Sorption behaviors of aromatic anions on loess soil modified with cationic surfactant

Modification of soils with hydrophobic cationic surfactants is an effective approach for enhancing the sorptive capabilities of soil in the vadose zone for the purpose of retaining organic contaminants prior to cleanup. The objective of this study was to examine the sorptive behavior of the cationic surfactant-modified loess soil for aromatic anions in the aqueous phase in an attempt to define the sorptive mechanisms. Some dominant factors governing the sorption, such as ionic strength and divalent heavy metal cation, were investigated. The sorption isotherms of 2,4-dinitrophenol (DNP) and benzoic acid (BA) in the modified soil samples were obtained using the batch equilibration method. Under the laboratory conditions, the modified loess soil utilized in this study was prepared by replacing the cations of loess soil with a cationic surfactant—hexadecyltrimethylammonium (HDTMA) bromide. The acidic aromatic compounds, DNP and BA existing as aromatic anions in the natural mixture of loess soil and aqueous phase, were selected as indicator compounds to measured the sorption behaviors of aromatic anions on the HDTMA-modified loess soil. The results confirmed that the sorptive capabilities of aromatic anions in loess soil were greatly enhanced by modification with HDTMA. The increase of ionic strength and the addition of divalent heavy metal cation Zn²⁺ significantly increased the sorption of aromatic anions on the HDTMA-modified loess soil. In binary solute systems, the sorbed amounts either of DNP or BA on the HDTMA-modified loess soil were reduced if two compounds existed simultaneously in the soil. This results indicated that competitive adsorption between the two aromatic anions occurred in soil matrix.     

Effects of soil properties on surfactant adsorption

Abstract

The effects of surface area, soil organic matter (SOM) content, and cation exchange capacity (CEC) of natural soils and clays on the adsorption capacity of cationic, anionic, and nonionic surfactants in water‐solid systems were investigated based on the adsorption isotherm analysis. The sorption capacity for a cationic surfactant was proportional to the CEC of the solids. For both anionic and nonionic surfactants, the sorption capacity was related to the soil mineral fraction. However, other soil properties probably affect the practical sorption. The investigated soil properties were treated case by case.     

The effect of surfactants on the distribution of organic compounds in the soil solid/water system

The efficiency of soil remediation by surfactant washing was evaluated via the measured distribution coefficients of a number of nonpolar compounds in several soil-water mixtures. The studied compounds (contaminants) are BTEX (benzene, toluene, ethylbenzene, and p-xylene) and three chlorinated pesticides (lindane, alpha-BHC, and heptachlor epoxide), which span several orders of magnitude in water solubility (S(w)). A peat, and two natural soils were used that comprise a wide range in soil organic matter (SOM) content. The surfactants tested included cationic, anionic and nonionic types, with concentrations up to five to six times the critical micelle concentration (CMC). The K(d)(*)/K(d), values were used to evaluate the remediation efficiency under various operation conditions. For relatively water soluble BTEX compounds, the surfactant adsorption on the soil surface is the deciding factor on contaminant desorption from soil. For the less-soluble pesticides, surfactant micelles in solution influence the contaminant desorption more. The contaminants partitioning to SOM or adsorbed surfactants lowers the desorption efficiency. Anionic surfactants are found to be a better choice on soil remediation because they do not form admicelle on soil surface that enhances the SOM content. Cationic surfactant, which adsorb onto soil surfaces, leads to poor remediation efficiency. An improper selection of surfactant would result in inefficiency in soil remediation by surfactant washing.     

The structural and sorptive characteristics of high-surface-area carbonaceous material (HSACM) in soils

The structural and sorptive characteristics of the high-surface-area carbonaceous material (HSACM) isolated from soils were investigated. The HSACM contents in soils were first identified by the organic petrology method. A novel isolation method using acid demineralization, base extraction, and ZnBr(2) floatation sequential steps was developed to extract the HSACM from soil. The differences in structural and sorptive characteristics with the HSACM and the intact soil were investigated using nitrogen adsorption isotherms and trichloroethylene (TCE) sorption isotherms at low concentrations (0 to about 2 mg/L) both with and without tetrachloroethylene (PCE) as the cosolute. It was found that HSACM possesses a much higher specific surface area and pore volume as well as a smaller pore size than the original soil. Moreover, the sorption of TCE to HSACM is noticeably more nonlinear and competitive than to the original soil. A small amount of highly adsorptive HSACM is largely responsible for the nonlinear soil sorption of a single solute at very low concentrations.     

