Attenuating toluene mobility in loess soil modified with anion-cation surfactants

Soils, subsoils, and aquifer materials can be modified with hydrophobic cationic surfactants to increase their sorption capabilities for organic contaminants. The objective of this study was to examine in detail the sorptive characteristics of the natural loess soil and the resultant organo-modified soils for aqueous-phase neutral organic compounds (NOCs) in an attempt to define the operative sorptive mechanisms. Under the laboratory conditions, a series of modified loess soils in this study were prepared by replacing the cations of loess soil with both cationic surfactant hexadecyltrimethylammonium bromide (HDTMA-Br) and anionic surfactant sodium dodethylbenzene sulfonate (SDBS). Toluene was selected as an indicator to study the sorption behavior of the NOCs in loess soils. The sorption isotherms of toluene in soil samples obtained using the batch equilibration method. The results indicated that natural loess had a poor sorption capability for NOCs, and sorption isotherms of toluene appeared likely nonlinear and fit the Freundlich equation very well. When the soils were coated with large alkyl surfactants such as HDTMA-Br, sorption isotherms correspondingly became linear and the sorptive capability was prominently dependent on the quantity of hexadecyltrimethylammonium (HDTMA) and SDBS added into the soils. The study could provide an essential basis on attenuation of organic contaminants in the subsurface environment.     

Effect of quaternary ammonium cation loading and pH on heavy metal sorption to Ca bentonite and two organobentonites

Sorption of four heavy metals (Pb, Cd, Zn and Hg) to calcium bentonite (Ca bentonite), hexadecyltrimethylammonium bentonite (HDTMA bentonite) and benzyltriethylammonium bentonite (BTEA bentonite) was measured as a function of the quaternary ammonium cation (QAC) loading at 25, 50 and 100% of the clay's cation-exchange capacity (CEC). The effects of pH on the surface charge of the clays and heavy metal sorption were also measured. Sorption of Cd, Pb, and Zn was non-linear and sorption of all three metals by HDTMA and BTEA bentonites decreased as the QAC loading increased from 25 to 100%. In most cases, sorption of these metals to 25% BTEA and 25% HDTMA bentonite was similar to or greater than sorption to Ca bentonite. Hg sorption was linear for both HDTMA and BTEA bentonite. No significant effect on Hg sorption was observed with increasing QAC loading on BTEA bentonite. However, an increase of Hg sorption was detected with increasing QAC loading on HDTMA bentonite. This behavior suggests that a process different than cation exchange was the predominant Hg sorption mechanism. Cd, Pb, and Zn sorption decreased with pH. However, this effect was stronger for Cd and Pb than Zn. Hg sorption varied inversely with pH. QAC loading affected the surface charge of the clays. Twenty-five and 50% loading of BTEA cations increased the negative charge on the clay's surface relative to the untreated clay, without affecting the zero point of charge (ZPC) of the clay. Increased QAC loading on HDTMA bentonite causes the surface charge to become more positive and the ZPC increased. One hundred percent of HDTMA bentonite maintained a positive surface charge over the range of pH values tested. The organoclays studied have considerable capacity for heavy metal sorption. Given that prior studies have demonstrated the strong sorption capacity of organoclays for nonionic organic pollutants, it is likely that organoclays can be useful sorbents for the treatment of effluent streams containing both organic contaminants and heavy metals.     

