Surfactant Optimization for PFAS Removal in Site Groundwater Using Colloidal Gas Aphrons ( CGAs )

The instability of colloidal gas aphrons (CGAs) in aquifers is one of the major obstacles influencing the remediation efficiency of CGAs-flushing. In this study, hydrophobic nano-SiO2 (HN-SiO2) was utilized to enhance the stability of CGAs. The batch experiments were carried out to investigate the effect of hydrogeochemical conditions on the stability of HN-SiO2 stabilized CGAs in aquifers, such as ions, pH, and nitrobenzene (NB); 2-D tank experiments designed with various injection velocities and medium particle sizes were conducted to determine the factors influencing the migration of CGAs in the aquifer; and 1-D column experiments were established to evaluate the remediation efficiency of HN-SiO2 stabilized CGAs flushing for NB removal. The results indicated that HN-SiO2 had a favorable effect on the stability of CGAs, which enhanced the half-life of CGAs from 328 to 1,050 s. HN-SiO2 particles formed a shell film on the gas-liquid interface of CGAs to slow down the gas escape and drainage velocity. The stability of CGAs decreased while pH<6 or pH>8, whereas this was enhanced with the addition of 0.1 wt.% NaCl. The 2-D tank experiments demonstrated that the HN-SiO2 stabilized CGAs had better stability when they flowed in aquifers compared to sodium dodecyl sulfate (SDS) CGAs. The fine medium and high injection velocity facilitated CGAs forming the larger radius remediation area. The injection pressure was inversely proportional to the medium grain sizes, whereas directly proportional to the injection velocities. In addition, column experiments demonstrated the remediation efficiency of HN-SiO2 stabilized CGAs (81.7%) flushing for NB removal was higher than that of SDS CGAs (61.4%) flushing. Therefore, in comparison with SDS CGAs, HN-SiO2 stabilized CGAs were more efficient reagents for NB removal. CGAs-flushing technique using HN-SiO2 stabilized CGAs is feasible to remedy the contaminated aquifers.

Mechanistic insight into the colloidal gas aphrons stability in the presence of petroleum hydrocarbons

De-oiling characteristics and mechanism of oil-bearing sludge cleaned by CGAs

Study on high-temperature resistance, salt calcium resistance of environment-friendly colloidal gas aphron drilling fluid

Formation and stability of colloidal gas aphron based drilling fluid considering dynamic surface properties

Colloidal gas aphrons (CGAs) are applied in pollutant removal due to their large specific surface area and high surface activity. The structure and properties of the prepared CGAs were investigated in the process of oil removal from oily sludge. The prepared CGAs had a liquid film thickness was 5-10 μm with high stability. CGA interfacial tension was as low as 3.157 mN/m. Then it was found that the oil removal rate of CGAs was higher than that of chemical treatments, showing that CGAs could increase the mass transfer surface area and provide additional attachment sites for pollutants, enhancing the oil removal. The treatment conditions of the oil removal were optimized through response surfaces, showing that under optimal treatment conditions, the oil removal rate of oily sludge reached 96.07%. Additionally, the interaction between surfactant concentration and temperature was the most significant of all of the influencing factors. The behavior and mechanism of CGAs in the cleaning process of oily sludge were further investigated using an inverted fluorescence microscope, SEM, FTIR, and two-dimensional fluorescence spectrometer, showing that pollutants transferred from the liquid film surface of CGAs to the inside the film, and CGAs could specifically adsorb negatively charged organic compounds and aromatic hydrocarbons. The results show that CGAs achieved liquid membrane solubilization. Many negatively charged organic compounds and aromatic hydrocarbons are adsorbed onto the CGAs liquid membrane surface via electrostatic and hydrophobic interactions and then migrated to the hydrophobic layer of the CGAs liquid membrane due to the distribution effect, thus enabling rapid pollutant migration between solid and liquid phases.

