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SUMMER 2019 - ERICA, KRISTINE, KLAUDINE, ANA AND SRDJAN

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GREENGO LAB

Green engineering, soil remediation and water protection

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RESEARCH

Our research interests are at the crossroads between the oil&gas, environmental and chemical engineering sectors. They encompass green process engineering, soil remediation, water treatment, colloid, polymer, emulsion and interface science.
For our full publication list, please visit our google scholar profile (https://scholar.google.com/citations?user=NOWkqbsAAAAJ&hl=en&oi=ao)

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December 2019

Reversible double water in oil in water (W/O/W) emulsions were developed to contain subsurface hydrocarbon spills during their remediation using surfactant flushing. Double emulsions were prepared by emulsifying CaCl2 solutions in canola oil, and subsequently by emulsifying the W/O emulsions in aqueous sodium alginate solutions. The formation of double emulsions was confirmed with confocal and optical microscopy. The double emulsions reversed and gelled when mixed with the surfactants sodium dodecyl sulfate (SDS) and cocamidopropyl betaine (CPB). Gels can act as ‘emulsion locks’ to prevent spreading of the hydrocarbon plume from the areas treated with surfactant flushing, as shown in sand column tests. Shear rheology was used to quantify the viscoelastic moduli increase (gelation) upon mixing the double emulsion with SDS and CPB. SDS was more effective than CPB in gelling the double emulsions. CPB and SDS could adsorb at the interface between water and model hydrocarbons (toluene and motor oil), lowering the interfacial tension and rigidifying the interface (as shown with a Langmuir trough). Bottle tests and optical microscopy showed that SDS and CPB produced W/O and O/W emulsions, with either toluene or motor oil and water. The emulsification of motor oil and toluene in water with SDS and CPB facilitated their flow through sand columns and their recovery. Toluene recovery from sand columns was quantitated using Gas-Chromatography Mass-Spectroscopy (GC-MS). The data show that SDS and CPB can be used both for surfactant flushing and to trigger the gelation of ‘emulsion locks’. Ethanol also gelled the emulsions at 100 mL/L. (K. Lamont, A. Marangoni, and E. Pensini. "‘Emulsion locks’ for the containment of hydrocarbons during surfactant flushing." Journal of Environmental Sciences (2019).)

Multiple emulsions for soil remediation

November 2019

Switchable double emulsions (water in oil in water, W/O/W) are proposed for the in situ immobilization of subsurface organic contaminants such as toluene, hexane or benzene. Primary W/O emulsions were prepared by emulsifying 250 mL of 0.36 M CaCl2 aqueous solutions in 1 L of canola oil (with 12.5 g/L of ethylcellulose, EC, and 2.5 g/L of calcium stearate). In the primary W/O emulsion the water droplets in oil were ≈8 μm, as observed using an optical and a confocal microscope. EC and calcium stearate adsorbed at the oil water interface (as demonstrated by interfacial tension measurements), forming films which stabilized the W/O emulsions (as verified with bottle tests). Experiments conducted using a Langmuir trough suggest that EC and calcium stearate films did not desorb from the oil-water interface upon compression. Crumpling tests and optical microscopy observations indicate that EC and calcium stearate films were skin-like, and buckled when deformed. To obtain double W/O/W emulsions the primary emulsions were emulsified in a 0.75 wt% solution of sodium alginate, with 2 mL/L of Tween 20 and 10 g/L of NaCl. The formation of W/O/W emulsions was verified through optical microscopy and confocal microscopy observations. In the absence of the contaminants the double emulsions were stable, as observed by resting them on the bench over three days and agitating them with a multi-action wrist shaker for 30 min. Also, they had low shear elastic (G′ = 2.67 ± 0.58 Pa) and viscous (G″ = 1.69 ± 0.24 Pa) moduli, which should facilitate their transport through geological media (e.g. soil) to polluted areas. Upon mixing with toluene, hexane or benzene at concentrations ranging from 5% to 17%, the double emulsions were destabilized. Emulsion destabilization caused the release of CaCl2, which crosslinked sodium alginate and formed gels in which the contaminants were incorporated. The gelation rate and the magnitude of the viscoelastic moduli depended on the contaminant type and concentration, and on the mixing time. Gelation occurred fastest with the highest toluene concentrations tested (9% to 17%), but the highest elastic moduli were measured with 9% toluene concentrations for the longest mixing times tested (90 s). Gelation occurred slowest with hexane, likely due to the poor solubility of EC in hexane. Because of their ability to gel exclusively in contaminant proximity, the double emulsions studied offer a potential strategy to control the migration of plumes of contaminants such as toluene, hexane or benzene. (Lamont, Kristine, Erica Pensini, and Alejandro Marangoni. "Gelation on Demand Using Switchable Double Emulsions: A Potential Strategy for the In Situ Immobilization of Organic Contaminants." Journal of Colloid and Interface Science (2019))

