Analyses on thermal stability of lignites and its derived humic acids

Abstract

ABSTRACT The thermal stabilities of humic acids (HAs) are critical for its effective utilization and relate closely with raw lignites. Thus, this work is to study the relationship of thermal stability between lignites and its derived HAs using Thermogravimetry – Fourier Transform Infrared Spectroscopy (TG-FTIR) and Differential Scanning Calorimetry Measurement (DSC) techniques. The TG-FTIR results indicated that the intensities of peaks from the evolution gases (H2O, CO2, CO, CH4) during thermal treatment of Zhaotong lignite (ZL) and its derived HAs (denoted as ZLHA) are higher compared with the Mile lignite (ML) and its derived HA (denoted as MLHA). TG-FTIR and DSC measurements of lignites showed that the thermal stability of ML is better than that of ZL, and the more oxygen containing functional groups existed in ZL. Similarly, the results indicated that the contents of oxygen containing functional groups of ZLHA are higher than that of MLHA. On the other hand, DSC experimental data showed that the MLHA has smaller peaks on the DSC profiles, which showed that MLHA has longer aliphatic chain and less oxygen containing functional groups. Briefly, the results obtained from TG-FTIR and DSC measurement are consistent. The thermal stabilities of HAs are highly associated with the physicochemical property of raw lignites.