Regulation Of Flotation Froth Stability And Emoval Of Unburned-carbon From Coal Fly Ash

The content of unburned carbon in coal fly ash is one of the most important indexeswhen the ash is used as construction materials. Currently, flotation is still the main approachto remove unburned carbon from the ash due to its resource characteristics. However,comparing with the flotation of usual ores, there are still some technical problems as “thepoor flotability of unburned carbon and the lack of the good froth stability” for the process ofunburned carbon removal, and this brings the huge challenge to the traditional flotation. Forthe above reasons, the conception about removal of unburned carbon based on the regulationof froth stability was raised in the paper. The foam structure, foam decay and stabilitymechanism were studied in the paper in order to get potential methods which can improvethe froth stability of the carbon removal flotation system.The composition of coal fly ash and froth behavior of unburned carbon removalflotation system were studied at the beginning of the paper, and the research idea in whichthe unburned carbon removal is intensified by the improvement of froth stability was made.The idea was carried out in the following three main lines: studying the foam or frothstability from the aspects of foam structure and decay mechanism, studying the froth stabilityon the basement of foam stability mechanism, studying the key technologies to unburnedcarbon flotation removal by combining the froth stability mechanism and flotation process.The structure of liquid foam was observed by the methods of microscopic analysis onthe basement of classical foam structure theory. The two drainage processes in the foamwhich result in the foam decay were analysed in theory, and the important result about “if thefoam structure factors is stability, and the foam will be stability” was obtained in the researchprocess. Specific phenomenon was captured and observed on the foam observation systemwith core of high-speed digital camera and microscope.The bubble coalescence observation system and the bubble size measurement systemwere set up respectively. The effects and function mechanism of surface tension andinterfacial elasticity on bubble generation, coalescence and foam stability were studied. Themicroscopic coalescence process of the two adjacent bubbles was observed by the high-speed and microscopic method. Studies show that: the stranger the surface activity of thefrother, the higher the value of interfacial elasticity, and the longer the bubble macroscopiccoalescence time, and the foam formed in the corresponding system will be more stability.The microscopic coalescence time of the two adjacent bubbles is at the level of tens ofmilliseconds, and the coalescence bubble present a phenomenon of “expanding andcontracting” like an elastic body in the process. The viscosity of the liquid was regulated by the addition of water soluble highmolecular polymer, and the effects of liquid viscosity on foam ability and stability werestudied. The cooperative effect of frother and viscosity regulator on the interfacial elasticityand foam stability was also revealed based on the above studies.The particle behavior of hydrophobic and hydrophilic minerals in froth was studied bythe design of drainage experiments. The results indicates that the hydrophobic particles existin the froth by the means of adhering on the bubble surface, the hydrophilic particles exist inthe plateau borders and vertexes of froth by the means of entrainment in the water fluid andwill be discharged with the drainage water.The effects of the typical composition in coal fly ash on the froth of unburned carbonflotation removal system were studied systematically, and the effect of the carbon particleswith different flotability on froth stability was also studied. The results demonstrated that theadhesion of hydrophobic particles on the bubble surface enhances the mechanical strength ofthe froth films. For the different kinds of carbon particles, the bigger the value of contactangle, the stranger the capability of stabilizing the froth. For the same kind of carbonparticles in different size, the smaller the particle size, the stranger the capability ofstabilizing the froth. The stabilization function of typical hydrophilic particles in coal fly ashon the froth was limited, but the slime (-74μm92.53%) settled in the sedimentation pond ofunburned carbon flotation removal plant can stabilize the froth to some extent, and thisfinding is of great importance to the industrial practice of unburned carbon flotation removal.The experiments on the choice of collector, frother and viscosity regulator wereconducted in the laboratory scale. Combining the theory study and the practice of unburnedcarbon flotation removal, some key technologies were summarized as follows: the separationintensification due to the use of flotation reagents as strong collector and viscous frother,micro-bubble generation technique based on column flotation and the water circulationmodel with a role of returning the slime to the flotation system. High-efficiency flotationtechnique with the characteristic of stabilizing froth was developed. A cleaning ashproduction line with a handling capacity of800thousands tons per year was built up. Losson ignition of the cleaning ash produced on this line was under3%, which can be provided tohigh-end building material markets.