Removal of Ash Contents from Coal by Flotation.

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The removal of ash contents from coal has been investigated by a flotation method which differs from a conventional flotation method in that ash contents are floated and coal is remained in the suspension.The results obtained are as follows :Clay minerals such as kaolinite, dickite, pyrophillite and sericite which are main constituents of ash contents of coal could be effectively floated by sodium oleate as a collector at pH above 11.5 after calcium activation.Pressure flotation experiments using kerosine as a collector showed that ash content of Dah Torng coal from China was more significantly decreased than those of Horonai, Taiheiyo and Goonyella coals. From this result, Dah Torng coal was chosen as a sample of this investigation.Flotation experiments of Dah Torng coal using sodium oleate as a collector and calcium chloride as an activator showed that ash content of sink(coal concentrate) decreased at pH about 11.5, but 40-60 % of coal was floated.Then, various reagents were tested in order to depress flotation of coal. Starch depressed ash contents as well as coal. Polyoxyethyleneoctylphenylether (HS-210, manufactured by Nippon Oil & Fats Co.,) had a slight effect on coal depression. Polyvinyl alcohol showed the most selective depressing action for coal among reagents tested in this investigation. But, satisfactory result could not be obtained, i.e., ash content of coal concentrate(sink) was about 5 % and coal recovery was about 80 %.