Multimodal assessment of the curing of agglomerated ores in the presence of chloride ions

Agglomeration and subsequent curing are widely used as pre-treatment for ore prior to heap leaching as it both improve the permeability of the heap and brings leaching solution into close contact with the ore, initializing the leaching reactions. Despite its widespread use there have been limited studies into the processes occurring within the agglomerates over the curing process. In this study both destructive and non-destructive imaging techniques are used to assess both the physical and chemical changes occurring within the agglomerates as they cure. The SEM/EDX is one of the most popular imaging techniques for mineral samples. It can only be carried out once for a given sample due to its destructive preparation method but provides detailed mineralogical information. A complementary tool is X-ray Microtomography (XMT), which is non-destructive and can be used to image the same object multiple times over the course of the experiment. Its main limitation, though, is that the acquired images are of X-ray attenuation values and need to be independently assigned to different mineral classifications based on, for instance, the corresponding SEM images. Combining the ability of SEM/EDX measurements to identify different mineral phases with the 3D time resolved XMT measurements can thus produce superior results to those achievable using either of the modalities on their own. In this study, we propose a methodology for quantifying the formation and depletion of mineral components of agglomerates. These methodologies will be demonstrated in ores agglomerated using a combination of sulphuric acid and ferric sulphate as well as in samples in which sodium chloride is added to the agglomeration recipe. The curing process was tracked beyond the typical time scales used industrially, highlighting that the presence of chloride ions makes a substantial difference to the chemical and structural evolution of the sample. Over this curing process most of the observed leaching occurs during the first 20 days in the presence of NaCl, while there is virtually no metal dissolution for the standard samples without NaCl. During curing the solution does not leave the agglomerates other than via evaporation. Thus, reprecipitation of metal containing mineral species was observed, especially near the agglomerate surfaces. In the presence of NaCl precipitated Cu-S-O-Cl complexes were observed suggesting that the chloride ions in solution are playing a key role in the leaching process. After 65 days of curing, the samples were water washed in order to remove soluble species, extracting 50% of the original sulphides from the agglomerates containing sodium chloride, but only 20% from the other agglomerates

Uncertainty quantification of landslide generated waves using gaussian process emulation and variance-based sensitivity analysis

Simulations of landslide generated waves (LGWs) are prone to high levels of uncertainty. Here we present a probabilistic sensitivity analysis of an LGW model. The LGW model was realised through a smooth particle hydrodynamics (SPH) simulator, which is capable of modelling fluids with complex rheologies and includes flexible boundary conditions. This LGW model has parameters defining the landslide, including its rheology, that contribute to uncertainty in the simulated wave characteristics. Given the computational expense of this simulator, we made use of the extensive uncertainty quantification functionality of the Dakota toolkit to train a Gaussian process emulator (GPE) using a dataset derived from SPH simulations. Using the emulator we conducted a variance-based decomposition to quantify how much each input parameter to the SPH simulation contributed to the uncertainty in the simulated wave characteristics. Our results indicate that the landslide’s volume and initial submergence depth contribute the most to uncertainty in the wave characteristics, while the landslide rheological parameters have a much smaller influence. When estimated run-up is used as the indicator for LGW hazard, the slope angle of the shore being inundated is shown to be an additional influential parameter. This study facilitates probabilistic hazard analysis of LGWs, because it reveals which source characteristics contribute most to uncertainty in terms of how hazardous a wave will be, thereby allowing computational resources to be focused on better understanding that uncertainty

Characterisation of the multiphase fluid dynamics of the CoarseAIR™ fluidised bed flotation cell using the Large Modular Array (LaMA) for positron emission particle tracking (PEPT)

