Study And Application Of Surfactants On Petroleum-contaminated Soil By Ex-situ Washing

Petroleum pollutant is a kind of series organic pollutant. Due to the vast consumption ofpetroleum and petrolic products, soil contaminate take place inevitably. During the production,refinery, transport and use of petroleum, large quantity of it enter the environment and leadingcontaminant in both soil and water, which destroy the ecosystem and do harm to human being. Forexample, diesel is one of the most used fuels in transportation. The ability of surfactants toenhance the aqueous solubility of organic compounds and its efficient, least time-consumingoffers a potential means of remediating contaminated soils and groundwater by use of surfactantsolutions. There has a great interest in surfactant remediation in recent years.Aiming at0#diesel is the contaminant in this paper. Surfactants including SDS, LAS,TX-100and Tween-80were used as detergents for diesel oil contaminated soil ex-situ washing inthis work. The washing effect is investigated.The physical and chemical properties of soil in this paper are stable. After the determination,we get that soil particle size distribution range is169—3043nm, belongs to clay texture. For drybasis moisture content is2.6%and dry matter content is97.6%. The value of pH in soil aqueoussolution is8.2, weak alkaline. Low organic matter content, accounted for1.26%of the proportionof dry basis. The volatilization of diesel oil is connected with soil particle size and initialconcentration of diesel. Diesel evolution curve can be used of quadratic polynomial fitting indifferent property soils. The equation is w=at2+bt+c, which w for diesel volatilization amountthe percentage of the initial amount of diesel, a, b and c for experimental constant, t(min) forvolatilization time. Diesel oil extraction experiment shows that surfactant concentration andvolume have a certain degree of influence for ultrasonic conditions. The ultrasonic extractionconditions for experiments are selected as follows: times of ultrasonic extraction is twice, thedosage of extract is20mL (twice) for each time, chose low power condition (100w) as ultrasonicpower, ultrasonic time is15minutes each time.In the surfactant washing diesel contaminated soil experiment, the influence of washing process conditions and parameters are studied on the washing effect. The influence of surfactantconcentration, pH value, sodium silicate concentration, liquid/solid ratio, washing time, stirringspeed and temperature was studied. It was demonstrated that the optimum surfactant concentrationwas3g/L,4g/L,0.8g/L and0.06g/L for SDS, LAS, TX-100or Tween-80, respectively. Sodiumsilicate exhibited no effect on the washing performance of anion surfactants (SDS or LAS), butrelatively higher concentration of sodium silicate(＞5g/L) enhanced the diesel oil contaminatedsoil washing with non-ionic surfactants(TX-100or Tween-80). At pH＞6,200r/min of stirringspeed,20:1of liquid/solid ratio,20℃of temperature and30min of washing time, washingefficiency of LAS reached90%which was the best of four surfactants.In the study of LAS washing filtrate, it has been found that filtrate system composition stateis complex. Filtration has some effect on treatment that can significantly change the filtrateturbidity. High turbidity value of washing liquid is get before filtering that is usually greater than2000NTU. While the value decreased significantly after filtering, the value can be lower than100NTU, filtering effect is considerable. However, the potential absolute value of particles in filtrateis on the contrary. The potential absolute value is bigger before filtering than after filtering, due tothe change of carrying capacity. Therein, the surfactant concentration and pH value have biggerinfluence on the wash filtrate properties, the next is washing time and Na2SiO3, the last is stirringstrength and temperature.LAS, TX-100and Tween-80as the research object in the study of aeration stirring. Resultsshow that bubbles produced by the low concentration of surfactants washing liquid are enhancedremoval of diesel. Alkaline solution and additive Na2SiO3have enhanced foam effect. Washingresult shows that the removal rate of diesel under the condition of aeration increased significantly,the degree of improve can reach2—3times, the washing effect is remarkable. With the increasingof washing time, LAS and Tween-80washing effect is greatly increased, the highest removal rateis59.3%and57.8%respectively. While the washing rate of TX-100changes slowly, as high as58.7%. Under the condition of stirring simplicity, corresponding to the highest removal rate is42.5%,31.7%and41%.Acidic condition is not conducive to diesel elution while alkaline conditions can improve theremoval rate of diesel. Aeration has no effect on LAS washing when solution pH value changes.Removal rate is similar to pure stirring condition and both of them diesel removal rate are60%when pH value is11. To TX-100and Tween-80aeration has a great influence. Both of themachieved the best when the pH value is11, that the removal rate for aeration conditions are52.7%and44.4%,37%and33.2%for pure stirring conditions, both have big enhancement. Inorganicadditives sodium silicate is big to the influence of three kinds of surfactants. Diesel removal rateof LAS can reach79.3%under aeration stirring condition at10g/L and70.1%under stirring condition at the same concentration. TX-100’s diesel oil removal rate reached maximum at12g/Lthat is68.5%under aeration stirring condition and56.1%under stirring condition. WhileTween-80’s diesel oil removal rate reached maximum at15g/L that is67.3%under aerationstirring condition and53.7%under stirring condition.The results prove that surface active agent has good washing effect. Washing processconditions on surfactants washing and aeration mixing method has a certain degree of influence.Bubble has significant effect in contaminate soil washing method. It can improve the efficiency ofthe diesel oil washing.