This study examines the basic properties of colloidal gas aphrons (CGAs) that are relevant to their applications in soil and groundwater decontamination. Results of experiments on the applicability of CGAs in the removal of organics from aqueous solutions and in the subsurface environment are presented. CGAs are dispersed microbubbles in an aqueous surfactant solution. When introduced into an aqueous system, CGAs undergo variation in sizes and numbers with time due to coalescence and/or creaming. To address the dynamic changes in the size, a particle size analyzer was utilized to characterize the suspension. An increase in the concentration of surfactant was found to increase air entrapment and the stability of the CGA suspension but reduced mean diameter of the dispersion. The study also revealed that CGA characteristics were influenced by the ionic nature of the surfactant. CGAs were utilized in a flotation process to remove pentachlorophenol (PCP) from an aqueous solution. The removal of PCP by CGAs generated from a cationic surfactant was found to be higher than that generated from anionic surfactant. However, the removal of PCP was found to be influenced more by air entrapment and the diameter of the suspension, than the charges on the encapsulating film. When compared with conventional flotation techniques used by other researchers, CGA flotation was found to be superior. 1-D solute transport and mixing were studied with CGA suspension and aqueous solution in packed sand columns. The breakthrough curves for both the solutions showed early breakthrough and tailing. Mobile-immobile model (MIM) was able to describe the solute transport in columns by both aqueous solutions and CGAs. For aqueous solutions the dispersivity was found to increase with the length of the column due to "scale effect". However, in case of CGA suspension the dispersivity was seen to reduce with the column length. Gamma ray densitometry was utilized to determine the mobility of the CGAs in soil columns. The gas saturation profile was found to be influenced by the concentration of the surfactants and the properties of the porous media.

Colloidal gas aphrons (CGAs) offer some advantages in improving oil recovery, but resin and asphaltene deposition problems still occur in CGA flooding. Based on this phenomenon, a new modified colloidal foam system is developed by incorporating a modifier in CGA preparation. The results indicate that the modified CGAs prepared by adding foaming agent sodium dodecyl sulfate (SDS) (concentration: 5 g/L) and GXJ-C (a CGAs modifier from a light fraction of petroleum; concentration: 0.1 g/L) attained the best performance. Oil displacement experiments show that modified CGA flooding had a better effect than water or CGA flooding. There are two important mechanisms via which modified CGAs enhance oil recovery, including decreasing the interfacial tension and enhancing the heavy components in the recovered oil. The developed modified CGA system attained a good oil displacement effect, which is of guiding significance to further improve the oil displacement efficiency and application of foam flooding.

Investigating fluid invasion control by Colloidal Gas Aphron (CGA) based fluids in micromodel systems

The colloidal gas aphron (CGA) drilling fluids are designed to minimize formation damage by blocking pores of the rock with microbubbles and reducing the filtration loss. In order to gain a better understanding of the factors controlling the pore blocking mechanisms of microbubbles, a set of core flooding experiments were conducted by using various CGA drilling fluid formulations. The differential pressure drop along the sand-pack was measured. Effects of CGA fluid composition, flow rates, type of reservoir saturating fluids, permeability and wettability on the resistance to CGA drilling fluid flow through porous media (i.e., pressure drop due to CGA fluid flow) have been investigated. An increasing resistance to flow of CGA drilling fluids through porous media was observed as more CGA fluid was injected. Results confirmed that CGA microbubble build-up across the pore structure could establish an effective seal for controlling filtration loss.

Application of light-weight drilling fluids is essential to develop depleted hydrocarbon reservoirs. Recently, colloidal gas aphron (CGA)-based fluids have been introduced for such applications due to their ability in controlling fluid losses. In this work, a comprehensive experimental study was performed to choose the best formulation for CGA fluids by implementing static stability tests, rheological behavior measurements, and bubble size analyses of CGAs. Xanthan gum polymer and sodium dodecyl benzene sulfonate (SDBS), an anionic surfactant, and cetyl trimethyl ammonium bromide (CTAB), a cationic surfactant, were utilized to prepare CGAs. For the range of experiments conducted, the performance of CGA fluids prepared with SDBS was improved by increasing the polymer and surfactant concentrations. However, for CTAB, it was improved by an increase in the polymer concentration and a decrease in the surfactant concentration. The formation of white, long hair-like precipitates observed at high levels of CTAB caused CGA fluid to become rapidly unstable. Also, it was observed that the size of CGAs was significantly influenced by the polymer and surfactant concentrations. The most stable bubbles were formed at 6.86 g/L of polymer concentration. The results of this study provide insights into appropriate formulation for CGA-based fluids which could be potentially applicable in drilling operations.

