RETRACTED: Micellar solubilization of TCE and PCE by mixed surfactant: Effects of surfactant partitioning and DNAPL mixing

Abstract

Efforts to remove the dense nonaqueous phase liquids (DNAPLs) in subsurface by mobilizing them face with risks of driving the contaminants deeper into aquifer zones. This spurs research for modifying the approach for in situ remediation. In this paper, micellar solubilization of trichloroethene (TCE), tetrachloroethene (PCE) and their mixture (TCE-PCE) by mixed nonionic and anionic surfactant, Triton X-100 (TX100) and sodium dodecylbenzene sulfonate (SDBS) in DNAPL/water systems was presented. Given 1:40 phase ratio of DNAPL/water (v/v) and the total surfactant concentration from 200 to 10,000mg/L, mixed TX100-SDBS at the total mass ratios of 3:1, 1:1 and 1:3 exhibited significant solubilization for TCE, PCE and TCE-PCE mixture (1:1, v/v). The solubilization extent of sole TCE by TX100-SDBS was much larger than by single TX100 and even larger than by single SDBS at the ratios of 1:1 and 1:3. The solubilization extent of sole PCE by TX100-SDBS was between those by single TX100 and single SDBS. In mixed TCE-PCE system, the solubilization extent of TCE or PCE by TX100-SDBS was larger than by single SDBS at the ratios of 1:1 and 1:3 while less than by single TX100 at large surfactant concentration. TX100 partitioning into the organic phase dictated the solubilization extent. The TX100 losses into TCE and TCE-PCE phases were great when single TX100 was used, while those into PCE phase were much less. No partitioning of SDBS into DNAPLs was observed. In mixed surfactant systems, SDBS decreased greatly the partition loss of TX100 into DNAPLs. The extent of TX100 partition decreased with the amount of SDBS increasing and the polarity of DNAPL decreasing. The mechanism for reduction of TX100 partition was discussed. TX100 and SDBS formed mixed micelles in the solution phase. The inability of SDBS to partition into DNAPLs and the mutual affinity of SDBS and TX100 in the mixed micelle controlled the partitioning of TX100 into DNAPL phase. The work presented here demonstrates that mixed nonionic-anionic surfactants may be probably potentially better systems than the corresponding single ones for remediation of polar DNAPLs, which could decrease risks of driving the contaminants deeper into aquifers.