The interfacial properties, flotation behavior and suspension rheology of coal and pyrite systems: The influence of various reagents

Coal constitutes an important commodity in the United States, used mainly by electrical utility and iron and steel industry. However, the electrical utility industry needs high-quality coal, which requires cleaning in order to increase the coal calorific content, reduce transportation costs, reduce the size of scrubbing facilities and meet government regulations on sulfur emission (0.5 kg/GJ). Therefore, the objective of the research undertaken for this investigation was to study the separation of coal from pyrite by using new reagents to inhibit the flotation of pyrite by modifying the hydrophobicity of pyrite and regulating the aggregative stability of the coal-pyrite system.;For this purpose, how a new family of reagents (designated as TEPA, IESA, S-CMIU and TMAE) affected the interfacial properties and flotation behavior of Arizona pyrite and three different high-sulfur bituminous coals (Illinois No. 6, Pittsburgh No. 8 and Upper Freeport PA) and the rheology of slurries of Pittsburgh No. 8 coal was studied in detail. Bulk characterization of coal and pyrite included chemical and mineralogical analyses. Surface characterization included determination of the wettability behavior, electrokinetic potentials and Hallimond tube flotation response. Wettability was assessed by means of contact angle and induction time measurements in the absence of reagents. Bulk characterization and wettability studies indicate that the hydrophobicity of the coals follows the order:;Bench-scale flotation tests of coal weathered and nonweathered, using a standard flotation method, were performed in single stage, two stage, and release analysis and tree analysis procedures. These tests showed that the separation efficiency decreases as the time of weathering increases. Furthermore, the two-stage flotation results indicated that for the three coals, this family of pyrite depressants increased the pyritic sulfur rejection up to 9% over the results obtained in the absence of pyrite depressants.;The effect of additives on the aggregative stability of Pittsburgh No. 8 coal and pyrite system was studied through rheological and flocculation measurements. The rheological studies included the effect of particle size, equilibration time, solid-liquid ratio, and the effect of certain experimental variables and procedures, with and without additions of reagents. Flocculation studies included relative sedimentation volume and size distribution of flocs. The results of both rheological and flocculation studies showed that TEPA, IESA and S-CMIU disperse the system, whereas TMAE first flocculates the system and then redisperses upon higher additions of the reagent.