Roy, Tyler

Naphthenic acids are a major contaminant of concern and a focus of much research around remediation of oil sand process affected waters, OSPW. Using activated carbon adsorbents are an attractive option given their low cost of fabrication and implementation. A deeper evaluation of the effect naphthenic acid structural differences have on uptake affinity is warranted. In this thesis an in-depth exploration of naphthenic acid adsorption onto activated carbon is provided including many more model naphthenic acid species than what have been assessed previously in adsorption studies. Both adsorption kinetics and isotherms at the relevant alkaline pH of OSPW using several different carbon adsorbents with pH buffering to simulate the behaviour of real OSPW were evaluated. Given the time sensitive application of most adsorbents towards treating contaminated waters such as OSPW, achieving fast adsorption rates for model naphthenic acids is an important goal worth considering. Textural properties of activated carbon most conducive for fast adsorption kinetics were assessed using several candidate model species. Clear evidence is presented, demonstrating the influence of both the pore size distribution and particle size of porous adsorbents on uptake rates of naphthenic acids, demonstrating that careful optimization of these adsorbent properties can result in adequate uptake rates. Adsorption isotherms were used to assess model naphthenic acid affinity towards activated carbon. Uptake for the model naphthenic acids varied considerably regardless of the activated carbon used, ranging from 350 mg g-1 to near zero highlighting recalcitrant species. The equilibrium data was explored to identify important structural features of these species and key physiochemical properties that influence adsorption. It was demonstrated that certain naphthenic acids are resistant to adsorption when hydrophobic adsorbents are used. Adsorption isotherm modelling helped explore interactions occurring at the interface between naphthenic acids and adsorbent surfaces. Naphthenic acid hydrophobicity was identified as an importance physiochemical property for achieving high adsorption capacities onto activated carbon. Evidence is also presented that indicates favorable hydrogen bonding between naphthenic acids and surface site hydroxyl groups, demonstrating the importance of adsorbent surface functionality for naphthenic acid uptake. The adsorption mechanism was further explored through use of a thermodynamic analysis of the model naphthenic acid system using activated carbon. Standard state enthalpy and isosteric enthalpy of adsorption values were used to further support the proposed mechanisms occurring between model species and activated carbons. This research highlights the challenges associated with removing naphthenic acids from OSPW through adsorption and identifies how adsorbent surface chemistry modification will need to be used to increase the removal efficiency of recalcitrant naphthenic acid species when using activated carbon.

Author Keywords: Activated Carbon, Isotherms, Kinetics, Modelling, Naphthenic Acids, Thermodynamics