| The entrainment of gangue minerals during coal flotation process is the main reason that restricts the quality of flotation concentrate.How to reduce the entrainment of gangue minerals and ash content of concentrate has been a hot topic.In this paper,the polyethylene oxide is chosen as the flocculating agent.The flocculation laws between coal and quartz are investigated under different shear rates and flow field distributions to explore the optimal flow field conditions for selective flocculation of quartz.At the same time,flotation experment was carried out under the selected flow field condition to verify the correctness of flocculation law.The main findings are as follows:When coal or quartz was flocculated individually,and the proportion of coal and quartz floccules decreased with the increase of shear rate during the formation process of floccules.The floccules proportion of coal or quartz reached a maximum when the shear rate was 25 s-1.The destroy process of floccules indicates that the floccules of quartz formed at any shear rate can not be destroyed ful y.However,the floccules of coal have different performances which formed at different shear rates.The coal floccules which formed at shear rate of 25s-1 could not be destoryed ful y at any high shear rate which we choosed.The one which formed at shear rate of 29s-1 were destoryed at 56 s-1 ful y.And when the coal floccules were formed at shear rate of 36 s-1 were destoryed at 49 s-1 and 56 s-1 ful y.At the same shear rate,the destructive effect on the two types of floccules was improved due to the addition of the baffle,which reduced the minimum shear rate 56 s-1 to 49 s-1when the floccules of coal was formed at the shear rate of 25 s-1.The calculation of the properties of the micro vortex shows that the size of the micro vortex gradually decreases with the increase of the shear rate,and the speed of the micro vortex gradually increases,which improves the effect of destroying the floc.When the shear rate of coal flocculation test is 49 s-1 and 56 s-1,the minimum vortex size is 24.32μm and 22.79μm,and the micro vortex velocities are 0.037 m/s and0.040 m/s,respectively.The the computational fluid dynamics was used to simulate the flow field in the stirred tank,and the influence of baffle on the velocity field distribution in the stirred tank was explained.The addition of baffle made the velocity gradient distribution in the stirred tank more rational,resulting in more microeddies the shear rateThe chord length distribution during the mixed flocculation experiments indicates that a large amount of floccules were still presented in the pulp after the destroy of high shear rate.The particle visual observation system shows that the floccules formed by the coal particles has been almost destroyed at action of the flow field.And the method of particle size distribution was used to determine the proportion of mixed floccules during the mixed flocculation process:the proportion of non-idea floccules was 3.87%which were formed at a shear rate of 29 s-1 with the baffle while the floccules were destroyed at a shear rate of 49 s-1;the proportion of non-idea floccules was 2.35%which were formed at a shear rate of 29 s-1 with the baffle while the floccules were destroyed at a shear rate of 56 s-1,while.The results of the selective flocculation flotation tests which with baffle show that the flotation flotation test is better than the conventional flotation without PEO when the minimum vortex size was 24.32μm.There are 46 figures,7 tables and 97 references in the thesis. |
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