting. These low recoveries indicate that there is still significant scope for the improvement of the process performance. This overall process performance is governed by chemical kinetics, mass transport and hydrodynamic effects, with hydrodynamics being particularly not completely understood at the heap scale. The authors have previously presented a model for the hydrodynamics which accounts for both liquid holdup hysteresis and the influence of particle porosity on the fluid flow. In this previous work the model form was only validated for narrowly sized particles. This shortcoming is addressed in this paper, with the validation of the models being extended to cover a range of more complex size distributions representative of those encountered in industrial heap leaching. In this work load cell based gravimetric measurements of liquid holdup values were complimented with electrical capacitance tomography (ECT) measurements, which gave not only the average holdup, but also the liquid distribution within the columns. This study demonstrates that these new hydrodynamic models remain applicable for more realistic particle size distributions, with the need to distinguish between the behaviour of the liquid held within the particle porosity compared to that flowing around the particles being critical to accurate prediction of the hydrodynamics.

Journal of Geophysical Research: Solid Earth, 120 (7), ISSN:2169-9313, ISSN:0148-0227, ISSN:2169-9356

A process for recovering copper from chalcopyrite is disclosed. The process includes oxidising sulphur in chalcopyrite with a solution under predetermined contact conditions and thereby releasing at least part of the copper in the chalcopyrite into the solution as copper ions. The process includes a subsequent step of reducing sulphur in a solid product from step (a) to a minus two, ie. Sulphide, valence state with a solution under predetermined contact conditions. The process further includes a subsequent step of oxidising sulphur in a solid product from step (b) with a solution under predetermined contact conditions and thereby releasing at least part of the remaining copper in the solid product into the solution as copper ions. The process further includes recovering copper from one or more of the solutions from steps (a) and (c).

This paper introduces a three-dimensional finite element (FE) formulation to accurately model the linear elastic deformation of fractured media under compressive loading. The presented method applies the classic Augmented Lagrangian(AL)-Uzawa method, to evaluate the growth of multiple interacting and intersecting discrete fractures. The volume and surfaces are discretized by unstructured quadratic triangle-tetrahedral meshes; quarter-point triangles and tetrahedra are placed around fracture tips. Frictional contact between crack faces for high contact precisions is modeled using isoparametric integration point-to-integration point contact discretization, and a gap-based augmentation procedure. Contact forces are updated by interpolating tractions over elements that are adjacent to fracture tips, and have boundaries that are excluded from the contact region. Stress intensity factors are computed numerically using the methods of displacement correlation and disk-shaped domain integral. A novel square-root singular variation of the penalty parameter near the crack front is proposed to accurately model the contact tractions near the crack front. Tractions and compressive stress intensity factors are validated against analytical solutions. Numerical examples of cubes containing one, two, twenty four and seventy interacting and intersecting fractures are presented.