Carbohydrate-Modified Microgels as a System for Extracting Naphthenic Acids from Tailings Pond Water

Abstract: Northern Alberta houses massive tailings ponds, that store aqueous waste as a result of the processes employed to recover bitumen from the oil sand deposits. The aqueous waste, or tailings pond water (TPW), houses numerous toxic chemicals including naphthenic acids (NAs) - a complex group of naturally occurring hydrophobic organic acids that can have adverse and even irreversible effects on their surrounding environment. The Lowary group has shown that methyl mannose polysaccharides (MMPs) have a high binding affinity for NAs, while the Serpe group has demonstrated that poly(N-isopropylacrylamide) (pNIPAM)-based micro-particles have a high binding affinity for organic molecules in general. Our research group has been developing a unique class of microgels for the removal of NAs from TPW by utilizing pNIPAM-based porous micro-particles and incorporating unmethylated and methylated derivatives of long-chained saccharide(s)-amines. Several pNIPAM-based microgels coupled or polymerized with a series of carbohydrates have been developed and their effectiveness to treat TPW was monitored using Microtox bioassay toxicity tests and Fourier-transform infrared spectroscopy (FT-IR). According to the Microtox data the carbohydrate-modified microgels have only a marginal effect treating medium fine tailings (MFT) and the top recyclable tailings water layer. However, FT-IR analysis shows that few carbohydrate-modified poly(N-isopropylacrylamide)-co-acrylic acid (pNIPAM-co-AAc) microgels lower NAs concentration in MFT: pNIPAM-co-50 % AAc-di-mann-octylamine shows the best performance by decreasing the NAs concentration within a similar range as the standard sorbent: powdered activated carbon (PAC). Overall, PAC shows the best performance treating MFT according to both Microtox bioassay and FT-IR analysis.