Enhanced Solubilization Of Petroleum Hydrocarbon Contaminated Soil By Composite Surfactants

In recent years,soil pollution by petroleum hydrocarbon has become increasingly serious for its characteristics of great harm and difficult governance,which has been a worldwide concern.Surfactant enhanced remediation,as a fast and effective technology for treating petroleum hydrocarbon contaminated soil,could effectively increase the solubility of pollutants by utilizing the hydrophilic-lipophilic properties of surfactants so as to remove petroleum hydrocarbons.The anionic-nonionic surfactant has a significant effect on the solubilization of organic pollutants,and their effects are not only affected by characteristics of the surfactants,but also influenced by the properties of soils and petroleum hydrocarbons.In this paper,anionic surfactants surfactant——Sodium dodecyl sulfate?Sodium dodecyl sulfate,SDS?and non-ionic surfactant——Polyethylene glycol sorbitan monooleate?Tween 80?were used to synthesize complex surfactants.First of all,the influence of complex surfactants and the salts on the solubilization of petroleum hydrocarbons were studied.Combined with the distribution of petroleum hydrocarbons in soil,the solubilization effect of total petroleum hydrocarbon?TPHs?in each fraction was further analyzed,and the range of soil particle size that TPHs could easily removed by leaching were explored.The conclusions are as follows:1)Surfactant SDS has better solubilization effect on petroleum-contaminated soil than Tween80,and the solubilization rates of both tended to be stable at 24 h.The soils with low pollution concentration?TPHs=3970 mg/kg?could be treated with 1:1 ratio of SDS/Tween80,while soils with high concentration?TPHs=25835 mg/kg?could be treated with SDS.The optimal concentration of surfactant was 5g/L.The additive Na₂SiO₃ has promoted the solubilization of surfactant on petroleum-contaminated soil,while NaCl inhibited its effect.2)The concentration of TPHs firstly decreased and then increased with the increase of soil particle size.The concentration of TPHs in soil particles below 75?m were higher.The contribution of 75-2000?m soil particles to TPHs is 77%,which mainly contain C16-C28 fractions,while soil particles below 75?m mainly contain C16-C28 and C28-C35 fractions,so it is difficult to get a large amount of soil with less toxicity through soil sieving directly.The concentrations of TPHs in different soil fractions were influenced by both total organic carbon?TOC?and specific surface area?SSA?,but mainly effected by TOC.With the decrease of particle size,the minerals of each soil fraction gradually transformed from primary minerals to secondary minerals of2:1 type.The minerals contained in soil particles under 75?m could promote the adsorption of TPHs.3)TPHs concentrations in 75-2000?m soil particles were below the standard limit when soils with low pollution concentrations have been treated with SDS/Tween80;After high concentrations of contaminated soil were solubilized by SDS,75-2000?m soil particles reached more than 87%solubilization rate.The residual amount of each petroleum hydrocarbon fraction were highest in the soil granules below 75?m,of which C21-C28 and C28-C35 fractions are more easily removed by the complex surfactant SDS/Tween80.Therefore,particle size range of the oil-contaminated soil suitable for washing was 75-2000?m,and 75-2000?m soil particles can be treated with soil washing.Soil particles below 75?m could be treated with other methods,and the solubilization amount of soil can be reduced by 19%.