Chemical, spectral and morphological characterization of humic acids extracted and membrane purified from lignite

Abstract

In this study, humic substances were extracted from lignite of Zarand coalfields, Kerman, Iran, using a stirred batch reactor. A membrane ultrafiltration system was used to purify humic acids (HAs) from lignitederived alkaline extracts obtained from the reactor. Gravimetric analysis along with several analytical methods including CHNOS, UV-Vis, FT-IR, ICP-OES and SEM were utilized to investigate the characteristics of the purified HAs. Gravimetric analysis showed that the purity of HA purified from membrane concentrated humates was higher than 95 %. CHNOS elemental analysis indicated the higher stability and condensation degree of the purified HA compared to the commercially available HAs. The ratios of E4/E6, E2/E3, and ΔlogK obtained from UV-Visible spectroscopy revealed that a purified HA had a higher molecular weight, aromaticity, and humification degree in comparison with commercial HAs. Furthermore, the peaks observed in the FT-IR analysis showed that HA had an aromatic structure. The very low concentrations of heavy metals and inorganic element contaminants observed by ICP-OES spectrometry showed a proper performance of the HA membrane purification. These results along with the results of SEM analysis showed the acceptable characteristics of purified HA from the lignite coal for agricultural and industrial applications.