Abstract
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.
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