Solubilization/Chelation Properties Of LED3A And Its Function To Washing Copper And Phenanthrene Co-contaminated Loess

Soil co-contamination has become a common phenomenon,in which the heavy metals and PAHs co-contamination accounts for a significant part.Generally,co-contaminated soil is more difficult to remedy than single polluted soil.Among the numerous methods of contaminated soil remediation,the chemical washing technology,which has a short operation period and remarkable removal efficiency,has been widely used in the remediation of single polluted soil or contaminated soils polluted by similar pollutants.For example,chelating agents and surfactants are used to remove heavy metals and organics respectively.In recent years,joint applications of chelating agent and surfactant have been adopted to remove heavy metals and PAHs co-contaminants from soils.However,there are difficulties both in separating and treating contaminants and in recycling washing agents when surfactant and chelating agent are used as admixture or as individuals through sequential washing.In addition,most of the chelating agents?for example,EDTA?are considered to possess a low biodegradability in soil.Thus,alternative methods are urgently needed for remediating co-contaminated soils.In this paper,a novel biodegradable chelating surfactant,sodium lauroyl ethylenediamine triacetate?LED3A?,was selected as the enhancing agent.LED3 A has the functions of both surface activity and chelation.A series of batch experiments were carried out to study the solubilization and chelating ability of LED3 A for PAHs and heavy metals in solution system,and the mechanism and main influencing factors were investigated.Solubilization enhancement extent and chelation competivity sequence in LED3 A solution were evaluated with mixed PAHs or heavy metals system.Solubilization and chelation and the interaction between them were discussed by using phenanthrene and Cu?OH?₂ coexisting system.The adsorption behavior of LED3 A,Cu???and phenanthrene onto loess under different conditions were investigated.Basing on these research results,the removal efficiencies and mechanisms of Cu???and phenanthrene for single Cu???or phenanthrene and mixed contaminated loess by LED3 A were evaluated by using batch washing process.The main results are as follows.?1?The critical micelle concentration?CMC?of LED3 A was 707 mg L^-1 at 25 °C.The effects of temperature,pH value and coexisting ions on the solubilization of performance by LED3 A were investigated.The solubility of phenanthrene was efficiently enhanced by LED3 A,especially with LED3 A concentrations being above the CMC.The pH value and coexisting cation were two primary factors that affected solubility enhancement of phenanthrene.The optimal pH ranges were from 4 to 7,and coexisting Cu???might significantly increase solubility of phenanthrene.The pseudo-first-order kinetic equation was suitable to describe the solubilization of phenanthrene in LED3 A solution.Sequence of solubilizing extent for single PAHs system was in the order of pyrene>phenanthrene> naphthalene.Solubilization capacity of LED3 A to phenanthrene was similar to those of two commonly used anionic surfactants,sodium dodecyl benzene sulfonate?SDBS?and sodium dodecyl sulfate?SDS??2?The chelation capacity of LED3 A micelles was stronger than that of monomers.LED3 A micelles could significantly enhance the water solubility of heavy metal hydroxide?M?OH?₂?via ligand-promoted dissolution mechanism to form water-soluble chelating complex LED3A-M.Conditional stability constants for LED3 A chelation of heavy metals followed the order of Cu???>Zn???>Cd???.The dissolution of Cu?OH?₂ by LED3 A was a spontaneous and endothermic process with entropy increasing.The pseudo-first-order kinetic equation was suitable to describe Cu?OH?₂ dissolution in LED3 A solution.The dissolution efficiency of Cu?OH?₂ by LED3 A highly depended on the initial pH value of LED3 A solution,and the optimal pH ranges were from 5 to 9.Coexisting Ca???or Mg???weakened the dissolution of Cu?OH?₂ due to the competition for LED3 A,and coexistence of phenanthrene had no impact on the dissolution of Cu?OH?₂ by LED3 A.?3?Coexistence of PAHs could produce mutual synergetic effect in binary or temary solubilization system.The sequence of solubilizing extent for temary mixed PAHs was in the order of pyrene>phenanthrene>naphthalene.However,the mutual competition of heavy metals in binary or temary heavy metal hydroxide system resulted in the decrease of LED3A-M concentration.The order of LED3 A dissolution of temary mixed hydroxides was Cu?OH?₂>Cd?OH?₂>Zn?OH?₂.The saturated chelating LED3A-Cu solution could promote the solubilization capability of LED3 A for phenanthrene,and the saturated solubilizing LED3A-phenanthrene system could also increase the chelating efficiency of LED3 A for Cu???.LED3 A could simultaneously solubilize PAHs and chelate heavy metals.?4?The adsorption of LED3 A,phenanthrene or Cu???on loess were in accordance with the pseudo-second-order kinetics model.The adsorption isotherm of LED3 A was well fitted by Langmuir,Freundlich and D-R model.Absorption amount of LED3 A on loess decreased with the increase of temperature and pH value,and increased with the increase of Na???concentration and water-soil ratio.Adsorption loss of LED3 A was 34.82 % at 25?.The adsorption isotherm of phenanthrene on loess was well fitted by Henry model.Adsorption amount of phenanthrene on loess decreased with the increase of temperature and pH value.Cu???had weak inhibitory effect on phenanthrene adsorption,and low concentration of LED3 A could promote the adsorption of phenanthrene.However,when the LED3 A reached its saturated adsorption on loess,it would inhibit phenanthrene adsorption.Langmuir model was suitable to describe the adsorption of Cu???on loess.The adsorption capacity of Cu???increased with the increase of temperature and pH value.The presence of phenanthrene could inhibit the adsorption of Cu???.LED3 A could promote the adsorption of Cu???when its concentration was above 3000 mg L^-1.?5?The desorption of Cu???and/or phenanthrene for single Cu???or phenanthrene and mixed contaminated loess by LED3 A were in accordance with the pseudo-second-order kinetics model.LED3 A could effectively remove two kinds of contaminants from single and mixed contaminated loess,and the removal efficiency of the former was slightly higher than that of the latter.For co-contaminated loess,both the optimal removal efficincy of Cu???and phenanthrene were higher than 60%.The interaction of Cu???and phenanthrene were investigated by using different loess with varying contaminated concentrations.The results indicated that Cu???could restrain the desorption of phenanthrene in co-contaminated soil,but the effect of phenanthrene on Cu???was not significant.LED3 A could be applied in a wide pH range from 5 to 10.The removal efficiency of Cu???and phenanthrene for co-contaminated loess by LED3 A and admixture of EDTA and SDS or polyethylene glycol octyl phenyl ether?TX100?were preliminarily compared.The removal rate of Cu???and phenanthrene by EDTA-SDS/TX100 was about 10²0% and 5¹5% higher than that by LED3 A,respectively.In short,the novel chelating surfactant LED3 A could effectively solubilize PAHs and chelate heavy metals in solution system.Furthermore,it could simultaneously remove heavy metals and PAHs from contaminated soils.Therefore,LED3 A might be used as an alternative washing agent for co-contaminated soils,with a favorable application prospect.