Selective adsorption of anionic polyacrylamide onto ultra-low ash coal and kaolinite

Abstract

To study the selectivity of polyacrylamide in the selective flocculation flotation of fine coal, the adsorption of anionic polyacrylamide (PAM A401) onto ultra-low ash coal and kaolinite was studied, including the adsorption thermodynamics, floc size distribution and wettability changes. The thermodynamics of the adsorption process at the low concentration of 0-16 mg/dm of PAM A401 were studied at different contact times, doses, temperatures and pH values. Thermodynamic parameters of ΔG, ΔH, ΔS and Ea were evaluated to understand the nature of the adsorption process. The results indicated that PAM A401 was selectively adsorbed onto ultra-low ash coal rather than kaolinite. Physical adsorption was the predominant mechanism, and the adsorption of PAM A401 at 12 mg·dm-3 onto coal was 2.15 times larger than the adsorption on kaolinite. After the adsorption of PAM A401, the lipophilic hydrophilic ratio (LHR) of coal decreased from 9.23 to 7.28, indicating that the coal became less hydrophobic than before. In contrast, the LHR of kaolinite increased from 1.44 to 1.65. Floc size measurements showed that the d10, d50 and d90 of coal flocculated by PAM A401 (at 12 mg/dm , pH 6.5) were 3.18, 2.76 and 2.59 times of the corresponding levels of these parameters for kaolinite floc, respectively. Moreover, the efficiency index of the selective flocculation flotation (PAM A401 2 g/Mg) increased by 5.43 percent compared with the efficiency index of conventional flotation of fine coal.