ADSORPTION OF ORTHO-CRESOL FROM AQUEOUS-SOLUTION ON COAL

The adsorption of o-cresol, which is commonly used in coal flotation as frother. on two lignites and a bituminous coal has been studied. Coal samples used for the adsorption experiments were: fresh; oxidized; demineralized: demineralized then oxidized. The oxidation processes were conducted by dry (in air at 100, 150 and 200-degrees-C) and wet (with 15% H2O2) methods. The extent of the coal oxidation was quantified by determining the amounts of the two principal oxygen-containing functional groups, carboxylic and phenolic. in the coal samples. The UV spectrophotometric technique was used for the analysis of o-cresol in solution. The adsorption for the lignites was found to increase by oxidation. but to decrease by demineralization, implying that o-cresol is adsorbed by hydrophilic interactions at the coal surface. In contrast, for the bituminous coal, the adsorption was increased by demineralization while it was decreased by slight oxidation. indicating that the adsorption occurs predominantly through hydrophobic interactions between the frother molecule and the coal surface. However, further oxidation of the bituminous coal resulted in an increase in the extent of adsorption in comparison with the fresh coal sample. Among the coal samples used, the adsorption on the bituminous coal samples conformed to the Langmuir equation, and adsorption free energies for these samples were found to be in the range -22.6 to -29.3 kJ mol-1.