Influence of clay mineral structure and surfactant nature on the adsorption capacity of surfactants by clays

Adsorption of three surfactants of different nature, Triton X-100 (TX100) (non-ionic), sodium dodecylsulphate (SDS) (anionic) and octadecyltrimethylammonium bromide (ODTMA) (cationic) by four layered (montmorillonite, illite, muscovite and kaolinite) and two non-layered (sepiolite and palygorskite) clay minerals was studied. The objective was to improve the understanding of surfactant behaviour in soils for the possible use of these compounds in remediation technologies of contaminated soils by toxic organic compounds. Adsorption isotherms were obtained using surfactant concentrations higher and lower than the critical micelle concentration (cmc). These isotherms showed different adsorption stages of the surfactants by the clay minerals, and were classified in different subgroups of the L-, S- or H-types. An increase in the adsorption of SDS and ODTMA by all clay minerals is observed up to the cmc of the surfactant in the equilibrium solution is reached. However, there was further TX100 adsorption when the equilibrium concentration was well above the cmc. Adsorption constants from Langmuir and Freundlich equations (TX100 and ODTMA) or Freundlich equation (SDS) were used to compare adsorption of different surfactants by clay minerals studied. These constants indicated the surfactant adsorption by clay minerals followed this order ODTMA>TX100>SDS. The adsorption of TX100 and ODTMA was higher by montmorillonite and illite, and the adsorption of SDS was found to be higher by kaolinite and sepiolite. Results obtained show the influence of clay mineral structure and surfactant nature on the adsorption capacity of surfactants by clays, and they indicate the interest to consider the soil mineralogical composition when one surfactant have to be selected in order to establish more efficient strategies for the remediation of soils and water contaminated by toxic organic pollutants.     

Adsorption of anionic surfactants onto sepiolite

Anionic surfactants constitute the main ingredients of detergents and a number of surfactant formulations used in a spectrum of diverse industries. The aim of this study is to examine the amenability of natural sepiolite to the adsorption of anionic surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzenesulfonate (SDBS). Adsorption isotherms exhibit three regions with distinctly different slopes. The first region is characterized by the complexation of anionic surfactants with Mg2+ ions at the octahedral sheet or hydrogen bonding between the oxygen groups of anionic head groups of surfactant and H+ of the bound or zeolitic water. The Mg2+ ions released from sepiolite leads to the precipitation of magnesium salt of surfactant in the second region. The third region marks both the beginning of plateau region and micellar dissolution of the precipitate. The effect of temperature on surfactant adsorption for SDS/sepiolite system was utilized to calculate such thermodynamic parameters as the free energy of adsorption (DeltaG(ads)(degrees)) and the heat of adsorption (DeltaH(ads)(degrees)). The low value of DeltaH(ads)(degrees) (1.87 kJ/mol) is an evidence for the physical adsorption of anionic surfactants onto sepiolite. The relatively large value of entropic contribution (-TDeltaS(ads)(degrees)) indicates that the adsorption of anionic surfactants onto sepiolite is entropically governed.     

Geotechnical properties of some organoclays

The engineering characteristics of clay are dependant on its mineral and chemical structure. When the clay soils interacted with water, their volume and shear strength and compressibility properties change gradually. Large amount of decrease in terms of the shear strength of clay soils due to swelling is observed. In order to solve these problems, the stabilization of clay soils using chemical additives is a prevalent subject of research. In view of this, previous research studies have employed surface active surfactants to modify the fundamental properties of soft clays. In this study, surfactant–clay complexes (organoclays) were developed using a raw clay modification with four surfactants and their geotechnical properties were determined in laboratory conditions. Two of the surfactants are cationic (cetyl trimethyl ammonium chloride, denoted as CTAC and quaternised ethoxylated fatty amine, denoted as QEFA) and the others are anionic (linear alkylbenzene sulphonic acid, denoted as LABSA and sodium lauryl ether sulfate, denoted as SLES). The experimental results indicated that the geotechnical properties of organoclays show significant change when compared to those of natural clay. The specific gravities, unconfined compression strengths and maximum dry densities of all organoclays were decreased. Optimum moisture content and swelling pressure values were decreased in cationic surfactant modified clays. However, the optimum moisture content and swelling pressure values of anionic surfactant clays are increased. A direct shear test was performed to determine the shear strength of organoclays. The test results also showed that the internal friction angles of organoclays were increased. Additionally, the change in the hydraulic conductivity was found to be insignificant.     

