Characterization of the humic acid isolated from Thar coal mines, Sindh, Pakistan

Abstract

Pakistan is rich with 185 billion tons of coal reserves in all provinces but as fuel coal’s rank is poor because excessive ash, evaporative contents, sulfur and wetness, these coals fall in the category of lignite to sub-bituminous rank but lignite make the largest share of coal which is rich with significant amount of humic acid that upgrade the agricultural topsoil for increasing Pakistan’s crop production. The objective of this study was to investigate the larger extraction and characterization of humic acid from low rank coal of Thar (Sindh Province). Respective coal samples were initially oxidized with 2% HNO3 and then treated with 1.0, 2.5, 3, and 3.5% NaOH solutions for the extraction of humic acid. The 3.5% concentration of NaOH was found to be the optimum for the extraction of humic acid. The extracted humic acid was investigated for its quantitative assessment through UV-Vis spectrophotometer procedure. The humic acid determined by UV-Vis spectrophotometry was 32.23%. FTIR analyses of extracted humic acid samples have shown the presence of carboxylic, phenols, alcoholic, amines and ethers functional groups. Zeta potential analysis of humic acid was -20.3 mv, negative value indicating the larger number of negative ions than positive. In XRD analysis of humic acid samples the major peak was obtained at 44.727170. The results of the study could be useful for selection of suitable coals for humic acid extraction.