Evaluation of peat and lignite phenanthrene sorption properties in relation to coal petrography: The impact of inertinite

The relationship between phenanthrene sorption properties and petrography of low rank organic particles was investigated to aid in understanding sorption mechanisms, and confirm the previously observed impact of inertinite. Sorption experiments, using phenanthrene as the model organic chemical, were conducted on peat and lignite, of matrix and xylite-rich lithotypes, that have significant differences in inertinite content. Both peat and lignite samples display non-linear isotherms described by the Freundlich model. In general, the sorption isotherm linearity decreases from peat to lignite, and lignite samples show higher sorption capacities (Kfr = 4.2 × 104–4.5 × 105) than peat (Kfr = 8.4 × 103–3 × 104). Regression analysis applied to the maceral data and sorption parameters showed a strong correlation between inertinite and the variability of isotherm non-linearity. This correlation implies the significant impact of oxidized tissues to the heterogeneity of sorption sites. Moreover, the organic carbon normalized sorption coefficient (Koc), at low phenanthrene concentrations, is related to the inertinite content, as well as to the organic carbon content (on dry, ash-free basis). The degree of inertinite effect on sorption (at low Ce) is higher in lignites than in peat or better, that it increases for samples with increasing organic carbon content (on dry, ash-free basis). This probably suggests that the inertinite content could be a measure of sorption non-linearity and affinity only among samples that have undergone common humification and/or coalification pathways.