Adsorption of As(V) on surfactant-modified natural zeolites

Natural mordenite (NM), natural clinoptilolite (NC), HDTMA-modified natural mordenite (SMNM) and HDTMA-modified natural clinoptilolite (SMNC) have been proposed for the removal of As(V) from aqueous solution (HDTMA=hexadecyltrimethylammonium bromide). Influence of time on arsenic sorption efficiency of different sorbents reveals that NM, NC, SMNM and SMNC require about 20, 10, 110 and 20h, respectively to reach at state of equilibrium. Pseudo-first-order model was applied to evaluate the As(V) sorption kinetics on SMNM and SMNC within the reaction time of 0.5h. The pseudo-first-order rate constants, k are 1.06 and 0.52h(-1) for 1 and 0.5g of SMNM, respectively. The observed k values 1.28 and 0.70h(-1) for 1 and 0.5g of SMNC, respectively are slightly high compared to SMNM. Surfactant surface coverage plays an important role and a significant increase in arsenate sorption capacity could be achieved as the HDTMA loading level on zeolite exceeds monolayer coverage. At a surfactant partial bilayer coverage, As(V) sorption capacity of 97.33 and 45.33mmolkg(-1) derived from Langmuir isotherm for SMNM and SMNC, respectively are significantly high compared to 17.33 and 9.33mmolkg(-1) corresponding to NM and NC. The As(V) uptake was also quantitatively evaluated using the Freundlich and Dubinin-Kaganer-Radushkevich (DKR) isotherm models. Both SMNM and SMNC removed arsenic effectively over the initial pH range 6-10. Desorption performance of SMNM and SMNC were 66.41% and 70.04%, respectively on 0.1M NaOH regeneration solution.     

Application of titanate nanotubes for dyes adsorptive removal from aqueous solution

The potential of adsorptive removal of basic dyes with titanate nanotubes (TNTs) and acid dyes with surfactant (hexadecyltrimethylammonium (HDTMA) chloride)-modified TNTs were investigated. TNTs were prepared via a hydrothermal method and subsequently washed with HCl aqueous solutions of different concentrations. The prepared TNTs were then mediated by the HDTMA ions through the cation exchange process. Effects of acid washing and HDTMA-modified process on the revolution of microstructure and surface chemistry characteristics of TNTs were characterized with XRD, nitrogen adsorption-desorption isotherms, and FTIR. The adsorption capacities of two basic dyes (two acid dyes) on TNTs (their HDTMA-modified version) at initial dye concentration of 2000 mg/L were measured. It was experimentally concluded that if the amount of Na(+) in the TNTs was not very low, the TNTs and their HDTMA-modified version might be a good adsorbent for the removal of basic and acid dyes from aqueous solution through the cation and anion exchange mechanism, respectively. The adsorption capacity for basic and acid dyes could reach 380 and 400 mg/g, respectively.     

Removal of toluidine blue from water using 1:1 layered clay minerals

Extensive use of color dyes in modern society resulted in their potential release into the environment. Dye removal often involved in sorption or reaction. For sorptive removal, materials with low cost and high efficiency are of great potential. In this study, the removal of toluidine blue (TB), a cationic dye, by 1:1 layered clay minerals kaolinite (KAO) and halloysite (HNC) was systematically studied under different physicochemical conditions. The TB removal was fast and equilibrium could be reached within an hour. The TB removal capacities were 47 and 149 mmol/kg by KAO and HNC slightly larger than their cation exchange capacity (CEC) of 37 and 120 meq/kg. The results indicated that both the CEC and specific surface area (SSA) of the minerals played a critical role in TB removal. Equilibrium solution pH and ionic strength had less effect on TB removal, suggesting preferred affinity of TB over other inorganic cations for mineral surfaces. X-ray diffraction data showed no interlayer expansion, indicating TB sorption sites were on the external surfaces of both minerals. The FTIR results indicated participation of N⁺ on the dimethyl group for TB sorption on negatively charged mineral surface. At the sorption capacities, TB may form a condensed monolayer on KAO surfaces, and a dimer or bilayer coverage on HNC surfaces, as suggested by molecular dynamic simulation. The results from this study suggest that clay minerals of high CEC and large SSA values would be good candidates for the removal of cationic dyes form water.     

Influence of the coexisting contaminants on bisphenol A sorption and desorption in soil

The effects of different heavy metals (Cd, Pb), surfactants (cetyltrimethylammonium bromide (CTAB), cetylpyridine chloride (CPC)) and the ionic strength (Ca2+, NH4+) on breakthrough curves (BTCs) for sorption and desorption of bisphenol A (BPA) were studied using soil column experiment. Results showed that the presence of heavy metals and cationic surfactants caused a significant increase on the BPA sorption. In addition, the volume required when effluent concentration reached half of the influent concentration (VC1/2) increased due to the introduction of heavy metals and surfactants. It was also found that the larger amount of BPA was absorbed with higher ionic strength. The cationic surfactants enhanced the desorption ability of BPA from the soil. The results provided a better understanding of BPA behavior in environment and facilitated more accurate assessment of its ecological risk and identification of appropriate management strategies.     

