| Flotation is the most widely used method in fine grained material separation. A lot of geological conditions of mineral resources in our country are bad, the ore are "poor, complex and fine". So, the perfect degree of the flotation process will directly affect the efficiency of resource utilization. However, there is still some shortcomings, such as low recovery, poor quality of concentrate and poor pertinence of the craft of flotation process. So far, to improve the efficiency of flotation, the domestic and foreign scholars and engineers have made great progress in the new agents, new flotation equipment, process optimization, etc. But, most of these studies were focused on the separation unit, the attention to and breakthrough of high efficient mixing technology is still lacks.Flotation is the most widely used method in fine grained material separation. A lot of geological conditions of mineral resources in our country are bad, the ore are "poor, complex and fine". So, the perfect degree of the flotation process will directly affect the efficiency of resource utilization. However, there is still some shortcomings, such as low recovery, poor quality of concentrate and poor pertinence of the craft of flotation process. So far, to improve the efficiency of flotation, the domestic and foreign scholars and engineers have made great progress in the new agents, new flotation equipment, process optimization, etc. But, most of these studies were focused on the separation unit, the attention to and breakthrough of high efficient mixing technology is still lacks.To strengthen the research of conditioning will fit in with the concepts and requirements of process intensification and deep separation. Refined the flotation process and the conditioning should be the truly starting point of the preparation, while crushing and grinding be treated as previous preparation. Surface physicochemical properties modifying is the prerequisite condition to high efficiency recovery of the fine and superfine grained mineral. Existing conditioning devices and methods play mixing effect simply, but meet no demands of high dispersion, strong activation and efficient collision contact by fine and superfine mineral particles. High intensity conditioning (HTC) is the important component of flotation process intensification. Its main purpose is to improve the fluid characteristic in conditioning tank. Strong turbulence flow will activate the surface of mineral particles by swill out the mud; disperse hydrocarbon oil collectors efficiently, improving the probability of collision and adsorption between the mineral particles and superfine flotation agents under the action of mechanical force. If so, it will be a high-efficiency conditioning technology.The particle properties that have influence on the effect of conditioning, especially the dispersion laws of non-polar hydrocarbon oil collector in the process of high shear mixing were explored and summarized. A series of classical collision rate (probability) models, such as velocity gradient, Sommerfeld moedl and Levich model were analyzed, and it was found that the Levich model was the most suitable mathematical model. As the Levich model not merely takes the inertia force elements such as the particle size and density into account but also contacts with the turbulent flow impaction caused by mixing impeller. The classic Levich model was optimized and extended, and a new collision model which suits for the process of HIC better was developed. It was found that fluid velocity is the main fact when R>105 is tenable. The flow field characteristics of high intensity conditioning tank were analyzed by PIV measurement and CFD simulation. Taking the coking coal from East Ningxia, coking coal from Kailuan and molybdenum from Luoyang mining area as the research object samples, obtained best parameters of high shear mixing process by laboratory and industrial scale test in comparison with blank test. The main research contents and conclusions are as follows:(1)Taked 0# diesel oil as the sample, a series of experiments search on the nonpolar hydrocarbon oil’s dispersion effect with mechanical agitation was conducted. Both the impactions of revolving speed and mixing time in conditioning were studied. The oil drop size distribution laws with different conditions mixing were determined by Laser Particle Size Analyzer. The results indicate that high revolving speed and short mixing time is better than low revolving speed but long mixing time to get more outstanding performance on the oil’s dispersion. This will be good to the next floatation process. The relationship between the average particle size and the impeller speed has been analized and concluded, it was found that the mathematical model accords with the following with 2 min conditioning time: Rf=5.55065·10-5·utip-1.2613Where Rf is the fine particles radius of collector drops, m; utip is the tip linear velocity of impeller, m/s;(2) The selection and optimization of collision probability model which is suited to the fine mineral pulp conditionging.The optimization and extension were maden combining with the classical Levich collision probability model. It is found that the following features of particles melely connected with the densities of particle and liquid when Reynolds number>105. The classic Levich collision probability model was optimized with the conditioning tank structure parameters and operating conditions. The new model is:Where Rc is the coarse particles radius of ore particle, m; Rf is the fine particles radius of collector drops, m; L is the diameter of conditioning tank, m; v is the Kinematic viscosity of fluid, m2/s; nc, is the coarse particle concentration of ore particles, 1/m3;nf is the fine particle concentration of collector particles,1/m3;ρ is the density of liquid, kg/m3; pp is the density of ore particles, kg/m3; u, is the fluid velocity, m/s.The design direction of fine-grained mineral conditioning equipment was given by this model. It indicated that to get larger collision probability between mineral particles and collector drops in conditioning tank, it is necessary to increase the liquid velocity on every spot in the tank room. And this will be helpful to increase the utility rate of tank space, save the collector dosage and create a good interface environment for the next floatation process;(3) PIV was used to research the slurry’s fluid characteristics in mixing tank with 300 mm diameter (T=300 mm), and the CFD was used to simulate the fluid environments of bigger conditioning with 2200 mm diameter (T=2200 mm). The results show that compared with the tank with vertical baffles only, the new tank with horizontal baffles and shear disks separated the tank into two or three conditioning room which were relatively independent each other. Overall liquid speed, turbulence intensity value k and the tank space utilization were remarkably improved by adding the horizontal baffles and shear disks.In every conditioning room, the liquid tossed out by impeller was separated to two directions, one turned up rapidly after reaching the bottom, and the other one flow to the wall along the floor (or the false floor made by horizontal baffle). The main flow direction before the vertical baffle was down, it separate into two directions too, one is still down, the other one turned to the shaft, the obove four flows intercourse to one diamond high velocity zone;(4) Taking the coking coal from East Ningxia, Kailuan and molybdenum from Luoyang mining area as the research objects, the best parameters of High intensity conditioning was obtained in laboratory and industrial scale test. The results comparison was conducted with pre-process by other pre-process equiment. The data indicated that the high intensity conditioning is of much help for the improvement of the floatation quantity and quality indexs of difficult-to-floate fine coal. As the process of HIC+ cleaning, both the recovery of roughing period and the impurity cleaning effect got improved. Finally, the results showed large advantage of "Double high" (high recovery and high quality) compared with traditional pretreatment method. |
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