Adsorbents for the Removal of Naphthenic Acids from Oil Sands Process Water: Investigation of Reclamation Materials from Surface Mining of Oil Sands and Development of Biochars from Biological Sludge and Peat
Creators: Crominski da Silva Medeiros, Deborah C.
Publisher: name: University of Alberta Library
Year: 2023

<p>Oil sands process water (OSPW) is generated in high quantities during the extraction of the bitumen from the oil sands. Naphthenic acids (NAs) are recalcitrant compounds, corresponding more than 50% of all organics in OSPW. The efficient management of OSPW is of importance to guarantee efficient water reuse or safe discharge of OSPW to compel with the aggressive timeline on OSPW reclamation. This thesis investigates the adsorption NAs from OSPW using two types of materials: (1) reclamation materials from the surface mining of oil sands and (2) biochars produced from sludge (municipal wastewater treatment plant) and peat (surface mining of oil sands). <br>
The reclamation materials peat-mineral mix (PT) and Pleistocene fluvial sands from different locations (PF-1 and PF-2) were investigated as adsorbents of decanoic acid (DA) and 5-phenylvaleric acid (PVA) as model NA compounds. Equilibrium of DA and PVA was reached at 2 days for PT, and 3 and 6 days for PF materials, respectively. Maximum adsorption capacities for DA and PVA were, respectively,  16.8 × 103 and 104 mg kg-1 for PT, 142.9 and 81.3 mg kg-1 for PF-1, and 600 and 476.2 mg kg-1 for PF-2. Hydrophobic interactions, hydrogen bonding, and π−π interaction were the main adsorption mechanisms. Desorption of model compounds from post-adsorption materials was not observed for 14 days. Removal of NAs from real OSPW ranged from 20 to 54%. PT is the most promising adsorbent of NAs from OSPW because it partially removed NAs with a wide range of molecular weights and structures at very low dosage. Adsorption of NAs was affected by the total organic carbon of the materials, emphasizing the hydrophobic interaction as an important adsorption mechanism. <br>
Pristine and zinc chloride (ZnCl2)-activated biochars produced from sludge were applied in the adsorption of NAs in real OSPW. By using ZnCl2-activated biochar instead of pristine biochar, the adsorption capacity for total NAs (classical and oxidized species) increased from 2.3 to 26.6 mg g-1, respectively. Abundance of mesopores and oxygen-containing surface groups made the ZnCl2-activated biochar an excellent adsorbent of NAs. The rate of adsorption of NAs from OSPW was fast, reaching equilibrium at 2 h. The adsorption followed pseudo-second order kinetics and Freundlich isotherm. The adsorption mechanisms were pore-filling, hydrogen bonding, and π-π interactions. ZnCl2-activated biochar has higher affinity for higher carbon and double bond equivalency (DBE) numbers, therefore, NAs with more hydrophobic, recalcitrant, and with higher cyclicity characteristics. The spent biochar can be regenerated through thermal regeneration and reused efficiently. Adsorption treatment with activated biochar decreased the concentration of magnesium (7%), calcium (21%), strontium (27%), barium (60%), dissolved organic carbon (63%), and chemical oxygen demand (66%). Reduction of 66% of the acute toxicity towards V. fischeri and 91% of bioavailability of organics was observed after activated biochar treatment.<br>
The effect of type of feedstock (sludge and peat) and the chemical activation (none, FeCl3- and FeCl3+ZnCl2-activated) on the changes in the characteristics of biochar was studied for adsorption of surrogate compounds of NAs and NAs from real OSPW. Higher inorganic fraction of sludge yielded in biochars with higher ash contents than peat-based biochars. After activation, the peat-based biochars presented higher porous properties and O/C ratios than sludge-based biochars. Chemical activation of biochar resulted in the enhancement of some functional groups, such as –OH stretching group and C=C of aromatic rings. The adsorption of NAs from real OSPW was impressive and better than surrogate compounds, in which the pristine biochars removed up to 23% of total NAs. Removal of classical and oxidized NAs surpassed 90% for FeCl3+ZnCl2-activated biochars. The biochar properties were correlated with the adsorption capacities obtained for surrogate compounds of NAs and NAs from OSPW, emphasizing the importance of the mesopore fraction of biochar and H/C ratio in the adsorption.<br>
The study of reclamation materials as adsorbents of NAs contributes to the understanding of the mobility potential of NAs from OSPW on reclamation materials used in oil sands reclamation landscapes. The research on biochars promotes circular economy by presenting efficient adsorbents for NAs in OSPW, reducing the environmental impact associated with waste disposal and allowing the efficient reclamation and reuse of OSPW. Further studies on biochar tailoring should focus on improving the mesopore volume and balancing the hydrophobicity and aromaticity of biochar.</p>