| Bioleaching system is a complex dynamic sytem. During leaching process, the pore strucuture of granular media evolves continuously, which influences the permeability of the media and then affects the processes of mass transport, heat transmission and momentum transfer. As a result, the heap leaching rate and recovery ratio are affected. Since the pore structure of granular media is very crucial for the whole heap leaching system, so it is very important to study the characteristics of pore structure, evolvement rules and its effects on the permeability of the heap.With the methods of field investigation, indoor test, theoretical analysis, and numerical simulation, begining with the relationship between mesoscale pore structure parameters and macro permeability, by introducing advanced X-ray computerized tomography (CT) and digital image process technology, the quantification of pore structures of single grade granular ore samples and graded granular ore samples were conducted. Furthermore, the evolvement rules and mechanisms of pore structure of granular ore media during heap leaching were studied. At last, the simulation of meso seepage flow of granular media was realized. The research achievements enriched the basic theoretical system of solution mining.The main works completed are as follows:(1) Starting from the theoretical research of multi-scales pore structure of granular ore media, the characteristics of granular ore media, the representative parameters of mesoscale pore structure and its relationship with macro permeabiltiy were systematically analyzed.(2) The new method based on X-ray CT technology was developed for studying the characteristics of granular ore media. A technical route for the three dimensional reconstruction of granular ore media's pore structure was put forward. Using volume ploting algorithm, the reconstruction of pore structure was realized with MATLAB programming.(3) For the first time, several groups of single grade granular ore samples and graded granular ore samples were scanned by X-ray CT. By using image process technologies, the pore structure parameters of all samples were quantified. The relationships between porosity, pore size distribution and particle size were explored. Moreover, based on fractal theory, the fractal dimensions of solid matrix, pore space and matrix-pore interface of each sample were measured and the correlations of the three fractal dimensions with particle size, porosity, and seepage coefficient were analyzed.(4) The pore evolvement experiment of granular ore media during bacteria column leaching was carried out by intergrating CT technology firstly. The concept of pore topological ratio was put forward and the permeability formula was improved by considering the change of pore connectivity. Based on this, the temporal and spatial variabilities of porosity, pore size distribution, pore connectivity and permeability along the height of column were analyzed in details. Thus the pore evolvement rules and its influence on permeability were disclosed.(5) Based on granular structural mechanics, seepage dynamics, physical chemistry, and microbiology, the evolvement mechanisms of pore structure of granular ore media under the action of solution were analyzed from multi-scale (micro-, meso-and macro-) and multi-process (physical, chemical and bacterial process) firstly.(6) Coupled with digital image processing technoloty (DIP) and finite element method (FEM), the finite element model of pore network was build directly based on CT image, realized the transformation of physical model for seepage simulation from ideal model to realistic model. For the first time, the mesoscale fluid flow in pore network of granular ore media was simulated with COMSOL Multiphysics and the characteristics of pore scale fluid flow was disclosed. |
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