Gravimetric Quantification of Hydrophobic Fulvic Acids in Lignite Material Using Acetone

Abstract

This study evaluated the gravimetric quantification of fulvic components in lignite material. The current standard method considered only components soluble in both alkali and acid solutions and adsorpted to a hydrophobic resin (DAX-8) at pH 1, identified as hydrophobic fulvic acids (HFA). HFA were desorpted using 0.1 M sodium hydroxide (NaOH) and run through a cation exchange resin (IR-120) to remove Na ions. HFA were quantified gravimetrically, including ash corrections. Steps involving IR-120, however, resulted in a large volume of analytical solution and a significant time of analysis, which became a disadvantage of this method. A modification to this method was proposed by replacing NaOH with acetone to desorpt HFA from DAX-8. IR-120 was not required, and a smaller volume of analytical solution was produced. Gravimetric, Fourier transform infrared (FTIR), and ionic analyses were completed in this study. Both standard and modified methods resulted in the presence of hydrophobic neutrals within the quantification of HFA. Acetone at 50% strength produced HFA results corresponding to those of NaOH. An adequate regeneration of DAX-8 was achieved using the modified method but not with the standard method. The modified method produced higher ash contents, but they did not affect its accuracy. This method significantly reduced the overall analytical time. This study showed the potential of acetone as a desorpting agent in the gravimetric quantification of HFA in lignite material.