Chen Luh Lin

Ultimate recovery in heap leaching operations as established from mineral exposure analysis by X-ray microtomography

The question of ultimate recovery in heap leaching operations is always of particular concern with respect to economic considerations. Of course, the particle size distribution is a critical factor which determines ultimate recovery and which must be established based on a balance between the extent of mineral exposure and transport phenomena. Now it seems that the ultimate recovery for a given particle size distribution can be established from mineral exposure analysis by X-ray microtomography (XMT). Using recently developed software, micro-computed tomography (CT) data can be used to determine the fraction of mineral exposed and thus the ultimate recovery. Examples of mineral exposure analysis are given for the copper heap leaching operation at Zaldivar, Chile.

Treatment of polished section data for detailed liberation analysis

Abstract A transformation equation can be used to describe the relationship between the one, two and three dimensional information regarding the composition of mineral particles of specified size. Linear or areal grade distribution f(gi) can be transformed to an estimate of the volumetric grade distribution p(g) via a transformation function H(gi|g, Nn, …), a conditional probability function. The effect of the external particle strucuture (shape) and internal grain characteristics (grade, dispersion density, and grain size distribution) on the transformation matrix have been evaluated by computer simulation of randomly oriented, irregularly shaped, multiphase particles. Volumetric grade and dispersion density (number of grains per particle) are the most important variables which influence the transformation matrix. Least square minimization of fitted functions and the Phillips-Twomey inversion technique have been used to solve the transformation equation. Three examples, a computer simulated volumetric grade distribution and two experimental depth profiles of different monosize particle samples (iron ore and copper ore), provide evidence that such an approach can be useful for detailed liberation analysis.

Cone beam X-ray microtomography for three-dimensional liberation analysis in the 21st century

A new method based on cone-beam X-ray microtomography is described for direct determination of the three-dimensional liberation spectrum of multiphase particles 100 microns in size or less. Such a technique may provide the basis for more detailed and accurate liberation analysis in the 21st century. Previous research had demonstrated the ability to use traditional medical X-ray CT scanners to determine the liberation spectrum of coarse coal particles of 1 cm in size (washability analysis). Rather than stacking a series of two-dimensional slices for volumetric imaging as is commonly done in traditional medical computed tomography, a three-dimensional reconstruction image array is prepared directly from the two-dimensional projections for cone beam geometry. The advantage of high spatial resolution (approximately 15 μm) with a microfocus X-ray generator combined with the benefit of direct processing of three-dimensional data, provide an excellent opportunity to overcome many of the limitations of current polished section techniques being used for the liberation analysis of multiphase particles.

Pore structure analysis of particle beds for fluid transport simulation during filtration

Abstract Accurate assessment of the transport properties of porous media (in our case, filter cake) is of major importance in the development of improved filtration processes. Implications from these studies are important in the design and operation of filtration equipment in order to enhance the efficiency of this important solid–liquid separation process. The microstructure and connectivity of pore space are important features to describe detailed fluid flow phenomena in filter cake during fine particle filtration. In this regard, 3D characterization of pore structure is essential. The pore structure has to be described by parameters which are of special relevance to the interpretation of fluid transport phenomena. These parameters should be based on directly measured variables of the pore system and not inferred from indirect variables (such as those determined empirically from transport processes) valid only for a particular pore structure. In this way, fundamental relationships between pore structure and fluid transport at the microstructure level can be described. In order to achieve this level of sophistication, the three-dimensional interconnected pore structure of filter cake must be determined. Study of fluid transport phenomena in filter cake using X-ray microtomography (XMT) to characterize the complex three-dimensional pore geometry is discussed. On this basis, the lattice Boltzmann (LB) method is used to simulate fluid flow and to begin to establish a fundamental relationship between pore microstructure and effective transport coefficients. For example, can network analysis using skeletonization procedures be used to confirm fundamental relationships that might be developed? Eventually then, with this detailed model, design and operating variables could be optimized for improved filtration efficiency.