Sorption of selenium oxyanions on TiO2 (rutile) studied by batch or column experiments and spectroscopic methods

Selenium is a known toxic element released in the environment by anthropogenic activities. The present study is devoted to the aqueous sorption behaviour of selenium oxyanions (selenate and selenite) on a reference oxide surface, namely rutile TiO(2). Batch sorption kinetics and isotherms have been studied using different physico-chemical conditions of the solution (changes of pH and ionic strength). The sorption was favoured for both anions in acidic conditions, in agreement with a surface complexation mechanism and CD-MUSIC predictions. Spectroscopic investigations of the sorbed rutile powder were also consistent with such a mechanism. EXAFS spectra confirmed that for selenite anions, an inner-sphere mechanism was the most probable process observed. Dynamic sorption experiments using a column filled with rutile powder also substantiated that a part of the surface complexes follows the inner-sphere mechanism, but also evidenced that an outer-sphere mechanism cannot be excluded, especially for selenate anions.     

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.     

Characterization of aqueous lead removal by phosphatic clay: equilibrium and kinetic studies

Immobilization of heavy metals from contaminated environments is an emerging field of interest from both resource conservation and environmental remediation points of view. This study investigated the feasibility of using phosphatic clay, a waste by-product of the phosphate mining industry, as an effective sorbent for Pb from aqueous effluents. The major parameters controlling aqueous Pb removal, viz. initial metal ion concentrations, solution pH, sorbent amounts, ionic strength and presence of both inorganic and organic ligands were evaluated using batch experiments. Results demonstrated that aqueous Pb removal efficiency of phosphatic clay is controlled mainly by dissolution of phosphatic clay associated fluoroapatite [Ca(10)(PO(4))(5)CaCO(3)(F,Cl,OH)(2)], followed by subsequent precipitation of geochemically stable pyromorphite [Pb(10)(PO(4))(6)(F,Cl,OH)(2)], which was confirmed by both X-ray diffraction (XRD) and scanning electron microscopic (SEM) analysis. Lead removal efficiency of phosphatic clay increased with increasing pH, sorbent amount and decreasing ionic strength. It also depends on the nature of complexing ligands. Formation of insoluble calcium oxalate and lead oxalate in the presence of oxalic acid explained high uptake of Pb by phosphatic clay from aqueous solution. However, Pb sorption kinetics onto phosphatic clay were biphasic, with initially fast reactions followed by slow and continuous Pb removal reactions. The slow reactions may include surface sorption, co-precipitation and diffusion. The exceptional capability of phosphatic clay to remove aqueous Pb demonstrated its potential as a cost effective way to remediate Pb-contaminated water, soils and sediments.     

Enhanced sorption of radiocobalt from water by Bi(III) modified montmorillonite: a novel adsorbent

In this study, Ca-montmorillonite (Ca-Mt) modified with Bi³⁺ was used as a novel adsorbent for the sorption of Co(II) from aqueous solutions. The sorption of Co(II) on Bi-montmorillonite (Bi-Mt) was investigated as a function of contact time, pH, ionic strength, adsorbent content, Co(II) concentrations, fulvic acid (FA) and temperature. Compared to Ca-Mt, Bi-Mt showed a higher affinity to bind Co(II) ions. The sorption percentage of Co(II) on Bi-Mt increased with increasing pH at pH 3.0-8.5, and then maintained the high level at pH 8.5-12. The sorption of Co(II) on Bi-Mt was dependent on ionic strength at low pH, and independent of ionic strength at high pH. The presence of FA enhanced Co(II) sorption at low pH, but suppressed Co(II) sorption at high pH. The thermodynamic data derived from temperature dependent sorption isotherms suggested that the sorption of Co(II) on Bi-Mt was spontaneous and endothermic process. Outer-sphere surface complexation and/or ion exchange were the main mechanisms of Co(II) sorption on Bi-Mt at low pH, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. From the experimental results, it is possible to conclude that Bi-Mt is suitable for application of Co(II) removal from aqueous solutions.     