Lecithin gels

August 2019

Natural sorbents for the removal of a free toluene phase from water were made using lecithin, food-grade oils (canola, sunflower, safflower and corn oil) and water, or lecithin, hydroxystearic acid (HSA) and canola oil, or lecithin, HSA and soy wax. Lecithin (5 g), food-grade oils (5 mL), and water (5 mL) formed emulsions, in which clusters of water droplets were dispersed in oil, as probed using confocal microscopy and cryo-scanning electron microscopy (cryo-SEM). These emulsions were gel-like, with shear elastic moduli (G’) greater than the shear viscous moduli (G”). Emulsion gels obtained with lecithin, canola oil and water could absorb up to 47% (volume based) of toluene freely floating on deionised water in 20 h. G’ increased from 1621 ± 203 Pa to 6372 ± 168 Pa upon mixing with up to 20% of toluene (volume based), and decreased to 2130 ± 376 Pa and to 846 ± 60 Pa with 33% and 47% toluene (volume based), respectively. However, the gels remained cohesive enough to be recovered from water even with 47% toluene, facilitating it removal. The gels lost instead cohesiveness with 67% of toluene. Similar trends were observed with all other food-grade oils used and in the presence of CaCl2 salt. With 35 g/L NaCl and 33% toluene gels less cohesive than with DI or CaCl2 salt. Optical microscopy showed that lecithin formed thick, heterogeneous films at the oil-water interface in the absence of toluene. Toluene addition to lecithin in canola decreased the interfacial tension (as probed with the pendant drop method), rendered the lecithin interfacial films homogeneous and improved the miscibility between the oil and the water phase, as observed through confocal microscopy. Toluene addition also affected the lamellar swelling of lecithin bilayers, which were studied using Wide and Small Angle X-ray Scattering (WAXS and SAXS). Addition of HSA or HSA and soy wax to the emulsion gels increased their shear viscoelastic moduli before and after mixing with toluene. Gels comprised of HSA (0.5 g), lecithin (4.5 g), canola oil (2.5 mL) and water (5 mL) or of HSA (0.5 g), lecithin (3 g), soy wax (1.5 g) and water (5 mL) could absorb approximately 10 mL of toluene (i.e. 67% of the lecithin gel volume) in 20 h. Addition of HSA also increased the cohesiveness of gels with toluene and 35 g/L NaCl. (Safieh, Peter, Erica Pensini, Alejandro Marangoni, Kristine Lamont, Saeed Mirzaee Ghazani, Nukhalu Callaghan-Patrachar, Michaela Strüder-Kypke, Fernanda Peyronel, Jay Chen, and Braulio Macias Rodriguez. "Natural emulsion gels and lecithin-based sorbents: A potential treatment method for organic spills on surface waters." Colloids and Surfaces A: Physicochemical and Engineering Aspects 574 (2019): 245-259)