Separation of protein by using colloidal gas aphrons (CGAs) is a promising method for removing organic materials from an aqueous solution. In this study, the continuous separation of lysozyme was carried out in a flotation column by using a CGA. The mechanism of adsorption of lysozyme on the CGA and the mass transfer from lysozyme to CGA were investigated. It was found that the adsorption of lysozyme on the CGA followed the Langmuir adsorption isotherm at a lysozyme volumetric flow rate of 2.37 mL/s. In the study of mass transfer, the overall mass transfer coefficient increased with the lysozyme and CGA volumetric flow rates, but decreased with increasing column height. The percentage of protein recovery increased with the lysozyme and CGA volumetric flow rates, column height, and residence time.

Experiments were conducted in which three selected metals-contaminated mine drainage water samples were treated by chemical precipitation followed by flotation using colloidal gas aphrons (CGAs) to concentrate the precipitates. Drainage water samples used in the experiments were collected from an abandoned turn-of-the-century copper mine in south-central Wyoming, an inactive gold mine in Colorado's historic Clear Creek mining district, and a relatively modern gold mine near Rapid City, South Dakota. The copper mine drainage sample was nearly neutral (pH 6.5) while the two gold mine samples were quite acidic (pH {approx}2.5). Metals concentrations ranged from a few mg/L for the copper mine drainage to several thousand mg/L for the sample from South Dakota. CGAs are emulsions of micrometer-sized soap bubbles generated in a surfactant solution. In flotation processes the CGA microbubbles provide a huge interfacial surface area and cause minimal turbulence as they rise through the liquid. CGA flotation can provide an inexpensive alternative to dissolved air flotation (DAF). The CGA bubbles are similar in size to the bubbles typical of DAF. However, CGAs are generated at ambient pressure, eliminating the need for compressors and thus reducing energy, capital, and maintenance costs associated with DAF systems. The experiments involved precipitation of dissolved metals as either hydroxides or sulfides followed by flotation. The CGAs were prepared using a number of different surfactants. Chemical precipitation followed by CGA flotation reduced contaminant metals concentrations by more than 90% for the copper mine drainage and the Colorado gold mine drainage. Contaminant metals were concentrated into a filterable sludge, representing less than 10% of the original volume. CGA flotation of the highly contaminated drainage sample from South Dakota was ineffective. All of the various surfactants used in this study generated a large sludge volume and none provided a significant concentration factor with this sample. For the two samples where CGA flotation was effective, the separation was very rapid and the concentrate volume was reduced when compared to gravity separation under similar conditions. Effective separations were achieved with very low chemical dosages and low residence times, suggesting the possibility of economic viability for processes based on this concept. The CGA flotation experiments described in the following report were conducted to provide preliminary data with which to assess the technical feasibility of using the method for remediation of metals-contaminated mine drainage waters. The experiments were conducted using common, low-cost, precipitating reagents and CGA prepared from several surfactants. Results were evaluated in terms of metals concentration reduction, reagent consumption, and concentrate volume. The results of these preliminary experiments indicate that CGA flotation may be a useful tool for the treatment of some types of mine drainage.

Optimization of pulp fibre removal by flotation using colloidal gas aphrons generated from a natural surfactant

This study explores the stability and rheological properties of colloidal gas aphrons (CGAs) prepared with varying concentrations of xanthan gum (XG) and sodium dodecyl sulfate (SDS). Static stability was assessed by monitoring CGA volume changes over time in a graduated cylinder, while dynamic flow behavior was analyzed using a rotational rheometer to measure yield stress and viscosity at different shear rates. Rheological models were employed to characterize CGA behavior. The results showed that increasing the concentrations of XG and SDS enhanced the structural stability and viscoelastic properties of CGAs. The CGAs exhibited non-Newtonian fluid behavior, which the Herschel-Bulkley-Papanastasiou model accurately described. Yield stress and viscosity increased with higher XG concentrations, demonstrating the system’s ability to maintain high viscosity at low shear rates while exhibiting shear-thinning behavior at higher shear rates. An optimal combination of XG and SDS concentrations was identified, which improved CGA stability, prolonged liquid retention, and minimized bubble coalescence. These findings provide important insights into how CGAs remain stable and flow. This knowledge will help in using CGAs in different industries and environmental processes.