The Solubilization Performance Of Surfactants And Its Effect On Enhancing Oxidation Of Toluene And Phenanthrene By KMnO₄

The soil and groundwater pollution have become increasingly severe in China.In situ chemical oxidation（ISCO）can quickly remove most organic contaminants,but the remove efficiency of hydrophobic organic contaminants is still low.This study attempts to build a mixed surfactant to enhance the phase transfer ability at low concentration and tries to combine surfactant and KMn O₄oxidation（S-KMn O₄）to increase the remove efficiency of hydrophobic organic contaminants（toluene and phenanthrene）.The high-efficiency mixed surfactant can reduce the cost and secondary pollution risk.The S-KMn O₄provides a new method for improving the remediation efficiency of organic contaminated sites.In this study,in order to clarify the main influencing factor on the phase transfer ability,the interface tension,hydrophile-lipophile balance,critical micelle concentration（CMC）,and aggregate size of 10 surfactants have been analyzed.Then,in order to further improve the phase transfer ability,different types of surfactants have been mixed.The proportion and concentration of mixed surfactants have been optimized.The mechanism of synergistic effects has also been analyzed.Thirdly,considering the compatibility between surfactants and KMn O₄,as well as the enhance effect of toluene and phenanthrene removal by different surfactants,the best S-KMn O₄combination system was screened.Finally,the impact of natural organic matter（NOM）,anion and cation on the S-KMn O₄system has been studied.In order to improve the stability of the S-KMn O₄system,the protective effect of Na₂Si₂O₅has also been studied.The results of this study show that the phase transfer ability of different surfactants is significantly positively correlated with the product of the multiplicativeinverse of CMC value and the average surface area of aggregates after solubilization.The aggregates after solubilization include micelle and micro-emulsion,where the micro-emulsion has a major contribution.Nonionic Tween20,anionic SDBS,and amphoteric BS-12 have highest phase transfer ability in their own types.The phase transfer ability of biosurfactant is poor.For different types of mixed surfactants,only SDBS/BS-12 has a synergy effect,resulting in improvement of phase transfer ability.The anion group of SDBS and the cation group of BS-12 will be attracted to each other,resulting in the actual CMC value lower than the theoretical CMC value,and at the same time a larger size mixed aggregates is formed,thereby the synergy effect is formed.The best molar ratio of SDBS/BS-12 is 2:1 and the best concentration of SDBS/BS-12 is 5 mmol·L^-1.KMn O₄is more inclined to rapidly oxidize the surfactants which contains glucose ring,C=C double bond and polyoxyethylene chain.SDBS/BS-12 has high solubilization efficiency and good compatibility with KMn O₄.The removal efficiency of toluene and phenanthrene is increased from 2%and 29%to 48%and 86%,respectively,after combining the SDBS/BS-12 and KMn O₄.High-priced cations Ca²⁺、Mg²⁺、Fe³⁺、Mn²⁺will react with SDBS/BS-12 to form precipitation showing inhibitory effects,however,Na₂Si₂O₅can eliminate negative effects.Na₂Si₂O₅has interlayer ion exchange capability due to its special layered structure,and high-priced cations can be replaced by Na⁺.The molar ratio of Na₂Si₂O₅and high-priced cations is at least 2:1.The optimized S-KMn O₄system has increased the removal efficiency of toluene and phenanthrene by about10%in sand tank test after one injection event.S-KMn O₄has very good performance under the low concentration of SDBS/BS-12,which can reduce remediation costs and secondary pollution risks.It is worth promoting in the future.