Cr(VI) trap and treat

February 2019

Guar, xanthan and carboxymethyl cellulose sodium salt (CMC), and the reducing agent sodium thiosulfate were used to produce water-based fluids to trap and reduce Cr(VI) to Cr(III) in the subsurface. Before mixing with Cr(VI) and sodium thiosulfate, 1 wt. % guar and CMC formed viscous fluids, whereas 1 wt. % xanthan formed weak viscoelastic fluids. Upon contact with Cr(VI), the viscoelastic moduli of the fluids increased significantly. Gelation was immediate for guar and occurred after ∼20 min and ∼180 min for xanthan and CMC, respectively. The compressional strength of gelled guar-based fluids increased with increasing pH and decreased with salts, but was significant in all water chemistries tested. Once Cr(VI) was reduced to Cr(III) by sodium thiosulfate, it crosslinked xanthan, guar and CMC. The fast gelation of guar-based fluids after contact with Cr(VI) suggest that they may form barriers around Cr(VI) contaminated zones, preventing its migration during reduction to Cr(III). (Siwik, Amanda, Erica Pensini, Abdallah Elsayed, Braulio Macias Rodriguez, Alejandro G. Marangoni, and Christopher M. Collier. "Natural guar, xanthan and carboxymethyl-cellulose-based fluids: Potential use to trap and treat hexavalent chromium in the subsurface." Journal of Environmental Chemical Engineering 7, no. 1 (2019): 102807)

Effect of elasticity on particle suspensions

March 2019

Composite fluids are comprised of particles and polymers and are used for fracking and the in‐situ treatment of subsurface contaminants. This study investigates the correlation between the shear viscoelasticity of guar aqueous solutions and their effectiveness in suspending sand, which is a common fracking proppant. In the absence of a crosslinker, the shear viscous modulus (G”) of 5 g/L guar solutions was greater than the shear elastic modulus (G’). When the crosslinker borax was added, the guar solutions behaved as yield stress fluids (G’ > G”). Sand was well‐suspended in the crosslinked guar solutions but settled in non‐crosslinked fluids. Similar results were obtained with fenugreek gum. This study also investigates the correlation between particle settling and the effect of particle addition on the rheology of the fluids. Granulated activated carbon (GAC) particles are utilized to remediate polluted sites and were used as model particles. Guar and xanthan effectively suspended the GAC. Anionic polyacrylamide effectively suspended the GAC but not after soaking in sodium dodecyl sulphate. Zetag 8167 did not effectively suspend the GAC. The addition of 10 g/L of GAC did not affect the shear rheology of the fluids that suspended them, but decreased the shear viscoelastic moduli of the polymeric fluids that could not suspend them. (Pensini, Erica, Braulio Macias Rodriguez, Alejandro G. Marangoni, Christopher M. Collier, Abdallah Elsayed, and Amanda Siwik. "Shear rheological properties of composite fluids and stability of particle suspensions: Potential implications for fracturing and environmental fluids." The Canadian Journal of Chemical Engineering)

February 2020

Phosphorus released in lakes due to agricultural water runoff causes eutrophication, deteriorating water quality and harming ecosystems. Two adsorbents were studied for the removal of phosphate from water: plaster of Paris powder and hydrogel beads produced using alginate, carboxymethylcellulose, and aluminum. The reaction kinetics, adsorption capacity, and ability to desorb were compared. Sorption of phosphate with either plaster of Paris or hydrogel beads was well described by the Langmuir model. In deionised water, hydrogel beads had a maximum sorption capacity of 90.5 mg PO43-/g dry bead with an equilibration time of approximately 24 hours. Monovalent anions (e.g. chloride) did not affect phosphorus sorption onto hydrogel beads, whereas divalent anions (e.g. sulfate) hindered sorption. In deionised water, plaster of Paris (POP) powder has a maximum capacity of 1.52 mg PO43-/g with an equilibrium time of less than 10 minutes. Sorbents can potentially be reused following phosphate desorption, and desorbed phosphate may be reused as fertilizer. At pH=9.5, hydrogel beads desorbed up to 60% of the original amount of phosphate sorbed, and lower amounts at lower pH. At pH=2, POP powder desorbed only 35% of the initial phosphate sorbed, and desorption decreased with increasing pH.

Reference: Malicevic, S., Garcia Pacheco, A.P., Lamont, K., Estepa, K.M., Daguppati, P., van de Vegte, J., Marangoni, A.G. and Pensini, E., 2020. Phosphate removal from water using alginate/carboxymethylcellulose/aluminum beads and plaster of Paris. Water Env. Res.)

