Adsorption of single-ring model naphthenic acid from oil sands tailings pond water using physically activated petroleum coke

摘要

Petroleum coke-derived activated cokes were prepared and used for the adsorptive removal of a single-ring naphthenic acid (NA) from synthetic oil sands process affected water (OSPW). CO2 activation produced carbon with a larger mesopore volume fraction (0.67) than steam activation (0.25). Interestingly, prolonging the activation time of CO2 from 6 to 9 h led to a simultaneous increase in specific surface area (276-405 m(2)/g) and mesopore volume (0.51-0.67). Furthermore, a positive relationship was found between the pseudo-second-order kinetic rate constant and the mesoporous volume of the activated coke. This suggests both the importance of pore size on kinetics and the fact that physical activation with a reagent such as CO2 may be better suited than chemical activation due to its ability to create mesopores. Although enlarging the pores and accelerating the adsorption rate, post-oxidation had detrimental effects on adsorption capacity, resulting in a decrease in equilibrium adsorbed amount from 115 to 34 mg/g, a 70% decrease, when post-oxidized with O-2, due to the negative charge of oxygen-containing functional groups. On the other hand, the measured adsorption capacity increased by over 60% when activated coke was treated with ammonia, a result of the positively charged nitrogen-containing surface groups. Finally, in real OSPW, the activated coke had a much lower capacity for total acid-extractable organics than for the model NA. Therefore, activated petroleum coke may not be the best choice for treating raw tailings pond water and may be better suited for polishing.

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