Fracking is an enhanced oil recovery technology, which uses viscoelastic fluids (fracking fluids) to fracture oil reservoirs and to transport sand within the fractures, to prop them open. This technology enables oil recovery from scarcely permeable formations. Fractured formations release saline water over time. This saline water (called “produced water”) is discarded rather than used to produce fracking fluids because it can decrease fracking fluid viscosity. Nonetheless, it would be advantageous to use produced water to reduce freshwater consumption and wastewater production. Our study analyzes the effect of chloride salts (CaCl2, MgCl2, and Fe­(III)­Cl) and of sulfate salts (MgSO4 and FeSO4) at different concentrations (0.05–1 M) on the viscosity of aqueous guar solutions. All chloride salts tested increase the viscosity of guar solutions in the concentration range analyzed and promote the formation of small guar aggregates. At 0.05 M concentrations, MgSO4 has effects similar to chloride salts. In contrast, 1 M MgSO4 decreases the viscosity of guar solutions. FeSO4 also decreases the viscosity of aqueous guar solutions, at either 0.05 or 1 M concentrations. The decrease in viscosity of guar solutions is attributed to large guar aggregate formation (as opposed to a cohesive network). Sodium cocoyl glutamate (SCG) increases the viscosity of non-cross-linked guar solutions and the shear viscoelastic moduli of guar solutions cross-linked with sodium tetraborate. Specifically, SCG restores the viscosity of guar solutions with MgSO4 and increases it above values measured in deionized (DI) water in the presence of MgCl2. Attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy shows that hydrogen bonding was more significant in guar + SCG + 0.7 M MgCl2 samples than in guar + SCG + 0.7 M MgSO4, indicating that the formation of a hydrogen-bonded network was correlated to high viscosity. ATR-FTIR also indicates that MgSO4 weakened hydrogen bonding of water clusters, whereas SCG restored it, enabling guar hydration even in the presence of MgSO4. Our study highlights which salts are most problematic (e.g., FeSO4) and proposes a potential additive (SCG) to enhance the viscosity of guar in the presence of selected salts (e.g., magnesium salts) by promoting hydrogen bonding.

Corrosion in carbon steel units of chemical, petrochemical and oil and gas plants poses safety and economic concerns. The goal of our study is to investigate the corrosion inhibition effectiveness of an environmentally benign surfactant, namely sodium lauroyl lactylate (SLL), in comparison to sodium cocoyl glutamate (SCG) and sodium dodecyl sulfate (SDS). The corrosion of carbon steel in 1 M HCl was markedly inhibited by 0.05 and 0.1 M of the anionic surfactant SLL, as determined from weight loss over 96 h, at ambient conditions. X-ray photoelectron spectroscopy (XPS) showed that SLL adsorbed at the carbon steel surface, forming a protective film that decreased corrosion. Scanning electron microscopy (SEM) showed that carbon steel surfaces immersed in 1 M HCl for 96 h had an etched appearance without SLL, whereas they retained their smoothness with 0.1 M SLL. Electrochemical impedance spectroscopy (EIS) measurements confirmed that SLL passivated carbon steel surfaces, markedly increasing the polarization resistance R p from ≈95 to ≈20,694 Ω cm 2 over a 12 h period. In contrast, without SLL, R p decreased from ≈92 to ≈12 Ω cm 2 . These results demonstrate for the first time that the environmentally friendly surfactant SLL is an efficient corrosion inhibitor in extreme environments such as 1 M HCl solutions. Dissimilar to SLL, SCG and SDS were not effective in inhibiting corrosion.

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Co-contamination by organic solvents (e.g., toluene and tetrahydrofuran) and metal ions (e.g., Cu2+) is common in industrial wastewater and in industrial sites. This manuscript describes the separation of THF from water in the absence of copper ions, as well as the treatment of water co-polluted with either THF and copper, or toluene and copper. Tetrahydrofuran (THF) and water are freely miscible in the absence of lauric acid. Lauric acid separates the two solvents, as demonstrated by proton nuclear magnetic resonance (1H NMR) and Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy (ATR-FTIR). The purity of the water phase separated from 3:7 (v/v) THF:water mixtures using 1 M lauric acid is ≈87%v/v. Synchrotron small angle X-Ray scattering (SAXS) indicates that lauric acid forms reverse micelles in THF, which swell in the presence of water (to host water in their interior) and ultimately lead to two free phases: 1) THF-rich and 2) water-rich. Deprotonated lauric acid (laurate ions) also induces the migration of Cu2+ ions in either THF (following separation from water) or in toluene (immiscible in water), enabling their removal from water. Laurate ions and copper ions likely interact through physical interactions (e.g., electrostatic interactions) rather than chemical bonds, as shown by ATR-FTIR. Inductively coupled plasma—optical emission spectrometry (ICP-OES) demonstrates up to 60% removal of Cu2+ ions from water co-polluted by CuSO4 or CuCl2 and toluene. While lauric acid emulsifies water and toluene in the absence of copper ions, copper salts destabilize emulsions. This is beneficial, to avoid that copper ions are re-entrained in the water phase alongside with toluene, following their migration in the toluene phase. The effect of copper ions on emulsion stability is explained based on the decreased interfacial activity and compressional rigidity of interfacial films, probed using a Langmuir trough. In wastewater treatment, lauric acid (a powder) can be mixed directly in the polluted water. In the context of groundwater remediation, lauric acid can be solubilized in canola oil to enable its injection to treat aquifers co-polluted by organic solvents and Cu2+. In this application, injectable filters obtained by injecting cationic hydroxyethylcellulose (HEC +) would impede the flow of toluene and copper ions partitioned in it, protecting downstream receptors. Co-contaminants can be subsequently extracted upstream of the filters (using pumping wells), to enable their simultaneous removal from aquifers.