Study On Solubilization And Washing Of PAHs By Mixed Surfactants

Surfactant-enhanced remediation (SER) is one of the most efficient, the least time-consuming and a promising technique among the remedy approaches for the contaminated soil and groundwater. It was pointed out that an improved strategy for SER is to reduce the concentration of surfactant, the expenditure of technique and risk on ecosystem while the efficiency of surfactant utilization was maintained.In this article, much reviewing was made on the principles, the current research results and the main problems of the surfactant remediafion for soils contaminated by PAHs. Firstly the solubility enhancements of naphthalene and phenanthrene in micellar solutions of single-surfactant, Triton X-100(TX100), TweenS0(TW80), sodium dodecylbenzyl sulfonate(SDBS), sodium dodecyl sulfate(SDS) and binary mixed-surfactant, TX100-SDBS, Tween80-SDS were studied in aqueous phase. Secondly the adsorption of the single surfactant, SDBS, TX100 and binary mixed surfactant, TX100-SDS onto the loess were studied in liquid-soil system. In the last, the washing of naphthalene and phenanthrene by micellar solutions of single-surfactant, TX100, TW80, SDBS, SDS and binary mixed-surfactant, TX100-SDBS, Tween80-SDS were studied and compared in water-soil system. The purpose is to offer the reference basis for chemical repair of PAHs of soil. The main original conclusions are drawn as following parts.(1) It was found that not only nonionic surfactants could enhance the solubilization of PAHs greatly in the range of concentration above its critical micellar concentration (CMC), but also the solubility was linerly related to the concentration of nonionie surfaetants. Such as when TWS0 is in the concentration of 2000 mg/L, it is 38.8mg/L to the apparent solubility of phenanthrene, it is 33.2 times that of phenanthrene water solubility.The solubilization extents of PAHs by nonionic surfactant were much larger than that by single anionic one.The order of the solubility is TW80＞TX100＞SDS＞SDBS.The solubilization extents by mixed surfactant were larger than that by single anionic one. Such as when the total concentration is 2000mg/L, the solubility of phenanthrene is 24.6, 41.8,54.5mg/L respectively to the mass ratio of mixed surfactant TW80-SDS is 1:3, 1:1, 3:1, and the same concentration of SDS is only 4.79mg/L.(2)Joining inorganic salts such as NaCl, MgCl₂, CaCl₂ can improve the solubilization of PAHs of surfactant, especially obvious for mixed surfactants. Such as when joining NaCl of the concentration of 2500mg/L ,the solubility of mixed surfactant SDBS-TX100 of the mass ratio of 1:3 to phenanthrene have increased 16.8mg/L, but has only increased 2.00 mg/L to TX100 under the same concentration.Mixed surfactants can improve its ability to resist hard water notably. Such as when joining MgCl₂ of the concentration of 50 mg./L into SDS of the concentration of 2000 mg/L, it has already been precipitated, but to mixed surfactant TW80-SDS of the same concentration until joining MgCl₂ of the concentration of 200 mg/L, it has not been precipitated.(3) There is synergistic solubilization of the anionic-nonionic mixed surfactant in aqueous phase and the liquid-soil system to naphthalene and phenanthrene.Such as in aqueous phase, when mixed surfactant TW80-SDS(1:3) is in the density of 6000 mg/L, the intensity of synergistic solubilization to phenanthrene is 9.36 %.(4) In the liquid-soil system, when adding the anionic surfactants, the adsorption of the nonionic surfactants onto the soil can be decreased.And the adsorption will be more little when the presence of the anionic surfactants is beginning larger.(5) Mixed surfactant of certain matching has already been better than single noni onic surfactant of the same density to the elution function of phenanthrene and naphth alene.Such as when in the same density, the elution function of naphthalene of TX100-SDBS(3:1)andTX100-SDBS(1:1) was better than the elution of single TX100.The result of study indicates that anionic-nonionic mixed surfactant can improve the efficiency of solubilization, reducing the losses of absorbing onto the soil and enhancing the washing efficiency to PAHs in the soil.