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.     

Simultaneous sorption of crystal violet and 2-naphthol to bentonite with different CECs

This work was to examine the feasibility and efficiency to use bentonite for simultaneous removal of cationic dyes and hydrophobic organic carbons (HOCs) from water. The sorption capacities of crystal violet (CV) on two bentonites and one activated carbon were compared. Simultaneous sorption of CV and 2-naphthol on the two bentonites were tested, and the removal efficiencies of 2-naphthol by the simultaneous sorption method and by CV modified bentonite was also compared. The experimental results in this study showed that the bentonite is more effective in sorption of CV than the activated carbon. With the sorption of CV, bentonite surfaces were altered from hydrophilicity to hydrophobicity, and thus 2-naphthol could be simultaneously removed. The aromatic effect between CV and 2-naphthol was supposed to be the primary driving force for the sorption of 2-naphthol. The simultaneous sorption method was shown to be more effective in the sorption of 2-naphthol than the CV modified bentonite. Results of this work could provide novel information for the treatment of wastewater containing both cationic dyes and HOCs.     

Removal of Cr(VI) and As(V) from aqueous solutions by HDTMA-modified zeolite Y

The synthesized zeolite NaY from rice husk ash (RHA) and the commercial zeolite NaY both modified with surfactants in amounts equal to 50%, 100% and 200% of their external cation exchange capacity (ECEC) were used to remove chromate and arsenate anions from aqueous solutions. While the unmodified zeolite Y had little or no affinity for the Cr(VI) and As(V) anionic species, the surfactant-modified zeolite Y (SMZY) showed significant ability to remove of these anions from the aqueous solutions. The highest chromates and arsenates adsorption efficiency was observed from solutions of pH values 3 and 8, respectively because of the dominance of the univalent species of both anions. The adsorption equilibrium data were best fitted with the Langmuir isotherm model with the highest removal capacities observed for the SMZY initially prepared considering the hexadecyltrimethyl ammonium (HDTMA) amount equal to the 100% of the ECEC of zeolite Y. Synthesized SMZY remove Cr(VI) and As(V) more than the corresponding commercial one due to its lower silica to alumina ratio. Thus, the HDTMA-covered modified zeolite Y synthesized using RHA can be used to remove Cr(VI) and As(V) from water.     

Thorough removal of inorganic and organic mercury from aqueous solutions by adsorption on Lemna minor powder

Sorption of the cationic surfactant, hexadecyltrimethylammonium cations (HDTMA), on the solid/liquid interface of the natural mordenite tuff (MT) was studied. The examined tuff originated from Croatia consisting of 30% of mordenite. SEM observations confirmed the crystalline nature of mordenite which can be described in terms of aggregates of many small platelets with diameters in the range of 1 μm. Studying the porosity properties of MT, it was found that the average pore diameter (4.42 nm) between mordenite's platelets allows penetration of HDTMA cations. The measurements of zeta potential indicated that in MT samples with surfactant concentration in the range between 0.013 and 0.25 mmol/g, HDTMA cations fill the mesopores of MT. By further increase in HDTMA concentration, the surfactant sorbs on the external zeolite surface, as revealed by the SEM micrographs. Vibrational (FTIR and FT Raman) spectra showed that in the MT samples with initial HDTMA concentration from 0.013 to 0.25 mmol/g, alkyl chains adopt mainly gauche conformation, whereas in the MT samples with higher initial HDTMA concentrations trans conformers are predominant and form a highly ordered structure on the mordenite surface.     

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.     

Adsorption of cholate anions on layered double hydroxides: effects of temperature,ionic strength and pH

Layered Double Hydroxides are a class of materials that can be described as positively charged planar layers consisting of divalent and trivalent cations in the center of edge-sharing octahedra. The positive charge in the LDH layers must be compensated by anion intercalation. These materials have applications that include adsorption and/or sorption of anionic species. Cholic acid is one of the main acids produced by the liver. It promotes transport of lipids through aqueous systems. This work reports on the adsorption of Cholic acid anions in MgAl–CO₃–LDH taking ionic strength, pH, and temperature effects into account. The adsorbent was characterized by different techniques. Cholate anion adsorption was performed at two different temperatures (298 and 323 K), two different ionic strength conditions (0.0 and 0.1 M of NaCl), and two different pH values (7.0 and 10.0). The results show that the sorption of Cholate anions in calcined LDH can remove a considerable amount of these anions from the medium. Cholate anion adsorption in the LDH with no calcining also occurs, but at a lower amount.     

