INFLUENCE OF THERMAOOXIDATIVE TREATMENT ON THE SURFACE-PROPERTIES OF ANTHRACITE

The chemical nature of oxidized anthracite, obtained by oxidation with air of Bulgarian anthracite at different temperatures was studied by EPR spectroscopy, C-13 NMR solid state, EPR and chemical methods. The X-ray analysis reveals that the oxidation process is confined to the s urface of the particles and does not cause considerable change in the internal structure of the material. The C-13 NMR solid state data show that up to 200 degrees C no change occurs in the anthracite compositi on. Only at 300 degrees C the oxidation process leads to noticeable ch anges, which become considerable at 400 degrees C. The C-13 NMR spectr oscopic data reveal an increase in the amount of the oxygen-containing groups with acid character after oxidation of anthracite at 400 degre es C. EPR investigations show that oxidation of anthracite with air to 300 degrees C does not change the EPR parameters. It was found that t he decrease of PMC concentration up to 400 degrees C depends on format ion of stable acid oxygen-containing groups, which cannot be removed i n the conditions of deep vacuum. The C-13 NMR and EPR data were confir med by determination of oxygen-containing groups on the oxidation anth racite surface with chemical methods. It was found that a thermooxidat ion treatment with air at 400 degrees C leads to considerable enhancem ent of the quantity of oxygen-containing groups on the anthracite surf ace. These groups were mainly of acidic character and variable chemica l nature and have different dissociation strength in aqueous suspensio n. The pH of oxidized at 400 degrees C anthracite is 4.3. (C) 1998 Els evier Science Ltd. All lights reserved.