Oil sands coke was activated with CO2 at 900°C in a tubular fixed bed reactor. Samples activated in a CO2 stream with 50% air contained a significant number of functional groups. Some activated samples were post-oxidised in air at 350°C to increase their surface functionality. Post-oxidation was necessary for the adsorption of ferric cations by the coke samples activated, except for the sample activated with 50% air. However, non-oxidised samples were also able to adsorb molybdate anions. Both organic and inorganic constituents of oil sands tailings water were successfully removed, but some inorganic species leached into water.