Minerals2015, 5(2), 164-188; doi:10.3390/min5020164 - published 30 March 2015 Show/Hide Abstract
Abstract: A new boundary condition treatment has been devised for two-phase flow numerical simulations in a self-aerated minerals flotation machine and applied to a Wemco 0.8 m3 pilot cell. Airflow rate is not specified a priori but is predicted by the simulations as well as power consumption. Time-dependent simulations of two-phase flow in flotation machines are essential to understanding flow behavior and physics in self-aerated machines such as the Wemco machines. In this paper, simulations have been conducted for three different uniform bubble sizes (db = 0.5, 0.7 and 1.0 mm) to study the effects of bubble size on air holdup and hydrodynamics in Wemco pilot cells. Moreover, a computational fluid dynamics (CFD)-based flotation model has been developed to predict the pulp recovery rate of minerals from a flotation cell for different bubble sizes, different particle sizes and particle size distribution. The model uses a first-order rate equation, where models for probabilities of collision, adhesion and stabilization and collisions frequency estimated by Zaitchik-2010 modelare used for the calculation of rate constant. Spatial distributions of dissipation rate and air volume fraction (also called void fraction) determined by the two-phase simulations are the input for the flotation kinetics model. The average pulp recovery rate has been calculated locally for different uniform bubble and particle diameters. The CFD-based flotation kinetics model is also used to predict pulp recovery rate in the presence of particle size distribution. Particle number density pdf and the data generated for single particle size are used to compute the recovery rate for a specific mean particle diameter. Our computational model gives a figure of merit for the recovery rate of a flotation machine, and as such can be used to assess incremental design improvements as well as design of new machines.
Minerals2015, 5(2), 142-163; doi:10.3390/min5020142 - published 30 March 2015 Show/Hide Abstract
Abstract: Froth image segmentation is an important and basic part in an online froth monitoring system in mineral processing. The fast and accurate bubble delineation in a froth image is significant for the subsequent froth surface characterization. This paper proposes a froth image segmentation method combining image classification and image segmentation. In the method, an improved Harris corner detection algorithm is applied to classify froth images first. Then, for each class, the images are segmented by automatically choosing the corresponding parameters for identifying bubble edge points through extracting the local gray value minima. Finally, on the basis of the edge points, the bubbles are delineated by using a number of post-processing functions. Compared with the widely used Watershed algorithm and others for a number of lead zinc froth images in a flotation plant, the new method (algorithm) can alleviate the over-segmentation problem effectively. The experimental results show that the new method can produce good bubble delineation results automatically. In addition, its processing speed can also meet the online measurement requirements.
Minerals2015, 5(2), 133-141; doi:10.3390/min5020133 - published 25 March 2015 Show/Hide Abstract
Abstract: Naturally occurring radionuclides such as uranium, thorium and their decay products (226Ra, 222Rn) are present in a number of geological settings in Jordan. Motivated by the existence of uranium anomalies coupled with its lack of conventional energy resources, Jordan decided that the development of this indigenes resource (uranium) is the first step in introducing nuclear power as part of its energy mix. Uranium deposits in Central Jordan were perceived not only as a secured resource that will fulfill Jordan’s energy needs, but also as an economic asset that will finance Jordan’s nuclear program. The average uranium concentration of 236 soil samples using ICP-Mass (inductively coupled plasma mass spectrometry) was found to be 109 parts per million (ppm). Results analysis revealed a wide range of 1066 ppm for uranium concentration, and a median of 41 ppm uranium. The measurements frequency distribution indicates that 72% of samples measured had a uranium content of less than 100 ppm, a concentration that characterizes overburden and tailings quality, rather than minable reserves. This paper presents and evaluates the concentration of uranium in central Jordan, being the most promising area with the highest radioactive anomalies in Jordan.
Minerals2015, 5(2), 117-132; doi:10.3390/min5020117 - published 24 March 2015 Show/Hide Abstract
Abstract: Abstract: The distribution and substitution mechanism of Ge in the Ge-rich sphalerite from the Tres Marias Zn deposit, Mexico, was studied using a combination of techniques at μm- to atomic scales. Trace element mapping by Laser Ablation Inductively Coupled Mass Spectrometry shows that Ge is enriched in the same bands as Fe, and that Ge-rich sphalerite also contains measurable levels of several other minor elements, including As, Pb and Tl. Micron- to nanoscale heterogeneity in the sample, both textural and compositional, is revealed by investigation using Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) combined with Synchrotron X-ray Fluorescence mapping and High-Resolution Transmission Electron Microscopy imaging of FIB-prepared samples. Results show that Ge is preferentially incorporated within Fe-rich sphalerite with textural complexity finer than that of the microbeam used for the X-ray Absorption Near Edge Structure (XANES) measurements. Such heterogeneity, expressed as intergrowths between 3C sphalerite and 2H wurtzite on [11
Minerals2015, 5(1), 104-116; doi:10.3390/min5010104 - published 12 March 2015 Show/Hide Abstract
Abstract: The impacts of temperature on the surface thermal damage of rock salt, gypsum and mudstone from the Yingcheng salt mine, China were investigated by the surface crack growth and propagation tests at different temperatures. We found that: (a) high temperature could strengthen the rock salt molecular thermal motion and weaken the cohesion among the rock salt grains, so that the grain boundaries were more prone to slip and thus develop into cracks; (b) high temperature could make the water molecules evaporate from rock specimens, which should change the physical properties of gypsum and mudstone; and (c) high temperature had a significant effect on the interface between rock salt and gypsum and mudstone, therefore it should be easy to produce cracks with white or light yellow cumulate powder here. The surface crack growth and propagation of the rock salt, gypsum and mudstone have a positive correlation with the temperature by stereo microscope and the method of binary images, which could observe the surface thermal damage properties. Finally, the fractal dimension of the rock salt surface cracks was calculated based on fractal theory, and the evolution of the surface thermal damage was found from 50 to 260 °C.
Minerals2015, 5(1), 86-103; doi:10.3390/min5010086 - published 3 February 2015 Show/Hide Abstract
Abstract: The failure of a tailing dam occurs due to damage to the particles’ micro-structure. Understanding the deformation characteristics of the particle’ micro-structure is important for understanding the mechanics of instability in tailing dams. In our study, a series of experiments was conducted using a testing apparatus for micro-mechanics and the deformation of tailings from the Huangcaoping tailing pond, Sichuan Province, China to investigate the loading capacity, micro-structure and deformation features of tailing particles. The latter two were analyzed quantitatively using concepts from fractal geometry. The results demonstrate that: (1) the structural loading capacity of tailings increases first and then decreases slightly with increasing particle size; (2) the particle micro-structure of the four tailing samples from the Huangcaoping tailing pond is described in terms of the fractal dimension based on the perimeter and area (D-value), which is between 1.288 and 1.533; (3) as the axial stress increases, the D-value gradually decreases along a wavy line with a decreasing rate of change; (4) under the same axial strain, the D-value first decreases and later increases slightly as the particle size increases; and (5) the number of fractured particles increases with the particle size.