Solubilization of DNAPLs by mixed surfactant: synergism and solubilization capacity

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. In this paper, a synergistical solubilization of DNAPLs 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), mixed TX100-SDBS exhibited significantly synergistical solubilization for the DNAPLs, trichloroethene (TCE), chlorobenzene (CB) and 1,2-dichlorobenzene (1,2-DCB), respectively, when the total surfactant concentration was up to 6000mg/L, i.e. the condition when solubilization by the mixture was better than those attainable with individual components by themselves. The synergistical extents depended on the initial ratios of TX100 to SDBS, the initial surfactant concentrations and the properties of DNAPLs. Given the total surfactant concentration, synergistical extents increased with the fraction of SDBS in mixed surfactant. On the contrary, did with the total surfactant concentration. The solubilization capacity by 3:1, 1:1 and 1:3 of mass ratio of TX100-SDBS were determined and compared with those by single ones. In the view of the mass solubilization ratio (SR), the mixed TX100-SDBS could solubilize more DNAPLs than single SDBS at given surfactant concentration. Reduction in partition of TX100 and synergistic solubilization were responsible for the significant solubilization extent of mixed system. The work presented here demonstrates that mixed nonionic-anionic surfactants would be preferred over the corresponding single surfactants for solubilization remediation of DNAPLs, which could decrease risks of driving the contaminants deeper into aquifers.     

Sorption of p-nitrophenol onto sediment in the presence of cetylpyridinium chloride and Pb(NO3)2: influence of pH

pH and the presence of compounds have a great effect on the sorption of organic contaminants. In this study, batch equilibrium experiments were carried out to investigate the influence of pH on the sorption of p-nitrophenol (PNP) onto sediment in the presence of Pb(NO₃)₂ and cetylpyridinium chloride (CPC) cationic surfactant. Results indicated that in the multi-solute system with PNP, Pb(NO₃)₂ and CPC, the sorption of PNP increased with the increasing pH and the amount of sorbed PNP at equilibrium was much higher than in the single-solute system. This can be attributed to the presence of Pb(NO₃)₂ and CPC. It is believed that the main reason for that was the larger sorption of CPC at higher pH allowing higher sorption of PNP. The results are believed to provide a useful insight into describing the transport and fate of PNP in natural environments.     

Cationic surfactants-modified natural zeolites: improvement of the excipients functionality

Context: In this study an investigation of cationic surfactants-modified natural zeolites as drug formulation excipient was performed. Objective: The aim of this work was to carry out a study of the purified natural zeolitic tuff with high amount of clinoptilolite as a potential carrier for molecules of pharmaceutical interest. Materials and methods: Two cationic surfactants (benzalkonium chloride and hexadecyltrimethylammonium bromide) were used for modification of the zeolitic surface in two levels (equal to and twice as external cation-exchange capacity of the zeolitic tuff). Prepared samples were characterized by Fourier transform infrared spectroscopy, thermogravimetric, high-performance liquid chromatography analysis, and powder flow determination. Different surfactant/zeolite composites were used for additional investigation of three model drugs: diclofenac diethylamine, diclofenac sodium, and ibuprofen by means of adsorption isotherm measurements in aqueous solutions. Results: The modified zeolites with two levels of surfactant coverage within the short activation time were prepared. Determination of flow properties showed that modification of zeolitic surface reflected on powder flow characteristics. Investigation of the model drugs adsorption on the obtained composites revealed that a variation between adsorption levels was influenced by the surfactant type and the amount present at the surface of the composites. Discussion and conclusion: In vitro release profiles of the drugs from the zeolite-surfactant-drug composites revealed that sustained drug release could be attained over a period of 8 hours. The presented results for drug uptake by surfactant-zeolite composites and the afterward drug release demonstrated the potential use of investigated modified natural zeolite as excipients for advanced excipients in drug formulations.     

