| Surfactant-enhanced remediation (SER) is one of the most efficiency organic polluted soil remediation methods. However, mass deploy of SER has been restricted, it is due to the separation, recycle technology of surfactant and operation cost. Recent studies indicated that the formation and deformation of micelle could be manipulated by stimulating functional group of switchable surfactant in surfactant separation and recycle stage. By applying such feature, the separation and recycle of surfactant and pollution would be enhanced, as well as reducing operation cost of SER.This paper was mainly studied the reversibility of2-n-lauryl-1,1,3,3-tetramethylguanidine (DTMG) surfactant and its influence on reversible solubilization of typical PAHs, in order to solve the core issue of SER technology. This study includes four main parts:(1) Synthesis and characterization of DTMG (2) The reversibility of DTMG and DTMG·CO2.(3) The influence of DTMG and DTAB on solubilization of typical PAHs.(4) The influence of cationic-nonionic mixed surfactants (DTMG·CO2/Tween80) on solubilization of typical PAHs. Through research, this paper had the following conclusions:(1) Through analysis the charts of'HNMR and13CNMR of DTMG, showed that the compound was we need. Based on analyzing the surface tension and pH of DTMG surfactant in different conditions, we found that the reversibility of DTMG surfactant was excellent, and the reversible cycle was only25min.(2) DTMG·CO2surfactant increased the solubilization of PAHs significantly, the order as following:pyrene> phenanthrene> anthracene. It was relevant to the Kow and Kmc of PAHs. When the Kow growing, the hydrophobic is stronger, Kmc greater, the solubilization of PAHs is also significant. When DTMG·CO2would disintegrated into DTMG under80℃and N2environment, the surface activity would droped. The values of molar solubilization ratio (MSR) for DTMG had fallen by79.6%,69.5%and69.1%, respectively. However, the solubilization would regained after supplying enough CO2. PAHs would be released when DTMG-C02was converting to DTMG Release rate was greater under low surfactant concentration. However, it was reversed when surfactant concentration was raised. The release rate on three target pollutions was negative related to solubilization of surfactant under same concentration.(3) Compared with regular surfactant of DTAB, DTMG·CO2surfactant had better solubilization of PAHs and greater industrialization value.(4) The ratio of different quality of mixed surfactants DTMG·CO2/Tween80increased the solubilization of pyrene significantly, and in3:7was the best. Mixed surfactants DTMG·CO2/Tween80(3:7) also increases the solubilization of PAHs significantly, the order as following:pyrene> phenanthrene> anthracene. Compared with the solubilization of pyrene,phenanthrene,anthracene in water, when the concentration of the mixed surfactants DTMG-CO2/Tween80(3:7) under the1000mg/L, the solubilization of PAHs increased96.4,35.7,32.5multiples respectively. Compared with the sum solubilization of pyrene,phenanthrene,anthracene in solution of DTMG-C02and Tween80, the degree of synergy solubilization of mixed surfactants DTMG·CO2/Tween80(3:7) increased1.2,1.05,1.3multiples respectively.The study showed that the solubilization and release of PAHs could be manipulated by DTMG under CO2/N2. At active state, the micelle was formed, solubilization of PAHs. At inactive state, the micelle was deformed, release PAHs. And the conversion between DTMG·CO2and DTMG was reversibility. The surface activity of DTMG solution could be re-active by adding CO2into system. This showed a way to solve the key issue on deploying SER technology. |
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