Rules Of Air Flow And Enhanced Leaching Mechanism By Forced Aeration In Heap Bioleaching Of Copper Sulfides

Microbial heap leaching is a promising approach to exploit the low-grade copper sulfides. The essence of bioleaching is transferring the solid metal minerals to soluble sulfates with bacteria-bearing solutions. One of the key processes is air permeating into the heap and involves in the mineral dissolution and bacterial reproductions. To overcome the oxygen limitation within the heap, forced aeration was put forward as a reliable solution. Hence, primary investigations were Carried out with focuses on air flow rules in heap bioleaching of copper sulfides and leaching mechanism by forced aeration. The methods involved in this work included physical experiments, mathematical modeling, mechanism analysis, numerical simulation and industrial control. The work could be summarized as follows.(1) Experiments with respect to influences of variable factors on air permeability coefficients in the heap were operated. Apparatus were designed to test the air permeability coefficients. Horizontal and vertical permeability coefficients under conditions of variable aeration intensities, water contents, porosities, fine ore contents and compaction densities were successively conducted The effects of aforementioned factors on air permeability coefficients as well as anisotropy of air flows were proposed.(2) Series of column bioleaching of copper sulfides enhanced by forced aeration were carried out. A strain of native At. ferrooxidans was separated, domesticated and used in these experiments. The results showed that solution flow rates with forced aerations were 18.3% faster than that without aeration, and porosities in the middle and bottommost of the heap were expanded. Additionally, microbial concentrations were higher than 106/mL in the time frame of the experiments when aeration intensities were higher than 60 L/h, while copper leaching rates were about 10% higher than those with only 0-20 L/h aeration. The oxygen utilization rate was 1.59～10.4% in the aerated heap, and it decreased with the increase of aeration rates.(3) Establishment and solution of air flow model in the heap in the presence of forced aeration were realized. Characters and percolation mechanism of air flows in the heap were ascertained. Immigration models of air flow in the aerated heap were proposed, in which air pressures at a specified depth and a specified moment under conditions of steady or unsteady seepage field can be extrapolated. Equations of air flow rate in terms of variable aeration intensities were derived. Besides, heaps were classified into four stages on the basis of gas-solution forms, and reasonable construction pressures for forced aeration were suggested.(4) Enhanced leaching mechanism by forced aeration in bioleaching of copper sulfides was demonstrated. Heat equilibrium equations were proposed under the consideration of micro air flow in the heap. Microbial immigration model along the vertical axes was derived. Moreover, a concept called "valid heap aeration rate" was put forward to quantitatively evaluate the efficiency of forced aeration. Enhanced leaching mechanism of forced aeration from perspectives of microcosmic chemistry and microbial views were also analyzed.(5) A numerical simulation method coupled with seepage field, velocity field and temperature field was developed to simulate the heap bioleaching enhanced by forced aeration. COMSOL Multiphysics was introduced to simulate the heap bioleaching process under conditions of variable aeration intensities as well as variable-ratios of irrigation rates to aeration intensities. Moreover, distribution characters and progressions of air flow rate, oxygen concentration, temperature and copper leaching rates were also realized.(6) Primary technical approaches and industrial adjustments of forced aeration were optimized. Industry methods to promote the natural advection and forced aeration technologies were proposed. The results of operation simulation of forced aeration in a large-scale heap showed that valid heap aeration rate was 21.4-27%, while microbial oxygen consumptions were 2-5 times less than oxygen consumptions involved in mineral dissolutions.