Alginate based sorbents remove copper and zinc from water!

High concentrations of heavy metals in groundwater are harmful to humans and ecological receptors. This study uses natural alginate-based sorbents for the removal of heavy metals (e.g., copper, zinc, iron, and nickel) from water. The effectiveness of alginate-based sorbents was enhanced by adding calcium bentonite clay and by tuning the porosity of the sorbents. Controlled porosity was obtained by an acid base reaction, using sodium carbonate and acetic acid. The maximum sorption capacity of alginate-based sorbents was 127.9 ± 0.6 mg/g and 148.1 ± 0.2 mg/g for Cu(II) and Zn(II), respectively. The sorption of Zn(II) onto the sorbents followed pseudo first-order kinetics (k1 = 9.71 × 10−3), indicating that the rate limiting step was the diffusion of Zn(II) into the sorbents. In contrast, the sorption of Cu(II) onto the sorbents followed pseudo second-order kinetics (k2 = 5.80 × 10−5), indicating that the rate limiting step was chemisorption of Cu(II) into the sorbents. Optical microscopy images of the sorbent cross-section showed pore shrinking following sorption of either Zn(II) or Cu(II), due to crosslinking of alginate by these metal ions. Cu(II) diffusion into the sorbents was further demonstrated by blue discoloration (as shown by images of their cross sections) and by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Intraparticle diffusion plots of both Zn(II) and Cu(II) showed that the sorption process begins with surface adsorption and is followed by the rate controlled step of intraparticle diffusion. Alginate-based sorbents could also be used to effectively remove other divalent ions (e.g., Ni(II)), whereas removal of trivalent ions (e.g., Fe(III)) was less effective.

Reference: Hood, C. and Pensini, E., 2022. Alginate-bentonite clay composite porous sorbents for Cu (II) and Zn (II) removal from water. Water, Air, & Soil Pollution, 233(4), p.137.

Field trials were conducted a worked well!

Amphiphiles separate miscible pollutants and water (current key research)

For more details and a full publication list on the topic, please review Erica Pensini's Google Scholar profile.

 

Our most recent manuscript describes the phase behaviour of ternary mixtures:

Bartokova, B., Marangoni, A.G., Laredo, T., Stobbs, J., Mezaros, P. and Pensini, E., 2023. Effect of Hydrogen Bonding on the Mixing Behaviour of Ternary Aqueous Mixtures. Journal of Molecular Liquids, p.122124.

Abstract:

This study correlates the solution behaviour of an aqueous mixture to hydrogen bonding between its three components (water, liquid Pluronic L31 and either tetrahydrofuran, THF or dimethyl-sulfoxide, DMSO). Pluronic L31 is miscible in either THF, DMSO or water, but separates from ternary mixtures, at specific solvent to water ratios. Water species can either donate a single (SD) or two hydrogens (DD), and accept a single (SA) or two (DA) hydrogens, depending on the other components in the mixture. This is reflected in the OH stretch band, as probed using attenuated total reflectance-Fourier transform infrared spectroscopy. Pluronic L31 and THF both compete for hydrogen bonding with DD-DA, with up to 30% THF (v/v, relative to water), where separation occurs. Above 30% THF, Pluronic L31 and THF do not compete for the same water species and mix freely. Pluronic L31 separates from DMSO-water mixtures with 10–80% DMSO. Competition for similar water species explains separation up to 50% DMSO. Above 50% DMSO, we must also consider two-way interactions between all components. At low DMSO concentrations, DMSO mainly interacts with water trough the SO group, while methyl groups from DMSO can interact with Pluronic L31. At higher DMSO contents, the methyl groups of DMSO interact more markedly with water. The second derivative of the νasCH3 peak displays a split with ≤ 50% DMSO, which disappears at higher DMSO percentages. The four peaks in the second derivative of the of the νasCH3 peak correlate to the interactions between DMSO and the four water species.

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University of Guelph, 50 Stone Road E., Guelph (ON), Canada

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