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In order to study the selectivity of flocculant between coal and kaolinite in selective flocculation floatation, the adsorption isotherm and adsorbance difference of polyacrylamide onto kaolinite and coal was investigated. The laser particle size analyzer was used to measure the floes size distribution of coal and kaolinite in different polyacrylamide solution. Hydrodynamic radius and adsorption radius of polyacrylamide molecular were calculated to discuss its adsorption conformation. The adsorbance of anionic polyacrylamide onto coal is higher than that of kaolinite. The adsorbance difference between coal and kaolinite decreases with the increase of polyacrylamide molecular weight. The adsorbance of cationic polyacrylamide onto kaolinite is higher than that of coal, and the adsorbance difference is lower. Selectivity of anionic polyacrylamide with molecular weight 3x106 is the best. Adsorption process of coal and kaolinite is more accord with Langmuir adsorption model. The coal adsorbance of this polyacrylamide is 2.15 times larger than that of kaolinite. The indicators of particle size distribution, d10, d50 and d90 of coal floes are 8.42, 2.60 and 2.75 times of kaolinite floes, respectively. The calculated adsorption radius of polyacrylamide molecular is lower than its hydrodynamic radius. When different polyacrylamide is absorbed onto different mineral surfaces, the effect of compression or penetration with different intensity of polyacrylamide occurres. [ABSTRACT FROM AUTHOR]