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

The effect of impeller-stator design on bubble size: implications for froth stability and flotation performance

The impeller in a mechanical flotation tank plays a key role in keeping particles in suspension, dispersing and breaking-up air bubbles, and promoting particle-bubble collision. However, the turbulent regime generated by the impeller can also affect the pulp-froth interface, destabilising the lower regions of the froth and affecting the overall flotation performance. The effects that pulp zone design modifications have on the froth are, however, poorly understood and have not been well-studied. In this work, we study the impact of impeller-stator design on the performance of a large laboratory-scale flotation tank. Two different impeller designs, with and without a stator, were assessed under a range of air flow rates to determine changes in pulp bubble size, froth stability, and metallurgical recovery. The results allow us to quantify, for the first time, the reduction in bubble size in a three-phase flotation system and the improvement in froth stability due to the use of a stator, and thus the enhancement in flotation performance. An inverse relationship is found between the pulp bubble size and froth stability. It is shown that the impeller designs that exhibited smaller bubble sizes resulted in higher froth stability values and also higher flotation recoveries. These findings provide insights into the links between pulp and froth zone phenomena, paving the way for improvements in flotation tank design that lead towards flotation optimisation

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 [...

Evaluation of collector performance at the bubble-particle scale

Particle attachment and detachment in froth flotation are complex processes and their measurement presents many challenges. Of particular interest is the effect of collectors at the bubble-particle scale, in order to assess the strength or collecting ability of these reagents. However, studies of the effect of collectors on particle attachment at the bubble-particle scale are scarce. In this work, we propose a methodology to characterise collector strength by measuring the attachment rate of particles to a capillary-pinned bubble. An image processing technique was developed to quantify bubble surface coverage over time, which was then used to determine particle attachment kinetics. The image analysis strategy is based on the sessile drop method and uses curve fitting to determine accurately the particle coverage. The methodology was used to assess the collecting ability of three chalcopyrite collectors. Interestingly, although very similar contact angle measurements were found for two of the collectors, they showed distinctly different particle attachment kinetics. It is proposed that this particle-bubble attachment method can be used to gain additional information not currently available from either contact angle measurements or bulk collector performance tests

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

The behavior of rising bubbles covered by particles

A systematic investigation of the influence of particle coverage on the dynamics of rising bubbles was carried out using high-speed photography and image analysis techniques to study bubble behavior in terms of changes in velocity and aspect ratio. The buoyancy force and drag force exerted on the bubbles and the effect of particles were calculated to further understand their behavior. Results show that particles attached on the bubbles strongly dampen the oscillations observed in bubble aspect ratio and decrease its velocity and acceleration. The particles also render the bubbles more spherical and slow their velocity. It was found that the overall velocity of a bubble is directly correlated to its aspect ratio and inversely correlated to its particle coverage, while the acceleration and the aspect ratio and its change are inversely correlated. Interestingly, the trend observed in the oscillation and the oscillation period of particle-laden bubbles is similar for different levels of particle coating. A drag modification factor eta(p), which quantifies the drag influence of particles on bubble velocity, was identified from force analysis. A modified drag coefficient for uncoated and particle-laden bubbles was introduced, which allows, for the first time, to predict the behavior of rising bubbles in gas-liquid-particle systems

A Database for the Extraction, Trade, and Use of Sand and Gravel

Increasing demand for sand and gravel globally is leading to social, environmental, and political issues that are becoming more widely recognised. Lack of data and poor accessibility of the few available data contribute to exacerbating these issues and impair evidence-based management efforts. This article presents a database framework designed to describe stocks and flows data for sand and gravel from different sources. The classification system underlying the database builds on the Universal Materials Information System (UMIS) nomenclature, which is used to construct hierarchical order in the data. The common classification system is used to structure sand and gravel data records into a database formatted in the same manner as the Yale Stocks and Flow Database (YSTAFDB), a common data format. To illustrate how the database is built and used, a case study using UK data is presented. The UK is chosen owing to its relatively better access to data compared to other locations. Quantitative analyses of the UK data highlight possible risks in the supply chain of these materials for the UK. Results show that indigenous extraction only contributes 11% to UK sand and gravel production, with trade accounting for the rest of the inputs, of which 50% is reliant on only one nation

Retraction: Morley et al. A Database for the Extraction, Trade, and Use of Sand and Gravel. Resources 2022, 11, 38

The published article [...

Retraction: Morley et al. A Database for the Extraction, Trade, and Use of Sand and Gravel. <i>Resources</i> 2022, <i>11</i>, 38

The published article [...