| Flotation is one of the methods to purify heavy metal wastewater from beneficiation and metallurgy,in which micro bubble and stable flotation environment are the key to determine the flotation efficiency of heavy metal wastewater.Oscillatory air supply bubble generation through micropores is a high-efficiency and static bubble forming technology,which shows great potential in the purification of heavy metal wastewater.However,the size of the bubble is still significantly larger than the diameter of the micropore when it is desorbed from the micropore,and the longitudinal coalescence is the main reason for the large size of the final bubble.Oscillatory air supply is a new micro bubble forming technology in recent years.It changes the traditional continuous air supply mode and produces bubbles through micro hole cutting,which reduces the bubble size.However,through high-speed dynamic system observation,it is found that the bubble size of oscillatory air supply is still significantly larger than the pore size,and there is still a serious vertical coalescences phenomenon.In view of this,this paper proposes to optimize the micro bubble aerator(orifice plate thickness,orifice diameter and cavity volume)to drive the bubble desorption in advance,and increase the transverse shear micro flow field to reduce the bubble merger under the condition of oscillatory air supply,forming the oscillatory air supply-shear micro bubble forming technology,Research on flotation purification of heavy metal wastewater was carried out.Firstly,the results show that the bubble size is directly proportional to the volume of the air chamber under the condition of fixed oscillating air supply frequency of 60 Hz and valve on/off time ratio of 0.2 in a single cycle.When the volume of the air chamber is reduced from 200 m L to 5 m L,the bubble diameter is reduced from 1695?m to 1087 ?m,and the bubble diameter is reduced by 55.9%.The bubble diameter has a nonlinear relationship with the thickness of the orifice plate,and the hole diameter is increased When the thickness of the orifice plate is 0.1 mm,the bubble diameter is the smallest.Further reducing the thickness of the orifice plate will lead to the increase of the bubble diameter.The bubble size is proportional to the micropore diameter.When the micropore diameter is reduced from 140 ?m to 20 ?m,the bubble diameter is reduced from 1327 ?m to 852 ?m,but the decrease of the orifice diameter will increase the capillary resistance in the channel and reduce the bubble forming efficiency.Therefore,it is necessary to choose the appropriate pore size which can ensure the bubble size and bubble efficiency at the same time.Secondly,the experimental study of transverse shear micro flow field based on oscillatory air supply shows that providing shear micro flow above the micropore can differentiate the rising path of bubbles,thus significantly reducing the axial coalescence of bubbles.When the shear velocity increases from 0.083 m/s to 0.28 m/s,the number of vertical bubbles coalescence decreases from 8 to 0,and the bubble diameter decreases from 890 ?m to 482 ?m.Compared with the single oscillating air supply,the bubble diameter decreases by 45.8%;At the same time,it is found that the bubble diameter does not increase significantly with the increase of air velocity.When the air velocity increases from 4 L/min to 20 L/min,the bubble diameter only increases by20.1%,which indicates that the oscillating air supply-shear flow bubble forming technology can not only reduce the bubble size,but also improve the bubble forming efficiency.Finally,the experimental study on flotation purification of heavy metal wastewater containing copper ions shows that the average diameter D50 is 53.3 ?m.The ions removal rate of single flotation based on oscillating air supply-shear flow foaming is 98.64%.The results show that the oscillating air supply-shearing microporous foaming method is a relatively static and efficient flotation technology for the purification of heavy metal wastewater. |
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