| The research presented in this thesis demonstrates that NAs removal from OSPW using PC is an adsorption on carbon process. Both the Langmuir and Freundlich isotherms fit the experimental data reasonably well. For typical NAs concentrations in OSPW of 60 mg/L, the adsorption capacity averaged about 0.26 mg NAs/g PC. Consequently, for water treatment applications, the adsorbent would need to be used at percentage level concentrations. This is in contrast to commercially available activated carbons, which are generally applied at concentrations in the 1 to 200 mg/L range. The kinetic adsorption profiles offered an excellent fit using a second order rate model (r2 = 0.9998). Furthermore, the process is biphasic. Initially, the adsorption rate is fast but the overall rate of removal is ultimately governed by a slower diffusion controlled mechanism. The pH value of the OSPW is also a major factor controlling the extent of adsorption. When the pH of OSPW is lowered to values of about 5.9, there are significant improvements in the overall removal of NAs. A noteworthy change in OSPW quality following PC treatment was increased concentrations of vanadium. A portion of the vanadium present in the PC matrix leaches upon initial contact with OSPW. However, long-term contact between OSPW and PC---such as in an OSPW saturated PC deposit---tends to slowly remove vanadium from the aqueous phase. The removal mechanism is suspected to be an adsorption process. Vanadium leaching was more pronounced at higher pH values. Therefore, lowering the pH of OSPW using a weak acid such as carbon dioxide not only facilitates NAs adsorption but also helps mitigate vanadium leaching. Preliminary experiments indicate formal steam activation increases the PC surface area and markedly improves NAs adsorption. Because, the activation process increased the solubilization of vanadium by approximately an order of magnitude, practical applications using steam activated material could be limited. Fortunately, at SCL's integrated oil sands production facility, explicit formal activation is not necessarily required to exploit the water treatment properties of the material. |
