| Solvent extraction was studied in this subject to verify the effectiveness of theseparation between organic contaminants and aqueous surfactants synthetically interms of the problem needed to solve urgently. The study conducted contaminantremoval, surfactants losses in the solvent and solvent losses in the aqueous surfactantssolutions as its evaluation standard, and used different kinds of surfactants. Moreover,a series of batch experiments were conducted by using factors such as extraction time,solvent/solution volumetric ratio, surfactant type and concentration, contaminantstype and concentration, solution salinity and solvent equivalent alkyl carbon numbers(EACNs). Additionally, pumped groundwater produced during surfactants enhancedaquifer remediation (SEAR) was simulated, and the separation between surfactantsand organic contaminate was conducted with the device of counter-current solventextraction. The distribution coefficients KPNand Ksurbetween the two phases wereapplied to characterize the migration ability and the separation effect of contaminateand surfactants, respectively. And a model developed by the software of statisticalproduct and service solutions (SPSS) was to quantify the impacts of factors (includingsolvent/solution volumetric ratio, solvent flow rate and surfactant concentration) onthe equilibrium partition coefficients KPNand Ksur. To check the feasibility ofrecycling groundwater remediation, the performance of separated surfactants aqueoussolutions was assessed after the solvent extraction. And then the solvent was separatedand purified in the solvent phase, for which could be recycled efficiently and be usedin the subsequent solvent extraction process. The experiment results could provide asupport for the evaluation of solvent extraction efficiency during surfactant enhancedaquifer remediation in field applications.The results showed that, solvent extraction was an efficient technology toseparate organic contaminates and surfactants in pumped groundwater duringsurfactant-enhanced aquifer remediation (SEAR). The competition betweencontaminant and surfactant during the process of extraction may exist. And surfactant losses in the solvent almost depended on monomers instead of micelles within theaqueous surfactant solutions. Besides, the process of counter-current solventextraction used in the paper had been tested as a well-established technology for itssimple operation and high efficiency. After the process of extraction, the separatedaqueous surfactant solutions could be recycled to groundwater for the followingtreatment. The detailed experimental results are as follows:①The optimal extraction time and solvent/solution volumetric ratio in batchexperiment were2h and0.1, respectively. The kind of surfactants had great impact onextraction efficiency, in which reflected that the effect of separating Tween80andbenzene was better than SDS and benzene. The effect of partitioning benzene from themixed surfactants into the solvent was better than that from any single surfactant, andbenzene removal increased with the increasing proportion of Tween80. The surfactantlosses were mainly determined by the surfactant monomers rather than the micelles inthe aqueous surfactant solutions. Benzene was more efficient than nitrobenzene toseparate from whatever aqueous SDS and Tween80solutions. And there existedcompetition between organic contaminate and surfactants during the extractionprocess. Furthermore, the solvent n-hexane losses in the surfactants solutions werelower than1%. Increasing solution salinity could improve the extraction efficiency.The closer carbon atom numbers of contaminant hydrophobic groups and the solventwas beneficial to the extraction efficiency.②In the experiment system of the counter-current solvent extraction, anincrease in solvent/solution volumetric ratio could substantially increase naphthaleneremoval and Tween80losses in the solvent. And increasing solvent/solutionvolumetric ratio could also extend naphthalene extraction equilibrium time. Besides,distribution of naphthalene between the aqueous and solvent phases was notsynchronized with that of surfactant during the extraction. Increasing solvent flow ratecould merely speed up the extraction process and shorten naphthalene extractionequilibrium time, whereas had little influence on extraction efficiency. Increasingsurfactant concentration was adverse to the extraction efficiency. ③The separation of TX100and naphthalene was efficient in the experimentsystem that simulated pumped groundwater produced during SEAR. The criticalmicelle concentration (CMC) changed insignificantly after the extraction, whereas itssolubilization ability for organic contaminant decreased. And the turbidity ofseparated surfactant was higher than that was not used. After the process of solventextraction, the recovery rate of n-hexane in solvent phase was98.26%, by using themethod of distillation. |
PDF Full Text Request