| Although China is rich in coal resources,the coking coal and other scarce coal aremore and more less. Aiming at the separation problem of high ash refractory fineslime scarce coal, researchers seek surface modification, efficient mixing, highmineralization, new technology and equipment to improve the flotation effect, and toimprove the flotation concentrate yield. Ultrasonic pretreatment is an effective meanof pHysical conditions, This paper studies the effect of ultrasonic cavitation onflotation efficiency in details. and also its effect on coal, chemicals and pulp system,to reveal the strengthening mechanism of ultrasonic pretreatment on coal flotation,and to provide theoretical guidance for the industrial application of flotationultrasonic pretreatment technology.First of all, the structure, rock characteristics and mineral occurrence form of thecoking coal of one coal preparation plant are studied in this paper. Using a series ofmodern analysis methods, for example, coal maceral analysis, X-ray diffractionanalysis, SEM analysis, ect., to characterize the properties of the samples. The resultssuggest that the maceral content has great difference in raw-coal and cleaning coal. Inthis raw coal, the content of organic component is about93.4%, while the inorganiccomponent is about6.73%. The inorganic component is mainly clay such askaolinite.In addition, also contains a large amount of sulfide, and the contents are3.77%and2.96%respectively.Use ultrasonic of different powers to deal with pulp, Analysising the flotationeffect, It shows that clean coal ash after treatmented changed little than before, butthe yield is increased by about17.9%. Along with the time growth, the cleaned coalyield increases first and then decreases, achieves the best effect in3~4min. So we findthat over treatment is disadvantageous for flotation. Compare three kinds of ultrasonicflotation systems, use ultrasonic treat the pulp with collectors, the effect of flotation isbest.Analysis the effect of ultrasonic pretreatment on coal surface properties, theSEM analysis shows that ultrasonic pretreatment has cleaning and denudation effecton the surface of coal particle, removing the mineral adhere to the surface of coal,denudating the oxide layer on the surface of coal particle, enhancing the surfacehydropHobic. These results are consistent with the analysis of contact angle. Infrared analysis showes that oxygen containing functional groups on coal surface afterultrasonic treatmented reduced. The XRF analysis shows that Al、Si and otherelements in the oxide form content decrease.To sum up that ultrasonic cavitationcangenerate mechanical effect，clean the coal particle surface,denudate the oxidelayer; O radicals generated by cavitation interact with pHenolic, alcohol, ether, esterin coal, generate CO2and H2O. On the other hand, the mechanical effect of ultrasoniccavitation removes some minerals in coal samples, which also led to an increase in theporosity of coal, the result is consistent with the BET analysis. Ion chromatograpHyresult shows that ultrasonic cavitation can dissolve minerals in coal to ore pulp.Analysis the effect of ultrasonic pretreatment on collector, the result shows thatdiesel oiladsorption on coal surface reduced after ultrasonic treatment. The adsorptionability to the surface of coal of diesel oil of the same volume is enhanced, observingthe distribution of diesel oil after treatmented, the result shows that the oil droplets aremore decentralized and stable. Oil droplet size decreases about50%than that beforetreatment. The ultrasonic cavitation makes the diesel have better adsorption anddispersivity.Analysis the effect of ultrasonic pretreatment on the slurry system, the resultshows that the oxygen content in pulp reduced after ultrasonic treatment, the pulp PHincreased, this is caused by OH and H free radicals generated by cavitation. Alsoslurry temperature rises, this is caused by the collapse of cavitation bubbles makingpulp overall warming. In addition, there are a lot of microbubbles on the coal particlesurface in the pulp after ultrasonic treatment, This is because microbubbles nuclei inslurry separate in the sound field, and it is conducive to the bubble mineralization.In order to find the optimal ultrasonic flotation conditions, design orthogonal test,using the ultrasonic conditions and flotation process as the factors, the combustiblerecovery and perfect degree asindex, to find theoptimal combination of ultrasonicflotation conditions. Analysising the flotation results of ultrasonic treatment, the resultshows that the clean coal yield is71.13%, the ash content is8.65%, the combustiblerecovery is82.24%, the perfect degree is53.84%, The coal production can beincreased by68.9milliom t, increasing economic benefits about seventy millions.Diesel can be saved62.5t, having significant effect. |
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