Effect of acid treatment on volltmetric swelling ratios of coals

To remove Ca2+ ions, six low rank coals and one coking coal were treated wi th 0.1 and 1.0 N HCl for 24 h. IR spectra and proximate analysis of the lig nites indicated that only slight structural changes had occurred during aci d treatment. The swelling ratios of parent and acid-treated coal samples sh owed that removal of Ca2+ resulted in an increase in the swelling ratios. H igher swelling ratios were obtained with acid-washed coal samples. While th e highest swelling ratios of the parent lignites were obtained in ethylened iamine, those of acid-treated samples were obtained in pyridine and dimethy lformamide.