| landlords and causes water pollution,air pollution,and geological disasters.The unburned carbon content in fly ash is the main quality indicator affecting its resource utilization,and the removal of unburned carbon is the key to fly ash utilization.Flotation is currently the main way to decarbonise fly ash,but traditional flotation has problems such as fine fly ash feed particles,poor hydrophobicity of the unburned carbon surface,and poor stability of the flotation foam.In recent years,nano-bubble flotation has become a hot topic in the field of froth flotation,and nano-bubble flotation can significantly enhance the flotation of fine-grained minerals and is suitable for enhanced fly ash flotation decarbonisation.In this study,the composition,particle size,and morphological analysis of fly ash specimens were first investigated using fly ash from a thermal power plant in Shandong as a representative mineral sample.The study showed that the LOI of the fly ash sample was 16.90%,and the particle size was mainly distributed between 10-80μm.The surface of the fly ash unburned carbon was loose and porous,with glassy spheres adhering to the surface.The presence of these substances affected the hydrophobicity of the unburned carbon surface and was detrimental to the recovery of unburned carbon during flotation.The effect of nanobubbles on the decarbonisation of fly ash flotation was then systematically investigated and the optimum nanobubble fly ash flotation conditions were determined by response surface methodology.Finally,the mechanism of nanobubbles affecting fly ash flotation and decarbonisation was investigated through nanobubble concentration determination,particle adhesion experiments,surface tension determination,and froth stability determination.The experimental study of nano-bubbles and conventional bubble column flotation of fly ash showed that the presence of nano-bubbles could enhance the efficiency of fly ash flotation and decarbonisation under different parameters of frother dosage,collector dosage,air flow rate,feed rate,froth layer thickness,and wash water rate.Under the same flotation conditions,nanobubbles can increase fly ash recovery by 5%-10%,increase carbon removal rate by 3-15%and reduce tail ash loss on burn by 0.20%-2.50%.Nanobubble flotation effectively achieves the removal of unburned carbon from fly ash and also reduces the amount of flotation agents used.Using the Box Behnken test statistical analysis method to design and study the effect of operating parameters such as foaming agent dosage,collector dosage,aeration speed,ore feeding speed,foam layer thickness and flushing water speed on the condition of 8%solid concentration in the ore feeding,The influence of fly ash flotation decarburization,the determined optimum nano-bubble fly ash flotation conditions are the amount of diesel oil 1950 g/t,the amount of secondary octanol 2150 g/t,the gas filling speed of the flotation column is 1 L/min,and the ore feeding speed is 0.9 L/min,flushing water speed0.1 L/min,foam layer thickness 17 cm.Under optimal conditions,the predicted tailing loss on ignition and carbon removal rate were 2.53%and 87.30%,respectively.The actual test obtained a good index of tailing loss on ignition of 2.57%and carbon removal rate of 86.97%.Basically consistent with the predicted results.The nano-bubble concentration test,zeta potential test,particle-bubble adhesion test,mineral surface-bubble interaction test,froth stability test,and surface tension test were used to investigate the mechanism of nano-bubble-enhanced fly ash flotation:firstly,the nano-bubble concentration and zeta potential was tested by nano-particle tracking analyzer and zeta potential analyzer,and it was clear that the nano-bubble concentration and zeta potential of the nano-bubble generator used in the experiment can effectively produce nano-bubbles.The hydro-cavitation nano-bubble generator can effectively produce nano-bubbles with a concentration of 9.11*10~7nano-bubbles/m L at a cavitation time of 5 min;the size of the nano-bubbles produced also decreases with the increase of the frother dosage.Secondly,by using a high-speed camera to photograph the adhesion of the bubbles to the mineral particles and using Image J software to analyse the images and an interaction force test system to test the interaction between the bubbles and the mineral surface,it is clear that the presence of nano-bubbles promotes hydrophobic agglomeration of fine particles of unburned carbon,thus increasing the average apparent size of the fine particles in the slurry and increasing the probability of collision and adhesion between the particles and the bubbles.The presence of nano-bubbles also increases the interaction between the mineral surface and the bubbles,increasing the adhesion area between the unburned carbon particles and the bubbles.The presence of nano-bubbles also increased the interaction force between the mineral surface and the bubbles,increasing the adhesion area between the unburned carbon particles and the bubbles.Finally,the stability of the bubbles and the surface tension was tested by a dynamic foam analyser and a surface tension meter,respectively. |
PDF Full Text Request