Study On Influence Mechanism And Regulation Of Flotation Column Gas Hold-up

Fine and micro-fine particles in poor, mixed, difficult mineral are difficult to mineralize, which is one of the most difficult problems in column separation research. The ammount of gas hold-up and the quality of gas decide the hydrophobic mineral yield and load ability directly. Gas hold-up characterizes the ammount and quality of gas in flotation process. At present, the techology of regulating the ammount of gas based on inflating volume has been quite mature in column flotation process. However, the quality of bubbles can't always be ensured which has effect the recovery and selectivity of flotation. With the aims mentioned above, the study on the formation mechanism and regulation of flotation column gas hold-up has been made in this dissertation, which will provide theory fundamental for controlling the size of bubbles in the environment of strong turbulent with a great amount of inflating volume, and provide technology support for flotation column industrial concrol to achieve effective separation of micro-fine particles.First of all, the research on suitable gas hold-up of coal slime, copper sulfide, hematite and bauxite column flotation separation has been made. Using pressure-difference method to measure gas hold-up, under the condition of differernt gas hold-up, the column separation effect of coal slime, copper sulfide, hematite and bauxite have been analysized. The results show that the influence of gas hold-up on separation index has some kind of commonness. Increasing gas hold-up leads to increasing recovery of purpose mineral while the concentrate grade reduces gradually. While achieving the best separation effect, the corresponding gas hold-up of different mineral ores is different. Therefore, gas hold-up affects mineralization to some extent, which affects concentrate grade and recovery. By regulating gas hold-up the flotation process can be optimized to improve flotation effect.In flotation process, the size of bubbles affects gas hold-up directly. Circulating pressure, inflating volume and frother dosage are the key factors while there are many factors affect the size of bubbles and gas hold-up. To research the influence of these three factors on gas hold-up, experimental and flow field numerical simulation study has been made. During experimental study process, using software MATLAB as bubble image analysis tool to research the influence of circulating pressure, inflating volume and frother dosage on the size of bubbles and gas hold-up separately and get the effect regularity. During numerical simulation study process, using fluid dynamics software FLUENT to make numerical simulation research of gas-fluid two-phase flow field in flotation column. Effect regularity of each factor has been investigated theoretically, also the gas velocity variation regularity while changing circulating pressure and inflating volume has been analysized. The results show that two-phase flow field simulation results are consisitent with experimental results. The radial distribution of gas hold-up in column is higer in the middle and lower at around. The axial distribution is higher in the middle and lower on both sides. Factors experimental and flow field numerical simulation research has provided great basic for the study on the formation mechanism and regulation of gas hold-up.Basing on the research mentioned above, the formation mechanism and regulation of gas hold-up has been discussed. From the perspective of controlling the regulation strategy of gas hold-up has been made. Basing on conservation of mass to make balance caculation of gas-liquid-solid three-phase flow, the flotation column gas hold-up caculation formula has been achieved. On this basis, making force balance of mineralization bubble as a starting point, the relationship between the bubble size and the factors of circulating pressure, circulating flow, liquid-phase surface tension has been emphatically discussed. Combined with the factors analysis such as gas-phase volume flow, processing capacity and flotation recovery, the gas hold-up relationship model mathematical expression basing on working parameters has been got. Then make this mathematical expression single-factor change. Through fair-faced water experiment and mineral separation experiment the expression has been verified and it has been found out that the results caculated using expression are the same with experiment results. Then the regulation strategies has been discussed basing on gas hold-up analysis caculation. By analyzing flotation dynamics, the basic idea of gas hold-up regulation can be confirmed as follow: making flotation index as the final goal, through comprehensive regulation of the factors of frother dosage, circulating pressure and inflating volume, the gas hold-up regulation strategy with core of expert regulation system, feedforward of feed properties, feedback of parameter test quantity has been proposed.Finally, the separation experiments combined with Dahongshan copper ore have been carried out to strengthen flow-chart control and gas hold-up regulation. The results show that the index of concentrate grade 25.25%, recovery 93.39% has been achieved using flotation column one-coarse-one-regrade flow-chart in the situation of raw ore grade 0.72%, and the recovery is 0.97 percent point which is higer than that of flotation machine. separation experments have achieved flotation column gas hold-up contrallable and adjustable successfully, which is an important orientation for mineral separation process regulation and will promote the development of column short-flow separation regulation techonolgy greatly.