Extraction and characterization of humic acid from coal for the application as dispersant of ceramic powders

Abstract

Subbituminous coal was employed as raw material for the extraction of humic acid (HA) to be applied as ceramic dispersant. The extraction process is described in detail, showing it is a relatively simple procedure, which makes the production attractive and feasible on a laboratory scale. The HA was characterized via elemental analysis, infrared spectroscopy (FTIR), thermal behavior (TGA/DTA), zeta potential, turbidity and microstructure by scanning electron microscopy (SEM). Carboxylic and phenolic groups were identified and consequently the structure and surface properties were related to the polyelectrolyte nature of HA. The absence of complex-forming metals was confirmed by FTIR and TGA. The alkalization increased the negative surface charges as verified by the higher zeta potential. SEM analysis showed an extended pattern of molecules; therefore the HA can perform with maximum steric effect at pH 11. HA is a good dispersant for the ceramic industry according to the results of the rheological investigation in an alumina suspension. The decrease of the suspension viscosity using HA was significant and the values are compatible to those necessary to ceramic processing. The data of the characterization of HA correlated well with the parameters achieved in the rheological tests.