Fluorescing macerals in South African coals

Abstract

Maceral, microlithotype and fluorescing maceral content were analysed along with the vitrinite relative fluorescence measurements. Thirty samples from the South Africa Soutpansberg, Waterberg and Main Karoo Basins were investigated. These results were also compared with previously measured vitrinite reflectance values. The application of fluorescence techniques has allowed the identification of much higher liptinite content (about 5%) as compared with the results of routine maceral analysis in white light. Results presented provide an explanation of this difference, which is caused by difficulties in identifying fine liptodetrinite particles under illumination by the halogen lamp. Therefore, detritic particles of uncertain affinity should be verified under fluorescing light during routine maceral analysis. The presence and intensity of the fluorescing vitrinite in South African coals were also studied. The occurrence of this component is connected with the rank of coal but could be also affected by the facies (sample no. B 35) and in situ coal oxidation (sample no. B 3). The relative fluorescence intensity of vitrinite depends on the rank of the coal but also on its degree of oxidation. It seems also to be connected with the expulsion of oil which enhances its intensity. The influence of the fluorescing macerals content on some coal properties was proved by the positive correlation between fluorescing vitrinite as well as sum of fluorescing macerals and calorific value (0.66 and 0.74 corr. coeff., respectively). This proves the necessity of fluorescence application in routine maceral analysis carried out for coal quality evaluation.