Coadsorption Phenomena in the Separation of Pyrite from Coal by Reserve Flotation

The reverse flotation of pyrite from coal was studied to determine surface chemical aspects of this system. Included in the research was determination of the effect of dextrin on the adsorption of xanthate by pyrite, measurement of rest (mixed) potentials for crystal- and coal-pyrite electrodes and evaluation of the bench scale flotation response with respect to the understanding of the adsorption reactions. Although little dextrin is adsorbed by crystal pyrite in the absence of xanthate, significant adsorption of dextrin in the presence of xanthate occurs. These results further support the general hypothesis that dextrin adsorption involves a hydrophobic bonding mechanism, In this system hydrophobic bonding is thought to occur at the surface between the non-polar portion of the dextrin and the dixanthogen oil which forms on the crystal pyrite surface. On the other hand, the slightly hydrophobic character of coal pyrite (pyrite associated with locked coal) exhibits a higher adsorption potential for dextri...

Improved transformation technique for the prediction of liberation by a random fracture model

Abstract Kings Random Fracture Model (RFM) was implemented using the exponential model for the distribution of linear intercepts through both continuous and dispersed phases and the Finlayson function for the distribution of intercept lengths through particles. Accurately measured distribution of intercept lengths through particles and linear grade distributions were compared to those predicted by the model, and very good agreement was found. The inversion of the transformation equation, which describes the relationship between the one-, two- and three-dimensional information regarding the composition of mineral particles was implemented using the constrained Rosenbrock Hillclimb Procedure with an appropriate objective function. Volumetric grade distributions determined from depth profile measurement were compared with the results of inversion from either linear or areal grade distributions, and again very good agreement was found. Assuming both procedures were correct, the liberation spectrum of a copper ore containing 3.8 vol.% CuFeS2 was determined from very simple image analysis measurements using the RFM coupled with the implemented solution for the transformation equation.

Solutions to the transformation equation for volumetric grade distribution from linear and/or areal grade distributions

Abstract Liberation measurements on polished sections of composite particles using image analysis techniques yield linear grade and areal grade distribution information for the particle assembly. It is desirable to extract from this information estimates of the volumetric grade of each phase in the particles. A transformation equation can be used to describe the relationship between the one-, two- and three-dimensional information concerning the composition of mineral particles of specified size. A least-squares minimization with fitted functions technique and constrained linear (Phillips—Twomey) inversion have been applied to determine the volumetric grade distribution by inverting the transformation equation using one- and two-dimensional data. Three examples — one, a computer-simulated volumetric grade distribution and the other two experimental depth profile measurements on iron and copper ore samples — have been used to test the two methods. It is found that the Phillips—Twomey inversion technique gives the best estimates of volumetric grade distributions.

Coal Washability Analysis by X-ray Computed Tomography

Abstract X-ray computed tomography (CT) has been shown to be an excellent tool for the study of internal structure and multiphase texture of solids in a noninvasive, nondestructive manner. Now with new reconstruction algorithms and advanced computer systems, quantitative CT analysis is possible. In this regard, a step-by-step procedure for the determination of coal particle density by X-ray CT has been developed. Using appropriate algorithms, the feasibility of the construction of coal washability curves by quantitative X-ray CT analysis has been demonstrated

Characterization of pyrite in products from the reverse flotation of coal

The effectiveness of two-stage reverse flotation for desulfurization of coal is significantly dependent on the microstructural features of the heavy mineral fractions in the coal seam. This dependence has been evaluated by a systematic mineralogical analysis of the flotation products obtained from both Eastern (Lower Freeport) and Midwestern (Illinois No. 6) coals by SEM/EDAX and TGA. Comparison of the results from this detailed analysis suggests that the effectiveness of desulfurization during reverse flotation is determined by the relative degree of pyrite association with silicate minerals and carbonaceous material. When locked pyrite contains a higher relative percentage of silicate minerals desulfurization by reverse flotation is more effective.

Development of an On-line Coal Washability Analysis System Using X-ray Computed Tomography

Abstract Washability analysis determines the best separation results that can be achieved in the operation of coal preparation plants. Unfortunately, there are no on-line techniques for determining this most fundamental information. It now appears possible to determine coal washability on-line through the use of X-ray computed tomography (CT) analysis. This paper presents the results for the development of a CT-based, on-line coal washability analyzer. The development of appropriate hardware and software necessary to adapt a CT analyzer for use in determining coal washability is discussed. Testing of the analyzer using well characterized coal samples is presented.