Organic compound distribution between nonionic surfactant solution and natural solids: applicability of a solution property parameter

A solution property parameter phi was defined to examine the distribution characteristics of organic compounds between the solids and four nonionic surfactant solutions. The studied compounds consisted of BTEX (benzene, toluene, ethylbenzene, and p-xylene) and chlorinated pesticides (lindane, alpha-BHC, and heptachlor epoxide), which span several orders of magnitude in terms of water solubility (Sw). The solid samples were composed of a very low organic matter clay (Ca-montmorillonite), and a high organic matter natural soil (Shamou Mountain soil). The surfactants tested included two alkyl chain surfactants and two containing aromatic group surfactants with added concentrations both below and above their critical micelle concentration (CMC). By observing the Kom or Ksf variation, the result indicates, besides the Sw of the organic compounds, the distribution coefficient is regarded as a function of the soil organic matter (SOM) constituents, and the chemical structure of the organic compounds. Also, it can be found the greater phi values represent the higher releasing ratios of the organic compounds from the contaminated soil to groundwater. For the relatively higher Sw compounds, such as BTEX, all of the phi values are close to 1. The phi values for the relatively lower Sw compounds are far greater than 1, and increase with the increasing affinity of the compounds to the surfactants.     

Mechanism of p-nitrophenol adsorption from aqueous solution by HDTMA+-pillared montmorillonite--implications for water purification

HDTMA+-pillared montmorillonites were obtained by pillaring different amounts of the surfactant hexadecyltrimethylammonium bromide (HDTMAB) into sodium montmorillonite (Na-Mt) in an aqueous solution. The optimum conditions and batch kinetics of sorption of p-nitrophenol from aqueous solutions are reported. The solution pH had a very important effect on the sorption of p-nitrophenol. The maximum p-nitrophenol absorption/adsorption occurs when solution pH (7.15-7.35) is approximately equal to the pKa (7.16) of the p-nitrophenol ion deprotonation reaction. X-ray diffraction analysis showed that surfactant cations had been pillared into the interlayer and the p-nitrophenol affected the arrangement of surfactant. With the increased concentration of surfactant cations, the arrangement of HDTMA+ within the clay interlayer changes and the sorption of p-nitrophenol increases. HDTMA+-pillared montmorillonites are more effective than Na-Mt for the adsorption of p-nitrophenol from aqueous solutions. The Langmuir, Freundlich and dual-mode sorption were tested to fit the sorption isotherms.     

办公废纸脱墨中表面活性剂吸附作用研究

目的基于表面活性剂与油墨及废纸纤维之间的交互作用对于浮选脱墨的重要意义,研究办公废纸脱墨中表面活性剂的吸附行为。方法选取十二烷基苯磺酸钠(C12H25Na O4S,SDBS)和全氟辛酸钠(SPFOF15Na O2,SPFO)等2种常用的阴离子表面活性剂,以及疏水性炭黑和亲水性办公室废纸纤维等2种典型物质,通过润湿实验,研究它们在浮选脱墨时的吸附性能。同时,通过在表面活性剂中添加钙,进一步探索钙和表面活性剂的结合作用对炭黑和废纸纤维表面吸附性的影响。结果在不添加钙形成聚集时,随着SDBS或SPFO平衡浓度的增加,炭黑或废纸纸纤维表面的SDBS或SPFO吸附密度将增加,SPFO在废纸纤维和炭黑表面及SDBS在纸纤维表面能形成双分子层吸附,但SDBS在碳黑表面是单层吸附;在表面活性剂溶液中添加钙时,随着钙离子浓度的增加,炭黑表面的SDBS或SPFO吸附均增加,当溶液p H值为9时,纸纤维上SPFO最大吸附密度高于SDBS,在纸纤维上的SPFO吸附存在"钙排斥"效应;炭黑上的SDBS吸附性与p H值无关。结论钙在办公废纸脱墨中是有效的催化剂,可以与阴离子表面活性剂产生协同吸附作用,提高废纸脱墨效果。     

