Surface properties of photo-oxidized bituminous coals. Technical progress report, October--December 1995

During this report period, polished blocks of coal containing 3--4 mm wide vitrain bands were prepared for contact angle measurements of fresh and photo-oxidized surfaces using the advancing-drop technique. Contact angles were measured on two of the coals collected for this study, (the Ohio No. 4a (DECS-33) and Lower Kittanning (PSOC-1562) seams) and the results added to those presented in the last quarterly report. Although the new data give additional variation to the sample set, they are consistent with the original observations, i.e., that contact angle is influenced by irradiation time and coal rank. Using the maximum change in contact angle measured between fresh and photo-oxidized surfaces, a linear decrease is observed with increasing rank resulting from 5 and 10 minutes of irradiation. The magnitude of the decrease in contact angle diminishes with increasing rank. Also during this period, an ultraviolet spotlight was evaluated as a means of irradiating powdered vitrain. This 100 watt, long wavelength (366 nm) ultraviolet lamp is to be used in place of the optical microscope system to establish the influence of surface photo-oxidation on the flotation characteristics of vitrain concentrates. A series of experiments was designed to determine the magnitude of change in the luminescence intensity (at 600 nm measured in the optical microscope) with exposure to the ultraviolet light with time for vitrinite from different rank coals. The authors have established that there is a significant decrease in luminescence intensity with time of exposure which diminishes slightly as rank increases. The ultraviolet light appears to provide a level of photo-oxidation that is a factor of 10 lower than that obtained with their optical microscope system