Effects Of Surfactants On Leaching Of Heavy Metal/Aromatic Hydrocarbon In Soil

The process of industrial and agricultural economic development is accompanied by environmental pollution,especially the production and discharge of heavy metals and organic aromatic hydrocarbons,which has caused serious damage to soil environment and ecology in our country,and its remediation needs to be solved urgently.Among various remediation technologies for soil pollution control,chemical leaching is a more practical method,and the core is the selection of leaching agents.The elution technology using surfactant as eluent has the advantages of simple repair process,high efficiency,short cycle and environmental friendliness,and has good prospects for development.According to the characteristics of heavy metals and organic aromatic hydrocarbons pollution in Guizhou soil,this paper takes typical hilly loess clay as experimental soil,uses artificial simulation of nickel and nitrobenzene contaminated soil,and chooses suitable surfactants to treat contaminated soil,and studies the leaching experimental technology and pollutant removal effect.The main contents and results of the experiment are as follows:1.The preparation of contaminated soilAccording to the analysis of basic physical and chemical properties of the soil,the Loess used in the experiment is weak acidic,viscous and easy to compact,and has low fertility.The appropriate amount of nickel nitrate and nitrobenzene was added to the soil sample to prepare the corresponding contaminated soil reserve.2.Experimental study on leaching of nickel contaminated soilSelection of surfactants and determination of their mixing ratio.Based on literature analysis,two kinds of anionic surfactants,sodium dodecyl sulfate?SDS?and sodium fatty alcohol polyoxyethylene ether sulfate?AES?,were selected as leaching agents for heavy metal contaminated soil.The optimum solution/system of SDS/AES was determined by investigating the CMC value of the solution at different mass ratios.When the mass ratio of SDS is between 0 and 0.4,the CMC value of the mixed solution is lower than that of the single surfactant shows synergistic positive effect in this concentration range.When the mass ratio of SDS is 0.4,the CMC value of the compound solution is the lowest and the optimum mixture ratio is determined.The effects of AES,SDS and SDS/AES mixed solutions on the removal of nickel contamination in soils were studied under different eluent concentrations,pH values,oscillation time,soil-water ratios and temperatures.Under the set conditions,the results showed that the elution effect was AES>compound solution>SDS>deionized water in turn;Further study on AES elution experiment showed that the removal rate of Ni²⁺reached 81.47%at 30?,mass concentration of 2.5%,pH 4 and solid-liquid ratio of 1:30.The soil after washing reached 200 mg/kg of the third grade standard of"Soil Environmental Quality Standard GB15618-1995".Under the above optimum elution parts,the simulation experiment of soil column was studied.The results showed that the best elution effect was obtained when the ratio of soil to sand was 1:4,and the removal rate of Ni²⁺was 78.69%.The elution effect was slightly worse than oscillation experiment,with a decrease of2.78%.The best elution time was one time elution.3.Speciation analysis of metal in nickel contaminated soil leaching experimentTessier successive extraction method was used to determine the morphological changes of heavy metals before and after soil leaching and to analyze the migration and transformation mechanism of heavy metals.The results showed that AES can remove exchangeable,carbonate-bound,organic and ferromanganese-oxidized nickel forms from soil,with removal rates of 83.28%,84.95%,41.68%and 34.66%,respectively.The residual state is not eluted.4.Kinetics of leaching process of nickel contaminated soilFourequations,quasi-first-orderkinetics,quasi-second-orderkinetics,double-constant and parabolic diffusion,were used to fit the leaching process of nickel-contaminated soil.It was found that the fitting degree of the quasi-first-order kinetic equation was low,and the correlation coefficients of the quasi-second-order kinetic model were above 0.99,and the elution process accorded with the quasi-second-order kinetic equation;the double-constant equation analysis showed that the elution process had a large elution amount per unit time and a fast elution rate;The parabolic equation analysis showed that the elution process could be divided into two stages:rapid elution for 0² h and slowly release for 2¹2 h.5.Leaching experiment of nitrobenzene contaminated soilTX-100 and Tw-80 were selected as contaminated soil eluents.Oscillating leaching experiments of Nitrobenzene-Contaminated soil were designed with TX-100,Tw-80 and TX-100/Tw-80 solutions of different ratios?TX:Tw is 1:3,1:1 and 3:1,mass ratio?to study the effects of concentration of leaching agent,oscillating time,soil-water ratio,temperature and presence of inorganic salts on the removal of nitrobenzene.The experimental results showed that the removal rate of nitrobenzene increased rapidly at the concentration of 0⁸ g/L,decreased slightly at the elution rate of 8¹1 g/L,when TX-100 concentration is 8g/L,the maximum elution rate of nitrobenzene was 74.68%and reached the maximum removal rate of nitrobenzene after 30 minutes of oscillating elution,reached 85%above,and reached the elution equilibrium stage of 1⁴ h.The elution time was prolonged and the elution rate decreased.The mass ratio of TX:Tw is 1:3,1:1,and 3:1 respectively,and the removal rate of Tw-80 increases with the increase of soil-water ratio.Within a certain temperature range,the increase of temperature is beneficial to the removal of nitrobenzene,but at a higher temperature,the dissolution of nitrobenzene will be inhibited.The optimum temperature range is 25³5?.For five kinds of eluents,when the concentration of NaCl is 0⁵g/L,the removal rate of nitrobenzene increases slightly with the increase of NaCl concentration,indicating that NaCl can promote the elution of nitrobenzene to a certain extent.6.Kinetics of leaching process of nitrobenzene contaminated soilThe elution process of the five kinds of eluents are basically similar.The fitting results of quasi-first-order kinetics,quasi-second-order kinetics,double-constant and parabolic diffusion equation show that the fitting degree of quasi-first-order equation is low in a certain time range,the theoretical equilibrium of leaching is far from the actual value,the correlation coefficients of quasi-second-order kinetics model are all above 0.999,the leaching process conforms to quasi-second-order kinetics equation,and the reaction process has fast elution speed.The elution process can be divided into two stages,first rapid elution and then basically maintain balance.