Improvement In Floatability Of Weathered Coal By Attrition Pretreatment

In this paper, coal was naturally weathered to obtain weathered coal with differentweathering degree. Effect of weathering on industrial properties, size distributio n,density distribution, surface structure, physicochemical properties and floatability ofcoal were studied. The reason for reduction in floatability by weathering was discussed.Moreover, surface attrition and grinding pre-treatment were applied to improvefloatability of weathered coal. Main research contents and conclusions are as follows:Compared with industrial analysis, size distribution, density distribution betweenraw coal and weathered coal, we found that the coal ash content increased, but volatilecontent and the fixed carbon content slightly decreased. In addition, size distribution ofcoal had much less variation after weathered, but ash content of every size fractionsignificantly increased. After weathering process, density distribution of coal changedobviously, however wash ability almost unchanged.Surface physicochemical properties between raw coal and weathered coal weredetailed analyzed. During weathering process, the coal grain surface became muchrougher, many cracks and ravines generated, and even much clay minerals adhered onheavy weathered coal surface. After weathered, the carbon content on coal surfaceobviously decreased, oxygen content significantly increased. Moreover, large quantitiesof hydrophilic oxygen-containing functional groups such as C-O, C=O, O=C-Oproduced on weathered coal surface. Meanwhile, the contact angle of coal decreasedand wettability increased. Flotation results showed that clean coal yield andcombustible matter recovery significantly decreased. And the floatability significa ntlyreduced after weathering process.Surface attrition pre-treatment were employed to improve floatability of weatheredcoal with different weathering degree. Meanwhile, distance between stator and rotor,pulp concentration and attrition time were explored to study their influence onimprovement in floatability of weathered coal. Through surface attrition, grain size ofweathered coal decreased slightly, but floatability of mild weathered coal waseffectively improved. After surface attrition, flotation clean coal yield and combustib lematter recovery of mild weathered coal approached to a level of original coal Moreover,the ash content of flotation product just increased slightly. However, flotation clean coalyield and combustible matter recovery of heavy weathered coal had less increment aftersurface attrition pre-treatment. Grinding pre-treatment was applied to further improve floatability of heavyweathered coal. Effect of feed quantity, pulp concentration and grinding time on sizedistribution and flotation of heavy weathered coal was explored. Experimental resultsshowed that grinding pre-treatment could reduce coal grain size obviously. Moreover,floatability of heavy weathered coal was improved effectively. Clean coal yieldincreased by30.59%and the combustible matter recovery increased by34.52%aftergrinding treatment.Currently, faced with increasing energy shortage and environment issue, effect ofweathering on reduction in coal floatability was studied in this paper. Moreover, surfaceattrition and grinding pre-treatment was applied to improve weathered coal flotatio nand reached some ideal results. It is significant for development and utilization ofweathered coal.