Mixing Process Intensification In A Mixer Settler For Rare Earth Extraction

Rare earth elements are regarded as “the vitamins of modern industry” because of their excellent physical characteristics in optics, electricity, magnetism and so on. However,the extensive smelting technology, irrational industrial structure, production process pollution and low rare earth resource utilization have become a serious problem that China’s rare earth industry facing. Process intensification technology is an effective means to solve the problem of "high energy and material consumption, high pollution" in process industry, which is expected to change the face of rare earth smelting fundamentally. Therefore, having a profound understanding to the system dynamic behavior and mechanism of rare earth smelting process could guide the development and application of rare earth smelting process intensification technology, which has important theoretical and practical value.In this thesis, mixer settler(the most widely used rare earth separation equipment) was selected as the research object. Kerosene and water were used as the working fluid instead of extraction solvent and rare earth ion solution. Mixture and clarification experiments of oil-water two-phase fluid were performed. In mixer, a novel double rigid-flexible combination impeller was employed. The influence of rotational speed, flexible piece material, flexible piece geometry(length, width, etc.) and rigid-flexible combination impeller type to fluid flow field and chaos characteristic parameters in mixer settler were investigated respectivelly. By the wavelet analysis tool and Matlab, the largest Lyapunov exponents(LLE) and multi-scale entropies were calculated, and then the chaotic mixed performance of fluid in the mixer was studied. With the help of computational fluid dynamic(CFD), the analysis of the oil and water flow path in mixer settler were conducted, this made its flow structure and strengthen methods of chaotic mixing clear. The results would provide a theoretical basis for the mixer settler design and application, and then guid the development of rare earth smelting process intensification technology. The main conclusion of this thesis are as follows:①Through their multi-body motion, double rigid-flexible combination impellers intensified the motion characteristics of the fluid, suppressed the symmetry structure of the fluid field, and eliminated the isolation of mixing regions between the upper and lower impellers. Thus, more fluids entered the chaotic mixing state than the other states. In the optimum mixing point of each impeller, the LLEs of the double impeller, double rigid combination impeller, and double rigid-flexible combination impeller were 0.018, 0.055, and 0.057 respectively.②The double rigid-flexible impeller achieved the efficient dissipation of energy through the nonlinear coupling motion of rigid, flexible and flow, which facilitated the uniform energy distribution in the entire tank and improved the mixing efficiency. At 75 rpm, the MSE of the combination impellers were obviously greater than that of the double impeller. In addition, the rigid-flexible combination impeller had a better performance than the double rigid combination impeller because the former can make the fluid fluctuation violent through its own vibration.③In the choice of combination impeller material, soft PVC reinforced more fluid into chaotic state; in impeller structure, when the ratio of flexible piece length to layer spacing is 1.2, the best mixed state appeared. In addition, the mixing efficiency of the rigid-flexible combination impeller increased with increasing width of the flexible piece. However, for the consideration to a better clarification, the general choice is 1/40 D to 1/10 D.④Quantities of flexible piece and rigid blade slice significantly influenced the enhancement of mixing ability. The double rigid-flexible combination impeller strengthened the chaotic mixing of the two-phase fluid by changing the flow field structure and energy dissipation patterns, and it could achieve efficient-mixing operation.