Desorption of cadmium from a natural Shanghai clay using citric acid industrial wastewater

The sorption/desorption characteristics of heavy metals onto/from soil particle surfaces are the primary factors controlling the success of the remediation of heavy-metal contaminated soils. These characteristics are pH-dependent, chemical-specific, and reversible; and can be modified by enhancement agents such as chelates and surfactants. In this study, batch experiments were conducted to evaluate the feasibility of using citric acid industrial wastewater (CAIW) to desorb cadmium from a natural clay from Shanghai, China at different soil mixture pHs. It can be observed from the results that the proportion of cadmium desorbed from the soil using synthesized CAIW is generally satisfactory, i.e., >60%, when the soil mixture pH is lower than 6. However, the proportion of desorbed cadmium decreases significantly with increase in soil mixture pH. The dominant cadmium desorption mechanism using CAIW is the complexion of cadmium with citric acid and acetic acid in CAIW. It is concluded that CAIW can be a promising enhancement agent for the remediation of cadmium-contaminated natural soils when the environmental conditions are favorable. As a result, CAIW, a waste product itself, can be put into productive use in soil remediation.     

Sorption behavior of tetrabromobisphenol A in two soils with different characteristics

Sorption of tetrabromobisphenol A (TBBPA) in soil influences its fate and transport in the environment. The sorption behaviors of TBBPA in two soils with different characteristics were investigated using batch equilibration experiments in the study, and the impacts of ionic strength and pH on the sorption were also evaluated. The results showed that the fast sorption rather than the slow sorption played a main role in the sorption process. The nonlinear sorption isotherms of TBBPA in the soils were observed and the Freundlich model could describe the sorption behavior of TBBPA well. The calculated K_F were 78.5 and 364.6  (mg/kg)(mg/L)⁻ⁿ for LN soil (loamy clay) and GX soil (silt loam), respectively. Soil organic matter (SOM) played a main role in the sorption of TBBPA, which contributed about 90% to the sorption in the soils. The desorption hysteresis of TBBPA was revealed in the single-cycle sorption and desorption experiments. The sorbed amount of TBBPA decreased with the increase in solution pH and increased with the increase in ionic strength. It was found that the effects of ionic strength on the sorption were mainly caused by the change of solution pH.     

Carbon nano-onion composites: Physicochemical characteristics and biological activity

Carbon nano-onion/surfactant (CNO/surfactant) composites offer the possibility to easily produce the soluble nanostructures. That approach combines the hydrophilicity of surfactants with the robustness of carbon structures to produce composites with superior and unusual physicochemical properties. We used the following surfactants: hexadecyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), 4-(1,1,3,3-tetramethylbutyl)phenyl-polyethylene glycol (Triton X-100), and polyethylene glycol sorbitan monolaurate (Tween 20) to non-covalently modify CNO surfaces. The existence of stable CNO composites are clearly evidenced by direct transmission electron microscopy observations, which are also supported by thermogravimetric analyses. Dynamic light scattering and zeta potential confirmed their dispersion and stability. Additionally, the biological activity of well-dispersed CNO/surfactant composites against a strain of Escherichia coli was assayed. In vitro antimicrobial assays for the composites revealed that only the CNO/CTAB composite decreased cell viability. This activity could be assigned to the simple composite dissociation in water solutions, however antimicrobial properties of the composite are slightly better when compared with pure CTAB. This indicate some synergic effect with respect to the properties of the pure surfactant.     

