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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]

The poor selectivity and high ash content of clean coal are the prominent issues in fine coal flotation. Wettability is one of the important interface properties affecting the fine coal flotation. Thermodynamic characterization of fine coal and main impurity mineral kaolinite was investigated in this study. Washburn dynamic method was used to study the wetting process of different density level coal samples and kaolinite wetted by n-hexane, 1-bromine naphthalene, formamide and water as liquid molecular probe. Wetting rate and lipophilic hydrophilic ratio (LHR) was calculated by linear regression analysis method. Washburn equation and van Oss-Chaudhury-Good theory were used to estimate the surface free energy components of samples. The results show that n-hexane wetting rate of coal samples decreases with the increase of density level which is slight, but deionized water wetting rate of coal samples increases. The wetting rates of kaolinite wetted by n-hexane and water are 0. 010 1 and 0. 020 6 g²/s respectively, however, they are higher than that of coal samples. The LHR of kaolinite is 1.44 and kaolinite is hydrophilic; the LHR of coal samples increases with the increase of density level. The middle density level coal sample of 1.5-1.6 g/cm³ and 1.6-1.8 g/cm³ with similar wetting rates and LHR values are hydrophobic. Surface free energy polar component γsLW of each density level of coal samples reduces slightly and is all lower than γsLW of kaolinite. Furthermore, the alkaline force of the sample surface free energy polar components, which is of hydrogen bonding interaction, is correlated to LHR value. The results of regressive release flotation test coincides well with the coal sample surface properties. [ABSTRACT FROM AUTHOR]