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.     

Metal sorption on soils as affected by the dissolved organic matter in sewage sludge and the relative calculation of sewage sludge application

To evaluate the influences of sewage sludge-derived organic matters on metal sorption and on the resultant sludge loading estimates, a batch experiment was conducted to compare the sorption of Ni, Cu and Pb in sewage sludge filtrates (1:20 sewage sludge to water) on eight soils and the adsorption of metals in a reference solution which had the same matrix as the sewage sludge filtrate except dissolved organic material (henceforth referred to as reference solution). Metal sorption could be well fitted by linear isotherm and the dissolved organic matter in sludge significantly depressed the sorption (p<0.01). The main factor controlling sorption of Ni on different soils was dominated by soil cation exchange capacity (CEC) and sorption of Cu and Pb was by soil organic matter (SOM). The parameters obtained from the sorption isotherm equations were then used to estimate sludge loadings into the soils. When the sorption parameters derived from the reference solution were used for calculation, that is the effect of dissolved organic matter was not considered, the calculated safe application rates are approximately 47.8, 51.4, 34.2, 31.3, 21.7, 46.3, 187.1 and 27.6 t-sludge/ha for the Beijing, Jiangxi, Xiamen, Jilin, Guangdong, Wuhan, Gansu and Xinjiang soils, respectively. However, when the sorption parameters derived from the dissolved organo-metallic complexes are used for calculation, the corresponding application rates are reduced to approximately 6.0, 3.4, 1.9, 10.0, 6.3, 3.6, 7.3 and 3.5 t-sludge/ha, respectively. By this study we can get a conclusion that the effect of sewage sludge derived dissolved organic matter on heavy metal sorption and soil properties should be considered in the course of regulating the safe application rates of sewage sludge to soil.     

Metal-organic frameworks: Challenges and opportunities for ion-exchange/sorption applications

Exposure to common ionic pollutants, such as heavy metal ions and toxic anions, is a major concern throughout the world due to their potential impacts on human health and the environment. Recently, metal-organic frameworks (MOFs) with ion-exchange properties have attracted great interest with respect to the capture of diverse hazardous cationic and anionic species. In fact, according to the investigations on these ion exchangers, their sorption capacities are recognized to be considerably superior to conventional materials. This review focused on metal-organic materials as sorbents for ions by surveying MOFs with respect to their exchange/sorption capacities in association with their synthesis and structural characteristics. We also described the recent development in MOF composites and their practical applications toward wastewater treatment. The sorption characteristics were also evaluated among the reported MOFs and then between MOFs and other sorbents. Finally, we described the future prospects for the research and development in materials for ion-exchange based on MOF technology.     

Fabrication and characterization of a boehmite nanoparticle impregnated electrospun fiber membrane for removal of metal ions

The fabrication of a composite electrospun fiber membrane with sorptive characteristics intended for removal of heavy metals was investigated. The electrospun fiber membrane was impregnated with nano-boehmite particles. The latter had been selected to increase surface area of the active component. Cd (II) was chosen as the challenge bivalent cation. The sorption capacity of the nano-boehmite was studied as a function of pH and time. Electrospinning was used to prepare the composite submicron fiber membrane impregnated with boehmite nanoparticles. The later was blended with the polymer to produce a homogenous mixture before electrospinning. Two polymers, the hydrophobic/PCL/and hydrophilic/Nylon-6/, were chosen to serve as the support for the boehmite. The nanoparticles and resulting composite membranes were characterized using SEM, TEM, and XRD techniques. XRD data confirmed the presence of nano-boehmite particles in the nanofibers membrane. The membranes so prepared were challenged with aqueous solutions of Cd in batch isotherm tests. Atomic absorption spectroscopy results show sorption of Cd (II) by boehmite impregnated electospun membrane was possible and a capacity of 0.20 mg/g was achieved.