Surface properties of photo-oxidized bituminous vitrains

The principal aim of this research was to determine whether correlations could be established among surface oxygen functionality, hydrophobicity induced by photo-oxidation, and measurements of fluorescence alteration. Polished surfaces of vitrain bands were photo-oxidized using a blue-light flux and then changes in surface properties were measured. The data obtained reveal significant variations depending upon the level of surface oxidation. There is a progressive and significant increase in the amount of near-surface oxygen concentration which appear to lower the hydrophobicity as shown by contact angle measurements. Although this influence diminished as coal rank increased, the level of oxygen uptake was about the same, suggesting that the type of oxygen functionality formed during oxidation may be of great importance in modifying surface hydrophobicity. Changes in functional-group chemistry showed a general increase in the concentration of carbonyl-containing groups while those of CH2 groups decreased. All of these observations follow the trends observed in previous investigations of naturally weathered coals. The photo-oxidation technique also resulted in the development of phenolic, ester and anhydride moieties instead of the expected emplacement of carboxylic acid groups which are normally associated with naturally weathered coals. Increase in the concentration of esters and anhydrides would be expected to result in a more hydrophobic surface, the opposite of what was actually encountered. (c) 2004 Elsevier B.V. All rights reserved.