Fluidised bed flotation cells (FBFCs) present a compelling solution for coarse particle flotation, enabling an increase in the target particle size in comminution circuits, with the corresponding energy savings. Despite their potential and strong industrial interest, the three-phase fluid dynamics of large-scale FBFCs remain unexplored due to measurement complexities and size restrictions. This paper presents the first quantification of the fluid dynamics of the CoarseAir™-100, a 2 m tall laboratory-scale FBFC. Measurements were obtained using positron emission particle tracking (PEPT), a non-invasive technique that tracks the motion of a radiolabelled tracer. Leveraging the Large Modular Array (LaMA) PEPT system, consisting of 48 buckets, each housing four detector blocks, this study is the largest PEPT experiment to date. Particle tracks of hydrophobic and hydrophilic tracers were obtained under different fluidisation and airflow rates. Hydrophobic tracers exhibited buoyant behaviour despite their large size of up to 700 μm, while hydrophilic tracers engaged in recirculation patterns with rapid downward motion near the walls. The intricate motion of particles in the lamella plates was experimentally quantified, revealing an average path tortuosity of 7.3, providing essential information for design. These results represent a major advance in our understanding of fluidised bed flotation cells, contributing to the refinement of design and scale-up strategies for FBFCs

Characterisation of solid hydrodynamics in a three-phase stirred tank reactor with positron emission particle tracking (PEPT)

It is challenging to measure the hydrodynamics of stirred tank reactors when they contain multiphase flows comprising liquid, gas bubbles and particles. Radioactive particle tracking techniques such as positron emission particle tracking (PEPT) are the only established techniques to determine internal flow behaviour due to the inherent opacity and density of fluid and the vessel walls. The profiles of solids flow are an important tool for robust reactor design and optimisation and offer insight into underlying transport processes and particle–fluid–bubble interactions for applications such as froth flotation. In this work, measurements with PEPT were performed with two tracer particles differing in surface hydrophobicity to characterise the solids hydrodynamics in a baffled vessel agitated with a Rushton turbine. The location data from PEPT were averaged with time to estimate the probability density function (PDF) of particle velocity in individual voxels. The peaks of these voxel distributions were used to produce profiles of solids flow in different azimuthal and horizontal slices. Bimodal vertical velocity distributions were observed in the impeller radial jet which suggest the particles experienced trajectory crossing effects due to inertia. Statistical tests were performed to compare the velocity distributions of the hydrophilic and hydrophobic tracer particles, which indicated similar average flow behaviour in the liquid or pulp phase of the vessel and differences near the air inlet, in the impeller discharge stream and pulp–froth interface. With tracers designed to represent gangue and valuable mineral species, the differences in velocity reveal interactions such as bubble–particle attachment and entrainment

Development and Validation of a Dynamic Model for Flotation Predictive Control Incorporating Froth Physics

In mining, froth flotation is the largest tonnage separation process used to separate valuable minerals from waste rock [...

Effect of particle size on the rising behavior of particle-laden bubbles

The rising behavior of bubbles, initially half and fully coated with glass beads of various sizes, was investigated. The bubble velocity, aspect ratio, and oscillation periods were determined using high-speed photography and image analysis. In addition, the acting forces, drag modification factor, and modified drag coefficient were calculated and interpreted. Results show that the aspect ratio oscillation of the rising bubbles is similar, irrespective of the attached particle size. As the particle size is increased, the rising bubbles have a lower velocity and aspect ratio amplitude, with the time from release to each aspect ratio peak increasing. Higher particle coverage is shown to decrease the bubble velocity and dampen the oscillations, reducing the number of aspect ratio peaks observed. The highest rise velocities correspond to the lowest aspect ratios and vice versa, whereas a constant aspect ratio yields a constant rise velocity, independent of the particle size. Force analysis shows that the particle drag modification factor increases with the increased particle size and is greatest for fully laden bubbles. The modified drag coefficient of particle-laden bubbles increases with the increased particle size, although it decreases with the increased Reynolds number independent of the particle size. The drag force exerted by the particles plays a more dominant role in decreasing bubble velocities as the particle size increases. The results and interpretation produced a quantitative description of the behavior of rising particle-laden bubbles and the development of correlations will enhance the modeling of industrial applications