Significance of the long-chain organic cation structure in the sorption of the penconazole and metalaxyl fungicides by organo clays

Sorption-desorption of two different hydrophobic fungicides, penconazole and metalaxyl, by a series of clay minerals layered and non-layered (montmorillonite, illite, kaolinite, muscovite, sepiolite and palygorskite) modified with the two-chain cationic surfactant, dihexadecyldimetylammonium (DHDDMA) was studied by first time in this work. DHDDMA-clays showed a good capacity to sorb both fungicides from water. Freundlich sorption constants (K(f)) increased 22-268-fold for penconazole and 4-112-fold for metalaxyl in relation to natural clays. High sorption irreversibility was observed for penconazole for all modified clays, while for metalaxyl this occurred only for some of the modified clays. Additionally, a comparative study of the sorption of the fungicides by clay minerals modified with organic cations of different structure was carried out by a statistical approach. Non-layered and layered clay minerals modified with the two-chain alkylammonium organic cation DHDDMA, and with single-chain organic cations octadecyltrimethylammonium (ODTMA) and hexadecylpyridinium (HDPY) were used as sorbents. The study indicated a significant linear regression between the distribution coefficients K(d) of fungicides and the organic carbon (OC) content of the organo clays (r(2)>or=0.80, p<0.001). According to this sorption of fungicides by partition between the aqueous solution and the organic medium created by the alkyl chains of the exchanged ammonium cations regardless of the type and structure of these cations is suggested. However, linear relationships between K(d) values of each pesticide by the different organo clays and their relative OC contents revealed higher increase in sorption for HDPY-clays (penconazole) and for ODTMA-clays (metalaxyl) pointing out different effectiveness of the OC provided by each organic cation. These effects were also supported by the values of K(d) relative to OC, K(d)(oc). The results evidenced the different relative weight of alkyl cations to make organo clays effective barriers to prevent the mobility of pesticides from a point source of pollution.     

Preparation of lamellar hybrid inorganic–organic films of layered titanate and cationic or anionic surfactants

Hybrid inorganic–organic films were fabricated from aqueous colloidal solutions of a layered titanate salt and cationic and anionic surfactants. Cetyltrimethylammonium bromide and dodecyl phosphate were used as cationic and anionic surfactants, respectively. When the substrates dip-coated with mixtures of the titanate salt colloids and the surfactants were treated with steam in a closed vessel, hybrid inorganic–organic films with a lamellar structure were fabricated. Although the titanate layers have a negative charge, the hybrid inorganic–organic films consisting of the titanate layer and the anionic surfactant could be obtained, as well as the ones including the cationic surfactants.     

Removal of 2,4,6-trichlorophenol from a solution by humic acids repeatedly extracted from a peat soil

Humic acid (HA) is one of the major components of soil organic matter. It strongly affects the sorption behavior of organic and inorganic contaminants in soils. To obtain a better understanding of the interactions of contaminants with HA, a repeated extraction technique has been applied to a peat soil to obtain HA fractions with varying aliphaticity and aromaticity, which were subsequently correlated to the sorption properties of 2,4,6-trichlorophenol (TCP). HA fractions were extracted repeatedly using an alkaline solution and each HA fraction was separated into two portions with an air-drying or re-suspending (denoted as RSHAs) process. Solid-state (13)C NMR and elemental analysis demonstrated that the aromaticity and polarity of HAs decreased with extractions. Kinetic results indicated that air-dried HAs exhibited two-step first order sorption behavior with a rapid stage followed by a slower stage. The slower sorption is attributed to the diffusion of 2,4,6-TCP in the condensed aromatic domains of HAs. Conversely, sorption of 2,4,6-TCP on RSHAs was extremely rapid and could not be fitted with any kinetic model. For air-dried HAs the sorption capacity (K(oc)) was weakly correlated with the chemical compositions of HAs. However, a positive trend between K(oc) and aromaticity was observed for RSHAs. Compared with the results of air-dried HAs with their counterparts of RSHAs, it is therefore concluded that air-drying may alter the structure of HAs through artificially creating a more condensed domain in HAs. The structural alternation may result in an incorrect interpretation of the relationship between sorption capacity and chemical composition of HAs and a misjudgment of the transport behavior of 2,4,6-TCP in soils and sediments.     

Effects of concentration, head group, and structure of surfactants on the degradation of phenanthrene

The effects of concentration, polar/ionic head group, and structure of surfactants on the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the aqueous phase, as well as their effects on the bacterial activity were investigated. The toxicity ranking of studied surfactants is: non-ionic surfactants (Tween 80, Brij30, 10LE and Brij35)相似文献